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From: "Russell O'Connor" <roconnor@blockstream.io>
To: Johnson Lau <jl2012@xbt.hk>
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Safer sighashes and more granular SIGHASH_NOINPUT
Date: Thu, 22 Nov 2018 17:10:11 -0500	[thread overview]
Message-ID: <CAMZUoKkdjHYd8BR6PCae-UG_QRoujW36kYf8s4Gk2FVBeSJnrw@mail.gmail.com> (raw)
In-Reply-To: <8CD6C248-9ADF-4324-B4E3-DE41A1ED49A9@xbt.hk>

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On Thu, Nov 22, 2018 at 3:53 PM Johnson Lau <jl2012@xbt.hk> wrote:

> Assuming a script size of 128 bytes (including SHA256 padding), 2^20
> scripts is 134MB. Double it to 268MB for the merkle branch hashes. With
> roughly 100MB/s, this should take 2.5s (or 42min for 30 levels). However,
> memory use is not considered.
>
> >each call to this operation effectively takes O(script-size) time
> I’m not sure if this is correct. Actually,
> CTransactionSignatureSerializer() scans every script for OP_CODESEPARATOR.
> Scripts with and without OP_CODESEPARATOR should take exactly the same
> O(script-size) time (see https://github.com/bitcoin/bitcoin/pull/14786)
> Also, this is no longer a concern under segwit (BIP143), which
> CTransactionSignatureSerializer() is not used. Actually, OP_CODESEPARATOR
> under segwit is way simpler than the proposed OP_MASK. If one finds OP_MASK
> acceptable, there should be no reason to reject OP_CODESEPARATOR.
>

Even still, each call to OP_CODESEPARATOR / OP_CHECKSIG pair requires
recomputing a new #5. scriptCode from BIP 143, and hence computes a new
transaction digest.  I understood that this issue was the main motivation
for wanting to deprecate OP_CODESEPARATOR and remove it from later versions
of script.

However, given that we are looking at a combinatorial explosion in SIGHASH
flag combinations already, coupled with existing SigOp limitations, maybe
the cost of recomputing scriptCode with OP_CODESEPARATOR isn't such a big
deal.

And even if we choose remove the behavior of OP_CODESEPARATOR in new
versions of Script, it seems more than 30 layers of sequential OP_IFs can
be MASTified, so there is no need to use OP_CODESEPARATOR within that limit.

>One suggestion I heard (I think I heard it from Pieter) to achieve the
above is to add an internal counter that increments on every control flow
operator,……...

> If I have to choose among OP_CODESEPARATOR and “flow operator counting”,
> I’d rather choose OP_CODESEPARATOR. At least we don’t need to add more
> lines to the consensus code, just for something that is mostly archivable
> with MAST.
>

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  reply	other threads:[~2018-11-22 22:10 UTC|newest]

Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-19 22:37 [bitcoin-dev] Safer sighashes and more granular SIGHASH_NOINPUT Pieter Wuille
2018-11-20 20:29 ` Anthony Towns
2018-11-21 11:20   ` Christian Decker
2018-11-21 17:55   ` Johnson Lau
2018-11-21 11:15 ` Christian Decker
2018-11-23  6:04   ` Anthony Towns
2018-11-23  9:40     ` Christian Decker
2018-11-24  8:13       ` Johnson Lau
2018-11-21 17:07 ` Russell O'Connor
2018-11-22 14:28   ` Johnson Lau
2018-11-22 16:23     ` Russell O'Connor
2018-11-22 20:52       ` Johnson Lau
2018-11-22 22:10         ` Russell O'Connor [this message]
2018-11-23 10:47           ` Johnson Lau
2018-11-23  5:03   ` Anthony Towns
2018-11-23 20:18     ` Russell O'Connor
2018-11-28  3:41 ` Pieter Wuille
2018-11-28  8:31   ` Johnson Lau
2018-11-29 17:00   ` Christian Decker
2018-11-29 18:29     ` Christian Decker
2018-12-06 16:57   ` Russell O'Connor
2018-12-09 19:13     ` Johnson Lau
2018-12-11 22:50       ` Russell O'Connor
2018-12-12 19:53         ` Johnson Lau
2018-12-13 16:50           ` Russell O'Connor
2018-12-13  0:05         ` Anthony Towns
2018-12-13 16:21           ` Russell O'Connor
2018-12-14  0:47             ` Anthony Towns
     [not found]         ` <CAAS2fgRma+Pw-rHJSOKRVBqoxqJ3AxHO9d696fWoa-sb17JEOQ@mail.gmail.com>
2018-12-13 16:34           ` Russell O'Connor
2018-12-09 22:41     ` David A. Harding
2018-12-11 15:36       ` Russell O'Connor
2018-12-11 17:47         ` David A. Harding
2018-12-12  9:42 ` Rusty Russell
2018-12-12 20:00   ` Johnson Lau
2018-12-12 23:49     ` Rusty Russell
2018-12-13  0:37       ` Rusty Russell
2018-12-14  9:30         ` Anthony Towns
2018-12-14 13:55           ` Johnson Lau
2018-12-17  3:10             ` Rusty Russell
2018-12-20 19:34               ` Johnson Lau
2018-12-20 23:17                 ` Rusty Russell
2018-12-21 18:54                   ` Johnson Lau
2018-12-23  4:26                     ` Anthony Towns
2018-12-23 16:33                       ` Johnson Lau
2018-12-24 12:01                         ` ZmnSCPxj
2018-12-24 21:23                           ` Johnson Lau
2018-12-16  6:55           ` Rusty Russell
2018-12-17 19:08             ` Johnson Lau
2018-12-18  4:22               ` Peter Todd
2018-12-19  0:39               ` Rusty Russell
2019-02-09  0:39                 ` Pieter Wuille
2018-12-13  0:24   ` Anthony Towns
2018-11-28  0:54 Bob McElrath
2018-11-28  8:40 ` Johnson Lau
2018-11-28 14:04   ` Bob McElrath

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