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Justine Tunney 2020-06-15 07:18:57 -07:00
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libc/crypto/invmixcolumns.c Normal file
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/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi│
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney │
│ │
│ This program is free software; you can redistribute it and/or modify │
│ it under the terms of the GNU General Public License as published by │
│ the Free Software Foundation; version 2 of the License. │
│ │
│ This program 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 │
│ General Public License for more details. │
│ │
│ You should have received a copy of the GNU General Public License │
│ along with this program; if not, write to the Free Software │
│ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA │
│ 02110-1301 USA │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/crypto/rijndael.h"
#include "libc/dce.h"
static noinline aes_block_t xtime(aes_block_t x) {
return ((x ^ (x & 0x80808080)) << 1) ^ (((x & 0x80808080) >> 7) * 0x1b);
}
static aes_block_t gf256mulx4(aes_block_t x, aes_block_t c) {
return ((((c >> 0 & 0x01010101) * 0xff) & x) ^
(((c >> 1 & 0x01010101) * 0xff) & xtime(x)) ^
(((c >> 2 & 0x01010101) * 0xff) & xtime(xtime(x))) ^
(((c >> 3 & 0x01010101) * 0xff) & xtime(xtime(xtime(x)))) ^
(((c >> 4 & 0x01010101) * 0xff) & xtime(xtime(xtime(x)))));
}
/**
* Applies inverse of Rijndael MixColumns() transformation.
* @see FIPS-197
*/
aes_block_t InvMixColumns(aes_block_t x) {
uint32_t i;
aes_block_t y = {0, 0, 0, 0};
aes_block_t c = {0x090D0B0E, 0x090D0B0E, 0x090D0B0E, 0x090D0B0E};
for (i = 0; i < 4; ++i) {
y ^= gf256mulx4((x & 0xff) * 0x01010101,
(((c >> 000) & 0xff) << 000 | ((c >> 010) & 0xff) << 030 |
((c >> 020) & 0xff) << 020 | ((c >> 030) & 0xff) << 010));
x = x << 8 | x >> 24;
c = c << 8 | c >> 24;
}
return y;
}