Mercurial > dropbear

annotate 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
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1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis
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2 *
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3 * LibTomCrypt is a library that provides various cryptographic
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4 * algorithms in a highly modular and flexible manner.
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5 *
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6 * The library is free for all purposes without any express
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7 * guarantee it works.
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8 *
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9 * Tom St Denis, [email protected], http://libtomcrypt.org
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10 */
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11
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12 /**
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13 @file gcm_gf_mult.c
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14 GCM implementation, initialize state, by Tom St Denis
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15 */
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16 #include "tomcrypt.h"
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17
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18 #ifdef GCM_MODE
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19
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20 /* right shift */
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21 static void gcm_rightshift(unsigned char *a)
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22 {
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23 int x;
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24 for (x = 15; x > 0; x--) {
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25 a[x] = (a[x]>>1) | ((a[x-1]<<7)&0x80);
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26 }
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27 a[0] >>= 1;
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28 }
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29
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30 /* c = b*a */
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31 static const unsigned char mask[] = { 0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01 };
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32 static const unsigned char poly[] = { 0x00, 0xE1 };
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33
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34 /**
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35 GCM GF multiplier (internal use only)
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36 @param a First value
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37 @param b Second value
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38 @param c Destination for a * b
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39 */
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40 void gcm_gf_mult(const unsigned char *a, const unsigned char *b, unsigned char *c)
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41 {
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42 unsigned char Z[16], V[16];
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43 unsigned x, y, z;
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44
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45 zeromem(Z, 16);
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46 XMEMCPY(V, a, 16);
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47 for (x = 0; x < 128; x++) {
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48 if (b[x>>3] & mask[x&7]) {
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49 for (y = 0; y < 16; y++) {
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50 Z[y] ^= V[y];
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51 }
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52 }
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53 z = V[15] & 0x01;
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54 gcm_rightshift(V);
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55 V[0] ^= poly[z];
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56 }
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57 XMEMCPY(c, Z, 16);
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58 }
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59
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60 /**
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61 GCM multiply by H
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62 @param gcm The GCM state which holds the H value
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63 @param I The value to multiply H by
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64 */
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65 void gcm_mult_h(gcm_state *gcm, unsigned char *I)
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66 {
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67 unsigned char T[16];
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68 #ifdef GCM_TABLES
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69 int x, y;
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70 XMEMCPY(T, &gcm->PC[0][I[0]][0], 16);
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71 for (x = 1; x < 16; x++) {
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72 #ifdef LTC_FAST
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73 for (y = 0; y < 16; y += sizeof(LTC_FAST_TYPE)) {
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74 *((LTC_FAST_TYPE *)(T + y)) ^= *((LTC_FAST_TYPE *)(&gcm->PC[x][I[x]][y]));
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75 }
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76 #else
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77 for (y = 0; y < 16; y++) {
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78 T[y] ^= gcm->PC[x][I[x]][y];
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79 }
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80 #endif
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81 }
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82 #else
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83 gcm_gf_mult(gcm->H, I, T);
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84 #endif
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85 XMEMCPY(I, T, 16);
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86 }
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87
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88
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89 #endif