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

[Steve Davis <steven.charles.davis@gmail.com>]

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Yea, well. I don’t think it is ethical to post instructions without an associated remediation (BIP) if you don’t see the potential attack.

I was rather hoping that we could have a fuller discussion of what the best practical response would be to such an issue?


> On Feb 25, 2017, at 3:21 PM, Dave Scotese <dscotese@litmocracy.com> wrote:
> 
> 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 <mailto: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 <mailto: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 <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 <https://petertodd.org/> 'peter'[:-1]@petertodd.org <http://petertodd.org/>
> 
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> 
> 
> 
> 
> -- 
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> I own Litmocracy <http://www.litmocracy.com/> and Meme Racing <http://www.memeracing.net/> (in alpha). 
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