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/* cipher-xts.c - XTS mode implementation
* Copyright (C) 2017 Jussi Kivilinna <jussi.kivilinna@iki.fi>
*
* This file is part of Libgcrypt.
*
* Libgcrypt is free software; you can redistribute it and/or modify
* it under the terms of the GNU Lesser general Public License as
* published by the Free Software Foundation; either version 2.1 of
* the License, or (at your option) any later version.
*
* Libgcrypt is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this program; if not, see <http://www.gnu.org/licenses/>.
*/
#include <config.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include "g10lib.h"
#include "cipher.h"
#include "bufhelp.h"
#include "./cipher-internal.h"
static inline void xts_gfmul_byA (unsigned char *out, const unsigned char *in)
{
u64 hi = buf_get_le64 (in + 8);
u64 lo = buf_get_le64 (in + 0);
u64 carry = -(hi >> 63) & 0x87;
hi = (hi << 1) + (lo >> 63);
lo = (lo << 1) ^ carry;
buf_put_le64 (out + 8, hi);
buf_put_le64 (out + 0, lo);
}
static inline void xts_inc128 (unsigned char *seqno)
{
u64 lo = buf_get_le64 (seqno + 0);
u64 hi = buf_get_le64 (seqno + 8);
hi += !(++lo);
buf_put_le64 (seqno + 0, lo);
buf_put_le64 (seqno + 8, hi);
}
gcry_err_code_t
_gcry_cipher_xts_crypt (gcry_cipher_hd_t c,
unsigned char *outbuf, size_t outbuflen,
const unsigned char *inbuf, size_t inbuflen,
int encrypt)
{
gcry_cipher_encrypt_t tweak_fn = c->spec->encrypt;
gcry_cipher_encrypt_t crypt_fn =
encrypt ? c->spec->encrypt : c->spec->decrypt;
union
{
cipher_context_alignment_t xcx;
byte x1[GCRY_XTS_BLOCK_LEN];
u64 x64[GCRY_XTS_BLOCK_LEN / sizeof(u64)];
} tmp;
unsigned int burn, nburn;
size_t nblocks;
if (c->spec->blocksize != GCRY_XTS_BLOCK_LEN)
return GPG_ERR_CIPHER_ALGO;
if (outbuflen < inbuflen)
return GPG_ERR_BUFFER_TOO_SHORT;
if (inbuflen < GCRY_XTS_BLOCK_LEN)
return GPG_ERR_BUFFER_TOO_SHORT;
/* Data-unit max length: 2^20 blocks. */
if (inbuflen > GCRY_XTS_BLOCK_LEN << 20)
return GPG_ERR_INV_LENGTH;
nblocks = inbuflen / GCRY_XTS_BLOCK_LEN;
nblocks -= !encrypt && (inbuflen % GCRY_XTS_BLOCK_LEN) != 0;
/* Generate first tweak value. */
burn = tweak_fn (c->u_mode.xts.tweak_context, c->u_ctr.ctr, c->u_iv.iv);
/* Use a bulk method if available. */
if (nblocks && c->bulk.xts_crypt)
{
c->bulk.xts_crypt (&c->context.c, c->u_ctr.ctr, outbuf, inbuf, nblocks,
encrypt);
inbuf += nblocks * GCRY_XTS_BLOCK_LEN;
outbuf += nblocks * GCRY_XTS_BLOCK_LEN;
inbuflen -= nblocks * GCRY_XTS_BLOCK_LEN;
nblocks = 0;
}
/* If we don't have a bulk method use the standard method. We also
use this method for the a remaining partial block. */
while (nblocks)
{
/* Xor-Encrypt/Decrypt-Xor block. */
cipher_block_xor (tmp.x64, inbuf, c->u_ctr.ctr, GCRY_XTS_BLOCK_LEN);
nburn = crypt_fn (&c->context.c, tmp.x1, tmp.x1);
burn = nburn > burn ? nburn : burn;
cipher_block_xor (outbuf, tmp.x64, c->u_ctr.ctr, GCRY_XTS_BLOCK_LEN);
outbuf += GCRY_XTS_BLOCK_LEN;
inbuf += GCRY_XTS_BLOCK_LEN;
inbuflen -= GCRY_XTS_BLOCK_LEN;
nblocks--;
/* Generate next tweak. */
xts_gfmul_byA (c->u_ctr.ctr, c->u_ctr.ctr);
}
/* Handle remaining data with ciphertext stealing. */
if (inbuflen)
{
if (!encrypt)
{
gcry_assert (inbuflen > GCRY_XTS_BLOCK_LEN);
gcry_assert (inbuflen < GCRY_XTS_BLOCK_LEN * 2);
/* Generate last tweak. */
xts_gfmul_byA (tmp.x1, c->u_ctr.ctr);
/* Decrypt last block first. */
cipher_block_xor (outbuf, inbuf, tmp.x64, GCRY_XTS_BLOCK_LEN);
nburn = crypt_fn (&c->context.c, outbuf, outbuf);
burn = nburn > burn ? nburn : burn;
cipher_block_xor (outbuf, outbuf, tmp.x64, GCRY_XTS_BLOCK_LEN);
inbuflen -= GCRY_XTS_BLOCK_LEN;
inbuf += GCRY_XTS_BLOCK_LEN;
outbuf += GCRY_XTS_BLOCK_LEN;
}
gcry_assert (inbuflen < GCRY_XTS_BLOCK_LEN);
outbuf -= GCRY_XTS_BLOCK_LEN;
/* Steal ciphertext from previous block. */
cipher_block_cpy (tmp.x64, outbuf, GCRY_XTS_BLOCK_LEN);
buf_cpy (tmp.x64, inbuf, inbuflen);
buf_cpy (outbuf + GCRY_XTS_BLOCK_LEN, outbuf, inbuflen);
/* Decrypt/Encrypt last block. */
cipher_block_xor (tmp.x64, tmp.x64, c->u_ctr.ctr, GCRY_XTS_BLOCK_LEN);
nburn = crypt_fn (&c->context.c, tmp.x1, tmp.x1);
burn = nburn > burn ? nburn : burn;
cipher_block_xor (outbuf, tmp.x64, c->u_ctr.ctr, GCRY_XTS_BLOCK_LEN);
}
/* Auto-increment data-unit sequence number */
xts_inc128 (c->u_iv.iv);
wipememory (&tmp, sizeof(tmp));
wipememory (c->u_ctr.ctr, sizeof(c->u_ctr.ctr));
if (burn > 0)
_gcry_burn_stack (burn + 4 * sizeof(void *));
return 0;
}
gcry_err_code_t
_gcry_cipher_xts_encrypt (gcry_cipher_hd_t c,
unsigned char *outbuf, size_t outbuflen,
const unsigned char *inbuf, size_t inbuflen)
{
return _gcry_cipher_xts_crypt (c, outbuf, outbuflen, inbuf, inbuflen, 1);
}
gcry_err_code_t
_gcry_cipher_xts_decrypt (gcry_cipher_hd_t c,
unsigned char *outbuf, size_t outbuflen,
const unsigned char *inbuf, size_t inbuflen)
{
return _gcry_cipher_xts_crypt (c, outbuf, outbuflen, inbuf, inbuflen, 0);
}
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