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@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 */
eax_init(eax_state * eax,int cipher,const unsigned char * key,unsigned long keylen,const unsigned char * nonce,unsigned long noncelen,const unsigned char * header,unsigned long headerlen)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