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