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agent: Allow only specific digest size for ECDSA.

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* agent/pksign.c (do_encode_dsa): Fix validation of digest size.

--

Thanks to Steven Noonan <steven@uplinklabs.net> who offers patches
and a test case.

GnuPG-bug-id: 2702
Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>
This commit is contained in:
NIIBE Yutaka 2016-09-27 14:01:18 +09:00
parent df5353b95e
commit 98bc6f480a
1 changed files with 9 additions and 13 deletions
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20
agent/pksign.c
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@ -189,24 +189,20 @@ do_encode_dsa (const byte *md, size_t mdlen, int pkalgo, gcry_sexp_t pkey,
return gpg_error (GPG_ERR_INV_LENGTH);
}
/* ECDSA 521 is special has it is larger than the largest hash
we have (SHA-512). Thus we chnage the size for further
processing to 512. */
if (pkalgo == GCRY_PK_ECDSA && qbits > 512)
qbits = 512;
/* Check if we're too short. Too long is safe as we'll
* automatically left-truncate.
*
* This check would require the use of SHA512 with ECDSA 512. I
* think this is overkill to fail in this case. Therefore, relax
* the check, but only for ECDSA keys. We may need to adjust it
* later for general case. (Note that the check is really a bug for
* ECDSA 521 as the only hash that matches it is SHA 512, but 512 <
* 521 ).
*/
if (mdlen < ((pkalgo==GCRY_PK_ECDSA && qbits > 521) ? 512 : qbits)/8)
automatically left-truncate. */
if (mdlen < qbits/8)
{
log_error (_("a %zu bit hash is not valid for a %u bit %s key\n"),
mdlen*8,
gcry_pk_get_nbits (pkey),
gcry_pk_algo_name (pkalgo));
/* FIXME: we need to check the requirements for ECDSA. */
if (mdlen < 20 || pkalgo == GCRY_PK_DSA)
return gpg_error (GPG_ERR_INV_LENGTH);
}