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/* $OpenBSD: cipher-aesctr.c,v 1.1 2014/04/29 15:39:33 markus Exp $ */
/*
* Copyright (c) 2003 Markus Friedl <markus@openbsd.org>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
#include <sys/types.h>
#include <string.h>
#include "cipher-aesctr.h"
/*
* increment counter 'ctr',
* the counter is of size 'len' bytes and stored in network-byte-order.
* (LSB at ctr[len-1], MSB at ctr[0])
*/
static __inline__ void
aesctr_inc(u8 *ctr, u32 len)
{
ssize_t i;
#ifndef CONSTANT_TIME_INCREMENT
for (i = len - 1; i >= 0; i--)
if (++ctr[i]) /* continue on overflow */
return;
#else
u8 x, add = 1;
for (i = len - 1; i >= 0; i--) {
ctr[i] += add;
/* constant time for: x = ctr[i] ? 1 : 0 */
x = ctr[i];
x = (x | (x >> 4)) & 0xf;
x = (x | (x >> 2)) & 0x3;
x = (x | (x >> 1)) & 0x1;
add *= (x^1);
}
#endif
}
void
aesctr_keysetup(aesctr_ctx *x,const u8 *k,u32 kbits,u32 ivbits)
{
x->rounds = rijndaelKeySetupEnc(x->ek, k, kbits);
}
void
aesctr_ivsetup(aesctr_ctx *x,const u8 *iv)
{
memcpy(x->ctr, iv, AES_BLOCK_SIZE);
}
void
aesctr_encrypt_bytes(aesctr_ctx *x,const u8 *m,u8 *c,u32 bytes)
{
u32 n = 0;
u8 buf[AES_BLOCK_SIZE];
while ((bytes--) > 0) {
if (n == 0) {
rijndaelEncrypt(x->ek, x->rounds, x->ctr, buf);
aesctr_inc(x->ctr, AES_BLOCK_SIZE);
}
*(c++) = *(m++) ^ buf[n];
n = (n + 1) % AES_BLOCK_SIZE;
}
}
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