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 #include "tomcrypt.h" 12 13 /** 14 @file ctr_start.c 15 CTR implementation, start chain, Tom St Denis 16 */ 17 18 19 #ifdef LTC_CTR_MODE 20 21 /** 22 Initialize a CTR context 23 @param cipher The index of the cipher desired 24 @param IV The initial vector 25 @param key The secret key 26 @param keylen The length of the secret key (octets) 27 @param num_rounds Number of rounds in the cipher desired (0 for default) 28 @param ctr_mode The counter mode (CTR_COUNTER_LITTLE_ENDIAN or CTR_COUNTER_BIG_ENDIAN) 29 @param ctr The CTR state to initialize 30 @return CRYPT_OK if successful 31 */ 32 int ctr_start( int cipher, 33 const unsigned char *IV, 34 const unsigned char *key, int keylen, 35 int num_rounds, int ctr_mode, 36 symmetric_CTR *ctr) 37 { 38 int x, err; 39 40 LTC_ARGCHK(IV != NULL); 41 LTC_ARGCHK(key != NULL); 42 LTC_ARGCHK(ctr != NULL); 43 44 /* bad param? */ 45 if ((err = cipher_is_valid(cipher)) != CRYPT_OK) { 46 return err; 47 } 48 49 /* setup cipher */ 50 if ((err = cipher_descriptor[cipher].setup(key, keylen, num_rounds, &ctr->key)) != CRYPT_OK) { 51 return err; 52 } 53 54 /* copy ctr */ 55 ctr->blocklen = cipher_descriptor[cipher].block_length; 56 ctr->cipher = cipher; 57 ctr->padlen = 0; 58 ctr->mode = ctr_mode & 1; 59 for (x = 0; x < ctr->blocklen; x++) { 60 ctr->ctr[x] = IV[x]; 61 } 62 63 if (ctr_mode & LTC_CTR_RFC3686) { 64 /* increment the IV as per RFC 3686 */ 65 if (ctr->mode == CTR_COUNTER_LITTLE_ENDIAN) { 66 /* little-endian */ 67 for (x = 0; x < ctr->blocklen; x++) { 68 ctr->ctr[x] = (ctr->ctr[x] + (unsigned char)1) & (unsigned char)255; 69 if (ctr->ctr[x] != (unsigned char)0) { 70 break; 71 } 72 } 73 } else { 74 /* big-endian */ 75 for (x = ctr->blocklen-1; x >= 0; 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 } 82 } 83 84 return cipher_descriptor[ctr->cipher].ecb_encrypt(ctr->ctr, ctr->pad, &ctr->key); 85 } 86 87 #endif 88 89 /* $Source: /cvs/libtom/libtomcrypt/src/modes/ctr/ctr_start.c,v $ */ 90 /* $Revision: 1.11 $ */ 91 /* $Date: 2006/11/05 01:46:35 $ */ 92
