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From: Jeff King <>
To: Mike Hommey <>
Subject: Re: [PATCH] Remove non-SHA1dc sha1 implementations
Date: Sun, 23 Feb 2020 23:47:32 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Mon, Feb 24, 2020 at 07:37:58AM +0900, Mike Hommey wrote:

> It is 2020, and with the weakening of SHA1 security-wise, there doesn't
> seem to be a reason to support anything else than SHA1dc, with collision
> detection.

One possible reason is that they're way faster than sha1dc (block-sha1
maybe only a little, but openssl's sha1 is over twice as fast).

To be clear, I think the slowdown is worth the extra safety, but:

 - do we still want to care about people who prefer to make the tradeoff

 - when we first switched the default to sha1dc, the idea was raised of
   continuing to use a faster implementation for non-security checksums
   (e.g., the checksums at the end of packfiles, index files, etc). I
   don't think anybody ever implemented that, but it's not a terrible
   idea. OTOH, if nobody noticed the bottleneck enough to care, maybe
   it's not worth worrying about.

I'm not convinced the answer to those questions is "yes", but I think
it's worth at least raising them (and arguing against them in the commit

One thing that compels me is the recent report that we still build with
common crypto by default on macOS, which was definitely _not_ intended.
That's a bug that can be fixed, but it wouldn't have happened in the
first place if we only supported sha1dc.


  reply	other threads:[~2020-02-24  4:47 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-12  8:56 SHA1dc on mac Mike Hommey
2020-02-12 16:46 ` Eric Sunshine
2020-02-12 22:31   ` Mike Hommey
2020-02-12 22:40     ` Junio C Hamano
2020-02-23 22:37       ` [PATCH] Remove non-SHA1dc sha1 implementations Mike Hommey
2020-02-24  4:47         ` Jeff King [this message]
2020-02-24  4:52           ` Jeff King
2022-03-19  1:02         ` [PATCH] ppc: remove custom SHA-1 implementation Ævar Arnfjörð Bjarmason
2022-03-21 16:39           ` Junio C Hamano
2022-03-21 17:06           ` [PATCH v2] " Ævar Arnfjörð Bjarmason
2022-03-21 21:19             ` brian m. carlson
2022-08-31  9:18             ` [PATCH v3 0/2] Makefile + hash.h: remove PPC_SHA1 implementation Ævar Arnfjörð Bjarmason
2022-08-31  9:18               ` [PATCH v3 1/2] " Ævar Arnfjörð Bjarmason
2022-08-31  9:18               ` [PATCH v3 2/2] Makefile: use $(OBJECTS) instead of $(C_OBJ) Ævar Arnfjörð Bjarmason
2022-08-31 21:44                 ` Junio C Hamano
2022-09-01 14:52                   ` Ævar Arnfjörð Bjarmason
2022-09-01 15:48                     ` Junio C Hamano

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