From: Jacob Eliosoff <jacob.eliosoff@gmail•com>
To: Mats Jerratsch <mats@blockchain•com>
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists•linuxfoundation.org>
Subject: Re: [bitcoin-dev] Generalised Replay Protection for Future Hard Forks
Date: Wed, 15 Nov 2017 00:02:48 -0500 [thread overview]
Message-ID: <CAAUaCyjpH0hAxS7pUzZihft3KDtgB3nkZdT_6JUhmE9hJ7T4sA@mail.gmail.com> (raw)
In-Reply-To: <71A64D11-DE57-4AA2-A635-F2AA4DC04909@blockchain.com>
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>
> Sorry, I was careless with the use of `>=` there. You are correct, forks
> form a tree. For this proposal, every leaf must be assigned a unique
> `nForkId`. The relationship between `nForkId` is irrelevant (e.g. which
> number is bigger), as long as they are unique. Transactions are only valid
> IFF `nForkId` matches exactly the `nForkId` of the software validating it.
> As described above, the transaction doesn't even contain `nForkId`, and the
> node surely is not starting to guess which one it could be.
>
OK, but then it seems to me you have a dilemma for, eg, your LN commitment
tx. You either give it the specific nForkId of the fork it's created on -
making it invalid on *all* other forks (eg, any future "non-contentious
upgrade" HF that replaces that fork). Or you give it nForkId 0 - which has
the "BCH tx valid on Segwit2x (& vice versa)" flaw.
It may make sense to revise your proposal to incorporate Luke's
OP_CHECKBLOCKATHEIGHT
<https://github.com/bitcoin/bips/blob/master/bip-0115.mediawiki>, and make
the fork ID a (block height, hash) pair rather than just a number. But I
still think the idea of fork-specific addresses is a keeper!
On Tue, Nov 14, 2017 at 8:49 AM, Mats Jerratsch <mats@blockchain•com> wrote:
>
> But I like the 'old' idea of putting the hash of a block that MUST be on
> the chain that this txn can eventually be added to. If the hash is not a
> valid block on the chain, the txn can't be added.
>
> It means you can choose exactly which forks you want to allow your txn on,
> pre-fork for both, post-fork for only one, and gets round the issue of who
> gets to decide the nForkid value.. since you don't need one. Also, all the
> old outputs work fine, and LN not an issue.
>
> I'm missing why this scheme would be better ?
>
>
> I do agree that solutions like `SIGHASH_BLOCKCOMMIT` are superior in the
> sense that they are very difficult to circumvent. However, a fork could
> also follow the original chain in SPV mode and allow transactions protected
> with these mechanism. Since it's fundamentally impossible to disallow
> transactions in future projects, the goal shouldn't be to make this overly
> complicated.
>
> Furthermore, this schema is not just adding replay protection. It makes
> transacting safer overall (due to a dedicated address format per fork) and
> allows light clients to differentiate between multiple forks. In the past
> three months, at least $600k has been lost by users sending BCH to a BTC
> address [1].
>
> Thanks for the clarification. How would a tx specify a constraint like
>> "nForkId>=1"? I was thinking of it just as a number set on the tx.
>>
>
> Whether the transaction is replay protected or not is specified by setting
> a bit in the `SigHashId`. If this bit is set, then the signature *preimage*
> MUST have `nForkId` appended. `nForkId` is not part of the final
> transaction, someone who wants to verify the transaction must know which
> `nForkId` it was created with.
>
> If the bit isn't set, it means `nForkId=0`, which allows other forks to
> validate the signature.
>
> Also note that since forks form a partial order, but IDs (numbers) form a
>> total order, ">=" will miss some cases. Eg, suppose BCH had forked with
>> nForkId 2, and then you set up a LN funding tx on BCH with nForkId>=2, and
>> then Segwit2x forked (from BTC!) with nForkId 3. The BCH funding tx would
>> be valid on Segwit2x. This is more of a fundamental problem than a bug -
>> to avoid it you'd have to get into stuff like making each fork reference
>> its parent-fork's first block or something, someone has written about
>> this...
>>
>
> Sorry, I was careless with the use of `>=` there. You are correct, forks
> form a tree. For this proposal, every leaf must be assigned a unique
> `nForkId`. The relationship between `nForkId` is irrelevant (e.g. which
> number is bigger), as long as they are unique. Transactions are only valid
> IFF `nForkId` matches exactly the `nForkId` of the software validating it.
> As described above, the transaction doesn't even contain `nForkId`, and the
> node surely is not starting to guess which one it could be.
>
> [1]
> https://twitter.com/khannib/status/930223617744437253
>
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prev parent reply other threads:[~2017-11-15 5:02 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-05 23:48 Mats Jerratsch
[not found] ` <CAAUaCyii2U5VBLS+Va+F3h4Hka0OWDnFFmjtsvyaaD4TKVzV3Q@mail.gmail.com>
2017-11-06 19:21 ` Jacob Eliosoff
2017-11-08 16:45 ` Mats Jerratsch
2017-11-09 20:45 ` Jacob Eliosoff
2017-11-09 21:01 ` Sjors Provoost
[not found] ` <CAAUaCygeOxAK=EpzfWndx6uVvVO9B+=YTs1m-jHa3BFp82jA4w@mail.gmail.com>
[not found] ` <95ECB451-56AE-45E5-AAE6-10058C4B7FD7@sprovoost.nl>
[not found] ` <CAAUaCyg_PGT0F=RHfX89T54j-vuyz5wcbXaYoikJv95WKgsNPg@mail.gmail.com>
[not found] ` <55467A01-A8B2-4E73-8331-38C0A7CD90EF@sprovoost.nl>
[not found] ` <CAAUaCyhncyCt_ao9i0=33LswDOkCf6o-+36zrGxKWD+WranmZw@mail.gmail.com>
[not found] ` <46E317DF-C97C-4797-B989-594298BC6030@sprovoost.nl>
[not found] ` <CAAUaCyibOEHqw1J5O8yEp8v=j8t9sovn2vn=S8bZPZCzCY-gRw@mail.gmail.com>
2017-11-10 11:28 ` Mats Jerratsch
2017-11-11 5:18 ` Jacob Eliosoff
2017-11-13 10:03 ` Mats Jerratsch
2017-11-13 15:31 ` Jacob Eliosoff
2017-11-13 17:02 ` Spartacus Rex
2017-11-14 13:49 ` Mats Jerratsch
2017-11-15 5:02 ` Jacob Eliosoff [this message]
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