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/*
* QEMU Crypto XTS cipher mode
*
* Copyright (c) 2015-2016 Red Hat, Inc.
*
* This library 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 of the License, or (at your option) any later version.
*
* This library 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 library; if not, see <http://www.gnu.org/licenses/>.
*
* This code is originally derived from public domain / WTFPL code in
* LibTomCrypt crytographic library http://libtom.org. The XTS code
* was donated by Elliptic Semiconductor Inc (www.ellipticsemi.com)
* to the LibTom Projects
*
*/
#include "qemu/osdep.h"
#include "crypto/xts.h"
static void xts_mult_x(uint8_t *I)
{
int x;
uint8_t t, tt;
for (x = t = 0; x < 16; x++) {
tt = I[x] >> 7;
I[x] = ((I[x] << 1) | t) & 0xFF;
t = tt;
}
if (tt) {
I[0] ^= 0x87;
}
}
/**
* xts_tweak_uncrypt:
* @param ctxt: the cipher context
* @param func: the cipher function
* @src: buffer providing the cipher text of XTS_BLOCK_SIZE bytes
* @dst: buffer to output the plain text of XTS_BLOCK_SIZE bytes
* @iv: the initialization vector tweak of XTS_BLOCK_SIZE bytes
*
* Decrypt data with a tweak
*/
static void xts_tweak_decrypt(const void *ctx,
xts_cipher_func *func,
const uint8_t *src,
uint8_t *dst,
uint8_t *iv)
{
unsigned long x;
/* tweak encrypt block i */
for (x = 0; x < XTS_BLOCK_SIZE; x++) {
dst[x] = src[x] ^ iv[x];
}
func(ctx, XTS_BLOCK_SIZE, dst, dst);
for (x = 0; x < XTS_BLOCK_SIZE; x++) {
dst[x] = dst[x] ^ iv[x];
}
/* LFSR the tweak */
xts_mult_x(iv);
}
void xts_decrypt(const void *datactx,
const void *tweakctx,
xts_cipher_func *encfunc,
xts_cipher_func *decfunc,
uint8_t *iv,
size_t length,
uint8_t *dst,
const uint8_t *src)
{
uint8_t PP[XTS_BLOCK_SIZE], CC[XTS_BLOCK_SIZE], T[XTS_BLOCK_SIZE];
unsigned long i, m, mo, lim;
/* get number of blocks */
m = length >> 4;
mo = length & 15;
/* must have at least one full block */
g_assert(m != 0);
if (mo == 0) {
lim = m;
} else {
lim = m - 1;
}
/* encrypt the iv */
encfunc(tweakctx, XTS_BLOCK_SIZE, T, iv);
for (i = 0; i < lim; i++) {
xts_tweak_decrypt(datactx, decfunc, src, dst, T);
src += XTS_BLOCK_SIZE;
dst += XTS_BLOCK_SIZE;
}
/* if length is not a multiple of XTS_BLOCK_SIZE then */
if (mo > 0) {
memcpy(CC, T, XTS_BLOCK_SIZE);
xts_mult_x(CC);
/* PP = tweak decrypt block m-1 */
xts_tweak_decrypt(datactx, decfunc, src, PP, CC);
/* Pm = first length % XTS_BLOCK_SIZE bytes of PP */
for (i = 0; i < mo; i++) {
CC[i] = src[XTS_BLOCK_SIZE + i];
dst[XTS_BLOCK_SIZE + i] = PP[i];
}
for (; i < XTS_BLOCK_SIZE; i++) {
CC[i] = PP[i];
}
/* Pm-1 = Tweak uncrypt CC */
xts_tweak_decrypt(datactx, decfunc, CC, dst, T);
}
/* Decrypt the iv back */
decfunc(tweakctx, XTS_BLOCK_SIZE, iv, T);
}
/**
* xts_tweak_crypt:
* @param ctxt: the cipher context
* @param func: the cipher function
* @src: buffer providing the plain text of XTS_BLOCK_SIZE bytes
* @dst: buffer to output the cipher text of XTS_BLOCK_SIZE bytes
* @iv: the initialization vector tweak of XTS_BLOCK_SIZE bytes
*
* Encrypt data with a tweak
*/
static void xts_tweak_encrypt(const void *ctx,
xts_cipher_func *func,
const uint8_t *src,
uint8_t *dst,
uint8_t *iv)
{
unsigned long x;
/* tweak encrypt block i */
for (x = 0; x < XTS_BLOCK_SIZE; x++) {
dst[x] = src[x] ^ iv[x];
}
func(ctx, XTS_BLOCK_SIZE, dst, dst);
for (x = 0; x < XTS_BLOCK_SIZE; x++) {
dst[x] = dst[x] ^ iv[x];
}
/* LFSR the tweak */
xts_mult_x(iv);
}
void xts_encrypt(const void *datactx,
const void *tweakctx,
xts_cipher_func *encfunc,
xts_cipher_func *decfunc,
uint8_t *iv,
size_t length,
uint8_t *dst,
const uint8_t *src)
{
uint8_t PP[XTS_BLOCK_SIZE], CC[XTS_BLOCK_SIZE], T[XTS_BLOCK_SIZE];
unsigned long i, m, mo, lim;
/* get number of blocks */
m = length >> 4;
mo = length & 15;
/* must have at least one full block */
g_assert(m != 0);
if (mo == 0) {
lim = m;
} else {
lim = m - 1;
}
/* encrypt the iv */
encfunc(tweakctx, XTS_BLOCK_SIZE, T, iv);
for (i = 0; i < lim; i++) {
xts_tweak_encrypt(datactx, encfunc, src, dst, T);
dst += XTS_BLOCK_SIZE;
src += XTS_BLOCK_SIZE;
}
/* if length is not a multiple of XTS_BLOCK_SIZE then */
if (mo > 0) {
/* CC = tweak encrypt block m-1 */
xts_tweak_encrypt(datactx, encfunc, src, CC, T);
/* Cm = first length % XTS_BLOCK_SIZE bytes of CC */
for (i = 0; i < mo; i++) {
PP[i] = src[XTS_BLOCK_SIZE + i];
dst[XTS_BLOCK_SIZE + i] = CC[i];
}
for (; i < XTS_BLOCK_SIZE; i++) {
PP[i] = CC[i];
}
/* Cm-1 = Tweak encrypt PP */
xts_tweak_encrypt(datactx, encfunc, PP, dst, T);
}
/* Decrypt the iv back */
decfunc(tweakctx, XTS_BLOCK_SIZE, iv, T);
}
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