Allow generation of card keys up to 4096 bit.

This patch implementes a chunk mode to pass the key parameters from
scdaemon to gpg.  This allows to pass arbitrary long key paremeters;
it is used for keys larger than 3072 bit.

Note: the card key generation in gpg is currently broken.  The keys
are generated but it is not possible to create the self-signature
because at that time the gpg-agent does not yet know about the new
keys and thus can't divert the sign request to the card.  We either
need to run the learn command right after calling agent_scd_genkey or
implement a way to sign using the currently inserted card.  Another
option would be to get rid of agent_scd_genkey and implement the
feature directly in agent_genkey.

NEWS

@@ -1,7 +1,9 @@
 Noteworthy changes in version 2.1.0beta3
 -----------------------------------------------------
 
- * Fixed regression in GPG'S secret key export function.
+ * Fixed regression in GPG's secret key export function.
+
+ * Allow generation of card keys up to 4096 bit.
 
 
 Noteworthy changes in version 2.1.0beta2 (2011-03-08)

g10/ChangeLog

@@ -1,3 +1,11 @@
+2011-06-16  Werner Koch  <wk@g10code.com>
+
+	* card-util.c (ask_card_keysize): Bump key size limit to 4096.
+	* call-agent.c (scd_genkey_parm_s): New.
+	(agent_scd_genkey): Use new struct.
+	(scd_genkey_cb): Implement chunked mode for KEY-DATA.
+	(scd_genkey_cb_append_savedbytes): New.
+
 2011-06-13  Werner Koch  <wk@g10code.com>
 
 	* pkglue.c (mpi_from_sexp): Use GCRYMPI_FMT_USG to avoid problems

g10/call-agent.c

@@ -93,6 +93,13 @@ struct cache_nonce_parm_s
 };
 
 
+struct scd_genkey_parm_s
+{
+  struct agent_card_genkey_s *cgk;
+  char *savedbytes;     /* Malloced space to save key parameter chunks.  */
+};
+
+
 static gpg_error_t learn_status_cb (void *opaque, const char *line);
 
 
@@ -717,14 +724,43 @@ agent_scd_writekey (int keyno, const char *serialno,
 
 
 
+static gpg_error_t
+scd_genkey_cb_append_savedbytes (struct scd_genkey_parm_s *parm,
+                                 const char *line)
+{
+  gpg_error_t err = 0;
+  char *p;
+
+  if (!parm->savedbytes)
+    {
+      parm->savedbytes = xtrystrdup (line);
+      if (!parm->savedbytes)
+        err = gpg_error_from_syserror ();
+    }
+  else
+    {
+      p = xtrymalloc (strlen (parm->savedbytes) + strlen (line) + 1);
+      if (!p)
+        err = gpg_error_from_syserror ();
+      else
+        {
+          strcpy (stpcpy (p, parm->savedbytes), line);
+          xfree (parm->savedbytes);
+          parm->savedbytes = p;
+        }
+    }
+
+  return err;
+}
+
 /* Status callback for the SCD GENKEY command. */
 static gpg_error_t
 scd_genkey_cb (void *opaque, const char *line)
 {
-  struct agent_card_genkey_s *parm = opaque;
+  struct scd_genkey_parm_s *parm = opaque;
   const char *keyword = line;
   int keywordlen;
-  gpg_error_t rc;
+  gpg_error_t rc = 0;
 
   for (keywordlen=0; *line && !spacep (line); line++, keywordlen++)
     ;
@@ -733,7 +769,7 @@ scd_genkey_cb (void *opaque, const char *line)
 
   if (keywordlen == 7 && !memcmp (keyword, "KEY-FPR", keywordlen))
     {
-      parm->fprvalid = unhexify_fpr (line, parm->fpr);
+      parm->cgk->fprvalid = unhexify_fpr (line, parm->cgk->fpr);
     }
   else if (keywordlen == 8 && !memcmp (keyword, "KEY-DATA", keywordlen))
     {
@@ -745,29 +781,47 @@ scd_genkey_cb (void *opaque, const char *line)
       while (spacep (line))
         line++;
 
+      if (*name == '-' && spacep (name+1))
+        rc = scd_genkey_cb_append_savedbytes (parm, line);
+      else
+        {
+          if (parm->savedbytes)
+            {
+              rc = scd_genkey_cb_append_savedbytes (parm, line);
+              if (!rc)
+                rc = gcry_mpi_scan (&a, GCRYMPI_FMT_HEX,
+                                    parm->savedbytes, 0, NULL);
+            }
+          else
             rc = gcry_mpi_scan (&a, GCRYMPI_FMT_HEX, line, 0, NULL);
           if (rc)
-        log_error ("error parsing received key data: %s\n", gpg_strerror (rc));
+            log_error ("error parsing received key data: %s\n",
+                       gpg_strerror (rc));
           else if (*name == 'n' && spacep (name+1))
-        parm->n = a;
+            parm->cgk->n = a;
           else if (*name == 'e' && spacep (name+1))
-        parm->e = a;
+            parm->cgk->e = a;
           else
             {
               log_info ("unknown parameter name in received key data\n");
               gcry_mpi_release (a);
+              rc = gpg_error (GPG_ERR_INV_PARAMETER);
+            }
+
+          xfree (parm->savedbytes);
+          parm->savedbytes = NULL;
         }
     }
   else if (keywordlen == 14 && !memcmp (keyword,"KEY-CREATED-AT", keywordlen))
     {
-      parm->created_at = (u32)strtoul (line, NULL, 10);
+      parm->cgk->created_at = (u32)strtoul (line, NULL, 10);
     }
   else if (keywordlen == 8 && !memcmp (keyword, "PROGRESS", keywordlen))
     {
       write_status_text (STATUS_PROGRESS, line);
     }
 
-  return 0;
+  return rc;
 }
 
 /* Send a GENKEY command to the SCdaemon.  SERIALNO is not used in
@@ -781,9 +835,13 @@ agent_scd_genkey (struct agent_card_genkey_s *info, int keyno, int force,
   int rc;
   char line[ASSUAN_LINELENGTH];
   gnupg_isotime_t tbuf;
+  struct scd_genkey_parm_s parms;
 
   (void)serialno;
 
+  memset (&parms, 0, sizeof parms);
+  parms.cgk = info;
+
   rc = start_agent (NULL, 1);
   if (rc)
     return rc;
@@ -802,7 +860,9 @@ agent_scd_genkey (struct agent_card_genkey_s *info, int keyno, int force,
   memset (info, 0, sizeof *info);
   rc = assuan_transact (agent_ctx, line,
                         NULL, NULL, default_inq_cb, NULL,
-                        scd_genkey_cb, info);
+                        scd_genkey_cb, &parms);
+
+  xfree (parms.savedbytes);
 
   status_sc_op_failure (rc);
   return rc;

g10/card-util.c

@@ -1294,7 +1294,7 @@ static unsigned int
 ask_card_keysize (int keyno, unsigned int nbits)
 {
   unsigned int min_nbits = 1024;
-  unsigned int max_nbits = 3072; /* GnuPG limit due to Assuan.  */
+  unsigned int max_nbits = 4096;
   char *prompt, *answer;
   unsigned int req_nbits;
 

scd/ChangeLog

@@ -1,3 +1,9 @@
+2011-06-16  Werner Koch  <wk@g10code.com>
+
+	* app-openpgp.c (send_key_data): Implemented chunked mode.
+	(change_keyattr): Increase limit to 4096.
+	(do_decipher): Adjust padding for 4096 bit keys.
+
 2011-02-23  Werner Koch  <wk@g10code.com>
 
 	* apdu.c (apdu_open_reader): Lock in to CCID if used once.

scd/app-openpgp.c

@@ -756,20 +756,29 @@ static void
 send_key_data (ctrl_t ctrl, const char *name,
                const unsigned char *a, size_t alen)
 {
-  char *buf;
+  char *buffer, *buf;
+  size_t buflen;
 
-  buf = bin2hex (a, alen, NULL);
+  buffer = buf = bin2hex (a, alen, NULL);
-  if (!buf)
+  if (!buffer)
     {
       log_error ("memory allocation error in send_key_data\n");
       return;
     }
+  buflen = strlen (buffer);
 
+  /* 768 is the hexified size for the modulus of an 3072 bit key.  We
+     use extra chunks to transmit larger data (i.e for 4096 bit).  */
+  for ( ;buflen > 768; buflen -= 768, buf += 768)
+    send_status_info (ctrl, "KEY-DATA",
+                      "-", 1,
+                      buf, 768,
+                      NULL, 0);
   send_status_info (ctrl, "KEY-DATA",
                     name, (size_t)strlen(name),
-                    buf, (size_t)strlen (buf),
+                    buf, buflen,
                     NULL, 0);
-  xfree (buf);
+  xfree (buffer);
 }
 
 
@@ -2365,7 +2374,7 @@ change_keyattr (app_t app, int keyno, unsigned int nbits,
 
   assert (keyno >=0 && keyno <= 2);
 
-  if (nbits > 3072)
+  if (nbits > 4096)
     return gpg_error (GPG_ERR_TOO_LARGE);
 
   /* Read the current attributes into a buffer.  */
@@ -2823,7 +2832,7 @@ do_genkey (app_t app, ctrl_t ctrl,  const char *keynostr, unsigned int flags,
      already lead to a 527 byte long status line and thus a 4096 bit
      key would exceed the Assuan line length limit.  */
   keybits = app->app_local->keyattr[keyno].n_bits;
-  if (keybits > 3072)
+  if (keybits > 4096)
     return gpg_error (GPG_ERR_TOO_LARGE);
 
   /* Prepare for key generation by verifying the Admin PIN.  */
@@ -3377,6 +3386,8 @@ do_decipher (app_t app, const char *keyidstr,
         fixuplen = 256 - indatalen;
       else if (indatalen >= (384-16) && indatalen < 384) /* 3072 bit key.  */
         fixuplen = 384 - indatalen;
+      else if (indatalen >= (512-16) && indatalen < 512) /* 4096 bit key.  */
+        fixuplen = 512 - indatalen;
       else
         fixuplen = 0;
 

scd/command.c

@@ -1288,11 +1288,15 @@ static const char hlp_genkey[] =
   "\n"
   "Generate a key on-card identified by NO, which is application\n"
   "specific.  Return values are application specific.  For OpenPGP\n"
-  "cards 2 status lines are returned:\n"
+  "cards 3 status lines are returned:\n"
   "\n"
   "  S KEY-FPR  <hexstring>\n"
   "  S KEY-CREATED-AT <seconds_since_epoch>\n"
-  "  S KEY-DATA [p|n] <hexdata>\n"
+  "  S KEY-DATA [-|p|n] <hexdata>\n"
+  "\n"
+  "  'p' and 'n' are the names of the RSA parameters; '-' is used to\n"
+  "  indicate that HEXDATA is the first chunk of a parameter given\n"
+  "  by the next KEY-DATA.\n"
   "\n"
   "--force is required to overwrite an already existing key.  The\n"
   "KEY-CREATED-AT is required for further processing because it is\n"