Re: [saag] SHA-1 is a Shambles: First Chosen-Prefix Collision on SHA-1

I was just about to post. As it happens, I was in the middle of making an
intro video on digest functions for my free course on crypto. So I guess I
will tape it today rather than waiting till Friday (if the heavy equipment
laying new gas pipes in the street is quiet enough).

The need to move on from SHA-1 was one of the reasons I originally started
looking at an improved fingerprint presentation using Base32 encoding that
allowed for safe truncation etc. SHA-1 has more than enough bits for many
applications, the problem is the algorithm. I would like to move to
SHA-2-512/ SHA-3-512 and only 512 bits regardless of the precision required.

https://mathmesh.com/Documents/draft-hallambaker-mesh-udf.html

On Tue, Jan 7, 2020 at 10:23 AM Russ Housley <housley@vigilsec.com> wrote:

> https://eprint.iacr.org/2020/014
>
> > SHA-1 is a Shambles - First Chosen-Prefix Collision on SHA-1 and
> > Application to the PGP Web of Trust
> >
> > Gaëtan Leurent and Thomas Peyrin
> >
> > Abstract: The SHA-1 hash function was designed in 1995 and has been
> > widely used during two decades. A theoretical collision attack was first
> > proposed in 2004 [WYY05], but due to its high complexity it was only
> > implemented in practice in 2017, using a large GPU cluster [SBK+17].
> > More recently, an almost practical chosen-prefix collision attack
> > against SHA-1 has been proposed [LP19]. This more powerful attack allows
> > to build colliding messages with two arbitrary prefixes, which is much
> > more threatening for real protocols.
> >
> > In this paper, we report the first practical implementation of this
> > attack, and its impact on real-world security with a PGP/GnuPG
> > impersonation attack. We managed to significantly reduce the complexity
> > of collisions attack against SHA-1: on an Nvidia GTX 970,
> > identical-prefix collisions can now be computed with a complexity of
> > 2^61.2 rather than 2^64.7, and chosen-prefix collisions with a complexity
> > of 2^63.4 rather than 2^67.1. When renting cheap GPUs, this translates to
> > a cost of 11k US$ for a collision, and 45k US$ for a chosen-prefix
> > collision, within the means of academic researchers. Our actual attack
> > required two months of computations using 900 Nvidia GTX 1060 GPUs (we
> > paid 75k US$ because GPU prices were higher, and we wasted some time
> > preparing the attack).
> >
> > Therefore, the same attacks that have been practical on MD5 since 2009
> > are now practical on SHA-1. In particular, chosen-prefix collisions can
> > break signature schemes and handshake security in secure channel
> > protocols (TLS, SSH). We strongly advise to remove SHA-1 from those type
> > of applications as soon as possible. We exemplify our cryptanalysis by
> > creating a pair of PGP/GnuPG keys with different identities, but
> > colliding SHA-1 certificates. A SHA-1 certification of the first key can
> > therefore be transferred to the second key, leading to a forgery. This
> > proves that SHA-1 signatures now offers virtually no security in
> > practice. The legacy branch of GnuPG still uses SHA-1 by default for
> > identity certifications, but after notifying the authors, the modern
> > branch now rejects SHA-1 signatures (the issue is tracked as
> > CVE-2019-14855).
>
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