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.

3 files changed, 30 insertions, 9 deletions

diff --git a/scd/ChangeLog b/scd/ChangeLog
index 0a614c855..9c4d03592 100644
--- a/scd/ChangeLog
+++ b/scd/ChangeLog
@@ -1,3 +1,9 @@
+2011-06-16  Werner Koch  <[email protected]>
+
+	* 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  <[email protected]>
 
 	* apdu.c (apdu_open_reader): Lock in to CCID if used once.
diff --git a/scd/app-openpgp.c b/scd/app-openpgp.c
index 660519059..fef17faa9 100644
--- a/scd/app-openpgp.c
+++ b/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);
-  if (!buf)
+  buffer = buf = bin2hex (a, alen, NULL);
+  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;
 
diff --git a/scd/command.c b/scd/command.c
index be11ccb77..a579b24eb 100644
--- a/scd/command.c
+++ b/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"