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gpg: Forbid the creation of SHA-1 third-party key signatures. 

* g10/sign.c (SIGNHINT_KEYSIG, SIGNHINT_SELFSIG): New.
(do_sign): Add arg signhints and inhibit SHA-1 signatures.  Change
callers to pass 0.
(complete_sig): Add arg signhints and pass on.
(make_keysig_packet, update_keysig_packet): Set signhints.
--

Signed-off-by: Werner Koch <wk@gnupg.org>
This commit is contained in:
Werner Koch 2019-11-11 11:41:00 +01:00
parent eebd43d5b6
commit dd18be979e
No known key found for this signature in database
GPG Key ID: E3FDFF218E45B72B
1 changed files with 44 additions and 7 deletions
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51
g10/sign.c
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@ -49,6 +49,12 @@
#define LF "\n"
#endif
/* Bitflags to convey hints on what kind of signayire is created. */
#define SIGNHINT_KEYSIG 1
#define SIGNHINT_SELFSIG 2
/* Hack */
static int recipient_digest_algo;
@ -309,10 +315,12 @@ hash_sigversion_to_magic (gcry_md_hd_t md, const PKT_signature *sig,
/* Perform the sign operation. If CACHE_NONCE is given the agent is
advised to use that cached passphrase for the key. */
* advised to use that cached passphrase for the key. SIGNHINTS has
* hints so that we can do some additional checks. */
static int
do_sign (ctrl_t ctrl, PKT_public_key *pksk, PKT_signature *sig,
gcry_md_hd_t md, int mdalgo, const char *cache_nonce)
gcry_md_hd_t md, int mdalgo,
const char *cache_nonce, unsigned int signhints)
{
gpg_error_t err;
byte *dp;
@ -335,6 +343,19 @@ do_sign (ctrl_t ctrl, PKT_public_key *pksk, PKT_signature *sig,
if (!mdalgo)
mdalgo = gcry_md_get_algo (md);
if ((signhints & SIGNHINT_KEYSIG) && !(signhints & SIGNHINT_SELFSIG)
&& mdalgo == GCRY_MD_SHA1
&& !opt.flags.allow_weak_key_signatures)
{
/* We do not allow the creation of third-party key signatures
* using SHA-1 because we also reject them when verifying. Note
* that this will render dsa1024 keys unsuitable for such
* keysigs and in turn the WoT. */
print_sha1_keysig_rejected_note ();
err = gpg_error (GPG_ERR_DIGEST_ALGO);
goto leave;
}
/* Check compliance. */
if (! gnupg_digest_is_allowed (opt.compliance, 1, mdalgo))
{
@ -431,12 +452,12 @@ do_sign (ctrl_t ctrl, PKT_public_key *pksk, PKT_signature *sig,
static int
complete_sig (ctrl_t ctrl,
PKT_signature *sig, PKT_public_key *pksk, gcry_md_hd_t md,
const char *cache_nonce)
const char *cache_nonce, unsigned int signhints)
{
int rc;
/* if (!(rc = check_secret_key (pksk, 0))) */
rc = do_sign (ctrl, pksk, sig, md, 0, cache_nonce);
rc = do_sign (ctrl, pksk, sig, md, 0, cache_nonce, signhints);
return rc;
}
@ -842,7 +863,7 @@ write_signature_packets (ctrl_t ctrl,
hash_sigversion_to_magic (md, sig, extrahash);
gcry_md_final (md);
rc = do_sign (ctrl, pk, sig, md, hash_for (pk), cache_nonce);
rc = do_sign (ctrl, pk, sig, md, hash_for (pk), cache_nonce, 0);
gcry_md_close (md);
if (!rc)
{
@ -1607,6 +1628,8 @@ make_keysig_packet (ctrl_t ctrl,
int sigversion;
int digest_algo;
gcry_md_hd_t md;
u32 pk_keyid[2], pksk_keyid[2];
unsigned int signhints;
log_assert ((sigclass >= 0x10 && sigclass <= 0x13) || sigclass == 0x1F
|| sigclass == 0x20 || sigclass == 0x18 || sigclass == 0x19
@ -1634,6 +1657,12 @@ make_keysig_packet (ctrl_t ctrl,
else /* Use the default. */
digest_algo = DEFAULT_DIGEST_ALGO;
signhints = SIGNHINT_KEYSIG;
keyid_from_pk (pk, pk_keyid);
keyid_from_pk (pksk, pksk_keyid);
if (pk_keyid[0] == pksk_keyid[0] && pk_keyid[1] == pksk_keyid[1])
signhints |= SIGNHINT_SELFSIG;
if (gcry_md_open (&md, digest_algo, 0))
BUG ();
@ -1676,7 +1705,7 @@ make_keysig_packet (ctrl_t ctrl,
{
hash_sigversion_to_magic (md, sig, NULL);
gcry_md_final (md);
rc = complete_sig (ctrl, sig, pksk, md, cache_nonce);
rc = complete_sig (ctrl, sig, pksk, md, cache_nonce, signhints);
}
gcry_md_close (md);
@ -1712,6 +1741,8 @@ update_keysig_packet (ctrl_t ctrl,
gpg_error_t rc = 0;
int digest_algo;
gcry_md_hd_t md;
u32 pk_keyid[2], pksk_keyid[2];
unsigned int signhints = 0;
if ((!orig_sig || !pk || !pksk)
|| (orig_sig->sig_class >= 0x10 && orig_sig->sig_class <= 0x13 && !uid)
@ -1734,6 +1765,12 @@ update_keysig_packet (ctrl_t ctrl,
else
digest_algo = orig_sig->digest_algo;
signhints = SIGNHINT_KEYSIG;
keyid_from_pk (pk, pk_keyid);
keyid_from_pk (pksk, pksk_keyid);
if (pk_keyid[0] == pksk_keyid[0] && pk_keyid[1] == pksk_keyid[1])
signhints |= SIGNHINT_SELFSIG;
if (gcry_md_open (&md, digest_algo, 0))
BUG ();
@ -1787,7 +1824,7 @@ update_keysig_packet (ctrl_t ctrl,
{
hash_sigversion_to_magic (md, sig, NULL);
gcry_md_final (md);
rc = complete_sig (ctrl, sig, pksk, md, NULL);
rc = complete_sig (ctrl, sig, pksk, md, NULL, signhints);
}
leave: