Re: [bitcoin-dev] SHA1 collisions make Git vulnerable to attakcs by third-parties, not just repo maintainers

From: Dave Scotese <dscotese@litmocracy•com>
To: Peter Todd <pete@petertodd•org>,
	 Bitcoin Protocol Discussion
	<bitcoin-dev@lists•linuxfoundation.org>
Cc: Steve Davis <steven.charles.davis@gmail•com>
Subject: Re: [bitcoin-dev] SHA1 collisions make Git vulnerable to attakcs by third-parties, not just repo maintainers
Date: Sat, 25 Feb 2017 13:21:56 -0800	[thread overview]
Message-ID: <CAGLBAhdCb+QLWRm4FWkPvaM2sU24HuafdgNiS=wgnPTGzrW05w@mail.gmail.com> (raw)
In-Reply-To: <20170225210406.GA16196@savin.petertodd.org>

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I was under the impression that RIPEMD160(SHA256(msg)) is used to turn a
PUBLIC key (msg) into a bitcoin address, so yeah, you could identify
ANOTHER (or the same, I guess - how would you know?) public key that has
the same bitcoin address if RIPEMD-160 collisions are easy, but I don't see
how that has any effect on anyone.  Maybe I'm restating what Peter wrote.
If so, confirmation would be nice.

On Sat, Feb 25, 2017 at 1:04 PM, Peter Todd via bitcoin-dev <
bitcoin-dev@lists•linuxfoundation.org> wrote:

> On Sat, Feb 25, 2017 at 03:53:12PM -0500, Russell O'Connor wrote:
> > On Sat, Feb 25, 2017 at 2:12 PM, Peter Todd via bitcoin-dev <
> > bitcoin-dev@lists•linuxfoundation.org> wrote:
> >
> > > On Sat, Feb 25, 2017 at 11:10:02AM -0500, Ethan Heilman via bitcoin-dev
> > > wrote:
> > > > >SHA1 is insecure because the SHA1 algorithm is insecure, not because
> > > > 160bits isn't enough.
> > > >
> > > > I would argue that 160-bits isn't enough for collision resistance.
> > > Assuming
> > > > RIPEMD-160(SHA-256(msg)) has no flaws (i.e. is a random oracle),
> > > collisions
> > >
> > > That's something that we're well aware of; there have been a few
> > > discussions on
> > > this list about how P2SH's 160-bits is insufficient in certain
> use-cases
> > > such
> > > as multisig.
> > >
> > > However, remember that a 160-bit *security level* is sufficient, and
> > > RIPEMD160
> > > has 160-bit security against preimage attacks. Thus things like
> > > pay-to-pubkey-hash are perfectly secure: sure you could generate two
> > > pubkeys
> > > that have the same RIPEMD160(SHA256()) digest, but if someone does
> that it
> > > doesn't cause the Bitcoin network itself any harm, and doing so is
> > > something
> > > you choose to do to yourself.
> > >
> >
> > Be aware that the issue is more problematic for more complex contracts.
> > For example, you are building a P2SH 2-of-2 multisig together with
> someone
> > else if you are not careful, party A can hand their key over to party B,
> > who can may try to generate a collision between their second key and
> > another 2-of-2 multisig where they control both keys. See
> > https://lists.linuxfoundation.org/pipermail/bitcoin-dev/
> 2016-January/012205.html
>
> I'm very aware of that, in fact I think I may have even been the first
> person
> to post on this list the commit-reveal mitigation.
>
> Note how I said earlier in the message you're replying to that "P2SH's
> 160-bits
> is insufficient in certain use-cases such as multisig"
>
> --
> https://petertodd.org 'peter'[:-1]@petertodd.org
>
> _______________________________________________
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> bitcoin-dev@lists•linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
>

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