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 #include "tomcrypt.h"
10
11 /**
12 @file ctr_start.c
13 CTR implementation, start chain, Tom St Denis
14 */
15
16
17 #ifdef LTC_CTR_MODE
18
19 /**
20 Initialize a CTR context
21 @param cipher The index of the cipher desired
22 @param IV The initialization vector
23 @param key The secret key
24 @param keylen The length of the secret key (octets)
25 @param num_rounds Number of rounds in the cipher desired (0 for default)
26 @param ctr_mode The counter mode (CTR_COUNTER_LITTLE_ENDIAN or CTR_COUNTER_BIG_ENDIAN)
27 @param ctr The CTR state to initialize
28 @return CRYPT_OK if successful
29 */
ctr_start(int cipher,const unsigned char * IV,const unsigned char * key,int keylen,int num_rounds,int ctr_mode,symmetric_CTR * ctr)30 int ctr_start( int cipher,
31 const unsigned char *IV,
32 const unsigned char *key, int keylen,
33 int num_rounds, int ctr_mode,
34 symmetric_CTR *ctr)
35 {
36 int x, err;
37
38 LTC_ARGCHK(IV != NULL);
39 LTC_ARGCHK(key != NULL);
40 LTC_ARGCHK(ctr != NULL);
41
42 /* bad param? */
43 if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
44 return err;
45 }
46
47 /* ctrlen == counter width */
48 ctr->ctrlen = (ctr_mode & 255) ? (ctr_mode & 255) : cipher_descriptor[cipher].block_length;
49 if (ctr->ctrlen > cipher_descriptor[cipher].block_length) {
50 return CRYPT_INVALID_ARG;
51 }
52
53 if ((ctr_mode & 0x1000) == CTR_COUNTER_BIG_ENDIAN) {
54 ctr->ctrlen = cipher_descriptor[cipher].block_length - ctr->ctrlen;
55 }
56
57 /* setup cipher */
58 if ((err = cipher_descriptor[cipher].setup(key, keylen, num_rounds, &ctr->key)) != CRYPT_OK) {
59 return err;
60 }
61
62 /* copy ctr */
63 ctr->blocklen = cipher_descriptor[cipher].block_length;
64 ctr->cipher = cipher;
65 ctr->padlen = 0;
66 ctr->mode = ctr_mode & 0x1000;
67 for (x = 0; x < ctr->blocklen; x++) {
68 ctr->ctr[x] = IV[x];
69 }
70
71 if (ctr_mode & LTC_CTR_RFC3686) {
72 /* increment the IV as per RFC 3686 */
73 if (ctr->mode == CTR_COUNTER_LITTLE_ENDIAN) {
74 /* little-endian */
75 for (x = 0; x < ctr->ctrlen; x++) {
76 ctr->ctr[x] = (ctr->ctr[x] + (unsigned char)1) & (unsigned char)255;
77 if (ctr->ctr[x] != (unsigned char)0) {
78 break;
79 }
80 }
81 } else {
82 /* big-endian */
83 for (x = ctr->blocklen-1; x >= ctr->ctrlen; x--) {
84 ctr->ctr[x] = (ctr->ctr[x] + (unsigned char)1) & (unsigned char)255;
85 if (ctr->ctr[x] != (unsigned char)0) {
86 break;
87 }
88 }
89 }
90 }
91
92 return cipher_descriptor[ctr->cipher].ecb_encrypt(ctr->ctr, ctr->pad, &ctr->key);
93 }
94
95 #endif
96
97 /* ref: $Format:%D$ */
98 /* git commit: $Format:%H$ */
99 /* commit time: $Format:%ai$ */
100