diff options
Diffstat (limited to 'crypto/xts.c')
| -rw-r--r-- | crypto/xts.c | 230 |
1 files changed, 230 insertions, 0 deletions
diff --git a/crypto/xts.c b/crypto/xts.c new file mode 100644 index 0000000000..95212341f6 --- /dev/null +++ b/crypto/xts.c @@ -0,0 +1,230 @@ +/* + * 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); +} |