diff options
Diffstat (limited to 'g10/sig-check.c')
| -rw-r--r-- | g10/sig-check.c | 54 |
1 files changed, 52 insertions, 2 deletions
diff --git a/g10/sig-check.c b/g10/sig-check.c index 499a9cb14..a6707a1ed 100644 --- a/g10/sig-check.c +++ b/g10/sig-check.c @@ -75,11 +75,29 @@ signature_check2( PKT_signature *sig, MD_HANDLE digest, else if(!pk->is_valid && !pk->is_primary) rc=G10ERR_BAD_PUBKEY; /* you cannot have a good sig from an invalid subkey */ - else { + else + { if(r_expiredate) *r_expiredate = pk->expiredate; rc = do_check( pk, sig, digest, r_expired, r_revoked ); - } + + /* Check the backsig. This is a 0x19 signature from the + subkey on the primary key. The idea here is that it should + not be possible for someone to "steal" subkeys and claim + them as their own. The attacker couldn't actually use the + subkey, but they could try and claim ownership of any + signaures issued by it. */ + if(rc==0 && !pk->is_primary && pk->backsig<2) + { + if(pk->backsig==0) + log_info(_("WARNING: signing subkey %08lX is not" + " cross-certified\n"),(ulong)keyid_from_pk(pk,NULL)); + else + log_info(_("WARNING: signing subkey %08lX has an invalid" + " cross-certification\n"), + (ulong)keyid_from_pk(pk,NULL)); + } + } free_public_key( pk ); @@ -473,6 +491,38 @@ check_revocation_keys(PKT_public_key *pk,PKT_signature *sig) return rc; } +/* Backsigs (0x19) have the same format as binding sigs (0x18), but + this function is simpler than check_key_signature in a few ways. + For example, there is no support for expiring backsigs since it is + questionable what such a thing actually means. Note also that the + sig cache check here, unlike other sig caches in GnuPG, is not + persistent. */ +int +check_backsig(PKT_public_key *main_pk,PKT_public_key *sub_pk, + PKT_signature *backsig) +{ + MD_HANDLE md; + int rc; + + if(!opt.no_sig_cache && backsig->flags.checked) + { + if((rc=check_digest_algo(backsig->digest_algo))) + return rc; + + return backsig->flags.valid? 0 : G10ERR_BAD_SIGN; + } + + md=md_open(backsig->digest_algo,0); + hash_public_key(md,main_pk); + hash_public_key(md,sub_pk); + rc=do_check(sub_pk,backsig,md,NULL,NULL); + cache_sig_result(backsig,rc); + md_close(md); + + return rc; +} + + /**************** * check the signature pointed to by NODE. This is a key signature. * If the function detects a self-signature, it uses the PK from |