1 /* LibTomCrypt, modular cryptographic library -- Tom St Denis 2 * 3 * LibTomCrypt is a library that provides various cryptographic 4 * algorithms in a highly modular and flexible manner. 5 * 6 * The library is free for all purposes without any express 7 * guarantee it works. 8 * 9 * Tom St Denis, tomstdenis (at) gmail.com, http://libtomcrypt.com 10 */ 11 12 /** 13 @file eax_init.c 14 EAX implementation, initialized EAX state, by Tom St Denis 15 */ 16 #include "tomcrypt.h" 17 18 #ifdef EAX_MODE 19 20 /** 21 Initialized an EAX state 22 @param eax [out] The EAX state to initialize 23 @param cipher The index of the desired cipher 24 @param key The secret key 25 @param keylen The length of the secret key (octets) 26 @param nonce The use-once nonce for the session 27 @param noncelen The length of the nonce (octets) 28 @param header The header for the EAX state 29 @param headerlen The header length (octets) 30 @return CRYPT_OK if successful 31 */ 32 int eax_init(eax_state *eax, int cipher, 33 const unsigned char *key, unsigned long keylen, 34 const unsigned char *nonce, unsigned long noncelen, 35 const unsigned char *header, unsigned long headerlen) 36 { 37 unsigned char *buf; 38 int err, blklen; 39 omac_state *omac; 40 unsigned long len; 41 42 43 LTC_ARGCHK(eax != NULL); 44 LTC_ARGCHK(key != NULL); 45 LTC_ARGCHK(nonce != NULL); 46 if (headerlen > 0) { 47 LTC_ARGCHK(header != NULL); 48 } 49 50 if ((err = cipher_is_valid(cipher)) != CRYPT_OK) { 51 return err; 52 } 53 blklen = cipher_descriptor[cipher].block_length; 54 55 /* allocate ram */ 56 buf = XMALLOC(MAXBLOCKSIZE); 57 omac = XMALLOC(sizeof(*omac)); 58 59 if (buf == NULL || omac == NULL) { 60 if (buf != NULL) { 61 XFREE(buf); 62 } 63 if (omac != NULL) { 64 XFREE(omac); 65 } 66 return CRYPT_MEM; 67 } 68 69 /* N = OMAC_0K(nonce) */ 70 zeromem(buf, MAXBLOCKSIZE); 71 if ((err = omac_init(omac, cipher, key, keylen)) != CRYPT_OK) { 72 goto LBL_ERR; 73 } 74 75 /* omac the [0]_n */ 76 if ((err = omac_process(omac, buf, blklen)) != CRYPT_OK) { 77 goto LBL_ERR; 78 } 79 /* omac the nonce */ 80 if ((err = omac_process(omac, nonce, noncelen)) != CRYPT_OK) { 81 goto LBL_ERR; 82 } 83 /* store result */ 84 len = sizeof(eax->N); 85 if ((err = omac_done(omac, eax->N, &len)) != CRYPT_OK) { 86 goto LBL_ERR; 87 } 88 89 /* H = OMAC_1K(header) */ 90 zeromem(buf, MAXBLOCKSIZE); 91 buf[blklen - 1] = 1; 92 93 if ((err = omac_init(&eax->headeromac, cipher, key, keylen)) != CRYPT_OK) { 94 goto LBL_ERR; 95 } 96 97 /* omac the [1]_n */ 98 if ((err = omac_process(&eax->headeromac, buf, blklen)) != CRYPT_OK) { 99 goto LBL_ERR; 100 } 101 /* omac the header */ 102 if (headerlen != 0) { 103 if ((err = omac_process(&eax->headeromac, header, headerlen)) != CRYPT_OK) { 104 goto LBL_ERR; 105 } 106 } 107 108 /* note we don't finish the headeromac, this allows us to add more header later */ 109 110 /* setup the CTR mode */ 111 if ((err = ctr_start(cipher, eax->N, key, keylen, 0, CTR_COUNTER_BIG_ENDIAN, &eax->ctr)) != CRYPT_OK) { 112 goto LBL_ERR; 113 } 114 115 /* setup the OMAC for the ciphertext */ 116 if ((err = omac_init(&eax->ctomac, cipher, key, keylen)) != CRYPT_OK) { 117 goto LBL_ERR; 118 } 119 120 /* omac [2]_n */ 121 zeromem(buf, MAXBLOCKSIZE); 122 buf[blklen-1] = 2; 123 if ((err = omac_process(&eax->ctomac, buf, blklen)) != CRYPT_OK) { 124 goto LBL_ERR; 125 } 126 127 err = CRYPT_OK; 128 LBL_ERR: 129 #ifdef LTC_CLEAN_STACK 130 zeromem(buf, MAXBLOCKSIZE); 131 zeromem(omac, sizeof(*omac)); 132 #endif 133 134 XFREE(omac); 135 XFREE(buf); 136 137 return err; 138 } 139 140 #endif 141 142 /* $Source: /cvs/libtom/libtomcrypt/src/encauth/eax/eax_init.c,v $ */ 143 /* $Revision: 1.5 $ */ 144 /* $Date: 2006/03/31 14:15:35 $ */ 145
