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

[Jeffrey Walton <[e-mail]>]

On Tue, Jan 7, 2020 at 10:23 AM Russ Housley <[e-mail]> 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).

And if interested, Mozilla's cacert.pem
(https://curl.haxx.se/docs/caextract.html) has 52 certificates at
risk:

$ ./test.exe
Load certificates from cacert.pem
Certificates total: 138

ecdsa-with-SHA256: 5
ecdsa-with-SHA384: 16
id_sha1WithRSASignature: 52
id_sha256WithRSAEncryption: 56
id_sha256WithRSAEncryption: 8
id_sha512WithRSAEncryption: 1

Jeff