[Bitcoin-development] Re-enabling simple tx replacement

[Bitcoin-development] Re-enabling simple tx replacement

[Ross Nicoll]

Dear all,

I've been looking at atomic cross-chain trading (
https://en.bitcoin.it/wiki/Atomic_cross-chain_trading ) between the
Bitcoin and Dogecoin blockchains, and have a mostly functional
prototype. However as it stands if the refund transaction is relayed
before the actual spend transaction, it "blocks" the legitimate spend
transaction from being accepted into the memory pool.

I'd like to enable TX replacement in the case where all conflicting
transactions are not final, and the replacement is final. While yes,
this still leaves scope for "unpaid for" bandwidth, hopefully being able
to do a single replacement isn't a major issue.

For those wanting background on this,
https://github.com/bitcoin/bitcoin/pull/2516 may be useful reading.

I've drafted a patch for this
https://github.com/rnicoll/bitcoin/commit/e668d36607f008990ccaac7275e463a6efdd9b5a
but have not yet raised a PR, as historically this has lead to a lot of
discussion in Github which is better suited to this mailing list.

I'm therefore looking for feedback while I continue testing that patch,
and any comments would be welcomed.

Ross

Re: [Bitcoin-development] Re-enabling simple tx replacement

[Gregory Maxwell]

On Sun, Jan 4, 2015 at 2:43 PM, Ross Nicoll <jrn@jrn.me.uk> wrote:
> Dear all,
>
> I've been looking at atomic cross-chain trading (
> https://en.bitcoin.it/wiki/Atomic_cross-chain_trading ) between the
> Bitcoin and Dogecoin blockchains, and have a mostly functional
> prototype. However as it stands if the refund transaction is relayed
> before the actual spend transaction, it "blocks" the legitimate spend
> transaction from being accepted into the memory pool.

Unless there is a serious bug that I am not aware of this is not the
case. The unlocked transaction is not relayable and will not be
mempooled (well, until right before it locks).

> I've drafted a patch for this
> https://github.com/rnicoll/bitcoin/commit/e668d36607f008990ccaac7275e463a6efdd9b5a
> but have not yet raised a PR, as historically this has lead to a lot of
> discussion in Github which is better suited to this mailing list.
>
> I'm therefore looking for feedback while I continue testing that patch,
> and any comments would be welcomed.

This appears to have absolutely no protection against denial of
service, it seems to me that a single user can rapidly update their
transaction and exhaust the relay bandwidth of the entire network.

Re: [Bitcoin-development] Re-enabling simple tx replacement

[Ross Nicoll]

On 04/01/15 17:04, Gregory Maxwell wrote:
> On Sun, Jan 4, 2015 at 2:43 PM, Ross Nicoll <jrn@jrn.me.uk> wrote:
>> Dear all,
>>
>> I've been looking at atomic cross-chain trading (
>> https://en.bitcoin.it/wiki/Atomic_cross-chain_trading ) between the
>> Bitcoin and Dogecoin blockchains, and have a mostly functional
>> prototype. However as it stands if the refund transaction is relayed
>> before the actual spend transaction, it "blocks" the legitimate spend
>> transaction from being accepted into the memory pool.
> 
> Unless there is a serious bug that I am not aware of this is not the
> case. The unlocked transaction is not relayable and will not be
> mempooled (well, until right before it locks).

Grabbing a simple test case:
https://chain.so/tx/BTCTEST/f903a31f2474df737d324c60abf2407e1cf7e052844da4ccffbfab81cf6ac1f8
- that won't lock until 0028 UTC on the 5th.

I've tried closing the wallet, moving the wallet.dat file out of the
way, and then attempting the spend transaction (which can be locked
immediately), and it either rejects it on acceptance to mempool, or it
is never included in a block.

Compare with
https://chain.so/tx/BTCTEST/0b96eb0c9bf8a6ca08bb9d75e44970889db77779c6d3122296c0169959f979cc
where the refund was not sent first, and the transaction has succeeded.

>> I've drafted a patch for this
>> https://github.com/rnicoll/bitcoin/commit/e668d36607f008990ccaac7275e463a6efdd9b5a
>> but have not yet raised a PR, as historically this has lead to a lot of
>> discussion in Github which is better suited to this mailing list.
>>
>> I'm therefore looking for feedback while I continue testing that patch,
>> and any comments would be welcomed.
> 
> This appears to have absolutely no protection against denial of
> service, it seems to me that a single user can rapidly update their
> transaction and exhaust the relay bandwidth of the entire network.
> 

They can only replace a non-final transaction with a final transaction,
so the replacement can happen at most once (any later replacement would
be attempting to replace a final transaction, and therefore fails). So,
while they can expend twice the bandwidth compared to a non-replacement,
I don't think that's a major issue?

Re: [Bitcoin-development] Re-enabling simple tx replacement

[Gregory Maxwell]

On Sun, Jan 4, 2015 at 5:22 PM, Ross Nicoll <jrn@jrn.me.uk> wrote:
> Grabbing a simple test case:
> https://chain.so/tx/BTCTEST/f903a31f2474df737d324c60abf2407e1cf7e052844da4ccffbfab81cf6ac1f8
> - that won't lock until 0028 UTC on the 5th.
>
> I've tried closing the wallet, moving the wallet.dat file out of the
> way, and then attempting the spend transaction (which can be locked
> immediately), and it either rejects it on acceptance to mempool, or it
> is never included in a block.

Can you send me the actual raw transaction (that site doesn't appear
have a way to get it, only some cooked json output; which doesn't
include the sequence number).

As I said, it's a severe bug if unlocked transactions are being
relayed or mempooled far in advance.

> They can only replace a non-final transaction with a final transaction,

Ah I missed that the replacement had to be final. Thats indeed a much
more sane thing to do than I was thinking (sorry for some reason I saw
the +1 and thought it was just checking the sequence number was
higher.)

> I don't think that's a major issue?

If they can relay the first one to begin with its an an issue, the
replacement just makes it twice an issue. :)

Re: [Bitcoin-development] Re-enabling simple tx replacement

[Gregory Maxwell]

On Sun, Jan 4, 2015 at 5:35 PM, Gregory Maxwell <gmaxwell@gmail.com> wrote:
> Can you send me the actual raw transaction (that site doesn't appear
> have a way to get it, only some cooked json output; which doesn't
> include the sequence number).

Nevermind, I guess. I think I figured out your problem: The behaviour
on testnet is busted because the non-mempooling is enforced by
IsStandardTx which is bypassed in testnet. We should enforce that
elsewhere.

This isn't the case on the real network.

Re: [Bitcoin-development] Re-enabling simple tx replacement

[Peter Todd]

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On Sun, Jan 04, 2015 at 05:44:59PM +0000, Gregory Maxwell wrote:
> On Sun, Jan 4, 2015 at 5:35 PM, Gregory Maxwell <gmaxwell@gmail.com> wrote:
> > Can you send me the actual raw transaction (that site doesn't appear
> > have a way to get it, only some cooked json output; which doesn't
> > include the sequence number).
> 
> Nevermind, I guess. I think I figured out your problem: The behaviour
> on testnet is busted because the non-mempooling is enforced by
> IsStandardTx which is bypassed in testnet. We should enforce that
> elsewhere.
> 
> This isn't the case on the real network.

Yup.

I have a pull-req open to fix this:

https://github.com/bitcoin/bitcoin/pull/5521

-- 
'peter'[:-1]@petertodd.org
00000000000000000237ec84e4b02efbdf3bcbf62308c873da802caedd12432f

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Re: [Bitcoin-development] Re-enabling simple tx replacement

[Ross Nicoll]

On 04/01/15 17:44, Gregory Maxwell wrote:
> On Sun, Jan 4, 2015 at 5:35 PM, Gregory Maxwell <gmaxwell@gmail.com> wrote:
>> Can you send me the actual raw transaction (that site doesn't appear
>> have a way to get it, only some cooked json output; which doesn't
>> include the sequence number).
> 
> Nevermind, I guess. I think I figured out your problem: The behaviour
> on testnet is busted because the non-mempooling is enforced by
> IsStandardTx which is bypassed in testnet. We should enforce that
> elsewhere.
> 
> This isn't the case on the real network.
> 

Ah, thanks for that.

I'll try Peter's patch for testnet tomorrow, sounds like it should fix
this for my use case.

Re: [Bitcoin-development] Re-enabling simple tx replacement

[Gregory Maxwell]

On Sun, Jan 4, 2015 at 6:11 PM, Ross Nicoll <jrn@jrn.me.uk> wrote:
> Ah, thanks for that.
>
> I'll try Peter's patch for testnet tomorrow, sounds like it should fix
> this for my use case.

Thanks for presenting your solution as code in any case. In spite of
the fact that I gave it a crappy read this time, it really is a useful
way to communicate and I wish more people did that.

Re: [Bitcoin-development] Re-enabling simple tx replacement

[Jorge Timón]

On Sun, Jan 4, 2015 at 7:31 PM, Gregory Maxwell <gmaxwell@gmail.com> wrote:
> Thanks for presenting your solution as code in any case. It really is a useful
> way to communicate and I wish more people did that.

+1

Re: [Bitcoin-development] Re-enabling simple tx replacement

[Ross Nicoll]

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On 04/01/15 17:35, Gregory Maxwell wrote:
> On Sun, Jan 4, 2015 at 5:22 PM, Ross Nicoll <jrn@jrn.me.uk> wrote:
>> Grabbing a simple test case:
>> https://chain.so/tx/BTCTEST/f903a31f2474df737d324c60abf2407e1cf7e052844da4ccffbfab81cf6ac1f8
>> - that won't lock until 0028 UTC on the 5th.
>>
>> I've tried closing the wallet, moving the wallet.dat file out of the
>> way, and then attempting the spend transaction (which can be locked
>> immediately), and it either rejects it on acceptance to mempool, or it
>> is never included in a block.
> 
> Can you send me the actual raw transaction (that site doesn't appear
> have a way to get it, only some cooked json output; which doesn't
> include the sequence number).
> 
> As I said, it's a severe bug if unlocked transactions are being
> relayed or mempooled far in advance.

Attached. Sequence number for the input is set to 1, please do tell me
if I've misunderstood how it's used.

>> They can only replace a non-final transaction with a final transaction,
> 
> Ah I missed that the replacement had to be final. Thats indeed a much
> more sane thing to do than I was thinking (sorry for some reason I saw
> the +1 and thought it was just checking the sequence number was
> higher.)
> 
>> I don't think that's a major issue?
> 
> If they can relay the first one to begin with its an an issue, the
> replacement just makes it twice an issue. :)
> 

I'll set up a few nodes tomorrow and double check it's in fact relaying
in the latest version. If it's simply an issue of incorrect relaying,
that's significantly simpler at least, and the problem can be tackled
through that instead.


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