xref: /openssh-portable/cipher-aesctr.c (revision 60c2c4ea)
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 <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  */
28 static __inline__ void
29 aesctr_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 
52 void
53 aesctr_keysetup(aesctr_ctx *x,const u8 *k,u32 kbits,u32 ivbits)
54 {
55 	x->rounds = rijndaelKeySetupEnc(x->ek, k, kbits);
56 }
57 
58 void
59 aesctr_ivsetup(aesctr_ctx *x,const u8 *iv)
60 {
61 	memcpy(x->ctr, iv, AES_BLOCK_SIZE);
62 }
63 
64 void
65 aesctr_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 }
79