PBKDF2: Use gcry_md_reset to speed up calculation.
authorMilan Broz <gmazyland@gmail.com>
Mon, 13 Jan 2014 20:30:42 +0000 (21:30 +0100)
committerWerner Koch <wk@gnupg.org>
Tue, 14 Jan 2014 15:34:50 +0000 (16:34 +0100)
commit04cda6b7cc16f3f52c12d9d3e46c56701003496e
treef9942a9058230400055ffc5976373ed6db9da65d
parentdfde161355b15b25b1d1214d5ee0338e50b33517
PBKDF2: Use gcry_md_reset to speed up calculation.

* cipher/kdf.c (_gcry_kdf_pkdf2): Use gcry_md_reset
to speed up calculation.
--

Current PBKDF2 implementation uses gcry_md_set_key in every iteration
which is extremely slow (even in comparison with other implementations).

Use gcry_md_reset instead and set key only once.

With this test program:

  char input[32000], salt[8], key[16];
  gcry_kdf_derive(input, sizeof(input), GCRY_KDF_PBKDF2,
                  gcry_md_map_name("sha1"),
                  salt, sizeof(salt), 100000, sizeof(key), key);

running time without patch:
  real    0m11.165s
  user    0m11.136s
  sys     0m0.000s

and with patch applied
  real    0m0.230s
  user    0m0.184s
  sys     0m0.024s

(The problem was found when cryptsetup started to use gcrypt internal PBKDF2
and for very long keyfiles unlocking time increased drastically.
See https://bugzilla.redhat.com/show_bug.cgi?id=1051733)

Signed-off-by: Milan Broz <gmazyland@gmail.com>
cipher/kdf.c