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From: Steve Davis <steven.charles.davis@gmail.com>
In-Reply-To: <20170225010122.GA10233@savin.petertodd.org>
Date: Sat, 25 Feb 2017 06:04:28 -0600
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Message-Id: <208F93FE-B7C8-46BE-8E00-52DBD0F43415@gmail.com>
References: <mailman.22137.1487974823.31141.bitcoin-dev@lists.linuxfoundation.org>
	<8F096BE1-D305-43D4-AF10-2CC48837B14F@gmail.com>
	<20170225010122.GA10233@savin.petertodd.org>
To: Peter Todd <pete@petertodd.org>
Cc: Bitcoin Protocol Discussion <bitcoin-dev@lists.linuxfoundation.org>
Subject: Re: [bitcoin-dev] SHA1 collisions make Git vulnerable to attakcs by
 third-parties, not just repo maintainers
Precedence: list


> On Feb 24, 2017, at 7:01 PM, Peter Todd <pete@petertodd.org> wrote:
>=20
> On Fri, Feb 24, 2017 at 05:49:36PM -0600, Steve Davis via bitcoin-dev =
wrote:
>> If the 20 byte SHA1 is now considered insecure (with good reason), =
what about RIPEMD-160 which is the foundation of Bitcoin addresses?
>=20
> SHA1 is insecure because the SHA1 algorithm is insecure, not because =
160bits isn't enough.
>=20
> AFAIK there aren't any known weaknesses in RIPEMD160,

=E2=80=A6so far. I wonder how long that vacation will last?

> but it also hasn't been
> as closely studied as more common hash algorithms.

...but we can be sure that it will be, since the dollar value held in =
existing utxos continues to increase...

> That said, Bitcoin uses
> RIPEMD160(SHA256(msg)), which may make creating collisions harder if =
an attack
> is found than if it used RIPEMD160 alone.

Does that offer any greater protection? That=E2=80=99s not so clear to =
me as the outputs (at least for p2pkh) only verify the public key =
against the final 20 byte hash. Specifically, in the first (notional) =
case the challenge would be to find a private key that has a public key =
that hashes to the final hash. In the second (realistic) case, you =
merely need to add the sha256 hash into the problem, which doesn=E2=80=99t=
 seem to me to increase the difficulty by any significant amount?=20


/s=