gpg: Allow decryption w/o public key but with correct card inserted.

* agent/command.c (cmd_readkey): Add option --no-data and special
handling for $SIGNKEYID and $AUTHKEYID.
* g10/call-agent.c (agent_scd_getattr): Create shadow keys for KEY-FPR
output.
* g10/skclist.c (enum_secret_keys): Automagically get a missing public
key for the current card.

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

agent/command.c

@@ -1073,7 +1073,7 @@ cmd_genkey (assuan_context_t ctx, char *line)
 
 
 static const char hlp_readkey[] =
-  "READKEY <hexstring_with_keygrip>\n"
+  "READKEY [--no-data] <hexstring_with_keygrip>\n"
   "                    --card <keyid>\n"
   "\n"
   "Return the public key for the given keygrip or keyid.\n"
@@ -1087,12 +1087,14 @@ cmd_readkey (assuan_context_t ctx, char *line)
   gcry_sexp_t s_pkey = NULL;
   unsigned char *pkbuf = NULL;
   char *serialno = NULL;
+  char *keyidbuf = NULL;
   size_t pkbuflen;
-  int opt_card;
+  int opt_card, opt_no_data;
 
   if (ctrl->restricted)
     return leave_cmd (ctx, gpg_error (GPG_ERR_FORBIDDEN));
 
+  opt_no_data = has_option (line, "--no-data");
   opt_card = has_option (line, "--card");
   line = skip_options (line);
 
@@ -1108,6 +1110,11 @@ cmd_readkey (assuan_context_t ctx, char *line)
           goto leave;
         }
 
+      /* Hack to create the shadow key for the OpenPGP standard keys.  */
+      if ((!strcmp (keyid, "$SIGNKEYID") || !strcmp (keyid, "$ENCRKEYID"))
+          && !agent_card_getattr (ctrl, keyid, &keyidbuf, NULL))
+        keyid = keyidbuf;
+
       rc = agent_card_readkey (ctrl, keyid, &pkbuf, NULL);
       if (rc)
         goto leave;
@@ -1133,7 +1140,7 @@ cmd_readkey (assuan_context_t ctx, char *line)
             goto leave;
         }
 
-      rc = assuan_send_data (ctx, pkbuf, pkbuflen);
+        rc = opt_no_data? 0 : assuan_send_data (ctx, pkbuf, pkbuflen);
     }
   else
     {
@@ -1153,12 +1160,13 @@ cmd_readkey (assuan_context_t ctx, char *line)
             {
               pkbuflen = gcry_sexp_sprint (s_pkey, GCRYSEXP_FMT_CANON,
                                            pkbuf, pkbuflen);
-              rc = assuan_send_data (ctx, pkbuf, pkbuflen);
+              rc = opt_no_data? 0 : assuan_send_data (ctx, pkbuf, pkbuflen);
             }
         }
     }
 
  leave:
+  xfree (keyidbuf);
   xfree (serialno);
   xfree (pkbuf);
   gcry_sexp_release (s_pkey);

g10/call-agent.c

@@ -1232,6 +1232,16 @@ agent_scd_getattr (const char *name, struct agent_card_info_s *info)
   parm.ctx = agent_ctx;
   rc = assuan_transact (agent_ctx, line, NULL, NULL, default_inq_cb, &parm,
                         learn_status_cb, info);
+  if (!rc && !strcmp (name, "KEY-FPR"))
+    {
+      /* Let the agent create the shadow keys if not yet done.  */
+      if (info->fpr1len)
+        assuan_transact (agent_ctx, "READKEY --card --no-data -- $SIGNKEYID",
+                         NULL, NULL, NULL, NULL, NULL, NULL);
+      if (info->fpr2len)
+        assuan_transact (agent_ctx, "READKEY --card --no-data -- $ENCRKEYID",
+                         NULL, NULL, NULL, NULL, NULL, NULL);
+    }
 
   return rc;
 }

g10/skclist.c

@@ -31,6 +31,7 @@
 #include "keydb.h"
 #include "../common/util.h"
 #include "../common/i18n.h"
+#include "keyserver-internal.h"
 #include "call-agent.h"
 
 
@@ -322,11 +323,13 @@ enum_secret_keys (ctrl_t ctrl, void **context, PKT_public_key *sk)
 {
   gpg_error_t err = 0;
   const char *name;
+  int cardkey;
   kbnode_t keyblock;
   struct
   {
     int eof;
     int state;
+    int cardkey_done;
     strlist_t sl;
     keypair_info_t card_keyinfo;
     keypair_info_t card_keyinfo_list;
@@ -381,6 +384,7 @@ enum_secret_keys (ctrl_t ctrl, void **context, PKT_public_key *sk)
           do
             {
               name = NULL;
+              cardkey = 0;
               keyblock = NULL;
               switch (c->state)
                 {
@@ -431,6 +435,7 @@ enum_secret_keys (ctrl_t ctrl, void **context, PKT_public_key *sk)
                         c->fpr2[i] = *s;
                       c->fpr2[i] = 0;
                       name = c->fpr2;
+                      cardkey = 1;
 
                       c->card_keyinfo = c->card_keyinfo->next;
                     }
@@ -482,11 +487,47 @@ enum_secret_keys (ctrl_t ctrl, void **context, PKT_public_key *sk)
               err = getkey_byname (ctrl, NULL, NULL, name, 1, &c->keyblock);
               if (err)
                 {
+                  struct agent_card_info_s cinfo = { 0 };
+
                   /* getkey_byname might return a keyblock even in the
                      error case - I have not checked.  Thus better release
                      it.  */
                   release_kbnode (c->keyblock);
                   c->keyblock = NULL;
+                  /* If this was a card key we might not yet have the
+                   * public key for it.  Thus check whether the card
+                   * can return the fingerprint of the encryption key
+                   * and we can then find the public key via LDAP.  */
+                  if (cardkey && !c->cardkey_done
+                      && gpg_err_code (err) == GPG_ERR_NO_SECKEY
+                      && !agent_scd_getattr ("KEY-FPR", &cinfo)
+                      && cinfo.fpr2len)
+                    {
+                      /* Note that this code does not handle the case
+                       * for two readers having both openpgp
+                       * encryption keys. only one will be tried.  */
+                      c->cardkey_done = 1;
+                      if (opt.debug)
+                        log_debug ("using LDAP to find public key"
+                                   " for current card\n");
+                      if (!keyserver_import_fprint
+                          (ctrl, cinfo.fpr2, cinfo.fpr2len, opt.keyserver,
+                           KEYSERVER_IMPORT_FLAG_LDAP))
+                        {
+                          char fpr_string[MAX_FINGERPRINT_LEN * 2 + 1];
+
+                          bin2hex (cinfo.fpr2, cinfo.fpr2len, fpr_string);
+                          err = getkey_byname (ctrl, NULL, NULL, fpr_string, 1,
+                                               &c->keyblock);
+                          if (err)
+                            {
+                              release_kbnode (c->keyblock);
+                              c->keyblock = NULL;
+                            }
+                          else
+                            c->node = c->keyblock;
+                        }
+                    }
                 }
               else
                 c->node = c->keyblock;