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comparison src/encauth/gcm/gcm_gf_mult.c @ 192:9cc34777b479 libtomcrypt

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propagate from branch 'au.asn.ucc.matt.ltc-orig' (head 9ba8f01f44320e9cb9f19881105ae84f84a43ea9) to branch 'au.asn.ucc.matt.dropbear.ltc' (head dbf51c569bc34956ad948e4cc87a0eeb2170b768)
author Matt Johnston <matt@ucc.asn.au>
date Sun, 08 May 2005 06:36:47 +0000
parents 1c15b283127b
children 39d5d58461d6
comparison
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164:cd1143579f00 192:9cc34777b479
1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
2 *
3 * LibTomCrypt is a library that provides various cryptographic
4 * algorithms in a highly modular and flexible manner.
5 *
6 * The library is free for all purposes without any express
7 * guarantee it works.
8 *
9 * Tom St Denis, [email protected], http://libtomcrypt.org
10 */
11
12 /**
13 @file gcm_gf_mult.c
14 GCM implementation, initialize state, by Tom St Denis
15 */
16 #include "tomcrypt.h"
17
18 #ifdef GCM_MODE
19
20 /* right shift */
21 static void gcm_rightshift(unsigned char *a)
22 {
23 int x;
24 for (x = 15; x > 0; x--) {
25 a[x] = (a[x]>>1) | ((a[x-1]<<7)&0x80);
26 }
27 a[0] >>= 1;
28 }
29
30 /* c = b*a */
31 static const unsigned char mask[] = { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
32 static const unsigned char poly[] = { 0x00, 0xE1 };
33
34 /**
35 GCM GF multiplier (internal use only)
36 @param a First value
37 @param b Second value
38 @param c Destination for a * b
39 */
40 void gcm_gf_mult(const unsigned char *a, const unsigned char *b, unsigned char *c)
41 {
42 unsigned char Z[16], V[16];
43 unsigned x, y, z;
44
45 zeromem(Z, 16);
46 XMEMCPY(V, a, 16);
47 for (x = 0; x < 128; x++) {
48 if (b[x>>3] & mask[x&7]) {
49 for (y = 0; y < 16; y++) {
50 Z[y] ^= V[y];
51 }
52 }
53 z = V[15] & 0x01;
54 gcm_rightshift(V);
55 V[0] ^= poly[z];
56 }
57 XMEMCPY(c, Z, 16);
58 }
59
60 /**
61 GCM multiply by H
62 @param gcm The GCM state which holds the H value
63 @param I The value to multiply H by
64 */
65 void gcm_mult_h(gcm_state *gcm, unsigned char *I)
66 {
67 unsigned char T[16];
68 #ifdef GCM_TABLES
69 int x, y;
70 XMEMCPY(T, &gcm->PC[0][I[0]][0], 16);
71 for (x = 1; x < 16; x++) {
72 #ifdef LTC_FAST
73 for (y = 0; y < 16; y += sizeof(LTC_FAST_TYPE)) {
74 *((LTC_FAST_TYPE *)(T + y)) ^= *((LTC_FAST_TYPE *)(&gcm->PC[x][I[x]][y]));
75 }
76 #else
77 for (y = 0; y < 16; y++) {
78 T[y] ^= gcm->PC[x][I[x]][y];
79 }
80 #endif
81 }
82 #else
83 gcm_gf_mult(gcm->H, I, T);
84 #endif
85 XMEMCPY(I, T, 16);
86 }
87
88
89 #endif