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From: Matt Corallo <lf-lists@mattcorallo.com>
To: Greg Sanders <gsanders87@gmail.com>,
	Bitcoin Protocol Discussion
	<bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] Bech32 weakness and impact on bip-taproot addresses
Date: Thu, 7 Nov 2019 19:41:54 -0500	[thread overview]
Message-ID: <701F6185-EB2C-4EB1-AAAA-1133879CF541@mattcorallo.com> (raw)
In-Reply-To: <CAB3F3DsbPyqUutBNbVcHME0kGWsbTzTtb5tWV+zRERHwpibXBw@mail.gmail.com>

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Given the issue is in the address format, not the consensus/standardness layer, it does seem somewhat strange to jump to addressing it with a consensus/standardness fix. Maybe the ship has sailed, but for the sake of considering all our options, we could also redefine bech32 to not allow such addresses.

Matt

>> On Nov 7, 2019, at 17:47, Greg Sanders via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
> 
> Could the softer touch of just making them non-standard apply as a future preparation for an accepted softfork? Relaxations could easily be done later if desired.
> 
>>> On Thu, Nov 7, 2019, 5:37 PM Pieter Wuille via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org> wrote:
>> Hello all,
>> 
>> A while ago it was discovered that bech32 has a mutation weakness (see
>> https://github.com/sipa/bech32/issues/51 for details). Specifically,
>> when a bech32 string ends with a "p", inserting or erasing "q"s right
>> before that "p" does not invalidate it. While insertion/erasure
>> robustness was not an explicit goal (BCH codes in general only have
>> guarantees about substitution errors), this is very much not by
>> design, and this specific issue could have been made much less
>> impactful with a slightly different approach. I'm sorry it wasn't
>> caught earlier.
>> 
>> This has little effect on the security of P2WPKH/P2WSH addresses, as
>> those are only valid (per BIP173) for specific lengths (42 and 62
>> characters respectively). Inserting 20 consecutive "p"s in a typo
>> seems highly improbable.
>> 
>> I'm making this post because this property may unfortunately influence
>> design decisions around bip-taproot, as was brought up in the review
>> session (https://lists.linuxfoundation.org/pipermail/bitcoin-dev/2019-October/017427.html)
>> past tuesday. In the current draft, witness v1 outputs of length other
>> than 32 remain unencumbered, which means that for now such an
>> insertion or erasure would result in an output that can be spent by
>> anyone. If that is considered unacceptable, it could be prevented by
>> for example outlawing v1 witness outputs of length 31 and 33.
>> 
>> Thoughts?
>> 
>> Cheers,
>> 
>> -- 
>> Pieter
>> _______________________________________________
>> bitcoin-dev mailing list
>> bitcoin-dev@lists.linuxfoundation.org
>> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev

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  reply	other threads:[~2019-11-08  0:41 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-07 22:35 [bitcoin-dev] Bech32 weakness and impact on bip-taproot addresses Pieter Wuille
2019-11-07 22:45 ` Greg Sanders
2019-11-08  0:41   ` Matt Corallo [this message]
2019-11-08  2:15 ` David A. Harding
2019-11-08  3:15   ` Eric Voskuil
2019-11-10 21:51   ` Pieter Wuille
2019-11-11  1:02     ` Matt Corallo
2019-11-13  2:56       ` Clark Moody
2019-11-13  5:32         ` ZmnSCPxj
2019-11-13  6:30           ` Pieter Wuille
2020-07-15 20:56             ` Russell O'Connor
2020-07-15 21:05               ` Greg Sanders
2020-07-15 21:11                 ` Russell O'Connor
2019-11-08  5:11 ` ZmnSCPxj
2019-11-08 13:03   ` Russell O'Connor
2019-11-08 13:42     ` Damian Mee

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