gpg: Allow adding of Additional Decryption Subkeys.

* g10/free-packet.c (copy_public_key): Factor some code out to ...
(copy_public_key_basics): new.
* g10/build-packet.c (build_sig_subpkt_from_sig): New arg signhints.
* g10/packet.h (PUBKEY_USAGE_RENC): Fix value.
(SIGNHINT_KEYSIG, SIGNHINT_SELFSIG): Moved from sign.c.
(SIGNHINT_ADSK): New.
(PKT_public_key): Change pubkey_usage from byte to u16.
(PKT_user_id): Cosmetic fix: change help_key_usage from int to u16.
* g10/getkey.c (parse_key_usage): Make public.
* g10/misc.c (openpgp_pk_algo_usage): Take PUBKEY_USAGE_RENC in
account.
* g10/sign.c (update_keysig_packet): Set SIGNHINT_ADSK.
(make_keysig_packet): Ditto.
(do_sign): No time warp check in ADSK mode.
* g10/sig-check.c (check_signature_metadata_validity): Ditto.
* g10/keygen.c (struct opaque_data_usage_and_pk): Remove.
(write_keybinding): Do not use the removed struct.
(do_add_key_flags): Support PUBKEY_USAGE_RENC and others.
(keygen_add_key_flags_and_expire): Rewrite and make public.
* g10/keyedit.c (enum cmdids): Add cmdADDADSK.
(keyedit_menu): Add command "addadsk".
(menu_addadsk): New.
--

This makes use of a new encryption flag:

  The "restricted encryption key" (2nd,0x04) does not take part in any
  automatic selection of encryption keys.  It is only found on a
  subkey signature (type 0x18), one that refers to the key the flag
  applies to.

Followup patches will add encryption support and a --quick command.

GnuPG-bug-id: 6395

1 files changed, 18 insertions, 12 deletions

diff --git a/g10/sign.c b/g10/sign.c
index a66410ebd..b5e9d422d 100644
--- a/g10/sign.c
+++ b/g10/sign.c
@@ -50,11 +50,6 @@
 #endif
 
 
-/* Bitflags to convey hints on what kind of signayire is created.  */
-#define SIGNHINT_KEYSIG  1
-#define SIGNHINT_SELFSIG 2
-
-
 /* Hack */
 static int recipient_digest_algo;
 
@@ -416,7 +411,10 @@ do_sign (ctrl_t ctrl, PKT_public_key *pksk, PKT_signature *sig,
   byte *dp;
   char *hexgrip;
 
-  if (pksk->timestamp > sig->timestamp )
+  /* An ADSK key commonly has a creation date older than the primary
+   * key.  For example because the ADSK is used as an archive key for
+   * a group of users.  */
+  if (pksk->timestamp > sig->timestamp && !(signhints & SIGNHINT_ADSK))
     {
       ulong d = pksk->timestamp - sig->timestamp;
       log_info (ngettext("key %s was created %lu second"
@@ -964,7 +962,7 @@ write_signature_packets (ctrl_t ctrl,
       if (gcry_md_copy (&md, hash))
         BUG ();
 
-      build_sig_subpkt_from_sig (sig, pk);
+      build_sig_subpkt_from_sig (sig, pk, 0);
       mk_notation_policy_etc (ctrl, sig, NULL, pk);
       if (opt.flags.include_key_block && IS_SIG (sig))
         err = mk_sig_subpkt_key_block (ctrl, sig, pk);
@@ -1758,14 +1756,14 @@ sign_symencrypt_file (ctrl_t ctrl, const char *fname, strlist_t locusr)
  *
  * SIGCLASS is the type of signature to create.
  *
- * DIGEST_ALGO is the digest algorithm.  If it is 0 the function
- * selects an appropriate one.
- *
  * TIMESTAMP is the timestamp to use for the signature. 0 means "now"
  *
  * DURATION is the amount of time (in seconds) until the signature
  * expires.
  *
+ * If CACHED_NONCE is not NULL the agent may use it to avoid
+ * additional pinnetry popups for the same keyblock.
+ *
  * This function creates the following subpackets: issuer, created,
  * and expire (if duration is not 0).  Additional subpackets can be
  * added using MKSUBPKT, which is called after these subpackets are
@@ -1833,6 +1831,8 @@ make_keysig_packet (ctrl_t ctrl,
     {
       /* Hash the subkey binding/backsig/revocation.  */
       hash_public_key (md, subpk);
+      if ((subpk->pubkey_usage & PUBKEY_USAGE_RENC))
+        signhints |= SIGNHINT_ADSK;
     }
   else if (sigclass != 0x1F && sigclass != 0x20)
     {
@@ -1852,7 +1852,7 @@ make_keysig_packet (ctrl_t ctrl,
     sig->expiredate = sig->timestamp + duration;
   sig->sig_class = sigclass;
 
-  build_sig_subpkt_from_sig (sig, pksk);
+  build_sig_subpkt_from_sig (sig, pksk, signhints);
   mk_notation_policy_etc (ctrl, sig, pk, pksk);
 
   /* Crucial that the call to mksubpkt comes LAST before the calls
@@ -1976,6 +1976,12 @@ update_keysig_packet (ctrl_t ctrl,
       }
   }
 
+  /* Detect an ADSK key binding signature.  */
+  if ((sig->sig_class == 0x18
+       || sig->sig_class == 0x19 || sig->sig_class == 0x28)
+      && (pk->pubkey_usage & PUBKEY_USAGE_RENC))
+    signhints |= SIGNHINT_ADSK;
+
   /* Note that already expired sigs will remain expired (with a
    * duration of 1) since build-packet.c:build_sig_subpkt_from_sig
    * detects this case. */
@@ -1984,7 +1990,7 @@ update_keysig_packet (ctrl_t ctrl,
    * automagically lower any sig expiration dates to correctly
    * correspond to the differences in the timestamps (i.e. the
    * duration will shrink).  */
-  build_sig_subpkt_from_sig (sig, pksk);
+  build_sig_subpkt_from_sig (sig, pksk, signhints);
 
   if (mksubpkt)
     rc = (*mksubpkt)(sig, opaque);