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cipher-aesctr.c revision 1.3 
      1 /*	$NetBSD: cipher-aesctr.c,v 1.3 2026/04/08 18:58:40 christos Exp $	*/
      2 /* $OpenBSD: cipher-aesctr.c,v 1.3 2026/02/09 22:15:45 dtucker Exp $ */
      3 
      4 /*
      5  * Copyright (c) 2003 Markus Friedl.  All rights reserved.
      6  *
      7  * Permission to use, copy, modify, and distribute this software for any
      8  * purpose with or without fee is hereby granted, provided that the above
      9  * copyright notice and this permission notice appear in all copies.
     10  *
     11  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
     12  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
     13  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
     14  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
     15  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
     16  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
     17  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
     18  */
     19 #include "includes.h"
     20 __RCSID("$NetBSD: cipher-aesctr.c,v 1.3 2026/04/08 18:58:40 christos Exp $");
     21 
     22 #include <sys/types.h>
     23 #include <string.h>
     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
     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
     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
     63 aesctr_ivsetup(aesctr_ctx *x,const u8 *iv)
     64 {
     65 	memcpy(x->ctr, iv, AES_BLOCK_SIZE);
     66 }
     67 
     68 void
     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