xref: /openssh-portable/cipher-aesctr.c (revision a47ead7c)
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  */
32 static inline void
aesctr_inc(u8 * ctr,u32 len)33 aesctr_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 
56 void
aesctr_keysetup(aesctr_ctx * x,const u8 * k,u32 kbits,u32 ivbits)57 aesctr_keysetup(aesctr_ctx *x,const u8 *k,u32 kbits,u32 ivbits)
58 {
59 	x->rounds = rijndaelKeySetupEnc(x->ek, k, kbits);
60 }
61 
62 void
aesctr_ivsetup(aesctr_ctx * x,const u8 * iv)63 aesctr_ivsetup(aesctr_ctx *x,const u8 *iv)
64 {
65 	memcpy(x->ctr, iv, AES_BLOCK_SIZE);
66 }
67 
68 void
aesctr_encrypt_bytes(aesctr_ctx * x,const u8 * m,u8 * c,u32 bytes)69 aesctr_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