/* Check a signature.
*
* Looks up the public key that created the signature (SIG->KEYID)
* from the key db. Makes sure that the signature is valid (it was
* not created prior to the key, the public key was created in the
* past, and the signature does not include any unsupported critical
* features), finishes computing the hash of the signature data, and
* checks that the signature verifies the digest. If the key that
* generated the signature is a subkey, this function also verifies
* that there is a valid backsig from the subkey to the primary key.
* Finally, if status fd is enabled and the signature class is 0x00 or
* 0x01, then a STATUS_SIG_ID is emitted on the status fd.
*
* SIG is the signature to check.
*
* DIGEST contains a valid hash context that already includes the
* signed data. This function adds the relevant meta-data from the
* signature packet to compute the final hash. (See Section 5.2 of
* RFC 4880: "The concatenation of the data being signed and the
* signature data from the version number through the hashed subpacket
* data (inclusive) is hashed.")
*
* If R_EXPIREDATE is not NULL, R_EXPIREDATE is set to the key's
* expiry.
*
* If R_EXPIRED is not NULL, *R_EXPIRED is set to 1 if PK has expired
* (0 otherwise). Note: PK being expired does not cause this function
* to fail.
*
* If R_REVOKED is not NULL, *R_REVOKED is set to 1 if PK has been
* revoked (0 otherwise). Note: PK being revoked does not cause this
* function to fail.
*
* If R_PK is not NULL, the public key is stored at that address if it
* was found; other wise NULL is stored.
*
* Returns 0 on success. An error code otherwise. */
gpg_error_t
check_signature2 (ctrl_t ctrl,
PKT_signature *sig, gcry_md_hd_t digest, u32 *r_expiredate,
int *r_expired, int *r_revoked, PKT_public_key **r_pk)
{
int rc=0;
PKT_public_key *pk;
if (r_expiredate)
*r_expiredate = 0;
if (r_expired)
*r_expired = 0;
if (r_revoked)
*r_revoked = 0;
if (r_pk)
*r_pk = NULL;
pk = xtrycalloc (1, sizeof *pk);
if (!pk)
return gpg_error_from_syserror ();
if ((rc=openpgp_md_test_algo(sig->digest_algo)))
{
/* We don't have this digest. */
}
else if (!gnupg_digest_is_allowed (opt.compliance, 0, sig->digest_algo))
{
/* Compliance failure. */
log_info (_("digest algorithm '%s' may not be used in %s mode\n"),
gcry_md_algo_name (sig->digest_algo),
gnupg_compliance_option_string (opt.compliance));
rc = gpg_error (GPG_ERR_DIGEST_ALGO);
}
else if ((rc=openpgp_pk_test_algo(sig->pubkey_algo)))
{
/* We don't have this pubkey algo. */
}
else if (!gcry_md_is_enabled (digest,sig->digest_algo))
{
/* Sanity check that the md has a context for the hash that the
* sig is expecting. This can happen if a onepass sig header
* does not match the actual sig, and also if the clearsign
* "Hash:" header is missing or does not match the actual sig. */
log_info(_("WARNING: signature digest conflict in message\n"));
rc = gpg_error (GPG_ERR_GENERAL);
}
else if (get_pubkey_for_sig (ctrl, pk, sig))
rc = gpg_error (GPG_ERR_NO_PUBKEY);
else if (!gnupg_pk_is_allowed (opt.compliance, PK_USE_VERIFICATION,
pk->pubkey_algo, pk->pkey,
nbits_from_pk (pk),
NULL))
{
/* Compliance failure. */
log_error (_("key %s may not be used for signing in %s mode\n"),
keystr_from_pk (pk),
gnupg_compliance_option_string (opt.compliance));
rc = gpg_error (GPG_ERR_PUBKEY_ALGO);
}
else if (!pk->flags.valid)
{
/* You cannot have a good sig from an invalid key. */
rc = gpg_error (GPG_ERR_BAD_PUBKEY);
}
else
{
if (r_expiredate)
*r_expiredate = pk->expiredate;
rc = check_signature_end (pk, sig, digest, r_expired, r_revoked, NULL);
/* Check the backsig. This is a back signature (0x19) 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 signatures issued by it. */
if (!rc && !pk->flags.primary && pk->flags.backsig < 2)
{
if (!pk->flags.backsig)
{
log_info (_("WARNING: signing subkey %s is not"
" cross-certified\n"),keystr_from_pk(pk));
log_info (_("please see %s for more information\n"),
"https://gnupg.org/faq/subkey-cross-certify.html");
/* The default option --require-cross-certification
* makes this warning an error. */
if (opt.flags.require_cross_cert)
rc = gpg_error (GPG_ERR_GENERAL);
}
else if(pk->flags.backsig == 1)
{
log_info (_("WARNING: signing subkey %s has an invalid"
" cross-certification\n"), keystr_from_pk(pk));
rc = gpg_error (GPG_ERR_GENERAL);
}
}
}
if( !rc && sig->sig_class < 2 && is_status_enabled() ) {
/* This signature id works best with DLP algorithms because
* they use a random parameter for every signature. Instead of
* this sig-id we could have also used the hash of the document
* and the timestamp, but the drawback of this is, that it is
* not possible to sign more than one identical document within
* one second. Some remote batch processing applications might
* like this feature here.
*
* Note that before 2.0.10, we used RIPE-MD160 for the hash
* and accidentally didn't include the timestamp and algorithm
* information in the hash. Given that this feature is not
* commonly used and that a replay attacks detection should
* not solely be based on this feature (because it does not
* work with RSA), we take the freedom and switch to SHA-1
* with 2.0.10 to take advantage of hardware supported SHA-1
* implementations. We also include the missing information
* in the hash. Note also the SIG_ID as computed by gpg 1.x
* and gpg 2.x didn't matched either because 2.x used to print
* MPIs not in PGP format. */
u32 a = sig->timestamp;
int nsig = pubkey_get_nsig( sig->pubkey_algo );
unsigned char *p, *buffer;
size_t n, nbytes;
int i;
char hashbuf[20]; /* We use SHA-1 here. */
nbytes = 6;
for (i=0; i < nsig; i++ )
{
if (gcry_mpi_print (GCRYMPI_FMT_USG, NULL, 0, &n, sig->data[i]))
BUG();
nbytes += n;
}
/* Make buffer large enough to be later used as output buffer. */
if (nbytes < 100)
nbytes = 100;
nbytes += 10; /* Safety margin. */
/* Fill and hash buffer. */
buffer = p = xmalloc (nbytes);
*p++ = sig->pubkey_algo;
*p++ = sig->digest_algo;
*p++ = (a >> 24) & 0xff;
*p++ = (a >> 16) & 0xff;
*p++ = (a >> 8) & 0xff;
*p++ = a & 0xff;
nbytes -= 6;
for (i=0; i < nsig; i++ )
{
if (gcry_mpi_print (GCRYMPI_FMT_PGP, p, nbytes, &n, sig->data[i]))
BUG();
p += n;
nbytes -= n;
}
gcry_md_hash_buffer (GCRY_MD_SHA1, hashbuf, buffer, p-buffer);
p = make_radix64_string (hashbuf, 20);
sprintf (buffer, "%s %s %lu",
p, strtimestamp (sig->timestamp), (ulong)sig->timestamp);
xfree (p);
write_status_text (STATUS_SIG_ID, buffer);
xfree (buffer);
}
/*
* Get the session key from a pubkey enc packet and return it in DEK,
* which should have been allocated in secure memory by the caller.
*/
gpg_error_t
get_session_key (ctrl_t ctrl, PKT_pubkey_enc * k, DEK * dek)
{
PKT_public_key *sk = NULL;
int rc;
if (DBG_CLOCK)
log_clock ("get_session_key enter");
rc = openpgp_pk_test_algo2 (k->pubkey_algo, PUBKEY_USAGE_ENC);
if (rc)
goto leave;
if ((k->keyid[0] || k->keyid[1]) && !opt.try_all_secrets)
{
sk = xmalloc_clear (sizeof *sk);
sk->pubkey_algo = k->pubkey_algo; /* We want a pubkey with this algo. */
if (!(rc = get_seckey (ctrl, sk, k->keyid)))
{
/* Check compliance. */
if (! gnupg_pk_is_allowed (opt.compliance, PK_USE_DECRYPTION,
sk->pubkey_algo,
sk->pkey, nbits_from_pk (sk), NULL))
{
log_info (_("key %s is not suitable for decryption"
" in %s mode\n"),
keystr_from_pk (sk),
gnupg_compliance_option_string (opt.compliance));
rc = gpg_error (GPG_ERR_PUBKEY_ALGO);
}
else
rc = get_it (ctrl, k, dek, sk, k->keyid);
}
}
else if (opt.skip_hidden_recipients)
rc = gpg_error (GPG_ERR_NO_SECKEY);
else /* Anonymous receiver: Try all available secret keys. */
{
void *enum_context = NULL;
u32 keyid[2];
for (;;)
{
free_public_key (sk);
sk = xmalloc_clear (sizeof *sk);
rc = enum_secret_keys (ctrl, &enum_context, sk);
if (rc)
{
rc = GPG_ERR_NO_SECKEY;
break;
}
if (sk->pubkey_algo != k->pubkey_algo)
continue;
if (!(sk->pubkey_usage & PUBKEY_USAGE_ENC))
continue;
keyid_from_pk (sk, keyid);
if (!opt.quiet)
log_info (_("anonymous recipient; trying secret key %s ...\n"),
keystr (keyid));
/* Check compliance. */
if (! gnupg_pk_is_allowed (opt.compliance, PK_USE_DECRYPTION,
sk->pubkey_algo,
sk->pkey, nbits_from_pk (sk), NULL))
{
log_info (_("key %s is not suitable for decryption"
" in %s mode\n"),
keystr_from_pk (sk),
gnupg_compliance_option_string (opt.compliance));
continue;
}
rc = get_it (ctrl, k, dek, sk, keyid);
if (!rc)
{
if (!opt.quiet)
log_info (_("okay, we are the anonymous recipient.\n"));
break;
}
else if (gpg_err_code (rc) == GPG_ERR_FULLY_CANCELED)
break; /* Don't try any more secret keys. */
}
enum_secret_keys (ctrl, &enum_context, NULL); /* free context */
}
leave:
free_public_key (sk);
if (DBG_CLOCK)
log_clock ("get_session_key leave");
return rc;
}
