| // SPDX-License-Identifier: BSD-2-Clause |
| /* LibTomCrypt, modular cryptographic library -- Tom St Denis |
| * |
| * LibTomCrypt is a library that provides various cryptographic |
| * algorithms in a highly modular and flexible manner. |
| * |
| * The library is free for all purposes without any express |
| * guarantee it works. |
| */ |
| |
| /** |
| @file ocb3_decrypt.c |
| OCB implementation, decrypt data, by Tom St Denis |
| */ |
| #include "tomcrypt_private.h" |
| |
| #ifdef LTC_OCB3_MODE |
| |
| /** |
| Decrypt blocks of ciphertext with OCB |
| @param ocb The OCB state |
| @param ct The ciphertext (length multiple of the block size of the block cipher) |
| @param ctlen The length of the input (octets) |
| @param pt [out] The plaintext (length of ct) |
| @return CRYPT_OK if successful |
| */ |
| int ocb3_decrypt(ocb3_state *ocb, const unsigned char *ct, unsigned long ctlen, unsigned char *pt) |
| { |
| unsigned char tmp[MAXBLOCKSIZE]; |
| int err, i, full_blocks; |
| unsigned char *pt_b, *ct_b; |
| |
| LTC_ARGCHK(ocb != NULL); |
| if (ctlen == 0) return CRYPT_OK; /* no data, nothing to do */ |
| LTC_ARGCHK(ct != NULL); |
| LTC_ARGCHK(pt != NULL); |
| |
| if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) { |
| return err; |
| } |
| if (ocb->block_len != cipher_descriptor[ocb->cipher]->block_length) { |
| return CRYPT_INVALID_ARG; |
| } |
| |
| if (ctlen % ocb->block_len) { /* ctlen has to bu multiple of block_len */ |
| return CRYPT_INVALID_ARG; |
| } |
| |
| full_blocks = ctlen/ocb->block_len; |
| for(i=0; i<full_blocks; i++) { |
| pt_b = (unsigned char *)pt+i*ocb->block_len; |
| ct_b = (unsigned char *)ct+i*ocb->block_len; |
| |
| /* ocb->Offset_current[] = ocb->Offset_current[] ^ Offset_{ntz(block_index)} */ |
| ocb3_int_xor_blocks(ocb->Offset_current, ocb->Offset_current, ocb->L_[ocb3_int_ntz(ocb->block_index)], ocb->block_len); |
| |
| /* tmp[] = ct[] XOR ocb->Offset_current[] */ |
| ocb3_int_xor_blocks(tmp, ct_b, ocb->Offset_current, ocb->block_len); |
| |
| /* decrypt */ |
| if ((err = cipher_descriptor[ocb->cipher]->ecb_decrypt(tmp, tmp, &ocb->key)) != CRYPT_OK) { |
| goto LBL_ERR; |
| } |
| |
| /* pt[] = tmp[] XOR ocb->Offset_current[] */ |
| ocb3_int_xor_blocks(pt_b, tmp, ocb->Offset_current, ocb->block_len); |
| |
| /* ocb->checksum[] = ocb->checksum[] XOR pt[] */ |
| ocb3_int_xor_blocks(ocb->checksum, ocb->checksum, pt_b, ocb->block_len); |
| |
| ocb->block_index++; |
| } |
| |
| err = CRYPT_OK; |
| |
| LBL_ERR: |
| #ifdef LTC_CLEAN_STACK |
| zeromem(tmp, sizeof(tmp)); |
| #endif |
| return err; |
| } |
| |
| #endif |
| |
| /* ref: $Format:%D$ */ |
| /* git commit: $Format:%H$ */ |
| /* commit time: $Format:%ai$ */ |