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gpg: Fix the encrypt+sign hash algo preference selection for ECDSA.

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* g10/keydb.h (pref_hint): Change from union to struct and add field
'exact'.  Adjust callers.
* g10/pkclist.c (algo_available): Take care of the exact hint.
* g10/sign.c (sign_file): Rework the hash detection from
recipient prefs.
--

This fixes a encrypt+sign case like: One recipient key has SHA512 as
highest ranked hash preference but the the signing key is a 256 bit
curve.  Because we don't want to use a truncated hash with ECDSA, we
need to have an exact match - this is in particular important for
smartcard which check that the hash matches the curves.

Signed-off-by: Werner Koch <wk@gnupg.org>

Ported-from-stable: aeed0b93ff
This commit is contained in:
Werner Koch 2020-11-13 15:43:30 +01:00
parent e546cc78b7
commit e37c2e1844
No known key found for this signature in database
GPG key ID: E3FDFF218E45B72B
4 changed files with 58 additions and 35 deletions
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20
g10/pkclist.c
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@ -1444,7 +1444,7 @@ build_pk_list (ctrl_t ctrl, strlist_t rcpts, PK_LIST *ret_pk_list)
preference list, so I'm including it. -dms */
int
algo_available( preftype_t preftype, int algo, const union pref_hint *hint)
algo_available( preftype_t preftype, int algo, const struct pref_hint *hint)
{
if( preftype == PREFTYPE_SYM )
{
@ -1465,16 +1465,26 @@ algo_available( preftype_t preftype, int algo, const union pref_hint *hint)
{
if (hint && hint->digest_length)
{
if (hint->digest_length!=20 || opt.flags.dsa2)
unsigned int n = gcry_md_get_algo_dlen (algo);
if (hint->exact)
{
/* For example ECDSA requires an exact hash value so
* that we do not truncate. For DSA we allow truncation
* and thus exact is not set. */
if (hint->digest_length != n)
return 0;
}
else if (hint->digest_length!=20 || opt.flags.dsa2)
{
/* If --enable-dsa2 is set or the hash isn't 160 bits
(which implies DSA2), then we'll accept a hash that
is larger than we need. Otherwise we won't accept
any hash that isn't exactly the right size. */
if (hint->digest_length > gcry_md_get_algo_dlen (algo))
if (hint->digest_length > n)
return 0;
}
else if (hint->digest_length != gcry_md_get_algo_dlen (algo))
else if (hint->digest_length != n)
return 0;
}
@ -1511,7 +1521,7 @@ algo_available( preftype_t preftype, int algo, const union pref_hint *hint)
*/
int
select_algo_from_prefs(PK_LIST pk_list, int preftype,
int request, const union pref_hint *hint)
int request, const struct pref_hint *hint)
{
PK_LIST pkr;
u32 bits[8];