(main): New file.

Rev: nettle/gcmdata.c:1.1

gcmdata.c

+/* gcmdata.c
+ *
+ * Galois counter mode, specified by NIST,
+ * http://csrc.nist.gov/publications/nistpubs/800-38D/SP-800-38D.pdf
+ *
+ */
+
+/* Generation of fixed multiplication tables. */
+
+/* nettle, low-level cryptographics library
+ *
+ * Copyright (C) 2011 Niels Möller
+ *
+ * The nettle library is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation; either version 2.1 of the License, or (at your
+ * option) any later version.
+ * 
+ * The nettle library is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public
+ * License for more details.
+ * 
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with the nettle library; see the file COPYING.LIB.  If not, write to
+ * the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
+ * MA 02111-1307, USA.
+ */
+#if HAVE_CONFIG_H
+# include "config.h"
+#endif
+
+#include <stdio.h>
+#include <stdlib.h>
+
+#define GHASH_POLYNOMIAL 0xE1
+
+
+/* When x is shifted out over the block edge, add multiples of the
+   defining polynomial to eliminate each bit. */
+static unsigned
+reduce(unsigned x)
+{
+  unsigned p = GHASH_POLYNOMIAL << 1;
+  unsigned y = 0;
+  for (; x; x >>= 1, p <<= 1)
+    if (x & 1)
+      y ^= p;
+  return y;
+}
+
+int
+main(int argc UNUSED, char **argv UNUSED)
+{
+  unsigned i;
+  printf("4-bit table:\n");
+  
+  for (i = 0; i<16; i++)
+    {
+      unsigned x;
+      if (i && !(i%8))
+	printf("\n");
+
+      x = reduce(i << 4);
+      printf("W(%02x,%02x),", x >> 8, x & 0xff);
+    }
+  printf("\n\n");
+  printf("8-bit table:\n");
+  for (i = 0; i<256; i++)
+    {
+      unsigned x;
+      if (i && !(i%8))
+	printf("\n");
+
+      x = reduce(i);
+      printf("W(%02x,%02x),", x >> 8, x & 0xff);
+    }
+  printf("\n");
+  return EXIT_SUCCESS;
+}