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79 lines
2.0 KiB
C
79 lines
2.0 KiB
C
/* $OpenBSD: cipher-aesctr.c,v 1.2 2015/01/14 10:24:42 markus Exp $ */
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/*
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* Copyright (c) 2003 Markus Friedl. All rights reserved.
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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#include <sys/types.h>
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#include <string.h>
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#include "cipher-aesctr.h"
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/*
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* increment counter 'ctr',
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* the counter is of size 'len' bytes and stored in network-byte-order.
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* (LSB at ctr[len-1], MSB at ctr[0])
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*/
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static __inline__ void
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aesctr_inc(u8 *ctr, u32 len)
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{
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ssize_t i;
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#ifndef CONSTANT_TIME_INCREMENT
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for (i = len - 1; i >= 0; i--)
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if (++ctr[i]) /* continue on overflow */
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return;
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#else
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u8 x, add = 1;
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for (i = len - 1; i >= 0; i--) {
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ctr[i] += add;
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/* constant time for: x = ctr[i] ? 1 : 0 */
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x = ctr[i];
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x = (x | (x >> 4)) & 0xf;
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x = (x | (x >> 2)) & 0x3;
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x = (x | (x >> 1)) & 0x1;
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add *= (x^1);
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}
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#endif
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}
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void
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aesctr_keysetup(aesctr_ctx *x,const u8 *k,u32 kbits,u32 ivbits)
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{
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x->rounds = rijndaelKeySetupEnc(x->ek, k, kbits);
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}
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void
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aesctr_ivsetup(aesctr_ctx *x,const u8 *iv)
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{
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memcpy(x->ctr, iv, AES_BLOCK_SIZE);
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}
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void
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aesctr_encrypt_bytes(aesctr_ctx *x,const u8 *m,u8 *c,u32 bytes)
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{
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u32 n = 0;
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u8 buf[AES_BLOCK_SIZE];
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while ((bytes--) > 0) {
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if (n == 0) {
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rijndaelEncrypt(x->ek, x->rounds, x->ctr, buf);
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aesctr_inc(x->ctr, AES_BLOCK_SIZE);
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}
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*(c++) = *(m++) ^ buf[n];
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n = (n + 1) % AES_BLOCK_SIZE;
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}
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}
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