GnuPG 1.4.19 large key generation to be combined with ./configure --enable-large-secmem at compile time and gpg --gen-key --enable-large-rsa at runtime.

gnupg_1.4.19_xlarge_key_gen.patch

--- g10/keygen.c	2015-02-26 12:24:21.000000000 -0500
+++ g10/keygen.c	2015-03-02 22:12:09.028419377 -0500
@@ -1041,8 +1041,9 @@
 	nbits = 2048;
 	log_info(_("keysize invalid; using %u bits\n"), nbits );
     }
-    else if (nbits > 4096) {
-        nbits = 4096;
+    else if (nbits > 15489) {
+        /* fallback to RFC3766 256-bit symmetric equivalency */
+        nbits = 15489;
         log_info(_("keysize invalid; using %u bits\n"), nbits );
     }

@@ -1251,7 +1252,8 @@
     PKT_public_key *pk;
     MPI skey[6];
     MPI *factors;
-    const unsigned maxsize = (opt.flags.large_rsa ? 8192 : 4096);
+    /* New large key limit RFC3766 256-bit symmetric equivalency */
+    const unsigned maxsize = (opt.flags.large_rsa ? 15489 : 4096);

     assert( is_RSA(algo) );

@@ -1578,7 +1580,7 @@
 static unsigned int
 ask_keysize (int algo, unsigned int primary_keysize)
 {
-  unsigned nbits, min, def=2048, max=4096;
+  unsigned nbits, min, def=2048, max=15489;
   int for_subkey = !!primary_keysize;
   int autocomp = 0;

gnupg_1.4.19_xlarge_secmem.patch

--- configure	2015-02-27 03:37:52.000000000 -0500
+++ configure	2015-03-02 22:28:31.488401783 -0500
@@ -5076,7 +5076,7 @@
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: $large_secmem" >&5
 $as_echo "$large_secmem" >&6; }
 if test "$large_secmem" = yes ; then
-   SECMEM_BUFFER_SIZE=65536
+   SECMEM_BUFFER_SIZE=131072
 else
    SECMEM_BUFFER_SIZE=32768
 fi