Re: Exploiting SHA1's "XOR weakness" allows for faster hash calculation
- From
- Marko Kreen <markokr@gmail.com>
- Date
- Dec 5, 2012, 12:26 UTC
- Message-ID
- <CACMqXC+jfkvj_ot0x6La6gOHypuXE-LX41V04_yQdZ+gytSDDw@mail.gmail.com>
- In-Reply-To
- <k9n3jd$akg$1@ger.gmane.org>
On Wed, Dec 5, 2012 at 11:19 AM, Sebastian Schuberth <sschuberth@gmail.com> wrote:
Show 6 quoted lines
> to say it in advance: I do not want to trigger any bogus security discussion > here. Instead, I believe the findings from [1] allow for an up to 20% faster > SHA1 calculation, if my brief reading of the presentation is correct. Any > opinions on integration this optimization into Git? > > [1] https://hashcat.net/p12/js-sha1exp_169.pdf
Pretty cool find. Although it's not actual cryptographic weakness, it does show some gaps in designers thinking - as there are simple optimizations available to crackers but not users.
It does seem unusable for real implementation - the 20% win is available only after the data is processed properly once. Then after changing the data a little, you can calculate next hash faster.
There still small possibility that there is way to optimize W calculation for the first run, but it does seem really hard, and even impossible while trying to keep the cache usage small.
-- marko