Mercurial > dropbear

annotate libtomcrypt/src/modes/xts/xts_encrypt.c @ 1484:f68ee671bf6d

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author Matt Johnston <matt@ucc.asn.au>
date Sat, 10 Feb 2018 18:57:20 +0800
parents 6dba84798cd5
children
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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 #include "tomcrypt.h"
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10
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11 /**
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12 Source donated by Elliptic Semiconductor Inc (www.ellipticsemi.com) to the LibTom Projects
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13 */
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14
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15 #ifdef LTC_XTS_MODE
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16
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17 static int _tweak_crypt(const unsigned char *P, unsigned char *C, unsigned char *T, symmetric_xts *xts)
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18 {
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19 unsigned long x;
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20 int err;
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21
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22 /* tweak encrypt block i */
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23 #ifdef LTC_FAST
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24 for (x = 0; x < 16; x += sizeof(LTC_FAST_TYPE)) {
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25 *(LTC_FAST_TYPE_PTR_CAST(&C[x])) = *(LTC_FAST_TYPE_PTR_CAST(&P[x])) ^ *(LTC_FAST_TYPE_PTR_CAST(&T[x]));
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26 }
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27 #else
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28 for (x = 0; x < 16; x++) {
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29 C[x] = P[x] ^ T[x];
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30 }
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31 #endif
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32
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33 if ((err = cipher_descriptor[xts->cipher].ecb_encrypt(C, C, &xts->key1)) != CRYPT_OK) {
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34 return err;
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35 }
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36
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37 #ifdef LTC_FAST
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38 for (x = 0; x < 16; x += sizeof(LTC_FAST_TYPE)) {
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39 *(LTC_FAST_TYPE_PTR_CAST(&C[x])) ^= *(LTC_FAST_TYPE_PTR_CAST(&T[x]));
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40 }
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41 #else
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42 for (x = 0; x < 16; x++) {
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43 C[x] = C[x] ^ T[x];
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44 }
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45 #endif
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46
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47 /* LFSR the tweak */
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48 xts_mult_x(T);
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49
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50 return CRYPT_OK;
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51 }
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52
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53 /** XTS Encryption
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54 @param pt [in] Plaintext
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55 @param ptlen Length of plaintext (and ciphertext)
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56 @param ct [out] Ciphertext
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57 @param tweak [in] The 128--bit encryption tweak (e.g. sector number)
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58 @param xts The XTS structure
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59 Returns CRYPT_OK upon success
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60 */
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61 int xts_encrypt(const unsigned char *pt, unsigned long ptlen, unsigned char *ct, unsigned char *tweak,
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62 symmetric_xts *xts)
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63 {
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64 unsigned char PP[16], CC[16], T[16];
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65 unsigned long i, m, mo, lim;
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66 int err;
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67
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68 /* check inputs */
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69 LTC_ARGCHK(pt != NULL);
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70 LTC_ARGCHK(ct != NULL);
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71 LTC_ARGCHK(tweak != NULL);
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72 LTC_ARGCHK(xts != NULL);
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73
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74 /* check if valid */
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75 if ((err = cipher_is_valid(xts->cipher)) != CRYPT_OK) {
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76 return err;
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77 }
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78
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79 /* get number of blocks */
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80 m = ptlen >> 4;
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81 mo = ptlen & 15;
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82
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83 /* must have at least one full block */
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84 if (m == 0) {
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85 return CRYPT_INVALID_ARG;
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86 }
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87
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88 if (mo == 0) {
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89 lim = m;
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90 } else {
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91 lim = m - 1;
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92 }
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93
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94 if (cipher_descriptor[xts->cipher].accel_xts_encrypt && lim > 0) {
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95
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96 /* use accelerated encryption for whole blocks */
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97 if ((err = cipher_descriptor[xts->cipher].accel_xts_encrypt(pt, ct, lim, tweak, &xts->key1, &xts->key2)) !=
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98 CRYPT_OK) {
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99 return err;
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100 }
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101 ct += lim * 16;
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102 pt += lim * 16;
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103
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104 /* tweak is encrypted on output */
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105 XMEMCPY(T, tweak, sizeof(T));
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106 } else {
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107
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108 /* encrypt the tweak */
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109 if ((err = cipher_descriptor[xts->cipher].ecb_encrypt(tweak, T, &xts->key2)) != CRYPT_OK) {
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110 return err;
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111 }
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112
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113 for (i = 0; i < lim; i++) {
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114 if ((err = _tweak_crypt(pt, ct, T, xts)) != CRYPT_OK) {
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115 return err;
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116 }
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117 ct += 16;
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118 pt += 16;
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119 }
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120 }
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121
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122 /* if ptlen not divide 16 then */
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123 if (mo > 0) {
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124 /* CC = tweak encrypt block m-1 */
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125 if ((err = _tweak_crypt(pt, CC, T, xts)) != CRYPT_OK) {
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126 return err;
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127 }
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128
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129 /* Cm = first ptlen % 16 bytes of CC */
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130 for (i = 0; i < mo; i++) {
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131 PP[i] = pt[16 + i];
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132 ct[16 + i] = CC[i];
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133 }
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134
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135 for (; i < 16; i++) {
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136 PP[i] = CC[i];
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137 }
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138
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139 /* Cm-1 = Tweak encrypt PP */
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140 if ((err = _tweak_crypt(PP, ct, T, xts)) != CRYPT_OK) {
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141 return err;
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142 }
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143 }
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144
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145 /* Decrypt the tweak back */
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146 if ((err = cipher_descriptor[xts->cipher].ecb_decrypt(T, tweak, &xts->key2)) != CRYPT_OK) {
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147 return err;
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148 }
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149
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150 return err;
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151 }
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152
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153 #endif
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154
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155 /* ref: $Format:%D$ */
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156 /* git commit: $Format:%H$ */
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157 /* commit time: $Format:%ai$ */