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annotate libtomcrypt/src/encauth/ccm/ccm_add_nonce.c @ 1628:ff3f274ea56c

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Add missing word to readme (#77)
author Michael Jones <jonesmz@users.noreply.github.com>
date Wed, 20 Mar 2019 08:56:19 -0500
parents 6dba84798cd5
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
rev   line source
1471
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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 #ifdef LTC_CCM_MODE
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12
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13 /**
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14 Add nonce data to the CCM state
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15 @param ccm The CCM state
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16 @param nonce The nonce data to add
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17 @param noncelen The length of the nonce
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18 @return CRYPT_OK on success
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19 */
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20 int ccm_add_nonce(ccm_state *ccm,
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21 const unsigned char *nonce, unsigned long noncelen)
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22 {
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23 unsigned long x, y, len;
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24 int err;
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25
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26 LTC_ARGCHK(ccm != NULL);
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27 LTC_ARGCHK(nonce != NULL);
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28
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29 /* increase L to match the nonce len */
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30 ccm->noncelen = (noncelen > 13) ? 13 : noncelen;
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31 if ((15 - ccm->noncelen) > ccm->L) {
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32 ccm->L = 15 - ccm->noncelen;
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33 }
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34
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35 /* decrease noncelen to match L */
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36 if ((ccm->noncelen + ccm->L) > 15) {
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37 ccm->noncelen = 15 - ccm->L;
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38 }
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39
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40 /* form B_0 == flags | Nonce N | l(m) */
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41 x = 0;
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42 ccm->PAD[x++] = (unsigned char)(((ccm->aadlen > 0) ? (1<<6) : 0) |
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43 (((ccm->taglen - 2)>>1)<<3) |
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44 (ccm->L-1));
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45
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46 /* nonce */
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47 for (y = 0; y < (16 - (ccm->L + 1)); y++) {
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48 ccm->PAD[x++] = nonce[y];
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49 }
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50
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51 /* store len */
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52 len = ccm->ptlen;
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53
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54 /* shift len so the upper bytes of len are the contents of the length */
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55 for (y = ccm->L; y < 4; y++) {
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56 len <<= 8;
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57 }
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58
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59 /* store l(m) (only store 32-bits) */
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60 for (y = 0; ccm->L > 4 && (ccm->L-y)>4; y++) {
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61 ccm->PAD[x++] = 0;
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62 }
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63 for (; y < ccm->L; y++) {
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64 ccm->PAD[x++] = (unsigned char)((len >> 24) & 255);
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65 len <<= 8;
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66 }
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67
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68 /* encrypt PAD */
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69 if ((err = cipher_descriptor[ccm->cipher].ecb_encrypt(ccm->PAD, ccm->PAD, &ccm->K)) != CRYPT_OK) {
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70 return err;
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71 }
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72
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73 /* handle header */
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74 ccm->x = 0;
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75 if (ccm->aadlen > 0) {
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76 /* store length */
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77 if (ccm->aadlen < ((1UL<<16) - (1UL<<8))) {
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78 ccm->PAD[ccm->x++] ^= (ccm->aadlen>>8) & 255;
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79 ccm->PAD[ccm->x++] ^= ccm->aadlen & 255;
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80 } else {
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81 ccm->PAD[ccm->x++] ^= 0xFF;
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82 ccm->PAD[ccm->x++] ^= 0xFE;
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83 ccm->PAD[ccm->x++] ^= (ccm->aadlen>>24) & 255;
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84 ccm->PAD[ccm->x++] ^= (ccm->aadlen>>16) & 255;
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85 ccm->PAD[ccm->x++] ^= (ccm->aadlen>>8) & 255;
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86 ccm->PAD[ccm->x++] ^= ccm->aadlen & 255;
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87 }
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88 }
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89
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90 /* setup the ctr counter */
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91 x = 0;
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92
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93 /* flags */
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94 ccm->ctr[x++] = (unsigned char)ccm->L-1;
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95
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96 /* nonce */
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97 for (y = 0; y < (16 - (ccm->L+1)); ++y) {
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98 ccm->ctr[x++] = nonce[y];
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99 }
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100 /* offset */
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101 while (x < 16) {
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102 ccm->ctr[x++] = 0;
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103 }
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104
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105 ccm->CTRlen = 16;
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106 return CRYPT_OK;
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107 }
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108
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109 #endif
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110
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111 /* ref: $Format:%D$ */
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112 /* git commit: $Format:%H$ */
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113 /* commit time: $Format:%ai$ */