gpg: New option --include-key-block.

* common/openpgpdefs.h (SIGSUBPKT_KEY_BLOCK): New.
* g10/gpg.c (oIncludeKeyBlock): New.
(opts): New option --include-key-block.
(main): Implement.
* g10/options.h (opt): New flag include_key_block.
* g10/parse-packet.c (dump_sig_subpkt): Support SIGSUBPKT_KEY_BLOCK.
(parse_one_sig_subpkt): Ditto.
(can_handle_critical): Ditto.
* g10/sign.c (mk_sig_subpkt_key_block): New.
(write_signature_packets): Call it for data signatures.
--

This patch adds support for a to be proposed OpenPGP ferature:

  Introduce the Key Block subpacket to align OpenPGP with CMS.

  This new subpacket may be used similar to the CertificateSet of
  CMS (RFC-5652) and thus allows to start encrypted communication
  after having received a signed message.  In practice a stripped down
  version of the key should be including having only the key material
  and the self-signatures which are really useful and shall be used by
  the recipient to reply encrypted.

  #### Key Block

  (1 octet with value 0, N octets of key data)

  This subpacket MAY be used to convey key data along with a signature
  of class 0x00, 0x01, or 0x02.  It MUST contain the key used to create
  the signature; either as the primary key or as a subkey.  The key
  SHOULD contain a primary or subkey capable of encryption and the
  entire key must be a valid OpenPGP key including at least one User ID
  packet and the corresponding self-signatures.

  Implementations MUST ignore this subpacket if the first octet does not
  have a value of zero or if the key data does not represent a valid
  transferable public key.

GnuPG-bug-id: 4856
Signed-off-by: Werner Koch <wk@gnupg.org>

Backported from master.

Signed-off-by: Werner Koch <wk@gnupg.org>

g10/sign.c

@@ -185,6 +185,91 @@ mk_notation_policy_etc (PKT_signature *sig,
 }
 
 
+
+/*
+ * Put the Key Block subpakcet into SIG for key PKSK.  Returns an
+ * error code on failure.
+ */
+static gpg_error_t
+mk_sig_subpkt_key_block (ctrl_t ctrl, PKT_signature *sig, PKT_public_key *pksk)
+{
+  gpg_error_t err;
+  char *mbox;
+  char *filterexp = NULL;
+  int save_opt_armor = opt.armor;
+  int save_opt_verbose = opt.verbose;
+  char hexfpr[2*MAX_FINGERPRINT_LEN + 1];
+  void *data = NULL;
+  size_t datalen;
+  kbnode_t keyblock = NULL;
+
+  push_export_filters ();
+  opt.armor = 0;
+
+  hexfingerprint (pksk, hexfpr, sizeof hexfpr);
+
+  /* Get the user id so that we know which one to insert into the
+   * key.  */
+  if (pksk->user_id
+      && (mbox = mailbox_from_userid (pksk->user_id->name)))
+    {
+      if (DBG_LOOKUP)
+        log_debug ("including key with UID '%s' (specified)\n", mbox);
+      filterexp = xasprintf ("keep-uid= -- mbox = %s", mbox);
+      xfree (mbox);
+    }
+  else if (opt.sender_list)
+    {
+      /* If --sender was given we use the first one from that list.  */
+      if (DBG_LOOKUP)
+        log_debug ("including key with UID '%s' (--sender)\n",
+                   opt.sender_list->d);
+      filterexp = xasprintf ("keep-uid= -- mbox = %s", opt.sender_list->d);
+    }
+  else  /* Use the primary user id.  */
+    {
+      if (DBG_LOOKUP)
+        log_debug ("including key with primary UID\n");
+      filterexp = xstrdup ("keep-uid= primary -t");
+    }
+
+  if (DBG_LOOKUP)
+    log_debug ("export filter expression: %s\n", filterexp);
+  err = parse_and_set_export_filter (filterexp);
+  if (err)
+    goto leave;
+  xfree (filterexp);
+  filterexp = xasprintf ("drop-subkey= fpr <> %s && usage !~ e", hexfpr);
+  if (DBG_LOOKUP)
+    log_debug ("export filter expression: %s\n", filterexp);
+  err = parse_and_set_export_filter (filterexp);
+  if (err)
+    goto leave;
+
+
+  opt.verbose = 0;
+  err = export_pubkey_buffer (ctrl, hexfpr, EXPORT_MINIMAL|EXPORT_CLEAN,
+                              "", 1, /* Prefix with the reserved byte. */
+                              NULL, &keyblock, &data, &datalen);
+  opt.verbose = save_opt_verbose;
+  if (err)
+    {
+      log_error ("failed to get to be included key: %s\n", gpg_strerror (err));
+      goto leave;
+    }
+
+  build_sig_subpkt (sig, SIGSUBPKT_KEY_BLOCK, data, datalen);
+
+ leave:
+  xfree (data);
+  release_kbnode (keyblock);
+  xfree (filterexp);
+  opt.armor = save_opt_armor;
+  pop_export_filters ();
+  return err;
+}
+
+
 /*
  * Helper to hash a user ID packet.
  */
@@ -737,7 +822,7 @@ write_signature_packets (ctrl_t ctrl,
       PKT_public_key *pk;
       PKT_signature *sig;
       gcry_md_hd_t md;
-      int rc;
+      gpg_error_t err;
 
       pk = sk_rover->pk;
 
@@ -770,14 +855,18 @@ write_signature_packets (ctrl_t ctrl,
         {
           build_sig_subpkt_from_sig (sig, pk);
           mk_notation_policy_etc (sig, NULL, pk);
+          if (opt.flags.include_key_block && IS_SIG (sig))
+            err = mk_sig_subpkt_key_block (ctrl, sig, pk);
+          else
+            err = 0;
         }
-
       hash_sigversion_to_magic (md, sig);
       gcry_md_final (md);
 
-      rc = do_sign (ctrl, pk, sig, md, hash_for (pk), cache_nonce, 0);
+      if (!err)
+        err = do_sign (ctrl, pk, sig, md, hash_for (pk), cache_nonce, 0);
       gcry_md_close (md);
-      if (!rc)
+      if (!err)
         {
           /* Write the packet.  */
           PACKET pkt;
@@ -785,19 +874,19 @@ write_signature_packets (ctrl_t ctrl,
           init_packet (&pkt);
           pkt.pkttype = PKT_SIGNATURE;
           pkt.pkt.signature = sig;
-          rc = build_packet (out, &pkt);
-          if (!rc && is_status_enabled())
+          err = build_packet (out, &pkt);
+          if (!err && is_status_enabled())
             print_status_sig_created (pk, sig, status_letter);
           free_packet (&pkt, NULL);
-          if (rc)
+          if (err)
             log_error ("build signature packet failed: %s\n",
-                       gpg_strerror (rc));
+                       gpg_strerror (err));
 	}
       else
         free_seckey_enc (sig);
 
-      if (rc)
-        return rc;
+      if (err)
+        return err;
     }
 
   return 0;