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gnupg2/g10/sig-check.c

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/* sig-check.c - Check a signature
* Copyright (C) 1998, 1999, 2000, 2001, 2002, 2003,
* 2004, 2006 Free Software Foundation, Inc.
* Copyright (C) 2015, 2016 g10 Code GmbH
*
* This file is part of GnuPG.
*
* GnuPG is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* GnuPG is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see <https://www.gnu.org/licenses/>.
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "gpg.h"
#include "../common/util.h"
#include "packet.h"
#include "keydb.h"
#include "main.h"
#include "../common/status.h"
#include "../common/i18n.h"
#include "options.h"
#include "pkglue.h"
#include "../common/compliance.h"
static int check_signature_end (PKT_public_key *pk, PKT_signature *sig,
gcry_md_hd_t digest,
int *r_expired, int *r_revoked,
PKT_public_key *ret_pk);
static int check_signature_end_simple (PKT_public_key *pk, PKT_signature *sig,
gcry_md_hd_t digest);
/* Statistics for signature verification. */
struct
{
unsigned int total; /* Total number of verifications. */
unsigned int cached; /* Number of seen cache entries. */
unsigned int goodsig;/* Number of good verifications from the cache. */
unsigned int badsig; /* Number of bad verifications from the cache. */
} cache_stats;
/* Dump verification stats. */
void
sig_check_dump_stats (void)
{
log_info ("sig_cache: total=%u cached=%u good=%u bad=%u\n",
cache_stats.total, cache_stats.cached,
cache_stats.goodsig, cache_stats.badsig);
}
/* Check a signature. This is shorthand for check_signature2 with
the unnamed arguments passed as NULL. */
int
check_signature (ctrl_t ctrl, PKT_signature *sig, gcry_md_hd_t digest)
{
return check_signature2 (ctrl, sig, digest, NULL, NULL, NULL, NULL);
}
/* 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];
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);
}
if (r_pk)
*r_pk = pk;
else
{
release_public_key_parts (pk);
xfree (pk);
}
return rc;
}
/* The signature SIG was generated with the public key PK. Check
* whether the signature is valid in the following sense:
*
* - Make sure the public key was created before the signature was
* generated.
*
* - Make sure the public key was created in the past
*
* - Check whether PK has expired (set *R_EXPIRED to 1 if so and 0
* otherwise)
*
* - Check whether PK has been revoked (set *R_REVOKED to 1 if so
* and 0 otherwise).
*
* If either of the first two tests fail, returns an error code.
* Otherwise returns 0. (Thus, this function doesn't fail if the
* public key is expired or revoked.) */
static int
check_signature_metadata_validity (PKT_public_key *pk, PKT_signature *sig,
int *r_expired, int *r_revoked)
{
u32 cur_time;
if (r_expired)
*r_expired = 0;
if (r_revoked)
*r_revoked = 0;
if (pk->timestamp > sig->timestamp )
{
ulong d = pk->timestamp - sig->timestamp;
if ( d < 86400 )
{
log_info (ngettext
("public key %s is %lu second newer than the signature\n",
"public key %s is %lu seconds newer than the signature\n",
d), keystr_from_pk (pk), d);
}
else
{
d /= 86400;
log_info (ngettext
("public key %s is %lu day newer than the signature\n",
"public key %s is %lu days newer than the signature\n",
d), keystr_from_pk (pk), d);
}
if (!opt.ignore_time_conflict)
return GPG_ERR_TIME_CONFLICT; /* pubkey newer than signature. */
}
cur_time = make_timestamp ();
if (pk->timestamp > cur_time)
{
ulong d = pk->timestamp - cur_time;
if (d < 86400)
{
log_info (ngettext("key %s was created %lu second"
" in the future (time warp or clock problem)\n",
"key %s was created %lu seconds"
" in the future (time warp or clock problem)\n",
d), keystr_from_pk (pk), d);
}
else
{
d /= 86400;
log_info (ngettext("key %s was created %lu day"
" in the future (time warp or clock problem)\n",
"key %s was created %lu days"
" in the future (time warp or clock problem)\n",
d), keystr_from_pk (pk), d);
}
if (!opt.ignore_time_conflict)
return GPG_ERR_TIME_CONFLICT;
}
/* Check whether the key has expired. We check the has_expired
* flag which is set after a full evaluation of the key (getkey.c)
* as well as a simple compare to the current time in case the
* merge has for whatever reasons not been done. */
if (pk->has_expired || (pk->expiredate && pk->expiredate < cur_time))
{
char buf[11];
if (opt.verbose)
log_info (_("Note: signature key %s expired %s\n"),
keystr_from_pk(pk), asctimestamp( pk->expiredate ) );
snprintf (buf, sizeof buf, "%lu",(ulong)pk->expiredate);
write_status_text (STATUS_KEYEXPIRED, buf);
if (r_expired)
*r_expired = 1;
}
if (pk->flags.revoked)
{
if (opt.verbose)
log_info (_("Note: signature key %s has been revoked\n"),
keystr_from_pk(pk));
if (r_revoked)
*r_revoked=1;
}
return 0;
}
/* Finish generating a signature and check it. Concretely: make 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), finish computing the
* digest by adding the relevant data from the signature packet, and
* check that the signature verifies the digest.
*
* DIGEST contains a hash context, which has already hashed 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.")
*
* SIG is the signature to check.
*
* PK is the public key used to generate the signature.
*
* 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 RET_PK is not NULL, PK is copied into RET_PK on success.
*
* Returns 0 on success. An error code other. */
static int
check_signature_end (PKT_public_key *pk, PKT_signature *sig,
gcry_md_hd_t digest,
int *r_expired, int *r_revoked, PKT_public_key *ret_pk)
{
int rc = 0;
if ((rc = check_signature_metadata_validity (pk, sig,
r_expired, r_revoked)))
return rc;
if ((rc = check_signature_end_simple (pk, sig, digest)))
return rc;
if (!rc && ret_pk)
copy_public_key(ret_pk,pk);
return rc;
}
/* This function is similar to check_signature_end, but it only checks
* whether the signature was generated by PK. It does not check
* expiration, revocation, etc. */
static int
check_signature_end_simple (PKT_public_key *pk, PKT_signature *sig,
gcry_md_hd_t digest)
{
gcry_mpi_t result = NULL;
int rc = 0;
const struct weakhash *weak;
if (!opt.flags.allow_weak_digest_algos)
{
for (weak = opt.weak_digests; weak; weak = weak->next)
if (sig->digest_algo == weak->algo)
{
print_digest_rejected_note(sig->digest_algo);
return GPG_ERR_DIGEST_ALGO;
}
}
/* For key signatures check that the key has a cert usage. We may
* do this only for subkeys because the primary may always issue key
* signature. The latter may not be reflected in the pubkey_usage
* field because we need to check the key signatures to extract the
* key usage. */
if (!pk->flags.primary
&& IS_CERT (sig) && !(pk->pubkey_usage & PUBKEY_USAGE_CERT))
{
rc = gpg_error (GPG_ERR_WRONG_KEY_USAGE);
if (!opt.quiet)
log_info (_("bad key signature from key %s: %s (0x%02x, 0x%x)\n"),
keystr_from_pk (pk), gpg_strerror (rc),
sig->sig_class, pk->pubkey_usage);
return rc;
}
/* For data signatures check that the key has sign usage. */
if (!IS_BACK_SIG (sig) && IS_SIG (sig)
&& !(pk->pubkey_usage & PUBKEY_USAGE_SIG))
{
rc = gpg_error (GPG_ERR_WRONG_KEY_USAGE);
if (!opt.quiet)
log_info (_("bad data signature from key %s: %s (0x%02x, 0x%x)\n"),
keystr_from_pk (pk), gpg_strerror (rc),
sig->sig_class, pk->pubkey_usage);
return rc;
}
/* Make sure the digest algo is enabled (in case of a detached
* signature). */
gcry_md_enable (digest, sig->digest_algo);
/* Complete the digest. */
if (sig->version >= 4)
gcry_md_putc (digest, sig->version);
gcry_md_putc( digest, sig->sig_class );
if (sig->version < 4)
{
u32 a = sig->timestamp;
gcry_md_putc (digest, ((a >> 24) & 0xff));
gcry_md_putc (digest, ((a >> 16) & 0xff));
gcry_md_putc (digest, ((a >> 8) & 0xff));
gcry_md_putc (digest, ( a & 0xff));
}
else
{
byte buf[6];
size_t n;
gcry_md_putc (digest, sig->pubkey_algo);
gcry_md_putc (digest, sig->digest_algo);
if (sig->hashed)
{
n = sig->hashed->len;
gcry_md_putc (digest, (n >> 8) );
gcry_md_putc (digest, n );
gcry_md_write (digest, sig->hashed->data, n);
n += 6;
}
else
{
/* Two octets for the (empty) length of the hashed
* section. */
gcry_md_putc (digest, 0);
gcry_md_putc (digest, 0);
n = 6;
}
/* Add some magic per Section 5.2.4 of RFC 4880. */
buf[0] = sig->version;
buf[1] = 0xff;
buf[2] = n >> 24;
buf[3] = n >> 16;
buf[4] = n >> 8;
buf[5] = n;
gcry_md_write( digest, buf, 6 );
}
gcry_md_final( digest );
/* Convert the digest to an MPI. */
result = encode_md_value (pk, digest, sig->digest_algo );
if (!result)
return GPG_ERR_GENERAL;
/* Verify the signature. */
rc = pk_verify (pk->pubkey_algo, result, sig->data, pk->pkey);
gcry_mpi_release (result);
if (!rc && sig->flags.unknown_critical)
{
log_info(_("assuming bad signature from key %s"
" due to an unknown critical bit\n"),keystr_from_pk(pk));
rc = GPG_ERR_BAD_SIGNATURE;
}
return rc;
}
/* Add a uid node to a hash context. See section 5.2.4, paragraph 4
* of RFC 4880. */
static void
hash_uid_packet (PKT_user_id *uid, gcry_md_hd_t md, PKT_signature *sig )
{
if (uid->attrib_data)
{
if (sig->version >=4)
{
byte buf[5];
buf[0] = 0xd1; /* packet of type 17 */
buf[1] = uid->attrib_len >> 24; /* always use 4 length bytes */
buf[2] = uid->attrib_len >> 16;
buf[3] = uid->attrib_len >> 8;
buf[4] = uid->attrib_len;
gcry_md_write( md, buf, 5 );
}
gcry_md_write( md, uid->attrib_data, uid->attrib_len );
}
else
{
if (sig->version >=4)
{
byte buf[5];
buf[0] = 0xb4; /* indicates a userid packet */
buf[1] = uid->len >> 24; /* always use 4 length bytes */
buf[2] = uid->len >> 16;
buf[3] = uid->len >> 8;
buf[4] = uid->len;
gcry_md_write( md, buf, 5 );
}
gcry_md_write( md, uid->name, uid->len );
}
}
static void
cache_sig_result ( PKT_signature *sig, int result )
{
if (!result)
{
sig->flags.checked = 1;
sig->flags.valid = 1;
}
else if (gpg_err_code (result) == GPG_ERR_BAD_SIGNATURE)
{
sig->flags.checked = 1;
sig->flags.valid = 0;
}
else
{
sig->flags.checked = 0;
sig->flags.valid = 0;
}
}
/* SIG is a key revocation signature. Check if this signature was
* generated by any of the public key PK's designated revokers.
*
* PK is the public key that SIG allegedly revokes.
*
* SIG is the revocation signature to check.
*
* This function avoids infinite recursion, which can happen if two
* keys are designed revokers for each other and they revoke each
* other. This is done by observing that if a key A is revoked by key
* B we still consider the revocation to be valid even if B is
* revoked. Thus, we don't need to determine whether B is revoked to
* determine whether A has been revoked by B, we just need to check
* the signature.
*
* Returns 0 if sig is valid (i.e. pk is revoked), non-0 if not
* revoked. We are careful to make sure that GPG_ERR_NO_PUBKEY is
* only returned when a revocation signature is from a valid
* revocation key designated in a revkey subpacket, but the revocation
* key itself isn't present.
*
* XXX: This code will need to be modified if gpg ever becomes
* multi-threaded. Note that this guarantees that a designated
* revocation sig will never be considered valid unless it is actually
* valid, as well as being issued by a revocation key in a valid
* direct signature. Note also that this is written so that a revoked
* revoker can still issue revocations: i.e. If A revokes B, but A is
* revoked, B is still revoked. I'm not completely convinced this is
* the proper behavior, but it matches how PGP does it. -dms */
int
check_revocation_keys (ctrl_t ctrl, PKT_public_key *pk, PKT_signature *sig)
{
static int busy=0;
int i;
int rc = GPG_ERR_GENERAL;
log_assert (IS_KEY_REV(sig));
log_assert ((sig->keyid[0]!=pk->keyid[0]) || (sig->keyid[0]!=pk->keyid[1]));
/* Avoid infinite recursion. Consider the following:
*
* - We want to check if A is revoked.
*
* - C is a designated revoker for B and has revoked B.
*
* - B is a designated revoker for A and has revoked A.
*
* When checking if A is revoked (in merge_selfsigs_main), we
* observe that A has a designed revoker. As such, we call this
* function. This function sees that there is a valid revocation
* signature, which is signed by B. It then calls check_signature()
* to verify that the signature is good. To check the sig, we need
* to lookup B. Looking up B means calling merge_selfsigs_main,
* which checks whether B is revoked, which calls this function to
* see if B was revoked by some key.
*
* In this case, the added level of indirection doesn't hurt. It
* just means a bit more work. However, if C == A, then we'd end up
* in a loop. But, it doesn't make sense to look up C anyways: even
* if B is revoked, we conservatively consider a valid revocation
* signed by B to revoke A. Since this is the only place where this
* type of recursion can occur, we simply cause this function to
* fail if it is entered recursively. */
if (busy)
{
/* Return an error (i.e. not revoked), but mark the pk as
uncacheable as we don't really know its revocation status
until it is checked directly. */
pk->flags.dont_cache = 1;
return rc;
}
busy=1;
/* es_printf("looking at %08lX with a sig from %08lX\n",(ulong)pk->keyid[1],
(ulong)sig->keyid[1]); */
/* is the issuer of the sig one of our revokers? */
if( !pk->revkey && pk->numrevkeys )
BUG();
else
for(i=0;i<pk->numrevkeys;i++)
{
/* The revoker's keyid. */
u32 keyid[2];
keyid_from_fingerprint (ctrl, pk->revkey[i].fpr,
MAX_FINGERPRINT_LEN, keyid);
if(keyid[0]==sig->keyid[0] && keyid[1]==sig->keyid[1])
/* The signature was generated by a designated revoker.
Verify the signature. */
{
gcry_md_hd_t md;
if (gcry_md_open (&md, sig->digest_algo, 0))
BUG ();
hash_public_key(md,pk);
/* Note: check_signature only checks that the signature
is good. It does not fail if the key is revoked. */
rc = check_signature (ctrl, sig, md);
cache_sig_result(sig,rc);
gcry_md_close (md);
break;
}
}
busy=0;
return rc;
}
/* Check that the backsig BACKSIG from the subkey SUB_PK to its
* primary key MAIN_PK is valid.
*
* 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)
{
gcry_md_hd_t md;
int rc;
/* Always check whether the algorithm is available. Although
gcry_md_open would throw an error, some libgcrypt versions will
print a debug message in that case too. */
if ((rc=openpgp_md_test_algo (backsig->digest_algo)))
return rc;
if(!opt.no_sig_cache && backsig->flags.checked)
return backsig->flags.valid? 0 : gpg_error (GPG_ERR_BAD_SIGNATURE);
rc = gcry_md_open (&md, backsig->digest_algo,0);
if (!rc)
{
hash_public_key(md,main_pk);
hash_public_key(md,sub_pk);
rc = check_signature_end (sub_pk, backsig, md, NULL, NULL, NULL);
cache_sig_result(backsig,rc);
gcry_md_close(md);
}
return rc;
}
/* Check that a signature over a key is valid. This is a
* specialization of check_key_signature2 with the unnamed parameters
* passed as NULL. See the documentation for that function for more
* details. */
int
check_key_signature (ctrl_t ctrl, kbnode_t root, kbnode_t node,
int *is_selfsig)
{
return check_key_signature2 (ctrl, root, node, NULL, NULL,
is_selfsig, NULL, NULL);
}
/* Returns whether SIGNER generated the signature SIG over the packet
* PACKET, which is a key, subkey or uid, and comes from the key block
* KB. (KB is PACKET's corresponding keyblock; we don't assume that
* SIG has been added to the keyblock.)
*
* If SIGNER is set, then checks whether SIGNER generated the
* signature. Otherwise, uses SIG->KEYID to find the alleged signer.
* This parameter can be used to effectively override the alleged
* signer that is stored in SIG.
*
* KB may be NULL if SIGNER is set.
*
* Unlike check_key_signature, this function ignores any cached
* results! That is, it does not consider SIG->FLAGS.CHECKED and
* SIG->FLAGS.VALID nor does it set them.
*
* This doesn't check the signature's semantic mean. Concretely, it
* doesn't check whether a non-self signed revocation signature was
* created by a designated revoker. In fact, it doesn't return an
* error for a binding generated by a completely different key!
*
* Returns 0 if the signature is valid. Returns GPG_ERR_SIG_CLASS if
* this signature can't be over PACKET. Returns GPG_ERR_NOT_FOUND if
* the key that generated the signature (according to SIG) could not
* be found. Returns GPG_ERR_BAD_SIGNATURE if the signature is bad.
* Other errors codes may be returned if something else goes wrong.
*
* IF IS_SELFSIG is not NULL, sets *IS_SELFSIG to 1 if this is a
* self-signature (by the key's primary key) or 0 if not.
*
* If RET_PK is not NULL, returns a copy of the public key that
* generated the signature (i.e., the signer) on success. This must
* be released by the caller using release_public_key_parts (). */
gpg_error_t
check_signature_over_key_or_uid (ctrl_t ctrl, PKT_public_key *signer,
PKT_signature *sig, KBNODE kb, PACKET *packet,
int *is_selfsig, PKT_public_key *ret_pk)
{
int rc;
PKT_public_key *pripk = kb->pkt->pkt.public_key;
gcry_md_hd_t md;
int signer_alloced = 0;
int stub_is_selfsig;
if (!is_selfsig)
is_selfsig = &stub_is_selfsig;
rc = openpgp_pk_test_algo (sig->pubkey_algo);
if (rc)
return rc;
rc = openpgp_md_test_algo (sig->digest_algo);
if (rc)
return rc;
/* A signature's class indicates the type of packet that it
signs. */
if (IS_BACK_SIG (sig) || IS_KEY_SIG (sig) || IS_KEY_REV (sig))
{
/* Key revocations can only be over primary keys. */
if (packet->pkttype != PKT_PUBLIC_KEY)
return gpg_error (GPG_ERR_SIG_CLASS);
}
else if (IS_SUBKEY_SIG (sig) || IS_SUBKEY_REV (sig))
{
if (packet->pkttype != PKT_PUBLIC_SUBKEY)
return gpg_error (GPG_ERR_SIG_CLASS);
}
else if (IS_UID_SIG (sig) || IS_UID_REV (sig))
{
if (packet->pkttype != PKT_USER_ID)
return gpg_error (GPG_ERR_SIG_CLASS);
}
else
return gpg_error (GPG_ERR_SIG_CLASS);
/* PACKET is the right type for SIG. */
if (signer)
{
if (signer->keyid[0] == pripk->keyid[0]
&& signer->keyid[1] == pripk->keyid[1])
*is_selfsig = 1;
else
*is_selfsig = 0;
}
else
{
/* Get the signer. If possible, avoid a look up. */
if (sig->keyid[0] == pripk->keyid[0]
&& sig->keyid[1] == pripk->keyid[1])
{
/* Issued by the primary key. */
signer = pripk;
*is_selfsig = 1;
}
else
{
/* See if one of the subkeys was the signer (although this
* is extremely unlikely). */
kbnode_t ctx = NULL;
kbnode_t n;
while ((n = walk_kbnode (kb, &ctx, 0)))
{
PKT_public_key *subk;
if (n->pkt->pkttype != PKT_PUBLIC_SUBKEY)
continue;
subk = n->pkt->pkt.public_key;
if (sig->keyid[0] == subk->keyid[0]
&& sig->keyid[1] == subk->keyid[1])
{
/* Issued by a subkey. */
signer = subk;
break;
}
}
if (! signer)
{
/* Signer by some other key. */
*is_selfsig = 0;
if (ret_pk)
{
signer = ret_pk;
/* FIXME: Using memset here is probematic because it
* assumes that there are no allocated fields in
* SIGNER. */
memset (signer, 0, sizeof (*signer));
signer_alloced = 1;
}
else
{
signer = xmalloc_clear (sizeof (*signer));
signer_alloced = 2;
}
if (IS_CERT (sig))
signer->req_usage = PUBKEY_USAGE_CERT;
rc = get_pubkey_for_sig (ctrl, signer, sig);
if (rc)
{
xfree (signer);
signer = NULL;
signer_alloced = 0;
goto leave;
}
}
}
}
/* We checked above that we supported this algo, so an error here is
* a bug. */
if (gcry_md_open (&md, sig->digest_algo, 0))
BUG ();
/* Hash the relevant data. */
if (IS_KEY_SIG (sig) || IS_KEY_REV (sig))
{
log_assert (packet->pkttype == PKT_PUBLIC_KEY);
hash_public_key (md, packet->pkt.public_key);
rc = check_signature_end_simple (signer, sig, md);
}
else if (IS_BACK_SIG (sig))
{
log_assert (packet->pkttype == PKT_PUBLIC_KEY);
hash_public_key (md, packet->pkt.public_key);
hash_public_key (md, signer);
rc = check_signature_end_simple (signer, sig, md);
}
else if (IS_SUBKEY_SIG (sig) || IS_SUBKEY_REV (sig))
{
log_assert (packet->pkttype == PKT_PUBLIC_SUBKEY);
hash_public_key (md, pripk);
hash_public_key (md, packet->pkt.public_key);
rc = check_signature_end_simple (signer, sig, md);
}
else if (IS_UID_SIG (sig) || IS_UID_REV (sig))
{
log_assert (packet->pkttype == PKT_USER_ID);
if (sig->digest_algo == DIGEST_ALGO_SHA1 && !*is_selfsig
&& sig->timestamp > 1547856000
&& !opt.flags.allow_weak_key_signatures)
{
/* If the signature was created using SHA-1 we consider this
* signature invalid because it makes it possible to mount a
* chosen-prefix collision. We don't do this for
* self-signatures or for signatures created before the
* somewhat arbitrary cut-off date 2019-01-19. */
print_sha1_keysig_rejected_note ();
rc = gpg_error (GPG_ERR_DIGEST_ALGO);
}
else
{
hash_public_key (md, pripk);
hash_uid_packet (packet->pkt.user_id, md, sig);
rc = check_signature_end_simple (signer, sig, md);
}
}
else
{
/* We should never get here. (The first if above should have
* already caught this error.) */
BUG ();
}
gcry_md_close (md);
leave:
if (! rc && ret_pk && ret_pk != signer)
copy_public_key (ret_pk, signer);
if (signer_alloced)
{
/* We looked up SIGNER; it is not a pointer into KB. */
release_public_key_parts (signer);
/* Free if we also allocated the memory. */
if (signer_alloced == 2)
xfree (signer);
}
return rc;
}
/* Check that a signature over a key (e.g., a key revocation, key
* binding, user id certification, etc.) is valid. If the function
* detects a self-signature, it uses the public key from the specified
* key block and does not bother looking up the key specified in the
* signature packet.
*
* ROOT is a keyblock.
*
* NODE references a signature packet that appears in the keyblock
* that should be verified.
*
* If CHECK_PK is set, the specified key is sometimes preferred for
* verifying signatures. See the implementation for details.
*
* If RET_PK is not NULL, the public key that successfully verified
* the signature is copied into *RET_PK.
*
* If IS_SELFSIG is not NULL, *IS_SELFSIG is set to 1 if NODE is a
* self-signature.
*
* If R_EXPIREDATE is not NULL, *R_EXPIREDATE is set to the expiry
* date.
*
* If R_EXPIRED is not NULL, *R_EXPIRED is set to 1 if PK has been
* expired (0 otherwise). Note: PK being revoked does not cause this
* function to fail.
*
*
* If OPT.NO_SIG_CACHE is not set, this function will first check if
* the result of a previous verification is already cached in the
* signature packet's data structure.
*
* TODO: add r_revoked here as well. It has the same problems as
* r_expiredate and r_expired and the cache. */
int
check_key_signature2 (ctrl_t ctrl,
kbnode_t root, kbnode_t node, PKT_public_key *check_pk,
PKT_public_key *ret_pk, int *is_selfsig,
u32 *r_expiredate, int *r_expired )
{
PKT_public_key *pk;
PKT_signature *sig;
int algo;
int rc;
if (is_selfsig)
*is_selfsig = 0;
if (r_expiredate)
*r_expiredate = 0;
if (r_expired)
*r_expired = 0;
log_assert (node->pkt->pkttype == PKT_SIGNATURE);
log_assert (root->pkt->pkttype == PKT_PUBLIC_KEY);
pk = root->pkt->pkt.public_key;
sig = node->pkt->pkt.signature;
algo = sig->digest_algo;
/* Check whether we have cached the result of a previous signature
* check. Note that we may no longer have the pubkey or hash
* needed to verify a sig, but can still use the cached value. A
* cache refresh detects and clears these cases. */
if ( !opt.no_sig_cache )
{
cache_stats.total++;
if (sig->flags.checked) /* Cached status available. */
{
cache_stats.cached++;
if (is_selfsig)
{
u32 keyid[2];
keyid_from_pk (pk, keyid);
if (keyid[0] == sig->keyid[0] && keyid[1] == sig->keyid[1])
*is_selfsig = 1;
}
/* BUG: This is wrong for non-self-sigs... needs to be the
* actual pk. */
rc = check_signature_metadata_validity (pk, sig, r_expired, NULL);
if (rc)
return rc;
if (sig->flags.valid)
{
cache_stats.goodsig++;
return 0;
}
cache_stats.badsig++;
return gpg_error (GPG_ERR_BAD_SIGNATURE);
}
}
rc = openpgp_pk_test_algo(sig->pubkey_algo);
if (rc)
return rc;
rc = openpgp_md_test_algo(algo);
if (rc)
return rc;
if (IS_KEY_REV (sig))
{
u32 keyid[2];
keyid_from_pk( pk, keyid );
/* Is it a designated revoker? */
if (keyid[0] != sig->keyid[0] || keyid[1] != sig->keyid[1])
rc = check_revocation_keys (ctrl, pk, sig);
else
{
rc = check_signature_metadata_validity (pk, sig,
r_expired, NULL);
if (! rc)
rc = check_signature_over_key_or_uid (ctrl, pk, sig,
root, root->pkt,
is_selfsig, ret_pk);
}
}
else if (IS_SUBKEY_REV (sig) || IS_SUBKEY_SIG (sig))
{
kbnode_t snode = find_prev_kbnode (root, node, PKT_PUBLIC_SUBKEY);
if (snode)
{
rc = check_signature_metadata_validity (pk, sig,
r_expired, NULL);
if (! rc)
{
/* A subkey revocation (0x28) must be a self-sig, but a
* subkey signature (0x18) needn't be. */
rc = check_signature_over_key_or_uid (ctrl,
IS_SUBKEY_SIG (sig)
? NULL : pk,
sig, root, snode->pkt,
is_selfsig, ret_pk);
}
}
else
{
if (opt.verbose)
{
if (IS_SUBKEY_REV (sig))
log_info (_("key %s: no subkey for subkey"
" revocation signature\n"), keystr_from_pk(pk));
else if (sig->sig_class == 0x18)
log_info(_("key %s: no subkey for subkey"
" binding signature\n"), keystr_from_pk(pk));
}
rc = GPG_ERR_SIG_CLASS;
}
}
else if (IS_KEY_SIG (sig)) /* direct key signature */
{
rc = check_signature_metadata_validity (pk, sig,
r_expired, NULL);
if (! rc)
rc = check_signature_over_key_or_uid (ctrl, pk, sig, root, root->pkt,
is_selfsig, ret_pk);
}
else if (IS_UID_SIG (sig) || IS_UID_REV (sig))
{
kbnode_t unode = find_prev_kbnode (root, node, PKT_USER_ID);
if (unode)
{
rc = check_signature_metadata_validity (pk, sig, r_expired, NULL);
if (! rc)
{
/* If this is a self-sig, ignore check_pk. */
rc = check_signature_over_key_or_uid
(ctrl,
keyid_cmp (pk_keyid (pk), sig->keyid) == 0 ? pk : check_pk,
sig, root, unode->pkt, NULL, ret_pk);
}
}
else
{
if (!opt.quiet)
log_info ("key %s: no user ID for key signature packet"
" of class %02x\n",keystr_from_pk(pk),sig->sig_class);
rc = GPG_ERR_SIG_CLASS;
}
}
else
{
log_info ("sig issued by %s with class %d (digest: %02x %02x)"
" is not valid over a user id or a key id, ignoring.\n",
keystr (sig->keyid), sig->sig_class,
sig->digest_start[0], sig->digest_start[1]);
rc = gpg_error (GPG_ERR_BAD_SIGNATURE);
}
cache_sig_result (sig, rc);
return rc;
}
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