Attempt to clarify what the SHAttered attack means in practice for
Git. The previous version of the text made no mention whatsoever of
Git already having a mitigation for this specific attack, which the
SHAttered researchers claim will detect cryptanalytic collision
attacks.
I may have gotten some of the nuances wrong, but as far as I know this
new text accurately summarizes the current situation with SHA-1 in
git. I.e. git doesn't really use SHA-1 anymore, it uses
Hardened-SHA-1 (they just so happen to produce the same outputs
99.99999999999...% of the time).
Thus the previous text was incorrect in asserting that:
[...]As a result [of SHAttered], SHA-1 cannot be considered
cryptographically secure any more[...]
That's not the case. We have a mitigation against SHAttered, *however*
we consider it prudent to move to work towards a NewHash should future
vulnerabilities in either SHA-1 or Hardened-SHA-1 emerge.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Change the "Repository format extension" to accurately describe what
happens with different versions of Git when they encounter NewHash
repositories, instead of only saying what happens with versions v2.7.0
and later.
See ab9cb76f66 ("Repository format version check.", 2005-11-25) and
00a09d57eb ("introduce "extensions" form of
core.repositoryformatversion", 2015-06-23) for the relevant changes to
the setup code where these variables are checked.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This document describes what a transition to a new hash function for
Git would look like. Add it to Documentation/technical/ as the plan
of record so that future changes can be recorded as patches.
Also-by: Brandon Williams <bmwill@google.com>
Also-by: Jonathan Tan <jonathantanmy@google.com>
Also-by: Stefan Beller <sbeller@google.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
