aes_ctr.c revision 296465 
1/* crypto/aes/aes_ctr.c -*- mode:C; c-file-style: "eay" -*- */
2/* ====================================================================
3 * Copyright (c) 1998-2002 The OpenSSL Project.  All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 *
9 * 1. Redistributions of source code must retain the above copyright
10 *    notice, this list of conditions and the following disclaimer.
11 *
12 * 2. Redistributions in binary form must reproduce the above copyright
13 *    notice, this list of conditions and the following disclaimer in
14 *    the documentation and/or other materials provided with the
15 *    distribution.
16 *
17 * 3. All advertising materials mentioning features or use of this
18 *    software must display the following acknowledgment:
19 *    "This product includes software developed by the OpenSSL Project
20 *    for use in the OpenSSL Toolkit. (http://www.openssl.org/)"
21 *
22 * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
23 *    endorse or promote products derived from this software without
24 *    prior written permission. For written permission, please contact
25 *    openssl-core@openssl.org.
26 *
27 * 5. Products derived from this software may not be called "OpenSSL"
28 *    nor may "OpenSSL" appear in their names without prior written
29 *    permission of the OpenSSL Project.
30 *
31 * 6. Redistributions of any form whatsoever must retain the following
32 *    acknowledgment:
33 *    "This product includes software developed by the OpenSSL Project
34 *    for use in the OpenSSL Toolkit (http://www.openssl.org/)"
35 *
36 * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
37 * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
38 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
39 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
40 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
41 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
42 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
43 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
44 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
45 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
46 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
47 * OF THE POSSIBILITY OF SUCH DAMAGE.
48 * ====================================================================
49 *
50 */
51
52#ifndef AES_DEBUG
53# ifndef NDEBUG
54#  define NDEBUG
55# endif
56#endif
57#include <assert.h>
58
59#include <openssl/aes.h>
60#include "aes_locl.h"
61
62/*
63 * NOTE: the IV/counter CTR mode is big-endian.  The rest of the AES code is
64 * endian-neutral.
65 */
66
67/* increment counter (128-bit int) by 1 */
68static void AES_ctr128_inc(unsigned char *counter)
69{
70    unsigned long c;
71
72    /* Grab bottom dword of counter and increment */
73    c = GETU32(counter + 12);
74    c++;
75    c &= 0xFFFFFFFF;
76    PUTU32(counter + 12, c);
77
78    /* if no overflow, we're done */
79    if (c)
80        return;
81
82    /* Grab 1st dword of counter and increment */
83    c = GETU32(counter + 8);
84    c++;
85    c &= 0xFFFFFFFF;
86    PUTU32(counter + 8, c);
87
88    /* if no overflow, we're done */
89    if (c)
90        return;
91
92    /* Grab 2nd dword of counter and increment */
93    c = GETU32(counter + 4);
94    c++;
95    c &= 0xFFFFFFFF;
96    PUTU32(counter + 4, c);
97
98    /* if no overflow, we're done */
99    if (c)
100        return;
101
102    /* Grab top dword of counter and increment */
103    c = GETU32(counter + 0);
104    c++;
105    c &= 0xFFFFFFFF;
106    PUTU32(counter + 0, c);
107}
108
109/*
110 * The input encrypted as though 128bit counter mode is being used.  The
111 * extra state information to record how much of the 128bit block we have
112 * used is contained in *num, and the encrypted counter is kept in
113 * ecount_buf.  Both *num and ecount_buf must be initialised with zeros
114 * before the first call to AES_ctr128_encrypt(). This algorithm assumes
115 * that the counter is in the x lower bits of the IV (ivec), and that the
116 * application has full control over overflow and the rest of the IV.  This
117 * implementation takes NO responsability for checking that the counter
118 * doesn't overflow into the rest of the IV when incremented.
119 */
120void AES_ctr128_encrypt(const unsigned char *in, unsigned char *out,
121                        const unsigned long length, const AES_KEY *key,
122                        unsigned char ivec[AES_BLOCK_SIZE],
123                        unsigned char ecount_buf[AES_BLOCK_SIZE],
124                        unsigned int *num)
125{
126
127    unsigned int n;
128    unsigned long l = length;
129
130    assert(in && out && key && counter && num);
131    assert(*num < AES_BLOCK_SIZE);
132
133    n = *num;
134
135    while (l--) {
136        if (n == 0) {
137            AES_encrypt(ivec, ecount_buf, key);
138            AES_ctr128_inc(ivec);
139        }
140        *(out++) = *(in++) ^ ecount_buf[n];
141        n = (n + 1) % AES_BLOCK_SIZE;
142    }
143
144    *num = n;
145}
146