rsa_ssl.c revision 348343 
1/* crypto/rsa/rsa_ssl.c */
2/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
3 * All rights reserved.
4 *
5 * This package is an SSL implementation written
6 * by Eric Young (eay@cryptsoft.com).
7 * The implementation was written so as to conform with Netscapes SSL.
8 *
9 * This library is free for commercial and non-commercial use as long as
10 * the following conditions are aheared to.  The following conditions
11 * apply to all code found in this distribution, be it the RC4, RSA,
12 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation
13 * included with this distribution is covered by the same copyright terms
14 * except that the holder is Tim Hudson (tjh@cryptsoft.com).
15 *
16 * Copyright remains Eric Young's, and as such any Copyright notices in
17 * the code are not to be removed.
18 * If this package is used in a product, Eric Young should be given attribution
19 * as the author of the parts of the library used.
20 * This can be in the form of a textual message at program startup or
21 * in documentation (online or textual) provided with the package.
22 *
23 * Redistribution and use in source and binary forms, with or without
24 * modification, are permitted provided that the following conditions
25 * are met:
26 * 1. Redistributions of source code must retain the copyright
27 *    notice, this list of conditions and the following disclaimer.
28 * 2. Redistributions in binary form must reproduce the above copyright
29 *    notice, this list of conditions and the following disclaimer in the
30 *    documentation and/or other materials provided with the distribution.
31 * 3. All advertising materials mentioning features or use of this software
32 *    must display the following acknowledgement:
33 *    "This product includes cryptographic software written by
34 *     Eric Young (eay@cryptsoft.com)"
35 *    The word 'cryptographic' can be left out if the rouines from the library
36 *    being used are not cryptographic related :-).
37 * 4. If you include any Windows specific code (or a derivative thereof) from
38 *    the apps directory (application code) you must include an acknowledgement:
39 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
40 *
41 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
42 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
43 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
44 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
45 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
46 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
47 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
48 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
49 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
50 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
51 * SUCH DAMAGE.
52 *
53 * The licence and distribution terms for any publically available version or
54 * derivative of this code cannot be changed.  i.e. this code cannot simply be
55 * copied and put under another distribution licence
56 * [including the GNU Public Licence.]
57 */
58
59#include <stdio.h>
60#include "cryptlib.h"
61#include <openssl/bn.h>
62#include <openssl/rsa.h>
63#include <openssl/rand.h>
64#include "constant_time_locl.h"
65
66int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
67                           const unsigned char *from, int flen)
68{
69    int i, j;
70    unsigned char *p;
71
72    if (flen > (tlen - 11)) {
73        RSAerr(RSA_F_RSA_PADDING_ADD_SSLV23,
74               RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
75        return (0);
76    }
77
78    p = (unsigned char *)to;
79
80    *(p++) = 0;
81    *(p++) = 2;                 /* Public Key BT (Block Type) */
82
83    /* pad out with non-zero random data */
84    j = tlen - 3 - 8 - flen;
85
86    if (RAND_bytes(p, j) <= 0)
87        return (0);
88    for (i = 0; i < j; i++) {
89        if (*p == '\0')
90            do {
91                if (RAND_bytes(p, 1) <= 0)
92                    return (0);
93            } while (*p == '\0');
94        p++;
95    }
96
97    memset(p, 3, 8);
98    p += 8;
99    *(p++) = '\0';
100
101    memcpy(p, from, (unsigned int)flen);
102    return (1);
103}
104
105/*
106 * Copy of RSA_padding_check_PKCS1_type_2 with a twist that rejects padding
107 * if nul delimiter is not preceded by 8 consecutive 0x03 bytes. It also
108 * preserves error code reporting for backward compatibility.
109 */
110int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
111                             const unsigned char *from, int flen, int num)
112{
113    int i;
114    /* |em| is the encoded message, zero-padded to exactly |num| bytes */
115    unsigned char *em = NULL;
116    unsigned int good, found_zero_byte, mask, threes_in_row;
117    int zero_index = 0, msg_index, mlen = -1, err;
118
119    if (tlen <= 0 || flen <= 0)
120        return -1;
121
122    if (flen > num || num < 11) {
123        RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
124        return (-1);
125    }
126
127    em = OPENSSL_malloc(num);
128    if (em == NULL) {
129        RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, ERR_R_MALLOC_FAILURE);
130        return -1;
131    }
132    /*
133     * Caller is encouraged to pass zero-padded message created with
134     * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
135     * bounds, it's impossible to have an invariant memory access pattern
136     * in case |from| was not zero-padded in advance.
137     */
138    for (from += flen, em += num, i = 0; i < num; i++) {
139        mask = ~constant_time_is_zero(flen);
140        flen -= 1 & mask;
141        from -= 1 & mask;
142        *--em = *from & mask;
143    }
144
145    good = constant_time_is_zero(em[0]);
146    good &= constant_time_eq(em[1], 2);
147    err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);
148    mask = ~good;
149
150    /* scan over padding data */
151    found_zero_byte = 0;
152    threes_in_row = 0;
153    for (i = 2; i < num; i++) {
154        unsigned int equals0 = constant_time_is_zero(em[i]);
155
156        zero_index = constant_time_select_int(~found_zero_byte & equals0,
157                                              i, zero_index);
158        found_zero_byte |= equals0;
159
160        threes_in_row += 1 & ~found_zero_byte;
161        threes_in_row &= found_zero_byte | constant_time_eq(em[i], 3);
162    }
163
164    /*
165     * PS must be at least 8 bytes long, and it starts two bytes into |em|.
166     * If we never found a 0-byte, then |zero_index| is 0 and the check
167     * also fails.
168     */
169    good &= constant_time_ge(zero_index, 2 + 8);
170    err = constant_time_select_int(mask | good, err,
171                                   RSA_R_NULL_BEFORE_BLOCK_MISSING);
172    mask = ~good;
173
174    good &= constant_time_ge(threes_in_row, 8);
175    err = constant_time_select_int(mask | good, err,
176                                   RSA_R_SSLV3_ROLLBACK_ATTACK);
177    mask = ~good;
178
179    /*
180     * Skip the zero byte. This is incorrect if we never found a zero-byte
181     * but in this case we also do not copy the message out.
182     */
183    msg_index = zero_index + 1;
184    mlen = num - msg_index;
185
186    /*
187     * For good measure, do this check in constant time as well.
188     */
189    good &= constant_time_ge(tlen, mlen);
190    err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);
191
192    /*
193     * Move the result in-place by |num|-11-|mlen| bytes to the left.
194     * Then if |good| move |mlen| bytes from |em|+11 to |to|.
195     * Otherwise leave |to| unchanged.
196     * Copy the memory back in a way that does not reveal the size of
197     * the data being copied via a timing side channel. This requires copying
198     * parts of the buffer multiple times based on the bits set in the real
199     * length. Clear bits do a non-copy with identical access pattern.
200     * The loop below has overall complexity of O(N*log(N)).
201     */
202    tlen = constant_time_select_int(constant_time_lt(num - 11, tlen),
203                                    num - 11, tlen);
204    for (msg_index = 1; msg_index < num - 11; msg_index <<= 1) {
205        mask = ~constant_time_eq(msg_index & (num - 11 - mlen), 0);
206        for (i = 11; i < num - msg_index; i++)
207            em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);
208    }
209    for (i = 0; i < tlen; i++) {
210        mask = good & constant_time_lt(i, mlen);
211        to[i] = constant_time_select_8(mask, em[i + 11], to[i]);
212    }
213
214    OPENSSL_cleanse(em, num);
215    OPENSSL_free(em);
216    RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, err);
217    err_clear_last_constant_time(1 & good);
218
219    return constant_time_select_int(good, mlen, -1);
220}
221