Discussion:
BIP: OP_BRIBVERIFY - the op code needed for Blind Merge Mined drivechains
(too old to reply)
Chris Stewart via bitcoin-dev
2017-06-28 00:37:13 UTC
Permalink
Raw Message
<pre>
BIP: <BIP number>
Layer: Consensus (Soft fork)
Title: OP_BRIBEVERIFY
Author: Chris Stewart <***@suredbits.com>
Status: Draft
Type: Standards Track
Created: 2017-06-27
</pre>


==Abstract==

This BIP describes a new opcode, OP_BRIBEVERIFY, for the Bitcoin
scripting system that allows for a user to bribe a miner to include a hash
in the coinbase transaction's output.


==Summary==

BRIBEVERIFY redefines the existing NOP4 opcode. When executed, if the given
critical hash is included at the given vout index in the coinbase
transaction
the script evaluates to true. Otherwise, the script will fail.

This allows sidechains to be merged mined against
bitcoin without burdening bitcoin miners with extra resource requirements.

==Motivation==

The current political climate of bitcoin is extremely contentious. Many
community members
have different visions of what bitcoin is. This op code is meant to
enable [http://www.truthcoin.info/blog/blind-merged-mining/ Blind Merge
Mining].
This enables sidechains in Bitcoin. With OP_BRIBEVERIFY, sidechains miners
can
bribe bitcoin miners to to include their block hash in the bitcoin
blockchain. If their block
is included in the coinbase transaction's vout, it is assumed that block is
a mined block on the sidechain.

This will allow various factions of the community to realize their vision
on their own separate
blockchain that is interoperable with the bitcoin blockchain. This allows
those factions to use
bitcoin as a 'reserve currency' for their own network.


===Commitment Structure===

A new block rule is added which requires that the miner's coinbase reward
be at index 0 in the coinbase transaction's output vector.

It also fixes the witness commitment output to be at index 1 of the
coinbase transaction's output vector.

This is needed so we can reliably tell what vout corresponds to what
drivechain. For instance, the mimblewimble sidechain
could correspond to index 2 of the vector outputs on the coinbase
transaction.

The commitment is recorded in a <code>scriptPubKey</code> of the coinbase
transaction. It must be at least 34 bytes in size
1-byte - OP_RETURN (0x6a)
1-byte - Push the following 32 bytes (0x20)
32-byte - block hash

the 35th byte and onward have no consensus meaning.

===OP_BRIBEVERIFY op code===

This op code reads two arguments from the stack. The stack top is expected
to be a sidechain id for which this user attempting to blind merge mine for.
The next element on the stack is expected to be a block hash. This op code
looks into the coinbase transaction's output vector at the given index
(which is derived from the sidechain id) and checks
to see if the hash in the block matches the hash inside of the BRIBEVERIFY
program. If the hashes match, the OP_BRIBEVERIFY acts as an OP_NOP. If the
comparison between the two hashes fail, the script fails.

===BRIBEVERIFY program===

A standard BRIBEVERIFY program has the format:
1-byte - Push the following 32 bytes (0x20)
32-byte - block hash
1 byte - Push operation? (needed if number can't be encoded as OP_0 -
OP_16)
1 byte - sidechain id
1 byte - OP_BRIBEVERIFY op code

==Detailed Specification==

Refer to the reference implementation, reproduced below, for the precise
semantics and detailed rationale for those semantics.


case OP_NOP4:
{
//format: block_hash sidechain_id OP_BRIBEVERIFY
if (!(flags & SCRIPT_VERIFY_BRIBEVERIFY)) {
// not enabled; treat as a NOP4
if (flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS) {
return set_error(serror, SCRIPT_ERR_DISCOURAGE_UPGRADABLE_NOPS);
}
break;
}

if (stack.size() < 2)
return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);

const CScriptNum scriptNumSidechainId(stacktop(-1),fRequireMinimal);
uint8_t nSidechainId;
if (!checker.CheckSidechainId(scriptNumSidechainId,nSidechainId)) {
return set_error(serror, SCRIPT_ERR_UNKNOWN_SIDECHAIN);
}

// Check block hash
bool fHashCritical =
checker.CheckCriticalHash(stacktop(-2),nSidechainId);
if (!fHashCritical) {
return set_error(serror, SCRIPT_ERR_UNSATISFIED_BRIBE);
}
break;
}



https://github.com/Christewart/bitcoin/blob/94b6f33f2278c42d4d8758a3c8ffe2078e4ec933/src/script/interpreter.cpp#L427

https://github.com/drivechain-project/bitcoin/pull/13

==Deployment==

TODO

==Credits==

Credit to Paul Sztorc for the original idea of Blind Merge Mined sidechains.

Credit to CryptAxe for writing the foundational layer of software for
drivechains so I could implement OP_BRIBEVERIFY.


==References==

Blind Merge Mined Sidechains -
http://www.truthcoin.info/blog/blind-merged-mining/

Mailing list discussion -
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-May/014408.html

==Copyright==

This document is placed in the public domain.
Gregory Maxwell via bitcoin-dev
2017-06-28 04:07:43 UTC
Permalink
Raw Message
On Wed, Jun 28, 2017 at 12:37 AM, Chris Stewart via bitcoin-dev
A new block rule is added which requires that the miner's coinbase reward be
at index 0 in the coinbase transaction's output vector.
This is an absurd restriction-- I hope it was not your intent to
directly ban P2Pool and probably any other form of decentralized or
less centralized mining pooling... but thats what doing that does.
It also fixes the witness commitment output to be at index 1 of the coinbase transaction's output vector.
This removes important flexibility that was intentionally preserved.
What happens when an additional commitment is needed for bitcoin?
must some sidechain be irreparably destroyed? looks like it in your
proposal.
For instance, the mimblewimble sidechain could correspond to index 2 of the vector outputs on the coinbase transaction.
And what happens if index 1 isn't present? if index 35 is used must
there be 34 dummy outputs?
This op code looks into the coinbase transaction's output vector at the given index (which is derived from the sidechain id) and checks to see if the hash in the block matches the hash inside of the BRIBEVERIFY progra
This is not monotone/reorg safe. It means that the output coins (if
any) are not equivalently fungible with other bitcoins (for, e.g. 100
blocks) because if there is a reorg this transaction cannot be
restored to the chain. It's also impure and not compatible with
caching, which would be unfortunate and slow block propagation.
Paul Sztorc via bitcoin-dev
2017-06-28 16:35:32 UTC
Permalink
Raw Message
Chris/Greg,

For pending withdrawals (side-to-main transfers), all of the data is
stored in a teeny tiny extension block which contains all the drivechain
data (which we called "MinerDB"). And miners were supposed to commit to
this and put it in the coinbase in some locate-able place (for example,
index 1).

I had assumed that this would go the same for BMM, since it is all
drivechain-themed. Thus, all drivechains, and all drivechain-stuff (BMM
included), would claim one output index.

Moreover, while DC claims an output "slot", the claim doesn't need to be
permanent...if the BTC-value of the relevant output is not equal to
zero, the BMM code could just ignore it. The sidechains would each
assume that no sidechain block was merged-mined in this period. And DC
would assume that no forward progress was made on any side-to-main
transfers (ie, that everyone "abstained").

Perhaps that addresses Greg's third, first, and second concerns.

I am having some trouble understanding concern #4. I think you mean to
say that the output coins of a transaction which is encumbered by OP
BribeVerify are different from other coins. Indeed they are, and coins
locked by OP BribeVerify cannot be moved until their associated
sidechain header ("h*") is ~100 blocks deep in the sidechain (hence the
earlier conversation about the "ratchet", which attempts to measure this).

The timeline that CryptAxe and I discussed, as I last remember it, is that:
0. (setup) The sidechain node is run by a briber, and this briber
constructs a sidechain block paying himself all the fees. These fees
total q=4 BTC.
1. Negotiations happen out of bound, between Briber and all miners.
(still setting up) Each new transaction the Briber makes, he chooses a
completely new h* (which is trivial for him to do by incrementing a
nonce/anything), and he may as well also fund each of these txns with
the same unspent output (owned by him). This prevents a miner from
annoying the Briber by including many ultimately-invalid transactions.
2. Miner1 includes h* in the coinbase of today's block thus BMMing a
sidechain block today, he also includes the transaction he just
negotiated with the Briber (call it, "tx1"). This tx1 is one where
Briber pays z=(q-0.001) to an op_bribe script that will eventually pay z
BTC to Bitcoin address M owned by "miner1".
3. After ~123 blocks, the ratchet (on mainchain) indicates that the
sidechain headers have advanced sequentially by x=100 places. This
allows miner1 to spend from tx1 to address M.
3. OR, after ~250 blocks, the second timing threshold is reached*, and
the Briber can spend from his script back to an address he controls
(also predefined in steps 1 and 2).


*This is the dual-threshold time-locking technique that the LN uses to
prove a negative.

The second timelock setup is required because it is possible that miner
will earnestly BMM a sidechain block, but then reorg such that this
block is orphaned out of the longest (side)chain. In this case, the
Briber doesn't get paid his tx-fees, so he is entitled to a refund.


So, maybe this BIP will need to be edited a little. : ) Nonetheless, I'm
glad Chris is taking the initiative and doing this work. And I'm sorry
if the documentation has shifted too much. At the bottom of the spec
blog post there are some notes, but they probably aren't very helpful.
Post by Gregory Maxwell via bitcoin-dev
On Wed, Jun 28, 2017 at 12:37 AM, Chris Stewart via bitcoin-dev
A new block rule is added which requires that the miner's coinbase reward be
at index 0 in the coinbase transaction's output vector.
This is an absurd restriction-- I hope it was not your intent to
directly ban P2Pool and probably any other form of decentralized or
less centralized mining pooling... but thats what doing that does.
It also fixes the witness commitment output to be at index 1 of the coinbase transaction's output vector.
This removes important flexibility that was intentionally preserved.
What happens when an additional commitment is needed for bitcoin?
must some sidechain be irreparably destroyed? looks like it in your
proposal.
For instance, the mimblewimble sidechain could correspond to index 2 of the vector outputs on the coinbase transaction.
And what happens if index 1 isn't present? if index 35 is used must
there be 34 dummy outputs?
This op code looks into the coinbase transaction's output vector at the given index (which is derived from the sidechain id) and checks to see if the hash in the block matches the hash inside of the BRIBEVERIFY progra
This is not monotone/reorg safe. It means that the output coins (if
any) are not equivalently fungible with other bitcoins (for, e.g. 100
blocks) because if there is a reorg this transaction cannot be
restored to the chain. It's also impure and not compatible with
caching, which would be unfortunate and slow block propagation.
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Luke Dashjr via bitcoin-dev
2017-06-28 05:20:27 UTC
Permalink
Raw Message
Post by Chris Stewart via bitcoin-dev
BRIBEVERIFY redefines the existing NOP4 opcode. When executed, if the given
critical hash is included at the given vout index in the coinbase
transaction
the script evaluates to true. Otherwise, the script will fail.
This allows sidechains to be merged mined against
bitcoin without burdening bitcoin miners with extra resource requirements.
I don't see how. It seems like the logical outcome from this is "whoever pays
the most gets the next sidechain block"... That's not particularly useful for
merge mining.
Post by Chris Stewart via bitcoin-dev
This enables sidechains in Bitcoin.
There are different kinds of sidechains...

Federated peg: this already works on Bitcoin.
SPV/SNARK peg: this isn't enabled by your BIP.
Drivechains: this isn't enabled by your BIP.

How do you say this enables any kind of sidechain?
Post by Chris Stewart via bitcoin-dev
A new block rule is added which requires that the miner's coinbase reward
be at index 0 in the coinbase transaction's output vector.
It also fixes the witness commitment output to be at index 1 of the
coinbase transaction's output vector.
This is unacceptable, for reasons Greg already pointed out.
Post by Chris Stewart via bitcoin-dev
This document is placed in the public domain.
Note that this is not acceptable for BIPs anymore.

https://github.com/bitcoin/bips/blob/master/bip-0002.mediawiki#BIP_licensing
Adam Back via bitcoin-dev
2017-06-28 05:28:31 UTC
Permalink
Raw Message
On 27 June 2017 at 22:20, Luke Dashjr via bitcoin-dev
Post by Luke Dashjr via bitcoin-dev
Post by Chris Stewart via bitcoin-dev
BRIBEVERIFY redefines the existing NOP4 opcode. When executed, if the given
critical hash is included at the given vout index in the coinbase
transaction the script evaluates to true. Otherwise, the script will fail.
This allows sidechains to be merged mined against
bitcoin without burdening bitcoin miners with extra resource requirements.
I don't see how. It seems like the logical outcome from this is "whoever pays
the most gets the next sidechain block"... That's not particularly useful for
merge mining.
Maybe that's phrased badly but the point of the "blind merge mining"
is just that the sidechain fees are paid in main chain bitcoin (rather
than in sidechain bitcoin).

That means that a miner who solo mines the main chain could still mine
the sidechain by requesting a block-proposal from a trusted sidechain
fullnode. The sidechain fullnode would actually pay the mainchain
fee, and pay itself the sidechain fees as part of the side-chain
block-proposal.

This was viewed as less centralising than forcing miners to directly
process sidechain blocks, which could in principle be bandwidth and
CPU expensive to process, construct and validate.

Adam
Paul Sztorc via bitcoin-dev
2017-06-28 16:43:22 UTC
Permalink
Raw Message
Hi Luke,
Post by Luke Dashjr via bitcoin-dev
Post by Chris Stewart via bitcoin-dev
BRIBEVERIFY redefines the existing NOP4 opcode. When executed, if the given
critical hash is included at the given vout index in the coinbase
transaction
the script evaluates to true. Otherwise, the script will fail.
This allows sidechains to be merged mined against
bitcoin without burdening bitcoin miners with extra resource requirements.
I don't see how. It seems like the logical outcome from this is "whoever pays
the most gets the next sidechain block"... That's not particularly useful for
merge mining.
This is one of the assumptions which BMM exploits, see #4 of:
http://www.truthcoin.info/blog/blind-merged-mining/#focus

The idea is that this is a safe assumption, because it is already the
case today. If we assume that miners revenue-maximize, and further that
the "bidder" frames his payments in tx-fees, then a willing buyer can
control the next block by simply filling it with high tx-fee spam.
Anyone who is willing to pay the most can already 'get' the next
mainchain block (only, indirectly).
Post by Luke Dashjr via bitcoin-dev
Post by Chris Stewart via bitcoin-dev
This enables sidechains in Bitcoin.
There are different kinds of sidechains...
Federated peg: this already works on Bitcoin.
SPV/SNARK peg: this isn't enabled by your BIP.
Drivechains: this isn't enabled by your BIP.
How do you say this enables any kind of sidechain?
Yes, it is unclear, but Chris' email is specific to blind merged mining
(BMM), which is kind of a "sidechains +". So this does not directly
enable any sidechains. Instead, it enables the "+" part.

--Paul
ZmnSCPxj via bitcoin-dev
2017-06-28 08:26:37 UTC
Permalink
Raw Message
Good morning.
I still do not see what this does that cannot be done by:
OP_RETURN <sidechain-id> <sidechain-block-id>
A transaction with such an output would allow sidechain-miners to bribe mainchain-miners by paying a transaction fee if the transaction containing this OP_RETURN is included in a block and committed to by a mainchain-miner in the Merkle tree root.
It would not require a softfork.
--
I have an alternate proposal that sidechains and altcoins that want to do "blinded" merge mining can use without a softfork:
1. Encode a block header as a simple cons-pair, with the head as the block and the tail as the parent cons-pair.
1.1. This can be encoded as a 32-byte hash of the block including its header, and the 32-byte hash of the parent cons-pair.
1.2. This is now the actual "chain" in the sidecoin/altcoin blockchain.
2. When a sidechain-node wants to know the consensus, it downloads mainchain-blocks and looks for OP_RETURN's.
2.1. Starting with its genesis cons-pair hash (equivalent to the empty list) as the current cons-pair, it scans each OP_RETURN transaction.
2.1.1. If an OP_RETURN is 64-byte and has the parent cons-pair equal to the current cons-pair, look for the side block indicated and confirm its correctness. If correct, update the current cons-pair for the hash of the OP_RETURN data.
2.2. When reaching the latest mainchain block, the current cons-pair is now the sidecoin/altcoin latest block.
2.3. Note that if multiple OP_RETURN in a block match the current cons-pair, the first one is considered the correct chain. This property means that the sidechain/altchain can only have a chainsplit if the mainchain has a chainsplit.
3. When a sidechain-miner wants to create a side-block, it generates a new cons-pair and creates an OP_RETURN transaction for it, paying a mainchain-miner to include it in the next mainchain-block.
3.1. The sidechain-miner risks that its competitors will outbid it and get its OP_RETURN earlier in a mainchain-block (or earlier in the order of transactions). It can mitigate this risk by updating itself to become a mainchain-miner, it can then keep its OP_RETURN transaction private and put it earlier in the block, ensuring it will "win" the sidechain-consensus if it wins the mainchain-consensus.
Regards,
ZmnSCPxj
-------- Original Message --------
Subject: [bitcoin-dev] BIP: OP_BRIBVERIFY - the op code needed for Blind Merge Mined drivechains
Local Time: June 28, 2017 8:37 AM
UTC Time: June 28, 2017 12:37 AM
From: bitcoin-***@lists.linuxfoundation.org
To: Bitcoin Protocol Discussion <bitcoin-***@lists.linuxfoundation.org>
<pre>
BIP: <BIP number>
Layer: Consensus (Soft fork)
Title: OP_BRIBEVERIFY
Author: Chris Stewart <***@suredbits.com>
Status: Draft
Type: Standards Track
Created: 2017-06-27
</pre>
==Abstract==
This BIP describes a new opcode, OP_BRIBEVERIFY, for the Bitcoin
scripting system that allows for a user to bribe a miner to include a hash
in the coinbase transaction's output.
==Summary==
BRIBEVERIFY redefines the existing NOP4 opcode. When executed, if the given
critical hash is included at the given vout index in the coinbase transaction
the script evaluates to true. Otherwise, the script will fail.
This allows sidechains to be merged mined against
bitcoin without burdening bitcoin miners with extra resource requirements.
==Motivation==
The current political climate of bitcoin is extremely contentious. Many community members
have different visions of what bitcoin is. This op code is meant to
enable [http://www.truthcoin.info/blog/blind-merged-mining/ Blind Merge Mining].
This enables sidechains in Bitcoin. With OP_BRIBEVERIFY, sidechains miners can
bribe bitcoin miners to to include their block hash in the bitcoin blockchain. If their block
is included in the coinbase transaction's vout, it is assumed that block is a mined block on the sidechain.
This will allow various factions of the community to realize their vision on their own separate
blockchain that is interoperable with the bitcoin blockchain. This allows those factions to use
bitcoin as a 'reserve currency' for their own network.
===Commitment Structure===
A new block rule is added which requires that the miner's coinbase reward be at index 0 in the coinbase transaction's output vector.
It also fixes the witness commitment output to be at index 1 of the coinbase transaction's output vector.
This is needed so we can reliably tell what vout corresponds to what drivechain. For instance, the mimblewimble sidechain
could correspond to index 2 of the vector outputs on the coinbase transaction.
The commitment is recorded in a <code>scriptPubKey</code> of the coinbase transaction. It must be at least 34 bytes in size
1-byte - OP_RETURN (0x6a)
1-byte - Push the following 32 bytes (0x20)
32-byte - block hash
the 35th byte and onward have no consensus meaning.
===OP_BRIBEVERIFY op code===
This op code reads two arguments from the stack. The stack top is expected to be a sidechain id for which this user attempting to blind merge mine for.
The next element on the stack is expected to be a block hash. This op code looks into the coinbase transaction's output vector at the given index (which is derived from the sidechain id) and checks
to see if the hash in the block matches the hash inside of the BRIBEVERIFY program. If the hashes match, the OP_BRIBEVERIFY acts as an OP_NOP. If the
comparison between the two hashes fail, the script fails.
===BRIBEVERIFY program===
A standard BRIBEVERIFY program has the format:
1-byte - Push the following 32 bytes (0x20)
32-byte - block hash
1 byte - Push operation? (needed if number can't be encoded as OP_0 - OP_16)
1 byte - sidechain id
1 byte - OP_BRIBEVERIFY op code
==Detailed Specification==
Refer to the reference implementation, reproduced below, for the precise
semantics and detailed rationale for those semantics.
case OP_NOP4:
{
//format: block_hash sidechain_id OP_BRIBEVERIFY
if (!(flags & SCRIPT_VERIFY_BRIBEVERIFY)) {
// not enabled; treat as a NOP4
if (flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS) {
return set_error(serror, SCRIPT_ERR_DISCOURAGE_UPGRADABLE_NOPS);
}
break;
}
if (stack.size() < 2)
return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
const CScriptNum scriptNumSidechainId(stacktop(-1),fRequireMinimal);
uint8_t nSidechainId;
if (!checker.CheckSidechainId(scriptNumSidechainId,nSidechainId)) {
return set_error(serror, SCRIPT_ERR_UNKNOWN_SIDECHAIN);
}
// Check block hash
bool fHashCritical = checker.CheckCriticalHash(stacktop(-2),nSidechainId);
if (!fHashCritical) {
return set_error(serror, SCRIPT_ERR_UNSATISFIED_BRIBE);
}
break;
}
https://github.com/Christewart/bitcoin/blob/94b6f33f2278c42d4d8758a3c8ffe2078e4ec933/src/script/interpreter.cpp#L427
https://github.com/drivechain-project/bitcoin/pull/13
==Deployment==
TODO
==Credits==
Credit to Paul Sztorc for the original idea of Blind Merge Mined sidechains.
Credit to CryptAxe for writing the foundational layer of software for drivechains so I could implement OP_BRIBEVERIFY.
==References==
Blind Merge Mined Sidechains - http://www.truthcoin.info/blog/blind-merged-mining/
Mailing list discussion - https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-May/014408.html
==Copyright==
This document is placed in the public domain.
Paul Sztorc via bitcoin-dev
2017-06-28 22:20:35 UTC
Permalink
Raw Message
Hi ZmnSCPxj,

It seems that, in your version, the "bribers" would react to the scheme
in inefficient ways, particularly when the mainchain's tx-fee-rate (ie
fee per Kb) is low.

In short, there would be many bribe-attempts (each of which would take
up space in mainchain blocks), almost all of which would be unsuccessful.

In turn, miners would likely react to this, and try to improve the state
of affairs by offering users the privilege of occupying transaction slot
#2 (ie, the one right after the coinbase). Users would need to trust
miners for this, which introduces a cost friction which is pure
deadweight loss. And, it might be easier for larger/older miners to be
trustworthy than smaller/newer ones.

Your way is actually very similar to mine. Mine _forces_ the bribe to be
in the earliest txn (the coinbase) and to only occur once. Yours doesn't
do anything to refund the briber, if the sidechain (but not the
mainchain) reorganizes (as it can easily do, if an older sidechain
parent is extended while the mainchain proceeds normally). This creates
additional risk.

I think mine is also much more space-efficient. Even if ours each had
exactly one h* per sidechain per block, it seems that I only require one
hash to be communicated (plus an indicator byte, and a ~2 byte counter
for the ratchet), whereas you require two. Since its overhead per
sidechain per block, it actually might really add up.

Thanks,
Paul
Post by ZmnSCPxj via bitcoin-dev
Good morning.
OP_RETURN <sidechain-id> <sidechain-block-id>
A transaction with such an output would allow sidechain-miners to bribe
mainchain-miners by paying a transaction fee if the transaction
containing this OP_RETURN is included in a block and committed to by a
mainchain-miner in the Merkle tree root.
It would not require a softfork.
--
I have an alternate proposal that sidechains and altcoins that want to
1. Encode a block header as a simple cons-pair, with the head as the
block and the tail as the parent cons-pair.
1.1. This can be encoded as a 32-byte hash of the block including its
header, and the 32-byte hash of the parent cons-pair.
1.2. This is now the actual "chain" in the sidecoin/altcoin blockchain.
2. When a sidechain-node wants to know the consensus, it downloads
mainchain-blocks and looks for OP_RETURN's.
2.1. Starting with its genesis cons-pair hash (equivalent to the empty
list) as the current cons-pair, it scans each OP_RETURN transaction.
2.1.1. If an OP_RETURN is 64-byte and has the parent cons-pair equal to
the current cons-pair, look for the side block indicated and confirm its
correctness. If correct, update the current cons-pair for the hash of
the OP_RETURN data.
2.2. When reaching the latest mainchain block, the current cons-pair is
now the sidecoin/altcoin latest block.
2.3. Note that if multiple OP_RETURN in a block match the current
cons-pair, the first one is considered the correct chain. This property
means that the sidechain/altchain can only have a chainsplit if the
mainchain has a chainsplit.
3. When a sidechain-miner wants to create a side-block, it generates a
new cons-pair and creates an OP_RETURN transaction for it, paying a
mainchain-miner to include it in the next mainchain-block.
3.1. The sidechain-miner risks that its competitors will outbid it and
get its OP_RETURN earlier in a mainchain-block (or earlier in the order
of transactions). It can mitigate this risk by updating itself to
become a mainchain-miner, it can then keep its OP_RETURN transaction
private and put it earlier in the block, ensuring it will "win" the
sidechain-consensus if it wins the mainchain-consensus.
Regards,
ZmnSCPxj
-------- Original Message --------
Subject: [bitcoin-dev] BIP: OP_BRIBVERIFY - the op code needed for Blind
Merge Mined drivechains
Local Time: June 28, 2017 8:37 AM
UTC Time: June 28, 2017 12:37 AM
<pre>
BIP: <BIP number>
Layer: Consensus (Soft fork)
Title: OP_BRIBEVERIFY
Status: Draft
Type: Standards Track
Created: 2017-06-27
</pre>
==Abstract==
This BIP describes a new opcode, OP_BRIBEVERIFY, for the Bitcoin
scripting system that allows for a user to bribe a miner to include a hash
in the coinbase transaction's output.
==Summary==
BRIBEVERIFY redefines the existing NOP4 opcode. When executed, if the given
critical hash is included at the given vout index in the coinbase transaction
the script evaluates to true. Otherwise, the script will fail.
This allows sidechains to be merged mined against
bitcoin without burdening bitcoin miners with extra resource requirements.
==Motivation==
The current political climate of bitcoin is extremely contentious. Many community members
have different visions of what bitcoin is. This op code is meant to
enable [http://www.truthcoin.info/blog/blind-merged-mining/ Blind Merge Mining].
This enables sidechains in Bitcoin. With OP_BRIBEVERIFY, sidechains miners can
bribe bitcoin miners to to include their block hash in the bitcoin
blockchain. If their block
is included in the coinbase transaction's vout, it is assumed that block
is a mined block on the sidechain.
This will allow various factions of the community to realize their
vision on their own separate
blockchain that is interoperable with the bitcoin blockchain. This
allows those factions to use
bitcoin as a 'reserve currency' for their own network.
===Commitment Structure===
A new block rule is added which requires that the miner's coinbase
reward be at index 0 in the coinbase transaction's output vector.
It also fixes the witness commitment output to be at index 1 of the
coinbase transaction's output vector.
This is needed so we can reliably tell what vout corresponds to what
drivechain. For instance, the mimblewimble sidechain
could correspond to index 2 of the vector outputs on the coinbase transaction.
The commitment is recorded in a <code>scriptPubKey</code> of the
coinbase transaction. It must be at least 34 bytes in size
1-byte - OP_RETURN (0x6a)
1-byte - Push the following 32 bytes (0x20)
32-byte - block hash
the 35th byte and onward have no consensus meaning.
===OP_BRIBEVERIFY op code===
This op code reads two arguments from the stack. The stack top is
expected to be a sidechain id for which this user attempting to blind
merge mine for.
The next element on the stack is expected to be a block hash. This op
code looks into the coinbase transaction's output vector at the given
index (which is derived from the sidechain id) and checks
to see if the hash in the block matches the hash inside of the
BRIBEVERIFY program. If the hashes match, the OP_BRIBEVERIFY acts as an
OP_NOP. If the
comparison between the two hashes fail, the script fails.
===BRIBEVERIFY program===
1-byte - Push the following 32 bytes (0x20)
32-byte - block hash
1 byte - Push operation? (needed if number can't be encoded as OP_0 - OP_16)
1 byte - sidechain id
1 byte - OP_BRIBEVERIFY op code
==Detailed Specification==
Refer to the reference implementation, reproduced below, for the precise
semantics and detailed rationale for those semantics.
{
//format: block_hash sidechain_id OP_BRIBEVERIFY
if (!(flags & SCRIPT_VERIFY_BRIBEVERIFY)) {
// not enabled; treat as a NOP4
if (flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS) {
return set_error(serror, SCRIPT_ERR_DISCOURAGE_UPGRADABLE_NOPS);
}
break;
}
if (stack.size() < 2)
return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
const CScriptNum scriptNumSidechainId(stacktop(-1),fRequireMinimal);
uint8_t nSidechainId;
if (!checker.CheckSidechainId(scriptNumSidechainId,nSidechainId)) {
return set_error(serror, SCRIPT_ERR_UNKNOWN_SIDECHAIN);
}
// Check block hash
bool fHashCritical =
checker.CheckCriticalHash(stacktop(-2),nSidechainId);
if (!fHashCritical) {
return set_error(serror, SCRIPT_ERR_UNSATISFIED_BRIBE);
}
break;
}
https://github.com/Christewart/bitcoin/blob/94b6f33f2278c42d4d8758a3c8ffe2078e4ec933/src/script/interpreter.cpp#L427
https://github.com/drivechain-project/bitcoin/pull/13
==Deployment==
TODO
==Credits==
Credit to Paul Sztorc for the original idea of Blind Merge Mined sidechains.
Credit to CryptAxe for writing the foundational layer of software for
drivechains so I could implement OP_BRIBEVERIFY.
==References==
Blind Merge Mined Sidechains -
http://www.truthcoin.info/blog/blind-merged-mining/
Mailing list discussion -
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-May/014408.html
==Copyright==
This document is placed in the public domain.
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Russell O'Connor via bitcoin-dev
2017-06-28 22:49:54 UTC
Permalink
Raw Message
I haven't really been following the drivechain discussion; I have found the
documentation about how drivechains are supposed to work scattered and
difficult to follow. So, without advocating for or against this proposal,
I'd also suggest that adding an opcode is not the best way to implement
this bribe.

The problem I see is that to send a bribe one must first post a transaction
to a script that uses the OP_BRIBE code that fixes the critical hash (and
the sidechain id), and then a second transaction is needed to pay the bribe
to the miner.

I suggest instead to use a 0 output value with some currently non-standard
OP_RETURN output script that specifies the critical hash (and the sidechain
id), similar to ZmnSCPxj's idea. The difference is that I we would
soft-fork a rule that says that such an output is only legal when a miner
places the same critical hash suitably in their coinbase output.

OP_RETURN outputs are prunable from the UTXO set. The special bribe output
can be fixed to 0 value because the bribe will be paid using the
transaction's fees. To perform a bribe, a user creates and signs a
transaction containing one (or more) of these special bribe outputs. The
fee of this transaction constitutes the bribe, and any change the user has
can be sent back to themselves. This way only a single transaction is
required to make a bribe. I didn't really understand the bribe refund
mechanism, but I think the fact that the bribe can be done in a single
transaction this way alleviates any need for bribe refunds.

Hopefully I have understood the goal of this proposal.


On Wed, Jun 28, 2017 at 6:20 PM, Paul Sztorc via bitcoin-dev <
Post by Paul Sztorc via bitcoin-dev
Hi ZmnSCPxj,
It seems that, in your version, the "bribers" would react to the scheme
in inefficient ways, particularly when the mainchain's tx-fee-rate (ie
fee per Kb) is low.
In short, there would be many bribe-attempts (each of which would take
up space in mainchain blocks), almost all of which would be unsuccessful.
In turn, miners would likely react to this, and try to improve the state
of affairs by offering users the privilege of occupying transaction slot
#2 (ie, the one right after the coinbase). Users would need to trust
miners for this, which introduces a cost friction which is pure
deadweight loss. And, it might be easier for larger/older miners to be
trustworthy than smaller/newer ones.
Your way is actually very similar to mine. Mine _forces_ the bribe to be
in the earliest txn (the coinbase) and to only occur once. Yours doesn't
do anything to refund the briber, if the sidechain (but not the
mainchain) reorganizes (as it can easily do, if an older sidechain
parent is extended while the mainchain proceeds normally). This creates
additional risk.
I think mine is also much more space-efficient. Even if ours each had
exactly one h* per sidechain per block, it seems that I only require one
hash to be communicated (plus an indicator byte, and a ~2 byte counter
for the ratchet), whereas you require two. Since its overhead per
sidechain per block, it actually might really add up.
Thanks,
Paul
Post by ZmnSCPxj via bitcoin-dev
Good morning.
OP_RETURN <sidechain-id> <sidechain-block-id>
A transaction with such an output would allow sidechain-miners to bribe
mainchain-miners by paying a transaction fee if the transaction
containing this OP_RETURN is included in a block and committed to by a
mainchain-miner in the Merkle tree root.
It would not require a softfork.
--
I have an alternate proposal that sidechains and altcoins that want to
1. Encode a block header as a simple cons-pair, with the head as the
block and the tail as the parent cons-pair.
1.1. This can be encoded as a 32-byte hash of the block including its
header, and the 32-byte hash of the parent cons-pair.
1.2. This is now the actual "chain" in the sidecoin/altcoin blockchain.
2. When a sidechain-node wants to know the consensus, it downloads
mainchain-blocks and looks for OP_RETURN's.
2.1. Starting with its genesis cons-pair hash (equivalent to the empty
list) as the current cons-pair, it scans each OP_RETURN transaction.
2.1.1. If an OP_RETURN is 64-byte and has the parent cons-pair equal to
the current cons-pair, look for the side block indicated and confirm its
correctness. If correct, update the current cons-pair for the hash of
the OP_RETURN data.
2.2. When reaching the latest mainchain block, the current cons-pair is
now the sidecoin/altcoin latest block.
2.3. Note that if multiple OP_RETURN in a block match the current
cons-pair, the first one is considered the correct chain. This property
means that the sidechain/altchain can only have a chainsplit if the
mainchain has a chainsplit.
3. When a sidechain-miner wants to create a side-block, it generates a
new cons-pair and creates an OP_RETURN transaction for it, paying a
mainchain-miner to include it in the next mainchain-block.
3.1. The sidechain-miner risks that its competitors will outbid it and
get its OP_RETURN earlier in a mainchain-block (or earlier in the order
of transactions). It can mitigate this risk by updating itself to
become a mainchain-miner, it can then keep its OP_RETURN transaction
private and put it earlier in the block, ensuring it will "win" the
sidechain-consensus if it wins the mainchain-consensus.
Regards,
ZmnSCPxj
-------- Original Message --------
Subject: [bitcoin-dev] BIP: OP_BRIBVERIFY - the op code needed for Blind
Merge Mined drivechains
Local Time: June 28, 2017 8:37 AM
UTC Time: June 28, 2017 12:37 AM
<pre>
BIP: <BIP number>
Layer: Consensus (Soft fork)
Title: OP_BRIBEVERIFY
Status: Draft
Type: Standards Track
Created: 2017-06-27
</pre>
==Abstract==
This BIP describes a new opcode, OP_BRIBEVERIFY, for the Bitcoin
scripting system that allows for a user to bribe a miner to include a
hash
Post by ZmnSCPxj via bitcoin-dev
in the coinbase transaction's output.
==Summary==
BRIBEVERIFY redefines the existing NOP4 opcode. When executed, if the
given
Post by ZmnSCPxj via bitcoin-dev
critical hash is included at the given vout index in the coinbase transaction
the script evaluates to true. Otherwise, the script will fail.
This allows sidechains to be merged mined against
bitcoin without burdening bitcoin miners with extra resource
requirements.
Post by ZmnSCPxj via bitcoin-dev
==Motivation==
The current political climate of bitcoin is extremely contentious. Many
community members
have different visions of what bitcoin is. This op code is meant to
enable [http://www.truthcoin.info/blog/blind-merged-mining/ Blind Merge Mining].
This enables sidechains in Bitcoin. With OP_BRIBEVERIFY, sidechains miners can
bribe bitcoin miners to to include their block hash in the bitcoin
blockchain. If their block
is included in the coinbase transaction's vout, it is assumed that block
is a mined block on the sidechain.
This will allow various factions of the community to realize their
vision on their own separate
blockchain that is interoperable with the bitcoin blockchain. This
allows those factions to use
bitcoin as a 'reserve currency' for their own network.
===Commitment Structure===
A new block rule is added which requires that the miner's coinbase
reward be at index 0 in the coinbase transaction's output vector.
It also fixes the witness commitment output to be at index 1 of the
coinbase transaction's output vector.
This is needed so we can reliably tell what vout corresponds to what
drivechain. For instance, the mimblewimble sidechain
could correspond to index 2 of the vector outputs on the coinbase transaction.
The commitment is recorded in a <code>scriptPubKey</code> of the
coinbase transaction. It must be at least 34 bytes in size
1-byte - OP_RETURN (0x6a)
1-byte - Push the following 32 bytes (0x20)
32-byte - block hash
the 35th byte and onward have no consensus meaning.
===OP_BRIBEVERIFY op code===
This op code reads two arguments from the stack. The stack top is
expected to be a sidechain id for which this user attempting to blind
merge mine for.
The next element on the stack is expected to be a block hash. This op
code looks into the coinbase transaction's output vector at the given
index (which is derived from the sidechain id) and checks
to see if the hash in the block matches the hash inside of the
BRIBEVERIFY program. If the hashes match, the OP_BRIBEVERIFY acts as an
OP_NOP. If the
comparison between the two hashes fail, the script fails.
===BRIBEVERIFY program===
1-byte - Push the following 32 bytes (0x20)
32-byte - block hash
1 byte - Push operation? (needed if number can't be encoded as OP_0 - OP_16)
1 byte - sidechain id
1 byte - OP_BRIBEVERIFY op code
==Detailed Specification==
Refer to the reference implementation, reproduced below, for the precise
semantics and detailed rationale for those semantics.
{
//format: block_hash sidechain_id OP_BRIBEVERIFY
if (!(flags & SCRIPT_VERIFY_BRIBEVERIFY)) {
// not enabled; treat as a NOP4
if (flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS) {
return set_error(serror, SCRIPT_ERR_DISCOURAGE_
UPGRADABLE_NOPS);
Post by ZmnSCPxj via bitcoin-dev
}
break;
}
if (stack.size() < 2)
return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
const CScriptNum scriptNumSidechainId(stacktop(-1),fRequireMinimal);
uint8_t nSidechainId;
if (!checker.CheckSidechainId(scriptNumSidechainId,nSidechainId)) {
return set_error(serror, SCRIPT_ERR_UNKNOWN_SIDECHAIN);
}
// Check block hash
bool fHashCritical =
checker.CheckCriticalHash(stacktop(-2),nSidechainId);
if (!fHashCritical) {
return set_error(serror, SCRIPT_ERR_UNSATISFIED_BRIBE);
}
break;
}
https://github.com/Christewart/bitcoin/blob/
94b6f33f2278c42d4d8758a3c8ffe2078e4ec933/src/script/interpreter.cpp#L427
Post by ZmnSCPxj via bitcoin-dev
https://github.com/drivechain-project/bitcoin/pull/13
==Deployment==
TODO
==Credits==
Credit to Paul Sztorc for the original idea of Blind Merge Mined
sidechains.
Post by ZmnSCPxj via bitcoin-dev
Credit to CryptAxe for writing the foundational layer of software for
drivechains so I could implement OP_BRIBEVERIFY.
==References==
Blind Merge Mined Sidechains -
http://www.truthcoin.info/blog/blind-merged-mining/
Mailing list discussion -
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/
2017-May/014408.html
Post by ZmnSCPxj via bitcoin-dev
==Copyright==
This document is placed in the public domain.
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Russell O'Connor via bitcoin-dev
2017-06-29 01:09:27 UTC
Permalink
Raw Message
HI Chris,

My proposal isn't intended to assume that the bitcoin miner is also
following the sidechain. In line with my understanding of your proposal,
I'm only proposing to bribe miners to put particular data into the coinbase
output regardless of any semantics that doing so may entail. By my proposed
soft-fork rules, only one of these Bribe TXOs can be included per coinbase
slot (except unless there are identical Bribe TXOs), so there is a
competition of which one of a set of conflicting Bribe TXOs will be
included in the next block. (That said, the losing set Bribe TXOs can be
included in the later blocks; I don't know what this means semantically for
sidechains; however, the same thing occurs with your proposal as well.)
Hi Russell,
Post by Russell O'Connor via bitcoin-dev
I haven't really been following the drivechain discussion; I have found
the documentation about how drivechains are supposed to work scattered and
difficult to follow. So, without advocating for or against this proposal,
I'd also suggest that adding an opcode is not the best way to implement
this bribe.
Despite the flaws in this draft BIP, the goal is to start consolidating
this information into a more compact format. This BIP is *only*
meant to address the Blind Merging Mining Process of drivechains. It does
*not* address the withdrawal process from drivechain -> bitcoin.
Post by Russell O'Connor via bitcoin-dev
The problem I see is that to send a bribe one must first post a
transaction to a script that uses the OP_BRIBE code that fixes the critical
hash (and the sidechain id), and then a second transaction is needed to pay
the bribe to the miner.
That is intentional, this allows for a competitive process (like bitcoin
mining) for a block to be 'found' on the sidechain. The OP_BV output that
rewards
the bitcoin miner the most amount of money should be the one that is
included in the bitcoin blockchain. If I understand your scheme correctly,
you are
assuming the the bitcoin miner is *also* following the sidechain --
Sztorc's scheme does not make this assumption. The *number one goal* of BMM
is to *minimize* the resource burden on bitcoin miners for mining on a
drivechain.
To gmaxwell/luke-jr,
I agree my commitment scheme is flawed. Thanks for pointing it out. Is
there any way we could manipulate a coinbase transaction
into spending these OP_BV outputs? According to instagibbs, and AFIACT he
is right, we cannot have coinbase transactions
spend any outputs in previous blocks without a hard fork. This is
unfortunate because it might make more sense for the coinbase transaction
to spend these OP_BV outputs. We could design the coinbase transaction's
scriptSig to push the critical hash onto the stack and
place an OP_EQUAL on the OP_BV output to verify they were equal.
If I understand gmaxwell's concern about 'monotone' (or stateless) blocks
correctly, I *think*
this solution might fix that as well.
Another way we could fix this is by *fixing* the drivechain indices.
Therefore the mining rewards and witness commitments must
*not* occupy one of those indices -- but can occupy any other indice in
the coinbase output.
This would give us future flexibility for committing to new soft forks.
For instance, we would say
the mining reward must *not* be index 0 of the coinbase transaction, but
can occupy index 1 - 256. The same would apply for witness commitments.
-Chris
Post by Russell O'Connor via bitcoin-dev
I haven't really been following the drivechain discussion; I have found
the documentation about how drivechains are supposed to work scattered and
difficult to follow. So, without advocating for or against this proposal,
I'd also suggest that adding an opcode is not the best way to implement
this bribe.
The problem I see is that to send a bribe one must first post a
transaction to a script that uses the OP_BRIBE code that fixes the critical
hash (and the sidechain id), and then a second transaction is needed to pay
the bribe to the miner.
I suggest instead to use a 0 output value with some currently
non-standard OP_RETURN output script that specifies the critical hash (and
the sidechain id), similar to ZmnSCPxj's idea. The difference is that I we
would soft-fork a rule that says that such an output is only legal when a
miner places the same critical hash suitably in their coinbase output.
OP_RETURN outputs are prunable from the UTXO set. The special bribe
output can be fixed to 0 value because the bribe will be paid using the
transaction's fees. To perform a bribe, a user creates and signs a
transaction containing one (or more) of these special bribe outputs. The
fee of this transaction constitutes the bribe, and any change the user has
can be sent back to themselves. This way only a single transaction is
required to make a bribe. I didn't really understand the bribe refund
mechanism, but I think the fact that the bribe can be done in a single
transaction this way alleviates any need for bribe refunds.
Hopefully I have understood the goal of this proposal.
On Wed, Jun 28, 2017 at 6:20 PM, Paul Sztorc via bitcoin-dev <
Post by Paul Sztorc via bitcoin-dev
Hi ZmnSCPxj,
It seems that, in your version, the "bribers" would react to the scheme
in inefficient ways, particularly when the mainchain's tx-fee-rate (ie
fee per Kb) is low.
In short, there would be many bribe-attempts (each of which would take
up space in mainchain blocks), almost all of which would be unsuccessful.
In turn, miners would likely react to this, and try to improve the state
of affairs by offering users the privilege of occupying transaction slot
#2 (ie, the one right after the coinbase). Users would need to trust
miners for this, which introduces a cost friction which is pure
deadweight loss. And, it might be easier for larger/older miners to be
trustworthy than smaller/newer ones.
Your way is actually very similar to mine. Mine _forces_ the bribe to be
in the earliest txn (the coinbase) and to only occur once. Yours doesn't
do anything to refund the briber, if the sidechain (but not the
mainchain) reorganizes (as it can easily do, if an older sidechain
parent is extended while the mainchain proceeds normally). This creates
additional risk.
I think mine is also much more space-efficient. Even if ours each had
exactly one h* per sidechain per block, it seems that I only require one
hash to be communicated (plus an indicator byte, and a ~2 byte counter
for the ratchet), whereas you require two. Since its overhead per
sidechain per block, it actually might really add up.
Thanks,
Paul
Post by ZmnSCPxj via bitcoin-dev
Good morning.
OP_RETURN <sidechain-id> <sidechain-block-id>
A transaction with such an output would allow sidechain-miners to bribe
mainchain-miners by paying a transaction fee if the transaction
containing this OP_RETURN is included in a block and committed to by a
mainchain-miner in the Merkle tree root.
It would not require a softfork.
--
I have an alternate proposal that sidechains and altcoins that want to
1. Encode a block header as a simple cons-pair, with the head as the
block and the tail as the parent cons-pair.
1.1. This can be encoded as a 32-byte hash of the block including its
header, and the 32-byte hash of the parent cons-pair.
1.2. This is now the actual "chain" in the sidecoin/altcoin
blockchain.
Post by ZmnSCPxj via bitcoin-dev
2. When a sidechain-node wants to know the consensus, it downloads
mainchain-blocks and looks for OP_RETURN's.
2.1. Starting with its genesis cons-pair hash (equivalent to the empty
list) as the current cons-pair, it scans each OP_RETURN transaction.
2.1.1. If an OP_RETURN is 64-byte and has the parent cons-pair equal
to
Post by ZmnSCPxj via bitcoin-dev
the current cons-pair, look for the side block indicated and confirm
its
Post by ZmnSCPxj via bitcoin-dev
correctness. If correct, update the current cons-pair for the hash of
the OP_RETURN data.
2.2. When reaching the latest mainchain block, the current cons-pair
is
Post by ZmnSCPxj via bitcoin-dev
now the sidecoin/altcoin latest block.
2.3. Note that if multiple OP_RETURN in a block match the current
cons-pair, the first one is considered the correct chain. This
property
Post by ZmnSCPxj via bitcoin-dev
means that the sidechain/altchain can only have a chainsplit if the
mainchain has a chainsplit.
3. When a sidechain-miner wants to create a side-block, it generates a
new cons-pair and creates an OP_RETURN transaction for it, paying a
mainchain-miner to include it in the next mainchain-block.
3.1. The sidechain-miner risks that its competitors will outbid it and
get its OP_RETURN earlier in a mainchain-block (or earlier in the order
of transactions). It can mitigate this risk by updating itself to
become a mainchain-miner, it can then keep its OP_RETURN transaction
private and put it earlier in the block, ensuring it will "win" the
sidechain-consensus if it wins the mainchain-consensus.
Regards,
ZmnSCPxj
-------- Original Message --------
Subject: [bitcoin-dev] BIP: OP_BRIBVERIFY - the op code needed for
Blind
Post by ZmnSCPxj via bitcoin-dev
Merge Mined drivechains
Local Time: June 28, 2017 8:37 AM
UTC Time: June 28, 2017 12:37 AM
<pre>
BIP: <BIP number>
Layer: Consensus (Soft fork)
Title: OP_BRIBEVERIFY
Status: Draft
Type: Standards Track
Created: 2017-06-27
</pre>
==Abstract==
This BIP describes a new opcode, OP_BRIBEVERIFY, for the Bitcoin
scripting system that allows for a user to bribe a miner to include a
hash
Post by ZmnSCPxj via bitcoin-dev
in the coinbase transaction's output.
==Summary==
BRIBEVERIFY redefines the existing NOP4 opcode. When executed, if the
given
Post by ZmnSCPxj via bitcoin-dev
critical hash is included at the given vout index in the coinbase transaction
the script evaluates to true. Otherwise, the script will fail.
This allows sidechains to be merged mined against
bitcoin without burdening bitcoin miners with extra resource
requirements.
Post by ZmnSCPxj via bitcoin-dev
==Motivation==
The current political climate of bitcoin is extremely contentious. Many
community members
have different visions of what bitcoin is. This op code is meant to
enable [http://www.truthcoin.info/blog/blind-merged-mining/ Blind
Merge
Post by ZmnSCPxj via bitcoin-dev
Mining].
This enables sidechains in Bitcoin. With OP_BRIBEVERIFY, sidechains miners can
bribe bitcoin miners to to include their block hash in the bitcoin
blockchain. If their block
is included in the coinbase transaction's vout, it is assumed that
block
Post by ZmnSCPxj via bitcoin-dev
is a mined block on the sidechain.
This will allow various factions of the community to realize their
vision on their own separate
blockchain that is interoperable with the bitcoin blockchain. This
allows those factions to use
bitcoin as a 'reserve currency' for their own network.
===Commitment Structure===
A new block rule is added which requires that the miner's coinbase
reward be at index 0 in the coinbase transaction's output vector.
It also fixes the witness commitment output to be at index 1 of the
coinbase transaction's output vector.
This is needed so we can reliably tell what vout corresponds to what
drivechain. For instance, the mimblewimble sidechain
could correspond to index 2 of the vector outputs on the coinbase transaction.
The commitment is recorded in a <code>scriptPubKey</code> of the
coinbase transaction. It must be at least 34 bytes in size
1-byte - OP_RETURN (0x6a)
1-byte - Push the following 32 bytes (0x20)
32-byte - block hash
the 35th byte and onward have no consensus meaning.
===OP_BRIBEVERIFY op code===
This op code reads two arguments from the stack. The stack top is
expected to be a sidechain id for which this user attempting to blind
merge mine for.
The next element on the stack is expected to be a block hash. This op
code looks into the coinbase transaction's output vector at the given
index (which is derived from the sidechain id) and checks
to see if the hash in the block matches the hash inside of the
BRIBEVERIFY program. If the hashes match, the OP_BRIBEVERIFY acts as an
OP_NOP. If the
comparison between the two hashes fail, the script fails.
===BRIBEVERIFY program===
1-byte - Push the following 32 bytes (0x20)
32-byte - block hash
1 byte - Push operation? (needed if number can't be encoded as OP_0 - OP_16)
1 byte - sidechain id
1 byte - OP_BRIBEVERIFY op code
==Detailed Specification==
Refer to the reference implementation, reproduced below, for the
precise
Post by ZmnSCPxj via bitcoin-dev
semantics and detailed rationale for those semantics.
{
//format: block_hash sidechain_id OP_BRIBEVERIFY
if (!(flags & SCRIPT_VERIFY_BRIBEVERIFY)) {
// not enabled; treat as a NOP4
if (flags & SCRIPT_VERIFY_DISCOURAGE_UPGRADABLE_NOPS) {
return set_error(serror, SCRIPT_ERR_DISCOURAGE_UPGRADAB
LE_NOPS);
Post by ZmnSCPxj via bitcoin-dev
}
break;
}
if (stack.size() < 2)
return set_error(serror, SCRIPT_ERR_INVALID_STACK_OPERATION);
const CScriptNum scriptNumSidechainId(stacktop(
-1),fRequireMinimal);
Post by ZmnSCPxj via bitcoin-dev
uint8_t nSidechainId;
if (!checker.CheckSidechainId(scriptNumSidechainId,nSidechainId))
{
Post by ZmnSCPxj via bitcoin-dev
return set_error(serror, SCRIPT_ERR_UNKNOWN_SIDECHAIN);
}
// Check block hash
bool fHashCritical =
checker.CheckCriticalHash(stacktop(-2),nSidechainId);
if (!fHashCritical) {
return set_error(serror, SCRIPT_ERR_UNSATISFIED_BRIBE);
}
break;
}
https://github.com/Christewart/bitcoin/blob/94b6f33f2278c42d
4d8758a3c8ffe2078e4ec933/src/script/interpreter.cpp#L427
Post by ZmnSCPxj via bitcoin-dev
https://github.com/drivechain-project/bitcoin/pull/13
==Deployment==
TODO
==Credits==
Credit to Paul Sztorc for the original idea of Blind Merge Mined
sidechains.
Post by ZmnSCPxj via bitcoin-dev
Credit to CryptAxe for writing the foundational layer of software for
drivechains so I could implement OP_BRIBEVERIFY.
==References==
Blind Merge Mined Sidechains -
http://www.truthcoin.info/blog/blind-merged-mining/
Mailing list discussion -
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017
-May/014408.html
Post by ZmnSCPxj via bitcoin-dev
==Copyright==
This document is placed in the public domain.
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
ZmnSCPxj via bitcoin-dev
2017-06-30 04:00:27 UTC
Permalink
Raw Message
Good Morning Paul,
Post by Paul Sztorc via bitcoin-dev
It seems that, in your version, the "bribers" would react to the scheme
in inefficient ways, particularly when the mainchain"s tx-fee-rate (ie
fee per Kb) is low.
In short, there would be many bribe-attempts (each of which would take
up space in mainchain blocks), almost all of which would be unsuccessful.
In turn, miners would likely react to this, and try to improve the state
of affairs by offering users the privilege of occupying transaction slot
#2 (ie, the one right after the coinbase). Users would need to trust
miners for this, which introduces a cost friction which is pure
deadweight loss. And, it might be easier for larger/older miners to be
trustworthy than smaller/newer ones.
I understand.
Post by Paul Sztorc via bitcoin-dev
Your way is actually very similar to mine. Mine _forces_ the bribe to be
in the earliest txn (the coinbase) and to only occur once. Yours doesn"t
do anything to refund the briber, if the sidechain (but not the
mainchain) reorganizes (as it can easily do, if an older sidechain
parent is extended while the mainchain proceeds normally). This creates
additional risk.
I don't understand this part. In my scheme, a sidechain cannot reorganize unless the mainchain reorganizes, since the consensus loop only cares about matching the current block; it ignores splits and does not consider them valid.
But I suppose you are considering something like the Ethereum mutability feature, which I do not think is something you would want in a sidechain.
Post by Paul Sztorc via bitcoin-dev
I think mine is also much more space-efficient. Even if ours each had
exactly one h* per sidechain per block, it seems that I only require one
hash to be communicated (plus an indicator byte, and a ~2 byte counter
for the ratchet), whereas you require two. Since its overhead per
sidechain per block, it actually might really add up.
Do you not provide a single sidechain's h* twice in the block? Once in the coinbase and once in the briber's separate transaction?
In my scheme at least there is no indicator byte -- the "previous block" hash is the indicator of which sidechain it is extending. From your other emails on this list, it seems the ratchet is for withdrawals from sidechain to mainchain? If so, should it not only appear in only some of the sidechains (the ones which are currently doing some withdrawal?)?
Regards,
ZmnSCPxj
Chris Stewart via bitcoin-dev
2017-06-30 14:12:30 UTC
Permalink
Raw Message
I don't understand this part. In my scheme, a sidechain cannot reorganize
unless the mainchain reorganizes, since the consensus loop only cares about
matching the current block; it ignores splits and does not consider them
valid.

Maybe I am misunderstanding you, but isn't this a flaw not a feature? What
if a attacker pays a large fee to have his *invalid* block hash included in
the bitcoin mainchain? Would this block *have* to be included in the
sidechain's blockchain forever since *it was* included in bitcoin
blockchain?
Do you not provide a single sidechain's h* twice in the block? Once in
the coinbase and once in the briber's separate transaction?

Yes, my BIP proposal does this.
In my scheme at least there is no indicator byte -- the "previous block"
hash is the indicator of which sidechain it is extending. From your other
emails on this list, it seems the ratchet is for withdrawals from sidechain
to mainchain? If so, should it not only appear in only some of the
sidechains (the ones which are currently doing some withdrawal?)?

Maybe I am missing something here, but why we do *explicitly* commit to the
previous block hash? Isn't it implicitly committed to via SHA256(SHA256())?
If a drivechain node tries to sync the drivechain from bitcoin's commitment
headers, it will invalidate that block since
the block hash does not correctly reference the previous block hash. AFAICT
there is no need to explicitly specify the previous block hash in the OP_BV
output. In general, I don't think we should assume these commitment headers
dictate the strict ordering of blocks on the sidechain -- only potential
blocks that
*might* be valid. To guarantee full validity drivechain nodes will have to
download the full block and figure out if they follow all of the consensus
rules.

This is sort of like headers first sync in bitcoin core:

https://bitcoin.org/en/developer-guide#headers-first

-Chris
Good Morning Paul,
Post by Paul Sztorc via bitcoin-dev
It seems that, in your version, the "bribers" would react to the scheme
in inefficient ways, particularly when the mainchain"s tx-fee-rate (ie
fee per Kb) is low.
In short, there would be many bribe-attempts (each of which would take
up space in mainchain blocks), almost all of which would be unsuccessful.
In turn, miners would likely react to this, and try to improve the state
of affairs by offering users the privilege of occupying transaction slot
#2 (ie, the one right after the coinbase). Users would need to trust
miners for this, which introduces a cost friction which is pure
deadweight loss. And, it might be easier for larger/older miners to be
trustworthy than smaller/newer ones.
I understand.
Post by Paul Sztorc via bitcoin-dev
Your way is actually very similar to mine. Mine _forces_ the bribe to be
in the earliest txn (the coinbase) and to only occur once. Yours doesn"t
do anything to refund the briber, if the sidechain (but not the
mainchain) reorganizes (as it can easily do, if an older sidechain
parent is extended while the mainchain proceeds normally). This creates
additional risk.
I don't understand this part. In my scheme, a sidechain cannot reorganize
unless the mainchain reorganizes, since the consensus loop only cares about
matching the current block; it ignores splits and does not consider them
valid.
But I suppose you are considering something like the Ethereum mutability
feature, which I do not think is something you would want in a sidechain.
Post by Paul Sztorc via bitcoin-dev
I think mine is also much more space-efficient. Even if ours each had
exactly one h* per sidechain per block, it seems that I only require one
hash to be communicated (plus an indicator byte, and a ~2 byte counter
for the ratchet), whereas you require two. Since its overhead per
sidechain per block, it actually might really add up.
Do you not provide a single sidechain's h* twice in the block? Once in
the coinbase and once in the briber's separate transaction?
In my scheme at least there is no indicator byte -- the "previous block"
hash is the indicator of which sidechain it is extending. From your other
emails on this list, it seems the ratchet is for withdrawals from sidechain
to mainchain? If so, should it not only appear in only some of the
sidechains (the ones which are currently doing some withdrawal?)?
Regards,
ZmnSCPxj
CryptAxe via bitcoin-dev
2017-06-30 16:51:34 UTC
Permalink
Raw Message
To ZmnSCPxj:

I don't understand this part. In my scheme, a sidechain cannot reorganize
unless the mainchain reorganizes, since the consensus loop only cares about
matching the current block; it ignores splits and does not consider them
valid.

But I suppose you are considering something like the Ethereum mutability
feature, which I do not think is something you would want in a sidechain.


The goal was to allow for sidechain reorgs without effecting the mainchain
at all. With the ratchet system (WIP) the sidechain miners can either move
the side chain forward or start a split at some previous sidechain block
height. This happens as the main chain moves forward normally.

From your other emails on this list, it seems the ratchet is for
withdrawals from sidechain to mainchain? ...


The ratchet system is actually what links the h* data from bribes to
sidechain blocks. h*'s (which are sidechain block hashes) are added to the
ratchet system if they move the sidechain forward or start a split like I
mentioned before. Then a sidechain can request of their local mainchain
node to verify the headers they have downloaded from sidechain peers and
form the side chain.
Paul Sztorc via bitcoin-dev
2017-07-02 21:32:50 UTC
Permalink
Raw Message
Hi,

Sorry for the delay, I overlooked this email until now. I see that Chris
and CryptAxe both answered but I will also answer, because the message
was addressed to me.
Post by Paul Sztorc via bitcoin-dev
Your way is actually very similar to mine. Mine _forces_ the bribe to be
in the earliest txn (the coinbase) and to only occur once. Yours doesn"t
do anything to refund the briber, if the sidechain (but not the
mainchain) reorganizes (as it can easily do, if an older sidechain
parent is extended while the mainchain proceeds normally). This creates
additional risk.
I don't understand this part. In my scheme, a sidechain cannot
reorganize unless the mainchain reorganizes, since the consensus loop
only cares about matching the current block; it ignores splits and
does not consider them valid.
If I've understood you correctly, you have said that each OP Return
links the (ex)-latest block to a brand new block, and that whichever
message of this kind comes first (in the mainchain) wins and the rest
are discarded.

So what if I had a sidechain represented by a jumble of capital letters,
discarded entries as lowercase letters.

Mainchain Block #200001: [0 --> Q], [0 -->v], [0 -->s], [0 -->b],
Mainchain Block #200002: [Q --> H], [Q --> z],
Mainchain Block #200003: [H --> F]
Mainchain Block #200004: [F --> J], [F -->w]
Mainchain Block #200005: [H --> P], [J -->x]
Mainchain Block #200006: [P --> D]

Isn't the chain {{ Q --> H --> F --> J }} now starting to reorg, with a
competing chain {{ Q --> H --> P --> D }} ?
But I suppose you are considering something like the Ethereum
mutability feature, which I do not think is something you would want
in a sidechain.
What I do want to do, is retain the existing model to some extent.
Specifically, to the degree where sidechains could salvage some bad
situations (eg value overflow incident, or March 2013 incident).
Post by Paul Sztorc via bitcoin-dev
I think mine is also much more space-efficient. Even if ours each had
exactly one h* per sidechain per block, it seems that I only require one
hash to be communicated (plus an indicator byte, and a ~2 byte counter
for the ratchet), whereas you require two. Since its overhead per
sidechain per block, it actually might really add up.
Do you not provide a single sidechain's h* twice in the block? Once
in the coinbase and once in the briber's separate transaction?
That is a good point. Technically, we do include it twice, but the
second instance (briber-transaction) can be "shuffled" out if the
counterparties are part of the same Lightning Network (which I expect to
the be the case, in equilibrium).
In my scheme at least there is no indicator byte -- the "previous
block" hash is the indicator of which sidechain it is extending. From
your other emails on this list, it seems the ratchet is for
withdrawals from sidechain to mainchain? If so, should it not only
appear in only some of the sidechains (the ones which are currently
doing some withdrawal?)?
No, sorry. There are many tangled issues (Drivechain (total system);
side-to-main withdrawals (OP CountACKs); individual Drivechains
themselves; Blind Merged Mining (OP BribeVerify)). The ratchet is not
about withdrawals, it is exclusively about Blind Merged Mining, and
making a better OP BribeVerify that offers better guarantees to both sides.

Paul
ZmnSCPxj via bitcoin-dev
2017-07-04 07:21:23 UTC
Permalink
Raw Message
Good morning Paul, Chris, and CryptAxe,
@Paul
Post by Paul Sztorc via bitcoin-dev
Your way is actually very similar to mine. Mine _forces_ the bribe to be
in the earliest txn (the coinbase) and to only occur once. Yours doesn"t
do anything to refund the briber, if the sidechain (but not the
mainchain) reorganizes (as it can easily do, if an older sidechain
parent is extended while the mainchain proceeds normally). This creates
additional risk.
I don"t understand this part. In my scheme, a sidechain cannot
reorganize unless the mainchain reorganizes, since the consensus loop
only cares about matching the current block; it ignores splits and
does not consider them valid.
If I"ve understood you correctly, you have said that each OP Return
links the (ex)-latest block to a brand new block, and that whichever
message of this kind comes first (in the mainchain) wins and the rest
are discarded.
So what if I had a sidechain represented by a jumble of capital letters,
discarded entries as lowercase letters.
Mainchain Block #200001: [0 --> Q], [0 -->v], [0 -->s], [0 -->b],
Mainchain Block #200002: [Q --> H], [Q --> z],
Mainchain Block #200003: [H --> F]
Mainchain Block #200004: [F --> J], [F -->w]
Mainchain Block #200005: [H --> P], [J -->x]
Mainchain Block #200006: [P --> D]
Isn"t the chain {{ Q --> H --> F --> J }} now starting to reorg, with a
competing chain {{ Q --> H --> P --> D }} ?
No, because at block #20005, the topmost sidechain block is J, not H, and the H->P will not be considered as valid -- only the J->x is valid, even though H->P comes first.
Please see the pseudocode I sent before in detail and consider how it will work with your given mainchain blocks example.
But I suppose you are considering something like the Ethereum
mutability feature, which I do not think is something you would want
in a sidechain.
What I do want to do, is retain the existing model to some extent.
Specifically, to the degree where sidechains could salvage some bad
situations (eg value overflow incident, or March 2013 incident).
I suppose some kinds of mutability are desirable. In my model, a sidechain reorg can be forced if the sidechain code is forked to specifically force some previously-valid block to become invalid, by developer fiat. In the example you gave, basically, if you want to reorg from Q->H->F->J to Q->H->P->D then you would fork the sidechain consensus code to declare that block F is invalid.
I am hesitant to make mutability something that is easy to force, however.
Post by Paul Sztorc via bitcoin-dev
I think mine is also much more space-efficient. Even if ours each had
exactly one h* per sidechain per block, it seems that I only require one
hash to be communicated (plus an indicator byte, and a ~2 byte counter
for the ratchet), whereas you require two. Since its overhead per
sidechain per block, it actually might really add up.
Do you not provide a single sidechain"s h* twice in the block? Once
in the coinbase and once in the briber"s separate transaction?
That is a good point. Technically, we do include it twice, but the
second instance (briber-transaction) can be "shuffled" out if the
counterparties are part of the same Lightning Network (which I expect to
the be the case, in equilibrium).
Payments on LN are finalized when the payee provides a preimage for a hashlock, whether by chain or by LN. Although I suppose you can use a bribelocked timelocked contract instead of a hashlocked timelocked contract. I suppose it would be almost the same, except the bribelock is provided off-chain as a proof of existence in a mainblock coinbase.
In addition, it may be possible to create a payment channel specifically between a sidechain operator and a mainchain miner.
In my scheme at least there is no indicator byte -- the "previous
block" hash is the indicator of which sidechain it is extending. From
your other emails on this list, it seems the ratchet is for
withdrawals from sidechain to mainchain? If so, should it not only
appear in only some of the sidechains (the ones which are currently
doing some withdrawal?)?
No, sorry. There are many tangled issues (Drivechain (total system);
side-to-main withdrawals (OP CountACKs); individual Drivechains
themselves; Blind Merged Mining (OP BribeVerify)). The ratchet is not
about withdrawals, it is exclusively about Blind Merged Mining, and
making a better OP BribeVerify that offers better guarantees to both sides.
Can you describe the ratchet better? I am sorry but when I first heard of "blind" merge mining, the first thing that came to mind was the use of OP_RETURN. This is truly blind as the mainchain miner is given what is effectively a blob of data, and the mainchain miner cannot expect any kind of format from OP_RETURN. This has the tremendous advantage of not even requiring a softfork.
@Chris
What if a attacker pays a large fee to have his *invalid* block hash included in the bitcoin mainchain? Would this block *have* to be included in the sidechain's blockchain forever since *it was* included in bitcoin blockchain?
In my scheme, if you read carefully through the pseudocode, a block list node is valid only if its block is valid.
Basically, in my scheme, the OP_RETURN data *is* the sidechain block headers stored on the mainchain. To save space, the sidechain block headers are reduced to only the previous-block-header commitment and the current-block-data commitment. All of the other data you would want to put in the block header (e.g. UTXO set commitment, signalling bits, time-of-day...) would be part of the current-block-data instead of the block header. Thus if the current-block-data is invalid the sidechain block header is invalid and another sidechain block header based on the previous block header will be searched for.
My understanding is that your attack scenario is not helped by OP_BRIBEVERIFY alone, as a rich sidechain attacker can provide a bigger bribe to an invalid h* especially since the mainchain miner will not even check the h*, just insert it into the coinbase.
Maybe I am missing something here, but why we do *explicitly* commit to the previous block hash? Isn't it implicitly committed to via SHA256(SHA256())?
In order to eliminate having to specify a sidechain index, and to remove sidechain indexes altogether. Instead the sidechain is identified by its topmost block header hash.
@CryptAxe
The ratchet system is actually what links the h* data from bribes to sidechain blocks. h*'s (which are sidechain block hashes) are added to the ratchet system if they move the sidechain forward or start a split like I mentioned before. Then a sidechain can request of their local mainchain node to verify the headers they have downloaded from sidechain peers and form the side chain.
I see. However, then, I propose that my OP_RETURN scheme is superior as the sidechain block headers are indeed visible directly on the mainchain, and the mainchain node does not even need to be "local", but can be sourced anywhere, without requiring a ratchet structure (whose purpose I still have not managed to grok).
Regards,
ZmnSCPxj
Chris Stewart via bitcoin-dev
2017-07-04 15:06:06 UTC
Permalink
Raw Message
Hi ZmnSCPxj,


In my scheme, if you read carefully through the pseudocode, a block list
Post by ZmnSCPxj via bitcoin-dev
node is valid only if its block is valid.
It seems this is a contradiction against the "blind" part of blind merge
mining. How can a bitcoin blockchain node enforce this without tracking the
sidechain?

Basically, in my scheme, the OP_RETURN data *is* the sidechain block
Post by ZmnSCPxj via bitcoin-dev
headers stored on the mainchain. To save space, the sidechain block
headers are reduced to only the previous-block-header commitment and the
current-block-data commitment. All of the other data you would want to put
in the block header (e.g. UTXO set commitment, signalling bits,
time-of-day...) would be part of the current-block-data instead of the
block header. Thus if the current-block-data is invalid the sidechain
block header is invalid and another sidechain block header based on the
previous block header will be searched for.
It seems both of our schemes need to include 2 32 bit hashes in the
blockchain. Your scheme needs a previous block header hash and the current
block header hash, while mine includes the current block header hash
twice. We can just commit to all that information via the block header
hash and if a sidechain node lies to us will we are doing IBD the hashes
won't match with what was included in the bitcoin blockchain.

I'll follow your discussion with Paul about sidechain reorgs, but I think
his proposal is more desirable -- it follows what actually happens in the
bitcoin mining process where we *can* have chain splits when miners
simultaneously find a block. Other miners will pick one of the two blocks
to mine on top of and eventually one chain will become longer than the
other. Therefore that chain will have it's block's orphaned and the
miners/nodes following the dead chain will reorg on top of the longest
chain.

In Paul's scheme, we replace PoW with a bribe. At the conceptual level
these are somewhat similar. In PoW a miner is willing to pay a certain
amount of money (on electricity) to try to find a bitcoin block. With
OP_BRIBEVERIFY a sidechain miner is willing pay a certain amount of money
to find a block.

In PoW, there is nothing at the software level that says a miner cannot
just decide to build on a old block. I could decide to build on the genesis
block if I wanted to. Obviously this is a stupid idea as I'll never
overtake the bitcoin blockchain with 8 years of PoW behind it -- but it
doesn't mean I couldn't try if I wanted too. Your scheme from what I
understand prevents this from happening -- and I don't think that is
desirable. You might be able to make an argument that a rich attacker can
*stall* mining progress on the drivechain, but I think the same argument
can be made with a rich miner on the bitcoin blockchain as well. I think
miners have threatened to do that if BIP148 caused a chain split.

Can you link to the aforementioned pseudocode? I must have missed it on the
mailing list.

-Chris
Post by ZmnSCPxj via bitcoin-dev
Good morning Paul, Chris, and CryptAxe,
@Paul
Post by Paul Sztorc via bitcoin-dev
Your way is actually very similar to mine. Mine _forces_ the bribe to
be
Post by Paul Sztorc via bitcoin-dev
in the earliest txn (the coinbase) and to only occur once. Yours
doesn"t
Post by Paul Sztorc via bitcoin-dev
do anything to refund the briber, if the sidechain (but not the
mainchain) reorganizes (as it can easily do, if an older sidechain
parent is extended while the mainchain proceeds normally). This creates
additional risk.
I don"t understand this part. In my scheme, a sidechain cannot
reorganize unless the mainchain reorganizes, since the consensus loop
only cares about matching the current block; it ignores splits and
does not consider them valid.
If I"ve understood you correctly, you have said that each OP Return
links the (ex)-latest block to a brand new block, and that whichever
message of this kind comes first (in the mainchain) wins and the rest
are discarded.
So what if I had a sidechain represented by a jumble of capital letters,
discarded entries as lowercase letters.
Mainchain Block #200001: [0 --> Q], [0 -->v], [0 -->s], [0 -->b],
Mainchain Block #200002: [Q --> H], [Q --> z],
Mainchain Block #200003: [H --> F]
Mainchain Block #200004: [F --> J], [F -->w]
Mainchain Block #200005: [H --> P], [J -->x]
Mainchain Block #200006: [P --> D]
Isn"t the chain {{ Q --> H --> F --> J }} now starting to reorg, with a
competing chain {{ Q --> H --> P --> D }} ?
No, because at block #20005, the topmost sidechain block is J, not H, and
the H->P will not be considered as valid -- only the J->x is valid, even
though H->P comes first.
Please see the pseudocode I sent before in detail and consider how it will
work with your given mainchain blocks example.
But I suppose you are considering something like the Ethereum
mutability feature, which I do not think is something you would want
in a sidechain.
What I do want to do, is retain the existing model to some extent.
Specifically, to the degree where sidechains could salvage some bad
situations (eg value overflow incident, or March 2013 incident).
I suppose some kinds of mutability are desirable. In my model, a
sidechain reorg can be forced if the sidechain code is forked to
specifically force some previously-valid block to become invalid, by
developer fiat. In the example you gave, basically, if you want to reorg
from Q->H->F->J to Q->H->P->D then you would fork the sidechain consensus
code to declare that block F is invalid.
I am hesitant to make mutability something that is easy to force, however.
Post by Paul Sztorc via bitcoin-dev
I think mine is also much more space-efficient. Even if ours each had
exactly one h* per sidechain per block, it seems that I only require
one
Post by Paul Sztorc via bitcoin-dev
hash to be communicated (plus an indicator byte, and a ~2 byte counter
for the ratchet), whereas you require two. Since its overhead per
sidechain per block, it actually might really add up.
Do you not provide a single sidechain"s h* twice in the block? Once
in the coinbase and once in the briber"s separate transaction?
That is a good point. Technically, we do include it twice, but the
second instance (briber-transaction) can be "shuffled" out if the
counterparties are part of the same Lightning Network (which I expect to
the be the case, in equilibrium).
Payments on LN are finalized when the payee provides a preimage for a
hashlock, whether by chain or by LN. Although I suppose you can use a
bribelocked timelocked contract instead of a hashlocked timelocked
contract. I suppose it would be almost the same, except the bribelock is
provided off-chain as a proof of existence in a mainblock coinbase.
In addition, it may be possible to create a payment channel specifically
between a sidechain operator and a mainchain miner.
In my scheme at least there is no indicator byte -- the "previous
block" hash is the indicator of which sidechain it is extending. From
your other emails on this list, it seems the ratchet is for
withdrawals from sidechain to mainchain? If so, should it not only
appear in only some of the sidechains (the ones which are currently
doing some withdrawal?)?
No, sorry. There are many tangled issues (Drivechain (total system);
side-to-main withdrawals (OP CountACKs); individual Drivechains
themselves; Blind Merged Mining (OP BribeVerify)). The ratchet is not
about withdrawals, it is exclusively about Blind Merged Mining, and
making a better OP BribeVerify that offers better guarantees to both
sides.
Can you describe the ratchet better? I am sorry but when I first heard of
"blind" merge mining, the first thing that came to mind was the use of
OP_RETURN. This is truly blind as the mainchain miner is given what is
effectively a blob of data, and the mainchain miner cannot expect any kind
of format from OP_RETURN. This has the tremendous advantage of not even
requiring a softfork.
@Chris
What if a attacker pays a large fee to have his *invalid* block hash
included in the bitcoin mainchain? Would this block *have* to be included
in the sidechain's blockchain forever since *it was* included in bitcoin
blockchain?
In my scheme, if you read carefully through the pseudocode, a block list
node is valid only if its block is valid.
Basically, in my scheme, the OP_RETURN data *is* the sidechain block
headers stored on the mainchain. To save space, the sidechain block
headers are reduced to only the previous-block-header commitment and the
current-block-data commitment. All of the other data you would want to put
in the block header (e.g. UTXO set commitment, signalling bits,
time-of-day...) would be part of the current-block-data instead of the
block header. Thus if the current-block-data is invalid the sidechain
block header is invalid and another sidechain block header based on the
previous block header will be searched for.
My understanding is that your attack scenario is not helped by
OP_BRIBEVERIFY alone, as a rich sidechain attacker can provide a bigger
bribe to an invalid h* especially since the mainchain miner will not even
check the h*, just insert it into the coinbase.
Maybe I am missing something here, but why we do *explicitly* commit to
the previous block hash? Isn't it implicitly committed to via
SHA256(SHA256())?
In order to eliminate having to specify a sidechain index, and to remove
sidechain indexes altogether. Instead the sidechain is identified by its
topmost block header hash.
@CryptAxe
The ratchet system is actually what links the h* data from bribes to
sidechain blocks. h*'s (which are sidechain block hashes) are added to the
ratchet system if they move the sidechain forward or start a split like I
mentioned before. Then a sidechain can request of their local mainchain
node to verify the headers they have downloaded from sidechain peers and
form the side chain.
I see. However, then, I propose that my OP_RETURN scheme is superior as
the sidechain block headers are indeed visible directly on the mainchain,
and the mainchain node does not even need to be "local", but can be sourced
anywhere, without requiring a ratchet structure (whose purpose I still have
not managed to grok).
Regards,
ZmnSCPxj
ZmnSCPxj via bitcoin-dev
2017-07-12 08:50:52 UTC
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Post by ZmnSCPxj via bitcoin-dev
In my scheme, if you read carefully through the pseudocode, a block list node is valid only if its block is valid.
It seems this is a contradiction against the "blind" part of blind merge mining. How can a bitcoin blockchain node enforce this without tracking the sidechain?
From: https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-June/014668.html
Post by ZmnSCPxj via bitcoin-dev
Post by ZmnSCPxj via bitcoin-dev
2. When a sidechain-node wants to know the consensus, it downloads mainchain-blocks and looks for OP_RETURN's.
2.1. Starting with its genesis cons-pair hash (equivalent to the empty list) as the current cons-pair, it scans each OP_RETURN transaction.
2.1.1. If an OP_RETURN is 64-byte and has the parent cons-pair equal to the current cons-pair, look for the side block indicated and confirm its correctness. If correct, update the current cons-pair for the hash of the OP_RETURN data.
2.2. When reaching the latest mainchain block, the current cons-pair is now the sidecoin/altcoin latest block.
2.3. Note that if multiple OP_RETURN in a block match the current cons-pair, the first one is considered the correct chain. This property means that the sidechain/altchain can only have a chainsplit if the mainchain has a chainsplit.
It's the sidechain node which needs to learn about the sidechain blockchain anyway. So it's the one that does the checking of this.
For that matter, a mainchain miner can be bribed to commit to a random number rather than a valid h* block, and it will still lead all the sidechain nodes on a random chase to look for the indicated block.
I'll follow your discussion with Paul about sidechain reorgs, but I think his proposal is more desirable -- it follows what actually happens in the bitcoin mining process where we *can* have chain splits when
miners simultaneously find a block. Other miners will pick one of the two blocks to mine on top of and eventually one chain will become longer than the other. Therefore that chain will have it's block's
orphaned and the miners/nodes following the dead chain will reorg on top of the longest chain.
In this paper: http://diyhpl.us/~bryan/papers2/bitcoin/On%20the%20instability%20of%20Bitcoin%20without%20the%20block%20reward%20-%202016.pdf
As far as I understood that paper, it means that if the block reward no longer exists, miners can profitably attempt to undercut any full blocks.
Sidechains do not have block rewards (unless the sidechain issues its own asset type that is separate from and not convertible to mainchain bitcoins).
Thus, to protect against undercutting attacks in the sidechain, we would need to ensure that the sidechain cannot be reorged without the mainchain (which currently still has a block reward) being reorged.
At least, this is my consideration. Perhaps the paper is wrong?
---
In any case, let me propose actual improvements to the OP_BRIBEVERIFY proposal:
1. Remove the necessity of coinbase commitments. The miner commits to the sidechain_id and h* in the transaction that pays the OP_BRIBEVERIFY anyway. That way the h* commitment occurs only once in the block, in the transaction that does the OP_BRIBEVERIFY. In addition, there is no need to impose particular ordering on the coinbase outputs, which would be problematic as pointed out by others, for example if the miner is interested only in merge mining for sidechain id #35 and nobody else.
2. When verifying a block, keep a set of sidechain ID's. When processing a transaction in that block with OP_BRIBEVERIFY, check if the sidechain ID is in that set. If not in that set, add it to that set and continue script processing. If already in the set, fail the script processing. This ensures that at most one OP_BRIBEVERIFY exists for each sidechain_id in a mainchain block.
3. Don't number sidechain_id from 0, 1, 2, 3..., because people will fight over the small numbers. Instead identify sidechains by, for example, the hash of their names or the hash of their genesis block or whatever. This allows true permissionless creation of sidechains, without some authority existing that centrally allocates sidechain ID's.
Regards,
ZmnSCPxj
Russell O'Connor via bitcoin-dev
2017-07-12 13:39:17 UTC
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On Wed, Jul 12, 2017 at 4:50 AM, ZmnSCPxj via bitcoin-dev <
bitcoin-***@lists.linuxfoundation.org> wrote:

In any case, let me propose actual improvements to the OP_BRIBEVERIFY
1. Remove the necessity of coinbase commitments. The miner commits to
the sidechain_id and h* in the transaction that pays the OP_BRIBEVERIFY
anyway. That way the h* commitment occurs only once in the block, in the
transaction that does the OP_BRIBEVERIFY. In addition, there is no need to
impose particular ordering on the coinbase outputs, which would be
problematic as pointed out by others, for example if the miner is
interested only in merge mining for sidechain id #35 and nobody else.
2. When verifying a block, keep a set of sidechain ID's. When processing
a transaction in that block with OP_BRIBEVERIFY, check if the sidechain ID
is in that set. If not in that set, add it to that set and continue script
processing. If already in the set, fail the script processing. This
ensures that at most one OP_BRIBEVERIFY exists for each sidechain_id in a
mainchain block.
At this point can we eliminate the need to use the scripting system at all
and just use a special, currently non-standard, OP_RETURN output to hold
the sidechain_id and h* instead? We can soft fork in a rule that at most
one such output can appear in a block per sidechain_id.
Chris Stewart via bitcoin-dev
2017-07-12 18:02:30 UTC
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Hi Russell/ZmnSCPxj,

I think you guys are right. The only problem I can see with it is
replaceability of the bribe transaction. If the 'Bribe' is the fee on the
transaction it isn't clear to me what the best way to replace/remove it is.

If we have the amount in the output (instead of the fee) we can construct a
contract like this

OP_IF <id> <hash> OP_BV OP_ELSE OP_DUP OP_HASH160 <pubkey hash>
OP_EQUALVERIFY OP_CHECKSIG OP_ENDIF

That way, if the miner does *not* include your bribe, he is *still*
incentived to include your redemption.

If we decide to only an OP_RETURN output, we can replace the 'bribe'
transaction with a transaction that double spends the prevout. Thus if your
'bribe' transaction is not included in a block, a miner can still include
your double spend transaction to refund yourself (and a miner gets to
collect his normal mining fee).

I'm not 100% sure if there are mempool policies that would reject this
double spend tx or not -- but I guess this is an implementation detail not
a high level design one.

Also if there is not a commitment in the coinbase transaction it may be
harder to search for drivechain commitments. I've been floating around the
idea of a 'drivechain commitment tx' so we could easily see where all of
the voting is happening for withdrawal transactions -- but that is very
much up in the air.
Hi Russell/ZmnSCPxj,
I think you guys are right. The only problem I can see with it is
replaceability of the bribe transaction. If the 'Bribe' is the fee on the
transaction it isn't clear to me what the best way to replace/remove it is.
If we have the amount in the output (instead of the fee) we can construct
a contract like this
OP_IF <id> <hash> OP_BV OP_ELSE OP_DUP OP_HASH160 <pubkey hash>
OP_EQUALVERIFY OP_CHECKSIG OP_ENDIF
That way, if the miner does *not* include your bribe, he is *still*
incentived to include your redemption.
If we decide to only an OP_RETURN output, we can replace the 'bribe'
transaction with a transaction that double spends the prevout. Thus if your
'bribe' transaction is not included in a block, a miner can still include
your double spend transaction to refund yourself (and a miner gets to
collect his normal mining fee).
I'm not 100% sure if there are mempool policies that would reject this
double spend tx or not -- but I guess this is an implementation detail not
a high level design one.
Also if there is not a commitment in the coinbase transaction it may be
harder to search for drivechain commitments. I've been floating around the
idea of a 'drivechain commitment tx' so we could easily see where all of
the voting is happening for withdrawal transactions -- but that is very
much up in the air.
-Chris
On Wed, Jul 12, 2017 at 8:39 AM, Russell O'Connor via bitcoin-dev <
Post by Russell O'Connor via bitcoin-dev
On Wed, Jul 12, 2017 at 4:50 AM, ZmnSCPxj via bitcoin-dev <
In any case, let me propose actual improvements to the OP_BRIBEVERIFY
1. Remove the necessity of coinbase commitments. The miner commits to
the sidechain_id and h* in the transaction that pays the OP_BRIBEVERIFY
anyway. That way the h* commitment occurs only once in the block, in the
transaction that does the OP_BRIBEVERIFY. In addition, there is no need to
impose particular ordering on the coinbase outputs, which would be
problematic as pointed out by others, for example if the miner is
interested only in merge mining for sidechain id #35 and nobody else.
2. When verifying a block, keep a set of sidechain ID's. When
processing a transaction in that block with OP_BRIBEVERIFY, check if the
sidechain ID is in that set. If not in that set, add it to that set and
continue script processing. If already in the set, fail the script
processing. This ensures that at most one OP_BRIBEVERIFY exists for each
sidechain_id in a mainchain block.
At this point can we eliminate the need to use the scripting system at
all and just use a special, currently non-standard, OP_RETURN output to
hold the sidechain_id and h* instead? We can soft fork in a rule that at
most one such output can appear in a block per sidechain_id.
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Paul Sztorc via bitcoin-dev
2017-07-13 00:00:29 UTC
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I still think it may be more inefficient, in equilibrium. (In other
words, in the future steady state of Bitcoin that includes LN or
something LN-like).

Assume there are N sidechains.

In the coinbase version:
1. There is some single event, per N, that causes nodes to notice that a
new sidechain has been created.
2. Per block, there are N hash commitments (32 bytes) and N instances of
the ratchet's block counter (2 bytes).
3. Per block, some node operator _may_ have BMMed the block, and a miner
therefore might want redeem an OP Bribe that pays BTC from a sidechain
node operator to the miner. But they are likely to negotiate the payment
through the Lightning Network (when this is possible).
4. Sidechains running in SPV mode know exactly where to find the
information they need in order to discover the "longest" chain.

In the OP RETURN version:
1. [same] There is some single event, per N, that causes nodes to notice
that a new sidechain has been created.
2. [+30 bytes (+more?)] Per block, there are N hash commitments (32
bytes) and also N prevBlockHashes (32 bytes). Also, to make this
transaction, someone needs to spend something in the UTXO set (or select
no inputs in a kind of 'hollow transaction'), whereas one coinbase will
always exist per block.
3. [same] No need for a new transaction.
4. [same?] Due to Rusty's soft fork rule of only one h* per sidechain
per block, sidechains need just a merkle tree path, but they don't
necessarily know where it is. They must store extra [?] data to help
them find the data's location?
Post by Chris Stewart via bitcoin-dev
Hi Russell/ZmnSCPxj,
I think you guys are right. The only problem I can see with it is
replaceability of the bribe transaction. If the 'Bribe' is the fee on
the transaction it isn't clear to me what the best way to
replace/remove it is.
I think that that is the purpose of Rusty's soft fork rule about only
including one per sidechain -- miners would have one "slot" per
sidechain, and they would therefore have an incentive to make the slot
count, and would be only selecting the highest fee txn to fill each slot.
Chris Stewart via bitcoin-dev
2017-07-13 20:22:02 UTC
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I'm interested in hearing a reply from Russell/ZmnSCPxj in what they think
about lightning bribes. I hadn't given much thought about those while
writing my original BIP, but it does seem like my original BIP (minus the
fixed indexes in the coinbase output) fits this pretty well. If I
understand Paul correctly the OP_BV output will never hit the blockchain
then -- only the commitment in the coinbase transaction. This means no
extra data (if use lightning) has to be added to the blockchain *except*
the drivechain commitment (34 bytes in the coinbase tx vout). If this is
used for the vast majority bribes it may make the op code worth it.

In general though, I'm still unclear of what purpose the 'Ratchet' serves.
Can you either link to documentation about it or write something up quick?

-Chris
I still think it may be more inefficient, in equilibrium. (In other words,
in the future steady state of Bitcoin that includes LN or something
LN-like).
Assume there are N sidechains.
1. There is some single event, per N, that causes nodes to notice that a
new sidechain has been created.
2. Per block, there are N hash commitments (32 bytes) and N instances of
the ratchet's block counter (2 bytes).
3. Per block, some node operator _may_ have BMMed the block, and a miner
therefore might want redeem an OP Bribe that pays BTC from a sidechain node
operator to the miner. But they are likely to negotiate the payment through
the Lightning Network (when this is possible).
4. Sidechains running in SPV mode know exactly where to find the
information they need in order to discover the "longest" chain.
1. [same] There is some single event, per N, that causes nodes to notice
that a new sidechain has been created.
2. [+30 bytes (+more?)] Per block, there are N hash commitments (32 bytes)
and also N prevBlockHashes (32 bytes). Also, to make this transaction,
someone needs to spend something in the UTXO set (or select no inputs in a
kind of 'hollow transaction'), whereas one coinbase will always exist per
block.
3. [same] No need for a new transaction.
4. [same?] Due to Rusty's soft fork rule of only one h* per sidechain per
block, sidechains need just a merkle tree path, but they don't necessarily
know where it is. They must store extra [?] data to help them find the
data's location?
Hi Russell/ZmnSCPxj,
I think you guys are right. The only problem I can see with it is
replaceability of the bribe transaction. If the 'Bribe' is the fee on the
transaction it isn't clear to me what the best way to replace/remove it is.
I think that that is the purpose of Rusty's soft fork rule about only
including one per sidechain -- miners would have one "slot" per sidechain,
and they would therefore have an incentive to make the slot count, and
would be only selecting the highest fee txn to fill each slot.
Paul Sztorc via bitcoin-dev
2017-07-13 20:45:13 UTC
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Post by Chris Stewart via bitcoin-dev
In general though, I'm still unclear of what purpose the 'Ratchet'
serves. Can you either link to documentation about it or write
something up quick?
-Chris
In Bitcoin, new coins are held for 100 blocks. One result of this is
that the coins can't be spent until there is at least 100 blocks worth
of evidence that they actually are in the longest chain, and are
unlikely to be orphaned.

In BMM, we are concerned about exactly this. For example, imagine that I
bribe you $20 to find my side:block (and, in that block I earn $20.50
worth of side:BTC tx fees), which you do. But then, moments later, you
(or some other miner) orphans the block! So I don't get my $20.50, but
you still keep my $20!

And yet, we want the mainchain to validate as little as possible about
each sidechain. We want a "light touch". So we force the h* to be
accompanied by the modulus of its sidechain block number (we call it
"BlockMod"). The sidechain has a new rule that requires h* to be
included AND that the BlockMod be accurate, in order for the sidechain
block to meet the "synthetic" difficulty requirement. The mainchain has
a new rule forcing each new BlockMod to be in range [-X000,+1] relative
to the old BlockMod (ie, "no skipping ahead, but you can reorg by
starting a new chain from up to a=-X000 blocks ago" ... likely values of
X might be 2 or 4). And finally, BMM has a new rule that the bribe isn't
paid unless the sidechain block in question has been buried by [for
example] 100 sidechain blocks.

Hope that helps,
Paul

Paul Sztorc via bitcoin-dev
2017-07-12 23:31:18 UTC
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Post by ZmnSCPxj via bitcoin-dev
Post by Chris Stewart via bitcoin-dev
Post by ZmnSCPxj via bitcoin-dev
In my scheme, if you read carefully through the pseudocode, a block
list node is valid only if its block is valid.
Post by Chris Stewart via bitcoin-dev
It seems this is a contradiction against the "blind" part of blind
merge mining. How can a bitcoin blockchain node enforce this without
tracking the sidechain?
https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2017-June/014668.html
Post by Chris Stewart via bitcoin-dev
Post by ZmnSCPxj via bitcoin-dev
Post by ZmnSCPxj via bitcoin-dev
2. When a sidechain-node wants to know the consensus, it downloads
mainchain-blocks and looks for OP_RETURN's.
Post by Chris Stewart via bitcoin-dev
Post by ZmnSCPxj via bitcoin-dev
Post by ZmnSCPxj via bitcoin-dev
2.1. Starting with its genesis cons-pair hash (equivalent to the
empty list) as the current cons-pair, it scans each OP_RETURN transaction.
Post by Chris Stewart via bitcoin-dev
Post by ZmnSCPxj via bitcoin-dev
Post by ZmnSCPxj via bitcoin-dev
2.1.1. If an OP_RETURN is 64-byte and has the parent cons-pair
equal to the current cons-pair, look for the side block indicated and
confirm its correctness. If correct, update the current cons-pair for
the hash of the OP_RETURN data.
Post by Chris Stewart via bitcoin-dev
Post by ZmnSCPxj via bitcoin-dev
Post by ZmnSCPxj via bitcoin-dev
2.2. When reaching the latest mainchain block, the current
cons-pair is now the sidecoin/altcoin latest block.
Post by Chris Stewart via bitcoin-dev
Post by ZmnSCPxj via bitcoin-dev
Post by ZmnSCPxj via bitcoin-dev
2.3. Note that if multiple OP_RETURN in a block match the current
cons-pair, the first one is considered the correct chain. This
property means that the sidechain/altchain can only have a chainsplit
if the mainchain has a chainsplit.
It's the sidechain node which needs to learn about the sidechain
blockchain anyway. So it's the one that does the checking of this.
For that matter, a mainchain miner can be bribed to commit to a random
number rather than a valid h* block, and it will still lead all the
sidechain nodes on a random chase to look for the indicated block.
I do agree with this description. And I am not exactly comfortable with
it, but theoretically the random chase would serve no direct benefit to
any attacker (and thus be a ~purposeless use of attacker's money), and
empirically I do not recall anyone complaining about this happening in
Namecoin. And I think it is generally agreed that low-conf transactions
are of categorically lower reliability -- and therefore that we are
relatively less interested in taking care of users who want the
blockchain to provide them with...immediate gratification (for lack of a
better term).
Post by ZmnSCPxj via bitcoin-dev
Post by Chris Stewart via bitcoin-dev
I'll follow your discussion with Paul about sidechain reorgs, but I
think his proposal is more desirable -- it follows what actually
happens in the bitcoin mining process where we *can* have chain splits
when
Post by Chris Stewart via bitcoin-dev
miners simultaneously find a block. Other miners will pick one of the
two blocks to mine on top of and eventually one chain will become
longer than the other. Therefore that chain will have it's block's
Post by Chris Stewart via bitcoin-dev
orphaned and the miners/nodes following the dead chain will reorg on
top of the longest chain.
http://diyhpl.us/~bryan/papers2/bitcoin/On%20the%20instability%20of%20Bitcoin%20without%20the%20block%20reward%20-%202016.pdf
<http://diyhpl.us/%7Ebryan/papers2/bitcoin/On%20the%20instability%20of%20Bitcoin%20without%20the%20block%20reward%20-%202016.pdf>
As far as I understood that paper, it means that if the block reward
no longer exists, miners can profitably attempt to undercut any full
blocks.
Sidechains do not have block rewards (unless the sidechain issues its
own asset type that is separate from and not convertible to mainchain
bitcoins).
Thus, to protect against undercutting attacks in the sidechain, we
would need to ensure that the sidechain cannot be reorged without the
mainchain (which currently still has a block reward) being reorged.
At least, this is my consideration. Perhaps the paper is wrong?
Yes, it is a valid concern. I'm glad you brought this up. My view is
that there will be no undercutting attempts in the future, if Bitcoin is
popular enough and transactions are constantly arriving.

In short, the reason I feel that way is because miners will be both [1]
willing and [2] able, to maximize their fee income by imposing a
blocksize limit on themselves. They would do this by orphaning
non-compliants -- this would be something softfork-esque, but not
necessarily enforced by non-mining nodes as it is limited to miner
tx-acceptance policy.

Here is a link to a presentation of my thoughts on the issue:


As I say there, I believe that miners currently have no significant
reason to fee-maximize today, which is why we haven't seen this
behavior. (Also, someone would need to write the fee-maximization code
for this, and that not only would take time, but it would require a
person with a very complex intersection of skills.)

The paper you mention was written 1.5 months after my presentation was
recorded. My conclusion contradicts the first sentence of the last
paragraph of "3.1 Model of the system" which reads: "We also assume that
miners always have space to include all available transactions." In my
model miners do NOT always (or, really, ever) have space to include all
available transactions. And miners are happy that they do not, because
all of them make more total money as a result (both per block and overall).

I think the arguments of the presentation were original, so I would be
grateful to you if you offered me your thoughts on it.
Post by ZmnSCPxj via bitcoin-dev
1. Remove the necessity of coinbase commitments. The miner commits
to the sidechain_id and h* in the transaction that pays the
OP_BRIBEVERIFY anyway. That way the h* commitment occurs only once in
the block, in the transaction that does the OP_BRIBEVERIFY. In
addition, there is no need to impose particular ordering on the
coinbase outputs, which would be problematic as pointed out by others,
for example if the miner is interested only in merge mining for
sidechain id #35 and nobody else.
I don't understand the word "anyway" in the second sentence. Is that a
summary of my proposal, or an assertion of yours. Because as it stands,
the bribe part is quite optional -- miners could just mine both chains
themselves, and then they would know which h* to include, paying
themselves the sidechain's tx fees. (Of course, under what you propose
here, miners could also mine it themselves, by placing it in an
OP_BRIBEVERIFY). However, if it is limited to a coinbase, then there is
at most only 1 hash to process every 10 minutes, which I think is desirable.

I like your idea as it is simpler. But a second concern I have is that
if a sidechain user wants to use SPV mode, the software will want to
know exactly where to find the sidechain headers. If they are always in
a known part of the coinbase, then the spv sidechain wallet knows where
to look.

Re: impose ordering on coinbase outputs, what do you think of a scheme
which searches index 1 for an OP RETURN, and if it finds something it
interprets that as the root hash of merkle tree of merged mined
sidechain h*'s ? If it doesn't find a hash commitment in index 1 it just
assumes that no sidechains were mined in this ~10 minute period.
Post by ZmnSCPxj via bitcoin-dev
2. When verifying a block, keep a set of sidechain ID's. When
processing a transaction in that block with OP_BRIBEVERIFY, check if
the sidechain ID is in that set. If not in that set, add it to that
set and continue script processing. If already in the set, fail the
script processing. This ensures that at most one OP_BRIBEVERIFY
exists for each sidechain_id in a mainchain block.
3. Don't number sidechain_id from 0, 1, 2, 3..., because people will
fight over the small numbers. Instead identify sidechains by, for
example, the hash of their names or the hash of their genesis block or
whatever. This allows true permissionless creation of sidechains,
without some authority existing that centrally allocates sidechain ID's.
I am actually not in favor of permiessionless creation of sidechains,
because the sidechains can interfere with each other to a degree that
impacts their usefulness. We do not allow "permissionless creation of
transactions", because we do not allow invalid or double-spent
transactions. I feel the same logic should apply to the chains themselves.

Another youtube presenation about this:

(Much shorter) written post: http://www.truthcoin.info/blog/wise-contracts/

That said, I am fully in favor of forcing the sidechain's permanent
deposit address to be equal to some deterministic function of the sha256
hash of its version 0.1 release.

Paul
CryptAxe via bitcoin-dev
2017-07-12 23:58:07 UTC
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In case anyone wants to do this, I added the CSidechainAddress class to the
mainchainBMM branch of the Drivechain project a long time ago. The only
purpose it serves right now is to show that sidechain deposit addresses can
start with a '4'. We could simply add the sha256 hash described by Paul to
a script with OP_RETURN at the front and make that the standard.

On Jul 12, 2017 4:47 PM, "Paul Sztorc via bitcoin-dev" <
bitcoin-***@lists.linuxfoundation.org> wrote:

On 7/12/2017 4:50 AM, ZmnSCPxj wrote:

...


That said, I am fully in favor of forcing the sidechain's permanent
deposit address to be equal to some deterministic function of the sha256
hash of its version 0.1 release.

Paul
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