Discussion:
Thoughts on Forks, Scalability, and other Bitcoin inconveniences.
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Eric Lombrozo
2015-07-05 18:50:23 UTC
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Blockchain validation has become too expensive to properly secure the
network as per our original security model. The level of validation
required to comply with our security model has become completely
impractical for most use cases. Block space is still cheap only because of
block reward subsidy (which decreases exponentially with time). The
economics are already completely jacked - larger blocks will only worsen
this disparity.

The only practical way for the network to function at present (and what has
essentially ended up happening, if often tacitly) is by introducing trust,
in validators, miners, relayers, explorer websites, online wallets,
etc...which in and of itself wouldn't be the end of the world were it not
for the fact that the raison d'etre of bitcoin is trustlessness - and the
security model is very much based on this idea. Because of this, there's
been a tendency to deny that bitcoin cannot presently scale without trust.
This is horrible because our entire security model has gone out the
window...and has been replaced with something that isn't specified at all!

We don't really know the boundaries of our model, as the fork a couple of
days ago demonstrated. Right now we're basically trusting a few devs and
some mining pool operators that until now have been willing to cooperate
for the benefit of the network. It is dangerous to assume this will
continue perpetually. Even assuming the best intentions, an incident might
occur that this cooperation cannot easily repair.

We need to either solve the validation cost/bottleneck issue...or we need
to construct a new security model that takes these trust assumptions into
account.

- Eric Lombrozo
Eric Lombrozo
2015-07-05 19:55:47 UTC
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I should clarify that by "most use cases" I'm not envisioning a bunch of
cryptogeeks [us, or at least myself and a few of us] happily buying up hard
disks, waiting hours, days, weeks to spawn up new full nodes. I'm
envisioning a world where every person has access to this technology and
finds it practical, convenient, and safe ti use.

- Eric Lombrozo
Post by Eric Lombrozo
Blockchain validation has become too expensive to properly secure the
network as per our original security model. The level of validation
required to comply with our security model has become completely
impractical for most use cases. Block space is still cheap only because of
block reward subsidy (which decreases exponentially with time). The
economics are already completely jacked - larger blocks will only worsen
this disparity.
The only practical way for the network to function at present (and what
has essentially ended up happening, if often tacitly) is by introducing
trust, in validators, miners, relayers, explorer websites, online wallets,
etc...which in and of itself wouldn't be the end of the world were it not
for the fact that the raison d'etre of bitcoin is trustlessness - and the
security model is very much based on this idea. Because of this, there's
been a tendency to deny that bitcoin cannot presently scale without trust.
This is horrible because our entire security model has gone out the
window...and has been replaced with something that isn't specified at all!
We don't really know the boundaries of our model, as the fork a couple of
days ago demonstrated. Right now we're basically trusting a few devs and
some mining pool operators that until now have been willing to cooperate
for the benefit of the network. It is dangerous to assume this will
continue perpetually. Even assuming the best intentions, an incident might
occur that this cooperation cannot easily repair.
We need to either solve the validation cost/bottleneck issue...or we need
to construct a new security model that takes these trust assumptions into
account.
- Eric Lombrozo
Justus Ranvier
2015-07-05 20:33:40 UTC
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Post by Eric Lombrozo
The only practical way for the network to function at present (and what has
essentially ended up happening, if often tacitly) is by introducing trust,
in validators, miners, relayers, explorer websites, online wallets,
etc...which in and of itself wouldn't be the end of the world were it not
for the fact that the raison d'etre of bitcoin is trustlessness - and the
security model is very much based on this idea. Because of this, there's
been a tendency to deny that bitcoin cannot presently scale without trust.
This is horrible because our entire security model has gone out the
window...and has been replaced with something that isn't specified at all!
When I read this, I get the impression that you (and possibly many
others) never actually understood the Bitcoin security model in the
first place.

Bitcoin is a digital cash system that prevents double spending without
using a trusted third party.

More specifically, successful double spending in Bitcoin requires an
attacker to pay a proof of work cost that exceeds the cumulative proof
of work paid by all non-attackers since the original spend.

The security model holds for any user who has access to the complete
blockchain, and currently does not hold for all users who do not. An
attacker can double spend without paying the full PoW cost the security
model requires if users do not have a full copy of the blockchain which
which to verify the attacker's blocks.

That's a problem, but it's not an unfixable problem.

The reason an attacker can fool SPV clients into accepting invalid
blocks is because there exists no mechanism via which honest nodes can
prove the invalidity of blocks.

Implement that mechanism, and the security of SPV clients will far more
closely resemble the security of full nodes.
--
Justus Ranvier
Open Bitcoin Privacy Project
http://www.openbitcoinprivacyproject.org/
***@openbitcoinprivacyproject.org
E7AD 8215 8497 3673 6D9E 61C4 2A5F DA70 EAD9 E623
Eric Lombrozo
2015-07-05 20:53:51 UTC
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Perhaps I didn't write that so well if I gave that impression. Perhaps
taking a look at some of my work in this space would make you think
otherwise. (yes, I've implemented an entire SPV stack from scratch...look
it up.)

But all patronizing aside, your claim that "the reason an attacker can fool
SPV clients into accepting invalid blocks is because there exists no
mechanism via which honest nodes can prove the invalidity of blocks" is
exactly to the point...and building such a mechanism would address the
first of the two options I give: make it cheap to securely validate or take
trust into account.

- Eric Lombrozo

On Jul 5, 2015 1:34 PM, "Justus Ranvier" <
Post by Eric Lombrozo
Post by Eric Lombrozo
The only practical way for the network to function at present (and what
has
Post by Eric Lombrozo
essentially ended up happening, if often tacitly) is by introducing
trust,
Post by Eric Lombrozo
in validators, miners, relayers, explorer websites, online wallets,
etc...which in and of itself wouldn't be the end of the world were it not
for the fact that the raison d'etre of bitcoin is trustlessness - and the
security model is very much based on this idea. Because of this, there's
been a tendency to deny that bitcoin cannot presently scale without
trust.
Post by Eric Lombrozo
This is horrible because our entire security model has gone out the
window...and has been replaced with something that isn't specified at
all!
When I read this, I get the impression that you (and possibly many
others) never actually understood the Bitcoin security model in the
first place.
Bitcoin is a digital cash system that prevents double spending without
using a trusted third party.
More specifically, successful double spending in Bitcoin requires an
attacker to pay a proof of work cost that exceeds the cumulative proof
of work paid by all non-attackers since the original spend.
The security model holds for any user who has access to the complete
blockchain, and currently does not hold for all users who do not. An
attacker can double spend without paying the full PoW cost the security
model requires if users do not have a full copy of the blockchain which
which to verify the attacker's blocks.
That's a problem, but it's not an unfixable problem.
The reason an attacker can fool SPV clients into accepting invalid
blocks is because there exists no mechanism via which honest nodes can
prove the invalidity of blocks.
Implement that mechanism, and the security of SPV clients will far more
closely resemble the security of full nodes.
--
Justus Ranvier
Open Bitcoin Privacy Project
http://www.openbitcoinprivacyproject.org/
E7AD 8215 8497 3673 6D9E 61C4 2A5F DA70 EAD9 E623
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
Justus Ranvier
2015-07-05 21:05:43 UTC
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Post by Eric Lombrozo
Perhaps I didn't write that so well if I gave that impression. Perhaps
taking a look at some of my work in this space would make you think
otherwise. (yes, I've implemented an entire SPV stack from scratch...look
it up.)
I get concerned when I hear statement like "the raison d'etre of bitcoin
is trustlessness" because it implies that Bitcoin promises infinite
security, which has never been the case.

I don't think we can meaningfully discuss Bitcoin security issues if
every proposal is compared to a straw standard of perfection which is
achievable. When everybody expects infinite security then the perfect
turns into the enemy of the good (and the achievable).
--
Justus Ranvier
Open Bitcoin Privacy Project
http://www.openbitcoinprivacyproject.org/
***@openbitcoinprivacyproject.org
E7AD 8215 8497 3673 6D9E 61C4 2A5F DA70 EAD9 E623
Eric Lombrozo
2015-07-05 21:08:12 UTC
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I was saying that somewhat tongue-in-cheek...sorry that didn't come through
in the text.
On Jul 5, 2015 2:05 PM, "Justus Ranvier" <
Post by Justus Ranvier
Post by Eric Lombrozo
Perhaps I didn't write that so well if I gave that impression. Perhaps
taking a look at some of my work in this space would make you think
otherwise. (yes, I've implemented an entire SPV stack from scratch...look
it up.)
I get concerned when I hear statement like "the raison d'etre of bitcoin
is trustlessness" because it implies that Bitcoin promises infinite
security, which has never been the case.
I don't think we can meaningfully discuss Bitcoin security issues if
every proposal is compared to a straw standard of perfection which is
achievable. When everybody expects infinite security then the perfect
turns into the enemy of the good (and the achievable).
--
Justus Ranvier
Open Bitcoin Privacy Project
http://www.openbitcoinprivacyproject.org/
E7AD 8215 8497 3673 6D9E 61C4 2A5F DA70 EAD9 E623
_______________________________________________
bitcoin-dev mailing list
https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
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