Re: Questions about the hash function transition

Ævar Arnfjörð Bjarmason [off-list ref] writes:

On Thu, Aug 23 2018, Junio C Hamano wrote:

quoted

Ævar Arnfjörð Bjarmason [off-list ref] writes:

quoted

quoted

- The trailer consists of the following:
  - A copy of the 20-byte SHA-256 checksum at the end of the
    corresponding packfile.

  - 20-byte SHA-256 checksum of all of the above.

We need to update both of these to 32 byte, right? Or are we planning to
truncate the checksums?

https://public-inbox.org/git/CA+55aFwc7UQ61EbNJ36pFU_aBCXGya4JuT-TvpPJ21hKhRengQ@mail.gmail.com/

Thanks.

Yeah for this checksum purpose even 10 or 5 characters would do, but
since we'll need a new pack format anyway for SHA-256 why not just use
the full length of the SHA-256 here? We're using the full length of the
SHA-1.

I don't see it mattering for security / corruption detection purposes,
but just to avoid confusion. We'll have this one place left where
something looks like a SHA-1, but is actually a trunctated SHA-256.

I would prefer to see us at least explore if the gain in throughput
is sufficiently big if we switch to weaker checksum, like crc32.  If
does not give us sufficient gain, I'd agree with you that consistently
using full hash everywhere would conceptually be cleaner.