85 lines
2.2 KiB
C
85 lines
2.2 KiB
C
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/* LibTomCrypt, modular cryptographic library -- Tom St Denis */
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/* SPDX-License-Identifier: Unlicense */
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#include "tomcrypt_private.h"
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/**
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@file cbc_decrypt.c
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CBC implementation, encrypt block, Tom St Denis
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*/
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#ifdef LTC_CBC_MODE
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/**
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CBC decrypt
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@param ct Ciphertext
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@param pt [out] Plaintext
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@param len The number of bytes to process (must be multiple of block length)
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@param cbc CBC state
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@return CRYPT_OK if successful
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*/
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int cbc_decrypt(const unsigned char *ct, unsigned char *pt, unsigned long len, symmetric_CBC *cbc)
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{
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int x, err;
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unsigned char tmp[16];
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#ifdef LTC_FAST
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LTC_FAST_TYPE tmpy;
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#else
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unsigned char tmpy;
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#endif
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LTC_ARGCHK(pt != NULL);
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LTC_ARGCHK(ct != NULL);
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LTC_ARGCHK(cbc != NULL);
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if ((err = cipher_is_valid(cbc->cipher)) != CRYPT_OK) {
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return err;
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}
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/* is blocklen valid? */
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if (cbc->blocklen < 1 || cbc->blocklen > (int)sizeof(cbc->IV) || cbc->blocklen > (int)sizeof(tmp)) {
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return CRYPT_INVALID_ARG;
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}
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if (len % cbc->blocklen) {
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return CRYPT_INVALID_ARG;
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}
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#ifdef LTC_FAST
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if (cbc->blocklen % sizeof(LTC_FAST_TYPE)) {
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return CRYPT_INVALID_ARG;
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}
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#endif
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if (cipher_descriptor[cbc->cipher].accel_cbc_decrypt != NULL) {
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return cipher_descriptor[cbc->cipher].accel_cbc_decrypt(ct, pt, len / cbc->blocklen, cbc->IV, &cbc->key);
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}
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while (len) {
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/* decrypt */
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if ((err = cipher_descriptor[cbc->cipher].ecb_decrypt(ct, tmp, &cbc->key)) != CRYPT_OK) {
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return err;
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}
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/* xor IV against plaintext */
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#if defined(LTC_FAST)
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for (x = 0; x < cbc->blocklen; x += sizeof(LTC_FAST_TYPE)) {
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tmpy = *(LTC_FAST_TYPE_PTR_CAST((unsigned char *)cbc->IV + x)) ^ *(LTC_FAST_TYPE_PTR_CAST((unsigned char *)tmp + x));
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*(LTC_FAST_TYPE_PTR_CAST((unsigned char *)cbc->IV + x)) = *(LTC_FAST_TYPE_PTR_CAST((unsigned char *)ct + x));
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*(LTC_FAST_TYPE_PTR_CAST((unsigned char *)pt + x)) = tmpy;
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}
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#else
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for (x = 0; x < cbc->blocklen; x++) {
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tmpy = tmp[x] ^ cbc->IV[x];
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cbc->IV[x] = ct[x];
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pt[x] = tmpy;
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}
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#endif
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ct += cbc->blocklen;
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pt += cbc->blocklen;
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len -= cbc->blocklen;
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}
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return CRYPT_OK;
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}
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#endif
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