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111 lines
3.4 KiB
C
111 lines
3.4 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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/**
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@file ocb3_decrypt_last.c
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OCB implementation, internal helper, by Karel Miko
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*/
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#include "tomcrypt.h"
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#ifdef LTC_OCB3_MODE
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/**
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Finish an OCB (decryption) stream
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@param ocb The OCB state
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@param ct The remaining ciphertext
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@param ctlen The length of the ciphertext (octets)
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@param pt [out] The output buffer
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@return CRYPT_OK if successful
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*/
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int ocb3_decrypt_last(ocb3_state *ocb, const unsigned char *ct, unsigned long ctlen, unsigned char *pt)
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{
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unsigned char iOffset_star[MAXBLOCKSIZE];
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unsigned char iPad[MAXBLOCKSIZE];
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int err, x, full_blocks, full_blocks_len, last_block_len;
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LTC_ARGCHK(ocb != NULL);
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if (ct == NULL) LTC_ARGCHK(ctlen == 0);
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if (ctlen != 0) {
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LTC_ARGCHK(ct != NULL);
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LTC_ARGCHK(pt != NULL);
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}
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if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
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goto LBL_ERR;
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}
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full_blocks = ctlen/ocb->block_len;
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full_blocks_len = full_blocks * ocb->block_len;
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last_block_len = ctlen - full_blocks_len;
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/* process full blocks first */
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if (full_blocks>0) {
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if ((err = ocb3_decrypt(ocb, ct, full_blocks_len, pt)) != CRYPT_OK) {
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goto LBL_ERR;
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}
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}
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if (last_block_len>0) {
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/* Offset_* = Offset_m xor L_* */
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ocb3_int_xor_blocks(iOffset_star, ocb->Offset_current, ocb->L_star, ocb->block_len);
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/* Pad = ENCIPHER(K, Offset_*) */
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if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(iOffset_star, iPad, &ocb->key)) != CRYPT_OK) {
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goto LBL_ERR;
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}
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/* P_* = C_* xor Pad[1..bitlen(C_*)] */
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ocb3_int_xor_blocks(pt+full_blocks_len, (unsigned char *)ct+full_blocks_len, iPad, last_block_len);
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/* Checksum_* = Checksum_m xor (P_* || 1 || zeros(127-bitlen(P_*))) */
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ocb3_int_xor_blocks(ocb->checksum, ocb->checksum, pt+full_blocks_len, last_block_len);
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for(x=last_block_len; x<ocb->block_len; x++) {
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if (x == last_block_len)
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ocb->checksum[x] ^= 0x80;
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else
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ocb->checksum[x] ^= 0x00;
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}
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/* Tag = ENCIPHER(K, Checksum_* xor Offset_* xor L_$) xor HASH(K,A) */
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/* at this point we calculate only: Tag_part = ENCIPHER(K, Checksum_* xor Offset_* xor L_$) */
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for(x=0; x<ocb->block_len; x++) {
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ocb->tag_part[x] = (ocb->checksum[x] ^ iOffset_star[x]) ^ ocb->L_dollar[x];
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}
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if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(ocb->tag_part, ocb->tag_part, &ocb->key)) != CRYPT_OK) {
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goto LBL_ERR;
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}
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}
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else {
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/* Tag = ENCIPHER(K, Checksum_m xor Offset_m xor L_$) xor HASH(K,A) */
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/* at this point we calculate only: Tag_part = ENCIPHER(K, Checksum_m xor Offset_m xor L_$) */
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for(x=0; x<ocb->block_len; x++) {
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ocb->tag_part[x] = (ocb->checksum[x] ^ ocb->Offset_current[x]) ^ ocb->L_dollar[x];
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}
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if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(ocb->tag_part, ocb->tag_part, &ocb->key)) != CRYPT_OK) {
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goto LBL_ERR;
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}
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}
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err = CRYPT_OK;
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LBL_ERR:
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#ifdef LTC_CLEAN_STACK
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zeromem(iOffset_star, MAXBLOCKSIZE);
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zeromem(iPad, MAXBLOCKSIZE);
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#endif
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return err;
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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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