xref: /openssh-portable/cipher-aesctr.c (revision 1221b220)
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 #ifndef WITH_OPENSSL
22 
23 #include "cipher-aesctr.h"
24 
25 /*
26  * increment counter 'ctr',
27  * the counter is of size 'len' bytes and stored in network-byte-order.
28  * (LSB at ctr[len-1], MSB at ctr[0])
29  */
30 static inline void
31 aesctr_inc(u8 *ctr, u32 len)
32 {
33 	ssize_t i;
34 
35 #ifndef CONSTANT_TIME_INCREMENT
36 	for (i = len - 1; i >= 0; i--)
37 		if (++ctr[i])	/* continue on overflow */
38 			return;
39 #else
40 	u8 x, add = 1;
41 
42 	for (i = len - 1; i >= 0; i--) {
43 		ctr[i] += add;
44 		/* constant time for: x = ctr[i] ? 1 : 0 */
45 		x = ctr[i];
46 		x = (x | (x >> 4)) & 0xf;
47 		x = (x | (x >> 2)) & 0x3;
48 		x = (x | (x >> 1)) & 0x1;
49 		add *= (x^1);
50 	}
51 #endif
52 }
53 
54 void
55 aesctr_keysetup(aesctr_ctx *x,const u8 *k,u32 kbits,u32 ivbits)
56 {
57 	x->rounds = rijndaelKeySetupEnc(x->ek, k, kbits);
58 }
59 
60 void
61 aesctr_ivsetup(aesctr_ctx *x,const u8 *iv)
62 {
63 	memcpy(x->ctr, iv, AES_BLOCK_SIZE);
64 }
65 
66 void
67 aesctr_encrypt_bytes(aesctr_ctx *x,const u8 *m,u8 *c,u32 bytes)
68 {
69 	u32 n = 0;
70 	u8 buf[AES_BLOCK_SIZE];
71 
72 	while ((bytes--) > 0) {
73 		if (n == 0) {
74 			rijndaelEncrypt(x->ek, x->rounds, x->ctr, buf);
75 			aesctr_inc(x->ctr, AES_BLOCK_SIZE);
76 		}
77 		*(c++) = *(m++) ^ buf[n];
78 		n = (n + 1) % AES_BLOCK_SIZE;
79 	}
80 }
81 #endif /* !WITH_OPENSSL */
82