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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 /* EAX Implementation by Tom St Denis */ |
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13 #include "mycrypt.h" |
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14 |
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15 #ifdef EAX_MODE |
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16 |
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17 int eax_init(eax_state *eax, int cipher, const unsigned char *key, unsigned long keylen, |
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18 const unsigned char *nonce, unsigned long noncelen, |
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19 const unsigned char *header, unsigned long headerlen) |
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20 { |
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21 unsigned char buf[MAXBLOCKSIZE]; |
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22 int err, blklen; |
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23 omac_state omac; |
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24 unsigned long len; |
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25 |
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26 |
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27 _ARGCHK(eax != NULL); |
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28 _ARGCHK(key != NULL); |
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29 _ARGCHK(nonce != NULL); |
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30 if (headerlen > 0) { |
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31 _ARGCHK(header != NULL); |
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32 } |
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33 |
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34 if ((err = cipher_is_valid(cipher)) != CRYPT_OK) { |
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35 return err; |
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36 } |
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37 blklen = cipher_descriptor[cipher].block_length; |
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38 |
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39 /* N = OMAC_0K(nonce) */ |
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40 zeromem(buf, sizeof(buf)); |
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41 if ((err = omac_init(&omac, cipher, key, keylen)) != CRYPT_OK) { |
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42 return err; |
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43 } |
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44 |
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45 /* omac the [0]_n */ |
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46 if ((err = omac_process(&omac, buf, blklen)) != CRYPT_OK) { |
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47 return err; |
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48 } |
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49 /* omac the nonce */ |
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50 if ((err = omac_process(&omac, nonce, noncelen)) != CRYPT_OK) { |
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51 return err; |
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52 } |
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53 /* store result */ |
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54 len = sizeof(eax->N); |
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55 if ((err = omac_done(&omac, eax->N, &len)) != CRYPT_OK) { |
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56 return err; |
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57 } |
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58 |
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59 /* H = OMAC_1K(header) */ |
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60 zeromem(buf, sizeof(buf)); |
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61 buf[blklen - 1] = 1; |
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62 |
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63 if ((err = omac_init(&eax->headeromac, cipher, key, keylen)) != CRYPT_OK) { |
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64 return err; |
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65 } |
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66 |
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67 /* omac the [1]_n */ |
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68 if ((err = omac_process(&eax->headeromac, buf, blklen)) != CRYPT_OK) { |
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69 return err; |
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70 } |
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71 /* omac the header */ |
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72 if (headerlen != 0) { |
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73 if ((err = omac_process(&eax->headeromac, header, headerlen)) != CRYPT_OK) { |
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74 return err; |
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75 } |
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76 } |
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77 |
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78 /* note we don't finish the headeromac, this allows us to add more header later */ |
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79 |
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80 /* setup the CTR mode */ |
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81 if ((err = ctr_start(cipher, eax->N, key, keylen, 0, &eax->ctr)) != CRYPT_OK) { |
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82 return err; |
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83 } |
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84 /* use big-endian counter */ |
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85 eax->ctr.mode = 1; |
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86 |
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87 /* setup the OMAC for the ciphertext */ |
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88 if ((err = omac_init(&eax->ctomac, cipher, key, keylen)) != CRYPT_OK) { |
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89 return err; |
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90 } |
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91 |
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92 /* omac [2]_n */ |
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93 zeromem(buf, sizeof(buf)); |
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94 buf[blklen-1] = 2; |
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95 if ((err = omac_process(&eax->ctomac, buf, blklen)) != CRYPT_OK) { |
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96 return err; |
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97 } |
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98 |
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99 #ifdef CLEAN_STACK |
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100 zeromem(buf, sizeof(buf)); |
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101 zeromem(&omac, sizeof(omac)); |
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102 #endif |
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103 return CRYPT_OK; |
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104 } |
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105 |
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106 #endif |
