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cipher-aesctr.c revision 1.1.1.3 
      1 /* $OpenBSD: cipher-aesctr.c,v 1.3 2026/02/09 22:15:45 dtucker 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