cipher-aesctr.c revision 323134 
1/* $OpenBSD: cipher-aesctr.c,v 1.2 2015/01/14 10:24:42 markus Exp $ */
2/*
3 * Copyright (c) 2003 Markus Friedl.  All rights reserved.
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 "includes.h"
19
20#include <sys/types.h>
21#include <string.h>
22
23#ifndef WITH_OPENSSL
24
25#include "cipher-aesctr.h"
26
27/*
28 * increment counter 'ctr',
29 * the counter is of size 'len' bytes and stored in network-byte-order.
30 * (LSB at ctr[len-1], MSB at ctr[0])
31 */
32static inline void
33aesctr_inc(u8 *ctr, u32 len)
34{
35	ssize_t i;
36
37#ifndef CONSTANT_TIME_INCREMENT
38	for (i = len - 1; i >= 0; i--)
39		if (++ctr[i])	/* continue on overflow */
40			return;
41#else
42	u8 x, add = 1;
43
44	for (i = len - 1; i >= 0; i--) {
45		ctr[i] += add;
46		/* constant time for: x = ctr[i] ? 1 : 0 */
47		x = ctr[i];
48		x = (x | (x >> 4)) & 0xf;
49		x = (x | (x >> 2)) & 0x3;
50		x = (x | (x >> 1)) & 0x1;
51		add *= (x^1);
52	}
53#endif
54}
55
56void
57aesctr_keysetup(aesctr_ctx *x,const u8 *k,u32 kbits,u32 ivbits)
58{
59	x->rounds = rijndaelKeySetupEnc(x->ek, k, kbits);
60}
61
62void
63aesctr_ivsetup(aesctr_ctx *x,const u8 *iv)
64{
65	memcpy(x->ctr, iv, AES_BLOCK_SIZE);
66}
67
68void
69aesctr_encrypt_bytes(aesctr_ctx *x,const u8 *m,u8 *c,u32 bytes)
70{
71	u32 n = 0;
72	u8 buf[AES_BLOCK_SIZE];
73
74	while ((bytes--) > 0) {
75		if (n == 0) {
76			rijndaelEncrypt(x->ek, x->rounds, x->ctr, buf);
77			aesctr_inc(x->ctr, AES_BLOCK_SIZE);
78		}
79		*(c++) = *(m++) ^ buf[n];
80		n = (n + 1) % AES_BLOCK_SIZE;
81	}
82}
83#endif /* !WITH_OPENSSL */
84