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100 lines
2.9 KiB
C
100 lines
2.9 KiB
C
/* LibTomCrypt, modular cryptographic library -- Tom St Denis
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*
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* LibTomCrypt is a library that provides various cryptographic
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* algorithms in a highly modular and flexible manner.
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*
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* The library is free for all purposes without any express
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* guarantee it works.
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*/
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#include "tomcrypt.h"
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/**
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@file ctr_start.c
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CTR implementation, start chain, Tom St Denis
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*/
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#ifdef LTC_CTR_MODE
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/**
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Initialize a CTR context
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@param cipher The index of the cipher desired
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@param IV The initialization vector
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@param key The secret key
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@param keylen The length of the secret key (octets)
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@param num_rounds Number of rounds in the cipher desired (0 for default)
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@param ctr_mode The counter mode (CTR_COUNTER_LITTLE_ENDIAN or CTR_COUNTER_BIG_ENDIAN)
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@param ctr The CTR state to initialize
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@return CRYPT_OK if successful
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*/
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int ctr_start( int cipher,
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const unsigned char *IV,
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const unsigned char *key, int keylen,
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int num_rounds, int ctr_mode,
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symmetric_CTR *ctr)
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{
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int x, err;
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LTC_ARGCHK(IV != NULL);
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LTC_ARGCHK(key != NULL);
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LTC_ARGCHK(ctr != NULL);
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/* bad param? */
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if ((err = cipher_is_valid(cipher)) != CRYPT_OK) {
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return err;
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}
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/* ctrlen == counter width */
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ctr->ctrlen = (ctr_mode & 255) ? (ctr_mode & 255) : cipher_descriptor[cipher].block_length;
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if (ctr->ctrlen > cipher_descriptor[cipher].block_length) {
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return CRYPT_INVALID_ARG;
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}
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if ((ctr_mode & 0x1000) == CTR_COUNTER_BIG_ENDIAN) {
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ctr->ctrlen = cipher_descriptor[cipher].block_length - ctr->ctrlen;
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}
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/* setup cipher */
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if ((err = cipher_descriptor[cipher].setup(key, keylen, num_rounds, &ctr->key)) != CRYPT_OK) {
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return err;
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}
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/* copy ctr */
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ctr->blocklen = cipher_descriptor[cipher].block_length;
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ctr->cipher = cipher;
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ctr->padlen = 0;
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ctr->mode = ctr_mode & 0x1000;
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for (x = 0; x < ctr->blocklen; x++) {
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ctr->ctr[x] = IV[x];
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}
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if (ctr_mode & LTC_CTR_RFC3686) {
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/* increment the IV as per RFC 3686 */
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if (ctr->mode == CTR_COUNTER_LITTLE_ENDIAN) {
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/* little-endian */
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for (x = 0; x < ctr->ctrlen; x++) {
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ctr->ctr[x] = (ctr->ctr[x] + (unsigned char)1) & (unsigned char)255;
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if (ctr->ctr[x] != (unsigned char)0) {
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break;
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}
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}
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} else {
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/* big-endian */
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for (x = ctr->blocklen-1; x >= ctr->ctrlen; x--) {
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ctr->ctr[x] = (ctr->ctr[x] + (unsigned char)1) & (unsigned char)255;
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if (ctr->ctr[x] != (unsigned char)0) {
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break;
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}
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}
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}
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}
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return cipher_descriptor[ctr->cipher].ecb_encrypt(ctr->ctr, ctr->pad, &ctr->key);
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}
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#endif
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/* ref: HEAD -> master, tag: v1.18.2 */
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/* git commit: 7e7eb695d581782f04b24dc444cbfde86af59853 */
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/* commit time: 2018-07-01 22:49:01 +0200 */
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