doc hash-function-transition: clarify what SHAttered means
authorÆvar Arnfjörð Bjarmason <avarab@gmail.com>
Mon, 26 Mar 2018 18:27:08 +0000 (18:27 +0000)
committerJunio C Hamano <gitster@pobox.com>
Wed, 28 Mar 2018 02:08:31 +0000 (19:08 -0700)
commit5988eb631a3a3a42f82c1442fae79001ad2b90e7
tree8b96fcd0b241cd0aeafe0501ebcdbf0ffa98bdc0
parent45fa195ff0b7a440fae02da1d871f976afa32dff
doc hash-function-transition: clarify what SHAttered means

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>
Documentation/technical/hash-function-transition.txt