[bitcoin-dev] hypothetical: Could soft-forks be prevented?

[Dan Libby via bitcoin-dev]

Hi, I am interested in the possibility of a cryptocurrency software
(future bitcoin or a future altcoin) that strives to have immutable
consensus rules.

The goal of such a cryptocurrency would not be to have the latest and
greatest tech, but rather to be a long-term store of value and to offer
investors great certainty and predictability... something that markets
tend to like. And of course, zero consensus rule changes also means
less chance of new bugs and attack surface remains the same, which is
good for security.

Of course, hard-forks are always possible. But that is a clear split
and something that people must opt into. Each party has to make a
choice, and inertia is on the side of the status quo. Whereas
soft-forks sort of drag people along with them, even those who oppose
the changes and never upgrade. In my view, that is problematic,
especially for a coin with permanent consensus rule immutability as a
goal/ethic.

As I understand it, bitcoin soft-forks always rely on anyone-can-spend
transactions. If those were removed, would it effectively prevent
soft-forks, or are there other possible mechanisms? How important are
any-one-can spend tx for other uses?

More generally, do you think it is possible to programmatically
avoid/ban soft-forks, and if so, how would you go about it?

[ZmnSCPxj via bitcoin-dev]

Good morning Dan,

My understanding is that it is impossible for soft forks to be prevented.

1. Anyone-can-spend

There are a very large number of anyone-can-spend scripts, and it would be very impractical to ban them all.

For example, the below output script is anyone-can-spend

<random number> OP_TRUE

So is the below:

OP_SIZE <random small number> OP_EQUAL

Or:

OP_1ADD <random number> OP_EQUAL

Or:

OP_BOOLAND

Or:

OP_BOOLOR

And so on.

So no, it is not practically possible to ban anyone-can-spend outputs, as there are too many potential scriptPubKey that anyone can spend.

It is even possible to have an output that requires a proof-of-work, like so:

OP_HASH256 <difficulty target> OP_LESSTHAN

All the above outputs are disallowed from propagation by IsStandard, but a miner can put them validly in a block, and IsStandard is not consensus code and can be modified.

2. Soft fork = restrict

It is possible (although unlikely) for a majority of miners to run soft forking code which the rest of us are not privy to.

For example, for all we know, miners are already blacklisting spends on Satoshi's coins. We would not be able to detect this at all, since no transaction that spends Satoshi's coins have been broadcast, ever. It is thus indistinguishable from a world where Satoshi lost his private keys. Of course, the world where Satoshi never spent his coins and miners are blacklisting Satoshi's coins, is more complex than the world where Satoshi never spent his coins, so it is more likely that miners are not blacklisting.

But the principle is there. We may already be in a softfork whose rules we do not know, and it just so happens that all our transactions today do not violate those rules. It is impossible for us to know this, but it is very unlikely.

Soft forks apply further restrictions on Bitcoin. Hard forks do not. Thus, if everyone else is entering a soft fork and we are oblivious, we do not even know about it. Whereas, if everyone else is entering a hard fork, we will immediately see (and reject) invalid transactions and blocks.

Thus the only way to prevent soft fork is to hard fork against the new soft fork, like Bcash did.

Regards,
ZmnSCPxj

-------- Original Message --------
Subject: [bitcoin-dev] hypothetical: Could soft-forks be prevented?
Local Time: September 13, 2017 5:50 PM
UTC Time: September 13, 2017 9:50 AM
From: bitcoin-***@lists.linuxfoundation.org
To: Bitcoin Protocol Discussion <bitcoin-***@lists.linuxfoundation.org>

Hi, I am interested in the possibility of a cryptocurrency software
(future bitcoin or a future altcoin) that strives to have immutable
consensus rules.

The goal of such a cryptocurrency would not be to have the latest and
greatest tech, but rather to be a long-term store of value and to offer
investors great certainty and predictability... something that markets
tend to like. And of course, zero consensus rule changes also means
less chance of new bugs and attack surface remains the same, which is
good for security.

Of course, hard-forks are always possible. But that is a clear split
and something that people must opt into. Each party has to make a
choice, and inertia is on the side of the status quo. Whereas
soft-forks sort of drag people along with them, even those who oppose
the changes and never upgrade. In my view, that is problematic,
especially for a coin with permanent consensus rule immutability as a
goal/ethic.

As I understand it, bitcoin soft-forks always rely on anyone-can-spend
transactions. If those were removed, would it effectively prevent
soft-forks, or are there other possible mechanisms? How important are
any-one-can spend tx for other uses?

More generally, do you think it is possible to programmatically
avoid/ban soft-forks, and if so, how would you go about it?

[Adam Back via bitcoin-dev]

True however in principle a soft-fork can also be soft-forked out. Eg say a
publicly known soft-fork done by miners only that user node software did
not upgrade for first by opt-in adoption. If there was consensus against by
users and ecosystem a node/user flag day soft fork could block it's
effects. Or if a soft fork was determined to have a major bug.

However most types of soft fork are opt-in and so mostly that situation
seems unlikely. A censorship soft-fork is harder, that's a standard
hard-fork to bypass with current fungibility mechanisms.

Adam

On Sep 15, 2017 08:12, "ZmnSCPxj via bitcoin-dev" <

Post by ZmnSCPxj via bitcoin-dev
Good morning Dan,
My understanding is that it is impossible for soft forks to be prevented.
1. Anyone-can-spend
There are a very large number of anyone-can-spend scripts, and it would be
very impractical to ban them all.
For example, the below output script is anyone-can-spend
<random number> OP_TRUE
OP_SIZE <random small number> OP_EQUAL
OP_1ADD <random number> OP_EQUAL
OP_BOOLAND
OP_BOOLOR
And so on.
So no, it is not practically possible to ban anyone-can-spend outputs, as
there are too many potential scriptPubKey that anyone can spend.
OP_HASH256 <difficulty target> OP_LESSTHAN
All the above outputs are disallowed from propagation by IsStandard, but a
miner can put them validly in a block, and IsStandard is not consensus code
and can be modified.
2. Soft fork = restrict
It is possible (although unlikely) for a majority of miners to run soft
forking code which the rest of us are not privy to.
For example, for all we know, miners are already blacklisting spends on
Satoshi's coins. We would not be able to detect this at all, since no
transaction that spends Satoshi's coins have been broadcast, ever. It is
thus indistinguishable from a world where Satoshi lost his private keys.
Of course, the world where Satoshi never spent his coins and miners are
blacklisting Satoshi's coins, is more complex than the world where Satoshi
never spent his coins, so it is more likely that miners are not
blacklisting.
But the principle is there. We may already be in a softfork whose rules
we do not know, and it just so happens that all our transactions today do
not violate those rules. It is impossible for us to know this, but it is
very unlikely.
Soft forks apply further restrictions on Bitcoin. Hard forks do not.
Thus, if everyone else is entering a soft fork and we are oblivious, we do
not even know about it. Whereas, if everyone else is entering a hard fork,
we will immediately see (and reject) invalid transactions and blocks.
Thus the only way to prevent soft fork is to hard fork against the new
soft fork, like Bcash did.
Regards,
ZmnSCPxj
-------- Original Message --------
Subject: [bitcoin-dev] hypothetical: Could soft-forks be prevented?
Local Time: September 13, 2017 5:50 PM
UTC Time: September 13, 2017 9:50 AM
Hi, I am interested in the possibility of a cryptocurrency software
(future bitcoin or a future altcoin) that strives to have immutable
consensus rules.
The goal of such a cryptocurrency would not be to have the latest and
greatest tech, but rather to be a long-term store of value and to offer
investors great certainty and predictability... something that markets
tend to like. And of course, zero consensus rule changes also means
less chance of new bugs and attack surface remains the same, which is
good for security.
Of course, hard-forks are always possible. But that is a clear split
and something that people must opt into. Each party has to make a
choice, and inertia is on the side of the status quo. Whereas
soft-forks sort of drag people along with them, even those who oppose
the changes and never upgrade. In my view, that is problematic,
especially for a coin with permanent consensus rule immutability as a
goal/ethic.
As I understand it, bitcoin soft-forks always rely on anyone-can-spend
transactions. If those were removed, would it effectively prevent
soft-forks, or are there other possible mechanisms? How important are
any-one-can spend tx for other uses?
More generally, do you think it is possible to programmatically
avoid/ban soft-forks, and if so, how would you go about it?
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev

[Tier Nolan via bitcoin-dev]

On Fri, Sep 15, 2017 at 10:14 AM, Adam Back via bitcoin-dev <

Post by Adam Back via bitcoin-dev
True however in principle a soft-fork can also be soft-forked out. Eg say
a publicly known soft-fork done by miners only that user node software did
not upgrade for first by opt-in adoption.

It depends on what software that the general user-base is using (especially
exchanges). If a majority of miners have deployed a hidden soft fork, then
the soft fork will only last as long as they can maintain their majority.

If they drop below 50%, then the majority of miners will eventually make
and then build on a block that is invalid according to their hidden soft
fork rules.

If the userbase doesn't support a censorship soft fork, then it will only
last as long as a majority of miners support it. Once the cartel loses its
majority, there is a strong incentive for members to disable their soft
fork rule. Any that don't will end up mining a lower POW, but valid, chain.

Users updating their nodes to enforce the soft fork is what makes the soft
fork irreversible (without a hard fork).

Post by Adam Back via bitcoin-dev
A censorship soft-fork is harder, that's a standard hard-fork to bypass
with current fungibility mechanisms.

It's only a hard fork to reverse if the community is enforcing the soft
fork. Forking off a minority of miners doesn't make it a hard fork.

Post by Adam Back via bitcoin-dev
Adam

Post by ZmnSCPxj via bitcoin-dev
Good morning Dan,
My understanding is that it is impossible for soft forks to be prevented.
1. Anyone-can-spend
There are a very large number of anyone-can-spend scripts, and it would
be very impractical to ban them all.
For example, the below output script is anyone-can-spend
<random number> OP_TRUE
OP_SIZE <random small number> OP_EQUAL
OP_1ADD <random number> OP_EQUAL
OP_BOOLAND
OP_BOOLOR
And so on.
So no, it is not practically possible to ban anyone-can-spend outputs, as
there are too many potential scriptPubKey that anyone can spend.
OP_HASH256 <difficulty target> OP_LESSTHAN
All the above outputs are disallowed from propagation by IsStandard, but
a miner can put them validly in a block, and IsStandard is not consensus
code and can be modified.
2. Soft fork = restrict
It is possible (although unlikely) for a majority of miners to run soft
forking code which the rest of us are not privy to.
For example, for all we know, miners are already blacklisting spends on
Satoshi's coins. We would not be able to detect this at all, since no
transaction that spends Satoshi's coins have been broadcast, ever. It is
thus indistinguishable from a world where Satoshi lost his private keys.
Of course, the world where Satoshi never spent his coins and miners are
blacklisting Satoshi's coins, is more complex than the world where Satoshi
never spent his coins, so it is more likely that miners are not
blacklisting.
But the principle is there. We may already be in a softfork whose rules
we do not know, and it just so happens that all our transactions today do
not violate those rules. It is impossible for us to know this, but it is
very unlikely.
Soft forks apply further restrictions on Bitcoin. Hard forks do not.
Thus, if everyone else is entering a soft fork and we are oblivious, we do
not even know about it. Whereas, if everyone else is entering a hard fork,
we will immediately see (and reject) invalid transactions and blocks.
Thus the only way to prevent soft fork is to hard fork against the new
soft fork, like Bcash did.
Regards,
ZmnSCPxj
-------- Original Message --------
Subject: [bitcoin-dev] hypothetical: Could soft-forks be prevented?
Local Time: September 13, 2017 5:50 PM
UTC Time: September 13, 2017 9:50 AM
Hi, I am interested in the possibility of a cryptocurrency software
(future bitcoin or a future altcoin) that strives to have immutable
consensus rules.
The goal of such a cryptocurrency would not be to have the latest and
greatest tech, but rather to be a long-term store of value and to offer
investors great certainty and predictability... something that markets
tend to like. And of course, zero consensus rule changes also means
less chance of new bugs and attack surface remains the same, which is
good for security.
Of course, hard-forks are always possible. But that is a clear split
and something that people must opt into. Each party has to make a
choice, and inertia is on the side of the status quo. Whereas
soft-forks sort of drag people along with them, even those who oppose
the changes and never upgrade. In my view, that is problematic,
especially for a coin with permanent consensus rule immutability as a
goal/ethic.
As I understand it, bitcoin soft-forks always rely on anyone-can-spend
transactions. If those were removed, would it effectively prevent
soft-forks, or are there other possible mechanisms? How important are
any-one-can spend tx for other uses?
More generally, do you think it is possible to programmatically
avoid/ban soft-forks, and if so, how would you go about it?
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev

_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev

[Dan Libby via bitcoin-dev]

However most types of soft fork are opt-in...

my concern is that the community can be manipulated via political means.
marketing, social media, payoffs, fud, etc, etc, etc. And essentially
degrades to tyranny of the majority.


So if there is any way to make opt-in forks impractical/infeasible for
purpose of network wide consensus rule change, I'd love to hear it.

[Dan Libby via bitcoin-dev]

Ok, this is good stuff. thanks for the thoughtful reply.

Regarding anyone-can-spend:

all of the examples you gave do not satisfy isStandard. So if our
hypothetical cryptocurrency were to restrict all transactions to
isStandard at the consensus layer, would that not effectively prevent
anyone-can-spend?

Or more generally and with our thinking caps on, what would be the best
way to prevent anyone-can-spend, if that is our goal?


Regarding soft-fork = restrict:

Your example of miners running secret soft-fork code that blacklists
satoshi's utxo's is intriguing and somewhat troubling.

I think the main takeaways are that:
1) there are other ways to soft-fork besides anyone-can-spend.
2) it is impossible to prevent hidden soft-forks.

Is that accurate?

Still, I would put forth the following question: If anyone-can-spend tx
were no longer allowed according to consensus rules (assuming that is
possible/practical), then could the network still be practically
"upgraded" with new features (eg opcodes) via soft-fork, and if so, what
would be the mechanism for backwards compatibility in this scenario?


or from another angle: even if it is impossible to prevent all
soft-forks, can you see any way at all to make it logistically
infeasible to use soft-forks as a network-wide consensus change mechanism?

and another thought: as I understand it, bitcoin is presently able to
add new opcodes via soft-fork because Satoshi added 10 unused opcodes
via hardfork. What will happen when these run out? Can new opcodes
still be added without a hard-fork?


note: I ask these questions with the goal/vision of creating an
immutable altcoin or sidechain, not necessarily restricting bitcoin's path.

Post by ZmnSCPxj via bitcoin-dev
Good morning Dan,
My understanding is that it is impossible for soft forks to be prevented.
1. Anyone-can-spend
There are a very large number of anyone-can-spend scripts, and it would
be very impractical to ban them all.
For example, the below output script is anyone-can-spend
<random number> OP_TRUE
OP_SIZE <random small number> OP_EQUAL
OP_1ADD <random number> OP_EQUAL
OP_BOOLAND
OP_BOOLOR
And so on.
So no, it is not practically possible to ban anyone-can-spend outputs,
as there are too many potential scriptPubKey that anyone can spend.
OP_HASH256 <difficulty target> OP_LESSTHAN
All the above outputs are disallowed from propagation by IsStandard, but
a miner can put them validly in a block, and IsStandard is not consensus
code and can be modified.
2. Soft fork = restrict
It is possible (although unlikely) for a majority of miners to run soft
forking code which the rest of us are not privy to.
For example, for all we know, miners are already blacklisting spends on
Satoshi's coins. We would not be able to detect this at all, since no
transaction that spends Satoshi's coins have been broadcast, ever. It
is thus indistinguishable from a world where Satoshi lost his private
keys. Of course, the world where Satoshi never spent his coins and
miners are blacklisting Satoshi's coins, is more complex than the world
where Satoshi never spent his coins, so it is more likely that miners
are not blacklisting.
But the principle is there. We may already be in a softfork whose rules
we do not know, and it just so happens that all our transactions today
do not violate those rules. It is impossible for us to know this, but
it is very unlikely.
Soft forks apply further restrictions on Bitcoin. Hard forks do not.
Thus, if everyone else is entering a soft fork and we are oblivious, we
do not even know about it. Whereas, if everyone else is entering a hard
fork, we will immediately see (and reject) invalid transactions and blocks.
Thus the only way to prevent soft fork is to hard fork against the new
soft fork, like Bcash did.
Regards,
ZmnSCPxj
-------- Original Message --------
Subject: [bitcoin-dev] hypothetical: Could soft-forks be prevented?
Local Time: September 13, 2017 5:50 PM
UTC Time: September 13, 2017 9:50 AM
Hi, I am interested in the possibility of a cryptocurrency software
(future bitcoin or a future altcoin) that strives to have immutable
consensus rules.
The goal of such a cryptocurrency would not be to have the latest and
greatest tech, but rather to be a long-term store of value and to offer
investors great certainty and predictability... something that markets
tend to like. And of course, zero consensus rule changes also means
less chance of new bugs and attack surface remains the same, which is
good for security.
Of course, hard-forks are always possible. But that is a clear split
and something that people must opt into. Each party has to make a
choice, and inertia is on the side of the status quo. Whereas
soft-forks sort of drag people along with them, even those who oppose
the changes and never upgrade. In my view, that is problematic,
especially for a coin with permanent consensus rule immutability as a
goal/ethic.
As I understand it, bitcoin soft-forks always rely on anyone-can-spend
transactions. If those were removed, would it effectively prevent
soft-forks, or are there other possible mechanisms? How important are
any-one-can spend tx for other uses?
More generally, do you think it is possible to programmatically
avoid/ban soft-forks, and if so, how would you go about it?
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev

[Simone Bronzini via bitcoin-dev]

Since a soft-fork is a restriction of the consensus rules, I think the
only way to have an un-soft-forkable cryptocurrency is creating a
cryptocurrency where no transaction is valid.

Imagine I build a very minimal cryptocurrency where in the transaction
output you only indicate the public key to send your coins to and the
amount. One can still soft-fork it by deciding that, from now on, only
even amounts are valid or only public keys that are a multiple of 10 are
valid.

Post by Dan Libby via bitcoin-dev
Ok, this is good stuff. thanks for the thoughtful reply.
all of the examples you gave do not satisfy isStandard. So if our
hypothetical cryptocurrency were to restrict all transactions to
isStandard at the consensus layer, would that not effectively prevent
anyone-can-spend?
Or more generally and with our thinking caps on, what would be the best
way to prevent anyone-can-spend, if that is our goal?
Your example of miners running secret soft-fork code that blacklists
satoshi's utxo's is intriguing and somewhat troubling.
1) there are other ways to soft-fork besides anyone-can-spend.
2) it is impossible to prevent hidden soft-forks.
Is that accurate?
Still, I would put forth the following question: If anyone-can-spend tx
were no longer allowed according to consensus rules (assuming that is
possible/practical), then could the network still be practically
"upgraded" with new features (eg opcodes) via soft-fork, and if so, what
would be the mechanism for backwards compatibility in this scenario?
or from another angle: even if it is impossible to prevent all
soft-forks, can you see any way at all to make it logistically
infeasible to use soft-forks as a network-wide consensus change mechanism?
and another thought: as I understand it, bitcoin is presently able to
add new opcodes via soft-fork because Satoshi added 10 unused opcodes
via hardfork. What will happen when these run out? Can new opcodes
still be added without a hard-fork?
note: I ask these questions with the goal/vision of creating an
immutable altcoin or sidechain, not necessarily restricting bitcoin's path.

Post by ZmnSCPxj via bitcoin-dev
Good morning Dan,
My understanding is that it is impossible for soft forks to be prevented.
1. Anyone-can-spend
There are a very large number of anyone-can-spend scripts, and it would
be very impractical to ban them all.
For example, the below output script is anyone-can-spend
<random number> OP_TRUE
OP_SIZE <random small number> OP_EQUAL
OP_1ADD <random number> OP_EQUAL
OP_BOOLAND
OP_BOOLOR
And so on.
So no, it is not practically possible to ban anyone-can-spend outputs,
as there are too many potential scriptPubKey that anyone can spend.
OP_HASH256 <difficulty target> OP_LESSTHAN
All the above outputs are disallowed from propagation by IsStandard, but
a miner can put them validly in a block, and IsStandard is not consensus
code and can be modified.
2. Soft fork = restrict
It is possible (although unlikely) for a majority of miners to run soft
forking code which the rest of us are not privy to.
For example, for all we know, miners are already blacklisting spends on
Satoshi's coins. We would not be able to detect this at all, since no
transaction that spends Satoshi's coins have been broadcast, ever. It
is thus indistinguishable from a world where Satoshi lost his private
keys. Of course, the world where Satoshi never spent his coins and
miners are blacklisting Satoshi's coins, is more complex than the world
where Satoshi never spent his coins, so it is more likely that miners
are not blacklisting.
But the principle is there. We may already be in a softfork whose rules
we do not know, and it just so happens that all our transactions today
do not violate those rules. It is impossible for us to know this, but
it is very unlikely.
Soft forks apply further restrictions on Bitcoin. Hard forks do not.
Thus, if everyone else is entering a soft fork and we are oblivious, we
do not even know about it. Whereas, if everyone else is entering a hard
fork, we will immediately see (and reject) invalid transactions and blocks.
Thus the only way to prevent soft fork is to hard fork against the new
soft fork, like Bcash did.
Regards,
ZmnSCPxj
-------- Original Message --------
Subject: [bitcoin-dev] hypothetical: Could soft-forks be prevented?
Local Time: September 13, 2017 5:50 PM
UTC Time: September 13, 2017 9:50 AM
Hi, I am interested in the possibility of a cryptocurrency software
(future bitcoin or a future altcoin) that strives to have immutable
consensus rules.
The goal of such a cryptocurrency would not be to have the latest and
greatest tech, but rather to be a long-term store of value and to offer
investors great certainty and predictability... something that markets
tend to like. And of course, zero consensus rule changes also means
less chance of new bugs and attack surface remains the same, which is
good for security.
Of course, hard-forks are always possible. But that is a clear split
and something that people must opt into. Each party has to make a
choice, and inertia is on the side of the status quo. Whereas
soft-forks sort of drag people along with them, even those who oppose
the changes and never upgrade. In my view, that is problematic,
especially for a coin with permanent consensus rule immutability as a
goal/ethic.
As I understand it, bitcoin soft-forks always rely on anyone-can-spend
transactions. If those were removed, would it effectively prevent
soft-forks, or are there other possible mechanisms? How important are
any-one-can spend tx for other uses?
More generally, do you think it is possible to programmatically
avoid/ban soft-forks, and if so, how would you go about it?
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev

_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev

[Andrew Poelstra via bitcoin-dev]

Post by Simone Bronzini via bitcoin-dev
Since a soft-fork is a restriction of the consensus rules, I think the
only way to have an un-soft-forkable cryptocurrency is creating a
cryptocurrency where no transaction is valid.

Even this can be soft-forked to add an extension block that contains transactions :)

Ultimately I think the best you can do in this direction is to design for
maximal fungibility and/or transaction structures that minimize interaction
with the blockchain. This minimizes the surface for transaction censorship,
which is somewhat in the spirit of your goal.
--
Andrew Poelstra
Mathematics Department, Blockstream
Email: apoelstra at wpsoftware.net
Web: https://www.wpsoftware.net/andrew

"A goose alone, I suppose, can know the loneliness of geese
who can never find their peace,
whether north or south or west or east"
--Joanna Newsom

[Dan Libby via bitcoin-dev]

Post by Simone Bronzini via bitcoin-dev
Since a soft-fork is a restriction of the consensus rules, I think the
only way to have an un-soft-forkable cryptocurrency is creating a
cryptocurrency where no transaction is valid.
Imagine I build a very minimal cryptocurrency where in the transaction
output you only indicate the public key to send your coins to and the
amount. One can still soft-fork it by deciding that, from now on, only
even amounts are valid or only public keys that are a multiple of 10 are
valid.

sure, but in this scenario how would one meaningfully "upgrade" the
functionality, eg add a new opcode? We couldn't, right? so....
success! Preventing new functionality is the primary goal of this
thought experiment. I believe that common sense and market incentives
would prevent arbitrary tightening of the rules for no good reason...

[ZmnSCPxj via bitcoin-dev]

Good Morning Dan,

No.

Let us suppose that IsStandard is applied to outputs, but we support P2SH. Then we could encode those scripts in P2SH. The softfork could require the script preimageto be put elsewhere, such as an OP_RETURN in the same tx, to determine the script that is anyone can spend.

We could ban P2SH or restrict P2SH to be IsStandard also, but you are now unable to support HTLC (no atomic swap) or LN, unless you specifically add those scripts to IsStandard. And if a better layer 2 comes along or LN is updated to use better scripts, you have to hardfork those in.

Even then, you can still be softforked. Remember that if we pay to a P2PKH, then publish the private key, every output paying to that address is now practically anyone can spend. Then a softfork can implement desired rules in an extensiom block, where money in UTXOs paying to the special publicized "private" key are controlled, post softfork, by data in a block that is not published to pre softfork nodes, like witness data is treated in SegWit.

Sent with [ProtonMail](https://protonmail.com) Secure Email.

Post by ZmnSCPxj via bitcoin-dev
-------- Original Message --------
Subject: Re: [bitcoin-dev] hypothetical: Could soft-forks be prevented?
Local Time: September 16, 2017 3:55 AM
UTC Time: September 15, 2017 7:55 PM
Ok, this is good stuff. thanks for the thoughtful reply.
all of the examples you gave do not satisfy isStandard. So if our
hypothetical cryptocurrency were to restrict all transactions to
isStandard at the consensus layer, would that not effectively prevent
anyone-can-spend?
Or more generally and with our thinking caps on, what would be the best
way to prevent anyone-can-spend, if that is our goal?
Your example of miners running secret soft-fork code that blacklists
satoshi"s utxo"s is intriguing and somewhat troubling.
1) there are other ways to soft-fork besides anyone-can-spend.
2) it is impossible to prevent hidden soft-forks.
Is that accurate?
Still, I would put forth the following question: If anyone-can-spend tx
were no longer allowed according to consensus rules (assuming that is
possible/practical), then could the network still be practically
"upgraded" with new features (eg opcodes) via soft-fork, and if so, what
would be the mechanism for backwards compatibility in this scenario?
or from another angle: even if it is impossible to prevent all
soft-forks, can you see any way at all to make it logistically
infeasible to use soft-forks as a network-wide consensus change mechanism?
and another thought: as I understand it, bitcoin is presently able to
add new opcodes via soft-fork because Satoshi added 10 unused opcodes
via hardfork. What will happen when these run out? Can new opcodes
still be added without a hard-fork?
note: I ask these questions with the goal/vision of creating an
immutable altcoin or sidechain, not necessarily restricting bitcoin"s path.

Post by ZmnSCPxj via bitcoin-dev
Good morning Dan,
My understanding is that it is impossible for soft forks to be prevented.
1. Anyone-can-spend
There are a very large number of anyone-can-spend scripts, and it would
be very impractical to ban them all.
For example, the below output script is anyone-can-spend
<random number> OP_TRUE
OP_SIZE <random small number> OP_EQUAL
OP_1ADD <random number> OP_EQUAL
OP_BOOLAND
OP_BOOLOR
And so on.
So no, it is not practically possible to ban anyone-can-spend outputs,
as there are too many potential scriptPubKey that anyone can spend.
OP_HASH256 <difficulty target> OP_LESSTHAN
All the above outputs are disallowed from propagation by IsStandard, but
a miner can put them validly in a block, and IsStandard is not consensus
code and can be modified.
2. Soft fork = restrict
It is possible (although unlikely) for a majority of miners to run soft
forking code which the rest of us are not privy to.
For example, for all we know, miners are already blacklisting spends on
Satoshi"s coins. We would not be able to detect this at all, since no
transaction that spends Satoshi"s coins have been broadcast, ever. It
is thus indistinguishable from a world where Satoshi lost his private
keys. Of course, the world where Satoshi never spent his coins and
miners are blacklisting Satoshi"s coins, is more complex than the world
where Satoshi never spent his coins, so it is more likely that miners
are not blacklisting.
But the principle is there. We may already be in a softfork whose rules
we do not know, and it just so happens that all our transactions today
do not violate those rules. It is impossible for us to know this, but
it is very unlikely.
Soft forks apply further restrictions on Bitcoin. Hard forks do not.
Thus, if everyone else is entering a soft fork and we are oblivious, we
do not even know about it. Whereas, if everyone else is entering a hard
fork, we will immediately see (and reject) invalid transactions and blocks.
Thus the only way to prevent soft fork is to hard fork against the new
soft fork, like Bcash did.
Regards,
ZmnSCPxj
-------- Original Message --------
Subject: [bitcoin-dev] hypothetical: Could soft-forks be prevented?
Local Time: September 13, 2017 5:50 PM
UTC Time: September 13, 2017 9:50 AM
Hi, I am interested in the possibility of a cryptocurrency software
(future bitcoin or a future altcoin) that strives to have immutable
consensus rules.
The goal of such a cryptocurrency would not be to have the latest and
greatest tech, but rather to be a long-term store of value and to offer
investors great certainty and predictability... something that markets
tend to like. And of course, zero consensus rule changes also means
less chance of new bugs and attack surface remains the same, which is
good for security.
Of course, hard-forks are always possible. But that is a clear split
and something that people must opt into. Each party has to make a
choice, and inertia is on the side of the status quo. Whereas
soft-forks sort of drag people along with them, even those who oppose
the changes and never upgrade. In my view, that is problematic,
especially for a coin with permanent consensus rule immutability as a
goal/ethic.
As I understand it, bitcoin soft-forks always rely on anyone-can-spend
transactions. If those were removed, would it effectively prevent
soft-forks, or are there other possible mechanisms? How important are
any-one-can spend tx for other uses?
More generally, do you think it is possible to programmatically
avoid/ban soft-forks, and if so, how would you go about it?
_______________________________________________
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[Dan Libby via bitcoin-dev]

Thanks for this link. From my reading though, it seems that only
soft-forks that attempt to freeze funds are problematic on ethereum.

The soft fork creates a new and fundamentally different class of
transactions in contrast with those that currently exist within the
protocol. Currently, transactions either complete successfully and
cause a state transition, or run into an exception, in which case
state is reverted but the maximum possible gas is still charged. With
the soft fork, transactions which interact with a DAO will not fit
within these two classes: they will fail execution but no gas will be
charged. This must inevitably be the case in any soft fork that aims
to freeze the stolen funds;

So in the general case ethereum can still soft-fork I think...

From my understanding, the blockchain can be designed in such a way as
to make soft-forks be impossible or at least impractical due to attack
vectors.
http://hackingdistributed.com/2016/06/28/ethereum-soft-fork-dos-vector/
Ethereum, for example, can't soft-fork. They have to always hardfork.
On 13 September 2017 at 10:50, Dan Libby via bitcoin-dev
Hi, I am interested in the possibility of a cryptocurrency software
(future bitcoin or a future altcoin) that strives to have immutable
consensus rules.
The goal of such a cryptocurrency would not be to have the latest and
greatest tech, but rather to be a long-term store of value and to offer
investors great certainty and predictability... something that markets
tend to like. And of course, zero consensus rule changes also means
less chance of new bugs and attack surface remains the same, which is
good for security.
Of course, hard-forks are always possible. But that is a clear split
and something that people must opt into. Each party has to make a
choice, and inertia is on the side of the status quo. Whereas
soft-forks sort of drag people along with them, even those who oppose
the changes and never upgrade. In my view, that is problematic,
especially for a coin with permanent consensus rule immutability as a
goal/ethic.
As I understand it, bitcoin soft-forks always rely on anyone-can-spend
transactions. If those were removed, would it effectively prevent
soft-forks, or are there other possible mechanisms? How important are
any-one-can spend tx for other uses?
More generally, do you think it is possible to programmatically
avoid/ban soft-forks, and if so, how would you go about it?
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
<https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev>

[Daniel Wilczynski via bitcoin-dev]

Hi Dan.

What might be better aim is to have built in wipeout protection? In
softfork scenario this would protect a majority threatening a minority
with a wipeout if they do not opt in to some soft-fork consensus
change.


This could be partly done done by having automoated consensus critical
checkpoints, for example at 100 blocks deep. Maybe there are better
ways?


This would in effect turn softforks into hardforks.




Regards,


Daniel Wilczynski