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

* 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): Fix indentation.  Rework the hash 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>
This commit is contained in:
Werner Koch 2020-11-13 15:43:30 +01:00
parent f400ff4e7d
commit aeed0b93ff
No known key found for this signature in database
GPG Key ID: E3FDFF218E45B72B
3 changed files with 57 additions and 37 deletions
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9
g10/keydb.h
View File

@ -128,9 +128,10 @@ struct pubkey_find_info {
/* Helper type for preference functions. */
union pref_hint
struct pref_hint
{
int digest_length;
int digest_length; /* We want at least this digest length. */
int exact; /* We need to use exactly this length. */
};
@ -262,9 +263,9 @@ gpg_error_t find_and_check_key (ctrl_t ctrl,
pk_list_t *pk_list_addr);
int algo_available( preftype_t preftype, int algo,
const union pref_hint *hint );
const struct 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);
int select_mdc_from_pklist (PK_LIST pk_list);
void warn_missing_mdc_from_pklist (PK_LIST pk_list);
void warn_missing_aes_from_pklist (PK_LIST pk_list);

20
g10/pkclist.c
View File

@ -1369,7 +1369,7 @@ 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 )
{
@ -1395,16 +1395,26 @@ 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;
}
@ -1441,7 +1451,7 @@ 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];

65
g10/sign.c
View File

@ -905,7 +905,8 @@ write_signature_packets (ctrl_t ctrl,
* and ignore the detached mode. Sign the file with all secret keys
* which can be taken from LOCUSR, if this is NULL, use the default one
* If ENCRYPTFLAG is true, use REMUSER (or ask if it is NULL) to encrypt the
* signed data for these users.
* signed data for these users. If ENCRYPTFLAG is 2 symmetric encryption
* is also used.
* If OUTFILE is not NULL; this file is used for output and the function
* does not ask for overwrite permission; output is then always
* uncompressed, non-armored and in binary mode.
@ -1035,17 +1036,16 @@ sign_file (ctrl_t ctrl, strlist_t filenames, int detached, strlist_t locusr,
select_algo_from_prefs(pk_list,PREFTYPE_HASH,
opt.def_digest_algo,
NULL)!=opt.def_digest_algo)
log_info(_("WARNING: forcing digest algorithm %s (%d)"
" violates recipient preferences\n"),
gcry_md_algo_name (opt.def_digest_algo),
opt.def_digest_algo );
log_info(_("WARNING: forcing digest algorithm %s (%d)"
" violates recipient preferences\n"),
gcry_md_algo_name (opt.def_digest_algo),
opt.def_digest_algo );
}
else
{
int algo, smartcard=0;
union pref_hint hint;
hint.digest_length = 0;
int algo;
int conflict = 0;
struct pref_hint hint = { 0 };
/* Of course, if the recipient asks for something
unreasonable (like the wrong hash for a DSA key) then
@ -1073,31 +1073,40 @@ sign_file (ctrl_t ctrl, strlist_t filenames, int detached, strlist_t locusr,
(sk_rover->pk->pkey[1]));
if (sk_rover->pk->pubkey_algo == PUBKEY_ALGO_ECDSA)
temp_hashlen = ecdsa_qbits_from_Q (temp_hashlen);
temp_hashlen = (temp_hashlen+7)/8;
{
temp_hashlen = ecdsa_qbits_from_Q (temp_hashlen);
if (!temp_hashlen)
conflict = 1; /* Better don't use the prefs. */
temp_hashlen = (temp_hashlen+7)/8;
/* Fixup for that funny nistp521 (yes, 521)
* were we need to use a 512 bit hash algo. */
if (temp_hashlen == 66)
temp_hashlen = 64;
}
else
temp_hashlen = (temp_hashlen+7)/8;
/* Pick a hash that is large enough for our
largest q */
largest q or matches our Q but if tehreare
several of them we run into a conflict and
don't use the preferences. */
if (hint.digest_length<temp_hashlen)
hint.digest_length=temp_hashlen;
if (hint.digest_length < temp_hashlen)
{
if (sk_rover->pk->pubkey_algo == PUBKEY_ALGO_ECDSA)
{
if (hint.exact)
conflict = 1;
hint.exact = 1;
}
hint.digest_length = temp_hashlen;
}
}
/* FIXME: need to check gpg-agent for this. */
/* else if (sk_rover->pk->is_protected */
/* && sk_rover->pk->protect.s2k.mode == 1002) */
/* smartcard = 1; */
}
/* Current smartcards only do 160-bit hashes. If we have
to have a >160-bit hash, then we can't use the
recipient prefs as we'd need both =160 and >160 at the
same time and recipient prefs currently require a
single hash for all signatures. All this may well have
to change as the cards add algorithms. */
if ((!smartcard || (smartcard && hint.digest_length==20))
&& (algo = select_algo_from_prefs(pk_list,PREFTYPE_HASH,
-1,&hint)) > 0)
if (!conflict
&& (algo = select_algo_from_prefs (pk_list,PREFTYPE_HASH,
-1,&hint)) > 0)
{
/* Note that we later check that the algo is not weak. */
recipient_digest_algo = algo;