gpg: Pass ECDH parameters to OpenPGP smartcards

* g10/call-agent.c (agent_keytocard): Add arg ecdh_param_str.
* g10/keyid.c (ecdh_param_str_from_pk): New.
* g10/card-util.c (card_store_subkey): Pass ECDH params to writekey.
* g10/keygen.c (card_store_key_with_backup): Ditto.
--

Backported from 2.4 - here the gpg part.

See-commit: c03ba92576
This is related to
GnuPG-bug-id: 6378

g10/call-agent.c

@@ -957,7 +957,8 @@ agent_scd_apdu (const char *hexapdu, unsigned int *r_sw)
  */
 int
 agent_keytocard (const char *hexgrip, int keyno, int force,
-                 const char *serialno, const char *timestamp)
+                 const char *serialno, const char *timestamp,
+                 const char *ecdh_param_str)
 {
   int rc;
   char line[ASSUAN_LINELENGTH];
@@ -965,8 +966,9 @@ agent_keytocard (const char *hexgrip, int keyno, int force,
 
   memset (&parm, 0, sizeof parm);
 
-  snprintf (line, DIM(line), "KEYTOCARD %s%s %s OPENPGP.%d %s",
+  snprintf (line, DIM(line), "KEYTOCARD %s%s %s OPENPGP.%d %s%s%s",
-            force?"--force ": "", hexgrip, serialno, keyno, timestamp);
+            force?"--force ": "", hexgrip, serialno, keyno, timestamp,
+            ecdh_param_str? " ":"", ecdh_param_str? ecdh_param_str:"");
 
   rc = start_agent (NULL, 1);
   if (rc)

g10/call-agent.h

@@ -104,7 +104,8 @@ int agent_scd_getattr (const char *name, struct agent_card_info_s *info);
 
 /* Send the KEYTOCARD command. */
 int agent_keytocard (const char *hexgrip, int keyno, int force,
-                     const char *serialno, const char *timestamp);
+                     const char *serialno, const char *timestamp,
+                     const char *ecdh_param_str);
 
 /* Send a SETATTR command to the SCdaemon. */
 gpg_error_t agent_scd_setattr (const char *name,

g10/card-util.c

@@ -1749,8 +1749,9 @@ card_store_subkey (KBNODE node, int use, strlist_t *processed_keys)
   int  keyno;
   PKT_public_key *pk;
   gpg_error_t err;
-  char *hexgrip;
+  char *hexgrip = NULL;
   int rc;
+  char *ecdh_param_str = NULL;
   gnupg_isotime_t timebuf;
 
   log_assert (node->pkt->pkttype == PKT_PUBLIC_KEY
@@ -1824,8 +1825,17 @@ card_store_subkey (KBNODE node, int use, strlist_t *processed_keys)
     goto leave;
 
   epoch2isotime (timebuf, (time_t)pk->timestamp);
-  rc = agent_keytocard (hexgrip, keyno, rc, info.serialno, timebuf);
+  if (pk->pubkey_algo == PUBKEY_ALGO_ECDH)
-
+    {
+      ecdh_param_str = ecdh_param_str_from_pk (pk);
+      if (!ecdh_param_str)
+        {
+          err = gpg_error_from_syserror ();
+          goto leave;
+        }
+    }
+  rc = agent_keytocard (hexgrip, keyno, rc, info.serialno,
+                        timebuf, ecdh_param_str);
   if (rc)
     log_error (_("KEYTOCARD failed: %s\n"), gpg_strerror (rc));
   else
@@ -1834,9 +1844,10 @@ card_store_subkey (KBNODE node, int use, strlist_t *processed_keys)
       if (processed_keys)
         add_to_strlist (processed_keys, hexgrip);
     }
-  xfree (hexgrip);
 
  leave:
+  xfree (hexgrip);
+  xfree (ecdh_param_str);
   agent_release_card_info (&info);
   return okay;
 }

g10/keydb.h

@@ -552,6 +552,7 @@ char *format_hexfingerprint (const char *fingerprint,
                              char *buffer, size_t buflen);
 gpg_error_t keygrip_from_pk (PKT_public_key *pk, unsigned char *array);
 gpg_error_t hexkeygrip_from_pk (PKT_public_key *pk, char **r_grip);
+char *ecdh_param_str_from_pk (PKT_public_key *pk);
 
 
 /*-- kbnode.c --*/

g10/keygen.c

@@ -5128,22 +5128,41 @@ card_store_key_with_backup (ctrl_t ctrl, PKT_public_key *sub_psk,
   char *cache_nonce = NULL;
   void *kek = NULL;
   size_t keklen;
+  char *ecdh_param_str = NULL;
 
   sk = copy_public_key (NULL, sub_psk);
   if (!sk)
     return gpg_error_from_syserror ();
 
   epoch2isotime (timestamp, (time_t)sk->timestamp);
+  if (sk->pubkey_algo == PUBKEY_ALGO_ECDH)
+    {
+      ecdh_param_str = ecdh_param_str_from_pk (sk);
+      if (!ecdh_param_str)
+        {
+          free_public_key (sk);
+          return gpg_error_from_syserror ();
+        }
+    }
   err = hexkeygrip_from_pk (sk, &hexgrip);
   if (err)
-    return err;
+    {
+      xfree (ecdh_param_str);
+      free_public_key (sk);
+      return err;
+    }
 
   memset(&info, 0, sizeof (info));
   rc = agent_scd_getattr ("SERIALNO", &info);
   if (rc)
-    return (gpg_error_t)rc;
+    {
+      xfree (ecdh_param_str);
+      free_public_key (sk);
+      return (gpg_error_t)rc;
+    }
 
-  rc = agent_keytocard (hexgrip, 2, 1, info.serialno, timestamp);
+  rc = agent_keytocard (hexgrip, 2, 1, info.serialno,
+                        timestamp, ecdh_param_str);
   xfree (info.serialno);
   if (rc)
     {
@@ -5186,6 +5205,7 @@ card_store_key_with_backup (ctrl_t ctrl, PKT_public_key *sub_psk,
     agent_scd_learn (NULL, 1);
 
  leave:
+  xfree (ecdh_param_str);
   xfree (cache_nonce);
   gcry_cipher_close (cipherhd);
   xfree (kek);

g10/keyid.c

@@ -994,3 +994,25 @@ hexkeygrip_from_pk (PKT_public_key *pk, char **r_grip)
     }
   return err;
 }
+
+
+/* Return a hexfied malloced string of the ECDH parameters for an ECDH
+ * key from the public key PK.  Returns NULL on error.  */
+char *
+ecdh_param_str_from_pk (PKT_public_key *pk)
+{
+  const unsigned char *s;
+  unsigned int n;
+
+  if (!pk
+      || pk->pubkey_algo != PUBKEY_ALGO_ECDH
+      || !gcry_mpi_get_flag (pk->pkey[2], GCRYMPI_FLAG_OPAQUE)
+      || !(s = gcry_mpi_get_opaque (pk->pkey[2], &n)) || !n)
+    {
+      gpg_err_set_errno (EINVAL);
+      return NULL;  /* Invalid parameter */
+    }
+
+  n = (n+7)/8;
+  return bin2hex (s, n, NULL);
+}