gpg: Make use of the included key block in a signature.

* g10/import.c (read_key_from_file): Rename to ...
(read_key_from_file_or_buffer): this and add new parameters.  Adjust
callers.
(import_included_key_block): New.
* g10/packet.h (PKT_signature): Add field flags.key_block.
* g10/parse-packet.c (parse_signature): Set that flags.
* g10/sig-check.c (check_signature2): Add parm forced_pk and change
all callers.
* g10/mainproc.c (do_check_sig): Ditto.
(check_sig_and_print): Try the included key block if no key is
available.
--

This is is the second part to support the new Key Block subpacket.
The idea is that after having received a signed mail, it is instantly
possible to reply encrypted - without the need for any centralized
infrastructure.

There is one case where this does not work: A signed mail is received
using a specified signer ID (e.g. using gpg --sender option) and the
key block with only that user ID is thus imported.  The next time a
mail is received using the same key but with a different user ID; the
signatures checks out using the key imported the last time.  However,
the new user id is not imported.  Now when trying to reply to that
last mail, no key will be found.  We need to see whether we can update
a key in such a case.

GnuPG-bug-id: 4856
Signed-off-by: Werner Koch <[email protected]>

1 files changed, 8 insertions, 3 deletions

diff --git a/g10/sig-check.c b/g10/sig-check.c
index 8a46f7653..e622d9883 100644
--- a/g10/sig-check.c
+++ b/g10/sig-check.c
@@ -72,7 +72,8 @@ sig_check_dump_stats (void)
 int
 check_signature (ctrl_t ctrl, PKT_signature *sig, gcry_md_hd_t digest)
 {
-  return check_signature2 (ctrl, sig, digest, NULL, 0, NULL, NULL, NULL, NULL);
+  return check_signature2 (ctrl, sig, digest, NULL, 0, NULL,
+                           NULL, NULL, NULL, NULL);
 }
 
 
@@ -101,6 +102,9 @@ check_signature (ctrl_t ctrl, PKT_signature *sig, gcry_md_hd_t digest)
  * EXTRAHASH and EXTRAHASHLEN is additional data which is hashed with
  * v5 signatures.  They may be NULL to use the default.
  *
+ * If FORCED_PK is not NULL this public key is used to verify the
+ * signature and no other public key is looked up.
+ *
  * If R_EXPIREDATE is not NULL, R_EXPIREDATE is set to the key's
  * expiry.
  *
@@ -120,6 +124,7 @@ gpg_error_t
 check_signature2 (ctrl_t ctrl,
                   PKT_signature *sig, gcry_md_hd_t digest,
                   const void *extrahash, size_t extrahashlen,
+                  PKT_public_key *forced_pk,
                   u32 *r_expiredate,
 		  int *r_expired, int *r_revoked, PKT_public_key **r_pk)
 {
@@ -164,7 +169,7 @@ check_signature2 (ctrl_t ctrl,
       log_info(_("WARNING: signature digest conflict in message\n"));
       rc = gpg_error (GPG_ERR_GENERAL);
     }
-  else if (get_pubkey_for_sig (ctrl, pk, sig))
+  else if (get_pubkey_for_sig (ctrl, pk, sig, forced_pk))
     rc = gpg_error (GPG_ERR_NO_PUBKEY);
   else if (!gnupg_pk_is_allowed (opt.compliance, PK_USE_VERIFICATION,
                                  pk->pubkey_algo, pk->pkey,
@@ -970,7 +975,7 @@ check_signature_over_key_or_uid (ctrl_t ctrl, PKT_public_key *signer,
               if (IS_CERT (sig))
                 signer->req_usage = PUBKEY_USAGE_CERT;
 
-              rc = get_pubkey_for_sig (ctrl, signer, sig);
+              rc = get_pubkey_for_sig (ctrl, signer, sig, NULL);
               if (rc)
                 {
                   xfree (signer);