Re: [PATCH] replace sha1 with another algorithm
Jeff King venit, vidit, dixit 26.10.2011 02:12:
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> SHA-1 is due to be cryptographically broken sometime in the
> next decade, with collision attacks becoming possible. But
> we don't have to wait! We can act now and replace it,
> treating us to all of the pain of a flag day without any
> delay!
>
> We could of course use the SHA-2 family, or wait for the
> upcoming SHA-3. But any good cryptographer knows that you
> should _never_ use a standard algorithm. It's always better
> to roll your own. After all, if _you_ can't break it, how
> could anyone else?
>
> Signed-off-by: Jeff King <peff@peff.net>
> Reviewed-by: Brandon Casey <drafnel@gmail.com>
> Mocked-by: Rick Balocca <richard.balocca@ericsson.com>
> Enjoyed-by: Elijah Newren <newren@gmail.com>
Awaited-by: Michael J Gruber <git@drmicha.warpmail.net>
Still remembering an earlier GitTogether's l33t l10n....
Show 53 quoted lines
> ---
> block-sha1/sha1.h | 2 +-
> cache.h | 4 +++-
> sha1_file.c | 32 ++++++++++++++++++++++++++++++++
> 3 files changed, 36 insertions(+), 2 deletions(-)
>
> diff --git a/block-sha1/sha1.h b/block-sha1/sha1.h
> index b864df6..49331e3 100644
> --- a/block-sha1/sha1.h
> +++ b/block-sha1/sha1.h
> @@ -19,4 +19,4 @@
> #define git_SHA_CTX blk_SHA_CTX
> #define git_SHA1_Init blk_SHA1_Init
> #define git_SHA1_Update blk_SHA1_Update
> -#define git_SHA1_Final blk_SHA1_Final
> +#define real_git_SHA1_Final blk_SHA1_Final
> diff --git a/cache.h b/cache.h
> index 2e6ad36..068062b 100644
> --- a/cache.h
> +++ b/cache.h
> @@ -13,9 +13,11 @@
> #define git_SHA_CTX SHA_CTX
> #define git_SHA1_Init SHA1_Init
> #define git_SHA1_Update SHA1_Update
> -#define git_SHA1_Final SHA1_Final
> +#define real_git_SHA1_Final SHA1_Final
> #endif
>
> +void git_SHA1_Final(unsigned char out[20], git_SHA_CTX *ctx);
> +
> #include <zlib.h>
> typedef struct git_zstream {
> z_stream z;
> diff --git a/sha1_file.c b/sha1_file.c
> index 27f3b9b..23e0107 100644
> --- a/sha1_file.c
> +++ b/sha1_file.c
> @@ -2833,3 +2833,35 @@ void assert_sha1_type(const unsigned char *sha1, enum object_type expect)
> die("%s is not a valid '%s' object", sha1_to_hex(sha1),
> typename(expect));
> }
> +
> +static void xor_bytes(unsigned char *out, unsigned char *a, unsigned char *b,
> + unsigned n)
> +{
> + unsigned i;
> + for (i = 0; i < n; i++)
> + out[i] = a[i] ^ b[i];
> +}
> +
> +static void mix_hash(unsigned char *h, unsigned n)
> +{
> + unsigned char out[20];Show 12 quoted lines
> + unsigned mid = n / 2;
> +
> + if (2*mid < n)
> + return;
> +
> + xor_bytes(out, h, h + mid, mid);
> + xor_bytes(out + mid, h + mid, h, mid);
> + memcpy(h, out, n);
> +
> + /* If a little bit of mixing is good, then a lot must be GREAT! */
> + mix_hash(h, mid);
> + mix_hash(h + mid, mid);
Show 10 quoted lines
> +}
> +
> +void git_SHA1_Final(unsigned char out[20], git_SHA_CTX *ctx)
> +{
> + /* We build on top of the regular SHA1, but then "enhance" it. */
> + real_git_SHA1_Final(out, ctx);
> + mix_hash(out, 20);
> +}
>--
>1.7.7.trollMichael J Gruber <git@drmicha.warpmail.net>