Re: [PATCH 2/2] 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.
> [...]
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
> diff --git a/Documentation/technical/hash-function-transition.txt b/Documentation/technical/hash-function-transition.txt
> @@ -28,11 +28,30 @@ advantages:
>  Over time some flaws in SHA-1 have been discovered by security
> +researchers. On 23 February 2017 the SHAttered attack
> +(https://shattered.io) demonstrated a practical SHA-1 hash collision.
> +
> +Git v2.13.0 and later subsequently moved to a hardened SHA-1
> +implementation by default, which isn't vulnerable to the SHAttered
> +attack.
> +
> +Thus Git has in effect already migrated to a new hash that isn't SHA-1
> +and doesn't share its vulnerabilities, its new hash function just
> +happens to produce exactly the same output for all known inputs,
> +except two PDFs published by the SHAttered researchers, and the new
> +implementation (written by those researchers) claims to detect future
> +cryptanalytic collision attacks.
> +
> +Regardless, it's considered prudent to move past any variant of SHA-1
> +to a new hash. There's no guarantee that future attacks on SHA-1 won't
> +be published in the future, and those attacks may not have viable
> +mitigations.
> +
> +If SHA-1 and its variants were to be truly broken Git's hash function