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/* 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.
*
* Tom St Denis, tomstdenis@gmail.com, http://libtomcrypt.com
*/
/**
@file s_ocb_done.c
OCB implementation, internal helper, by Tom St Denis
*/
#include "tomcrypt.h"
#ifdef OCB_MODE
/* Since the last block is encrypted in CTR mode the same code can
* be used to finish a decrypt or encrypt stream. The only difference
* is we XOR the final ciphertext into the checksum so we have to xor it
* before we CTR [decrypt] or after [encrypt]
*
* the names pt/ptlen/ct really just mean in/inlen/out but this is the way I wrote it...
*/
/**
Shared code to finish an OCB stream
@param ocb The OCB state
@param pt The remaining plaintext [or input]
@param ptlen The length of the input (octets)
@param ct [out] The output buffer
@param tag [out] The destination for the authentication tag
@param taglen [in/out] The max size and resulting size of the authentication tag
@param mode The mode we are terminating, 0==encrypt, 1==decrypt
@return CRYPT_OK if successful
*/
int s_ocb_done(ocb_state *ocb, const unsigned char *pt, unsigned long ptlen,
unsigned char *ct, unsigned char *tag, unsigned long *taglen, int mode)
{
unsigned char *Z, *Y, *X;
int err, x;
LTC_ARGCHK(ocb != NULL);
LTC_ARGCHK(pt != NULL);
LTC_ARGCHK(ct != NULL);
LTC_ARGCHK(tag != NULL);
LTC_ARGCHK(taglen != NULL);
if ((err = cipher_is_valid(ocb->cipher)) != CRYPT_OK) {
return err;
}
if (ocb->block_len != cipher_descriptor[ocb->cipher].block_length ||
(int)ptlen > ocb->block_len || (int)ptlen < 0) {
return CRYPT_INVALID_ARG;
}
/* allocate ram */
Z = XMALLOC(MAXBLOCKSIZE);
Y = XMALLOC(MAXBLOCKSIZE);
X = XMALLOC(MAXBLOCKSIZE);
if (X == NULL || Y == NULL || Z == NULL) {
if (X != NULL) {
XFREE(X);
}
if (Y != NULL) {
XFREE(Y);
}
if (Z != NULL) {
XFREE(Z);
}
return CRYPT_MEM;
}
/* compute X[m] = len(pt[m]) XOR Lr XOR Z[m] */
ocb_shift_xor(ocb, X);
XMEMCPY(Z, X, ocb->block_len);
X[ocb->block_len-1] ^= (ptlen*8)&255;
X[ocb->block_len-2] ^= ((ptlen*8)>>8)&255;
for (x = 0; x < ocb->block_len; x++) {
X[x] ^= ocb->Lr[x];
}
/* Y[m] = E(X[m])) */
if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(X, Y, &ocb->key)) != CRYPT_OK) {
goto error;
}
if (mode == 1) {
/* decrypt mode, so let's xor it first */
/* xor C[m] into checksum */
for (x = 0; x < (int)ptlen; x++) {
ocb->checksum[x] ^= ct[x];
}
}
/* C[m] = P[m] xor Y[m] */
for (x = 0; x < (int)ptlen; x++) {
ct[x] = pt[x] ^ Y[x];
}
if (mode == 0) {
/* encrypt mode */
/* xor C[m] into checksum */
for (x = 0; x < (int)ptlen; x++) {
ocb->checksum[x] ^= ct[x];
}
}
/* xor Y[m] and Z[m] into checksum */
for (x = 0; x < ocb->block_len; x++) {
ocb->checksum[x] ^= Y[x] ^ Z[x];
}
/* encrypt checksum, er... tag!! */
if ((err = cipher_descriptor[ocb->cipher].ecb_encrypt(ocb->checksum, X, &ocb->key)) != CRYPT_OK) {
goto error;
}
cipher_descriptor[ocb->cipher].done(&ocb->key);
/* now store it */
for (x = 0; x < ocb->block_len && x < (int)*taglen; x++) {
tag[x] = X[x];
}
*taglen = x;
#ifdef LTC_CLEAN_STACK
zeromem(X, MAXBLOCKSIZE);
zeromem(Y, MAXBLOCKSIZE);
zeromem(Z, MAXBLOCKSIZE);
zeromem(ocb, sizeof(*ocb));
#endif
error:
XFREE(X);
XFREE(Y);
XFREE(Z);
return err;
}
#endif
/* $Source: /cvs/libtom/libtomcrypt/src/encauth/ocb/s_ocb_done.c,v $ */
/* $Revision: 1.6 $ */
/* $Date: 2006/03/31 14:15:35 $ */
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