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1/* $OpenBSD: cipher-aesctr.c,v 1.1 2014/04/29 15:39:33 markus Exp $ */
2/*
3 * Copyright (c) 2003 Markus Friedl <markus@openbsd.org>
4 *
5 * Permission to use, copy, modify, and distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16 */
17
18#include <sys/types.h>
19#include <string.h>
20
21#include "cipher-aesctr.h"
22
23/*
24 * increment counter 'ctr',
25 * the counter is of size 'len' bytes and stored in network-byte-order.
26 * (LSB at ctr[len-1], MSB at ctr[0])
27 */
28static __inline__ void
29aesctr_inc(u8 *ctr, u32 len)
30{
31 ssize_t i;
32
33#ifndef CONSTANT_TIME_INCREMENT
34 for (i = len - 1; i >= 0; i--)
35 if (++ctr[i]) /* continue on overflow */
36 return;
37#else
38 u8 x, add = 1;
39
40 for (i = len - 1; i >= 0; i--) {
41 ctr[i] += add;
42 /* constant time for: x = ctr[i] ? 1 : 0 */
43 x = ctr[i];
44 x = (x | (x >> 4)) & 0xf;
45 x = (x | (x >> 2)) & 0x3;
46 x = (x | (x >> 1)) & 0x1;
47 add *= (x^1);
48 }
49#endif
50}
51
52void
53aesctr_keysetup(aesctr_ctx *x,const u8 *k,u32 kbits,u32 ivbits)
54{
55 x->rounds = rijndaelKeySetupEnc(x->ek, k, kbits);
56}
57
58void
59aesctr_ivsetup(aesctr_ctx *x,const u8 *iv)
60{
61 memcpy(x->ctr, iv, AES_BLOCK_SIZE);
62}
63
64void
65aesctr_encrypt_bytes(aesctr_ctx *x,const u8 *m,u8 *c,u32 bytes)
66{
67 u32 n = 0;
68 u8 buf[AES_BLOCK_SIZE];
69
70 while ((bytes--) > 0) {
71 if (n == 0) {
72 rijndaelEncrypt(x->ek, x->rounds, x->ctr, buf);
73 aesctr_inc(x->ctr, AES_BLOCK_SIZE);
74 }
75 *(c++) = *(m++) ^ buf[n];
76 n = (n + 1) % AES_BLOCK_SIZE;
77 }
78}