--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libtomcrypt/src/encauth/gcm/gcm_gf_mult.c	Wed Mar 08 13:23:58 2006 +0000
@@ -0,0 +1,94 @@
+/* LibTomCrypt, modular cryptographic library -- Tom St Denis
+ *
+ * LibTomCrypt is a library that provides various cryptographic
+ * algorithms in a highly modular and flexible manner.
+ *
+ * The library is free for all purposes without any express
+ * guarantee it works.
+ *
+ * Tom St Denis, [email protected], http://libtomcrypt.org
+ */
+
+/**
+   @file gcm_gf_mult.c
+   GCM implementation, initialize state, by Tom St Denis
+*/
+#include "tomcrypt.h"
+
+#ifdef GCM_MODE
+
+/* right shift */
+static void gcm_rightshift(unsigned char *a)
+{
+   int x;
+   for (x = 15; x > 0; x--) {
+       a[x] = (a[x]>>1) | ((a[x-1]<<7)&0x80);
+   }
+   a[0] >>= 1;
+}
+
+/* c = b*a */
+static const unsigned char mask[] = { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
+static const unsigned char poly[] = { 0x00, 0xE1 };
+
+     
+/**
+  GCM GF multiplier (internal use only) 
+  @param a   First value
+  @param b   Second value
+  @param c   Destination for a * b
+ */  
+void gcm_gf_mult(const unsigned char *a, const unsigned char *b, unsigned char *c)
+{
+   unsigned char Z[16], V[16];
+   unsigned x, y, z;
+
+   zeromem(Z, 16);
+   XMEMCPY(V, a, 16);
+   for (x = 0; x < 128; x++) {
+       if (b[x>>3] & mask[x&7]) {
+          for (y = 0; y < 16; y++) {
+              Z[y] ^= V[y]; 
+          }
+       }
+       z     = V[15] & 0x01;
+       gcm_rightshift(V);
+       V[0] ^= poly[z];
+   }
+   XMEMCPY(c, Z, 16);
+}
+
+/**
+  GCM multiply by H
+  @param gcm   The GCM state which holds the H value
+  @param I     The value to multiply H by
+ */
+void gcm_mult_h(gcm_state *gcm, unsigned char *I)
+{
+   unsigned char T[16];
+#ifdef GCM_TABLES
+   int x, y;
+   XMEMCPY(T, &gcm->PC[0][I[0]][0], 16);
+   for (x = 1; x < 16; x++) {
+#ifdef LTC_FAST
+       for (y = 0; y < 16; y += sizeof(LTC_FAST_TYPE)) {
+           *((LTC_FAST_TYPE *)(T + y)) ^= *((LTC_FAST_TYPE *)(&gcm->PC[x][I[x]][y]));
+       }
+#else
+       for (y = 0; y < 16; y++) {
+           T[y] ^= gcm->PC[x][I[x]][y];
+       }
+#endif
+   }
+#else     
+   gcm_gf_mult(gcm->H, I, T); 
+#endif
+   XMEMCPY(I, T, 16);
+}
+
+
+#endif
+
+/* $Source: /cvs/libtom/libtomcrypt/src/encauth/gcm/gcm_gf_mult.c,v $ */
+/* $Revision: 1.16 $ */
+/* $Date: 2005/05/21 14:33:42 $ */