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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 /* OCB Implementation by Tom St Denis */ |
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13 #include "mycrypt.h" |
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14 |
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15 #ifdef OCB_MODE |
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16 |
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17 static const struct { |
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18 int len; |
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19 unsigned char poly_div[MAXBLOCKSIZE], |
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20 poly_mul[MAXBLOCKSIZE]; |
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21 } polys[] = { |
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22 { |
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23 8, |
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24 { 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x0D }, |
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25 { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x1B } |
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26 }, { |
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27 16, |
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28 { 0x80, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, |
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29 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x43 }, |
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30 { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, |
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31 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x87 } |
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32 } |
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33 }; |
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34 |
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35 int ocb_init(ocb_state *ocb, int cipher, |
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36 const unsigned char *key, unsigned long keylen, const unsigned char *nonce) |
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37 { |
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38 int poly, x, y, m, err; |
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39 |
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40 _ARGCHK(ocb != NULL); |
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41 _ARGCHK(key != NULL); |
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42 _ARGCHK(nonce != NULL); |
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43 |
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44 /* valid cipher? */ |
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45 if ((err = cipher_is_valid(cipher)) != CRYPT_OK) { |
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46 return err; |
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47 } |
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48 |
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49 /* determine which polys to use */ |
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50 ocb->block_len = cipher_descriptor[cipher].block_length; |
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51 for (poly = 0; poly < (int)(sizeof(polys)/sizeof(polys[0])); poly++) { |
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52 if (polys[poly].len == ocb->block_len) { |
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53 break; |
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54 } |
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55 } |
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56 if (polys[poly].len != ocb->block_len) { |
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57 return CRYPT_INVALID_ARG; |
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58 } |
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59 |
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60 /* schedule the key */ |
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61 if ((err = cipher_descriptor[cipher].setup(key, keylen, 0, &ocb->key)) != CRYPT_OK) { |
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62 return err; |
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63 } |
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64 |
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65 /* find L = E[0] */ |
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66 zeromem(ocb->L, ocb->block_len); |
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67 cipher_descriptor[cipher].ecb_encrypt(ocb->L, ocb->L, &ocb->key); |
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68 |
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69 /* find R = E[N xor L] */ |
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70 for (x = 0; x < ocb->block_len; x++) { |
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71 ocb->R[x] = ocb->L[x] ^ nonce[x]; |
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72 } |
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73 cipher_descriptor[cipher].ecb_encrypt(ocb->R, ocb->R, &ocb->key); |
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74 |
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75 /* find Ls[i] = L << i for i == 0..31 */ |
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76 memcpy(ocb->Ls[0], ocb->L, ocb->block_len); |
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77 for (x = 1; x < 32; x++) { |
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78 m = ocb->Ls[x-1][0] >> 7; |
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79 for (y = 0; y < ocb->block_len-1; y++) { |
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80 ocb->Ls[x][y] = ((ocb->Ls[x-1][y] << 1) | (ocb->Ls[x-1][y+1] >> 7)) & 255; |
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81 } |
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82 ocb->Ls[x][ocb->block_len-1] = (ocb->Ls[x-1][ocb->block_len-1] << 1) & 255; |
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83 |
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84 if (m == 1) { |
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85 for (y = 0; y < ocb->block_len; y++) { |
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86 ocb->Ls[x][y] ^= polys[poly].poly_mul[y]; |
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87 } |
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88 } |
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89 } |
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90 |
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91 /* find Lr = L / x */ |
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92 m = ocb->L[ocb->block_len-1] & 1; |
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93 |
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94 /* shift right */ |
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95 for (x = ocb->block_len - 1; x > 0; x--) { |
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96 ocb->Lr[x] = ((ocb->L[x] >> 1) | (ocb->L[x-1] << 7)) & 255; |
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97 } |
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98 ocb->Lr[0] = ocb->L[0] >> 1; |
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99 |
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100 if (m == 1) { |
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101 for (x = 0; x < ocb->block_len; x++) { |
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102 ocb->Lr[x] ^= polys[poly].poly_div[x]; |
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103 } |
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104 } |
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105 |
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106 /* set Li, checksum */ |
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107 zeromem(ocb->Li, ocb->block_len); |
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108 zeromem(ocb->checksum, ocb->block_len); |
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109 |
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110 /* set other params */ |
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111 ocb->block_index = 1; |
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112 ocb->cipher = cipher; |
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113 |
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114 return CRYPT_OK; |
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115 } |
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116 |
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117 #endif |
