rsa_ssl.c revision 344604 
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 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 (flen < 10) {
120        RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
121        return (-1);
122    }
123
124    em = OPENSSL_malloc(num);
125    if (em == NULL) {
126        RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, ERR_R_MALLOC_FAILURE);
127        return -1;
128    }
129    /*
130     * Caller is encouraged to pass zero-padded message created with
131     * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
132     * bounds, it's impossible to have an invariant memory access pattern
133     * in case |from| was not zero-padded in advance.
134     */
135    for (from += flen, em += num, i = 0; i < num; i++) {
136        mask = ~constant_time_is_zero(flen);
137        flen -= 1 & mask;
138        from -= 1 & mask;
139        *--em = *from & mask;
140    }
141    from = em;
142
143    good = constant_time_is_zero(from[0]);
144    good &= constant_time_eq(from[1], 2);
145    err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);
146    mask = ~good;
147
148    /* scan over padding data */
149    found_zero_byte = 0;
150    threes_in_row = 0;
151    for (i = 2; i < num; i++) {
152        unsigned int equals0 = constant_time_is_zero(from[i]);
153
154        zero_index = constant_time_select_int(~found_zero_byte & equals0,
155                                              i, zero_index);
156        found_zero_byte |= equals0;
157
158        threes_in_row += 1 & ~found_zero_byte;
159        threes_in_row &= found_zero_byte | constant_time_eq(from[i], 3);
160    }
161
162    /*
163     * PS must be at least 8 bytes long, and it starts two bytes into |from|.
164     * If we never found a 0-byte, then |zero_index| is 0 and the check
165     * also fails.
166     */
167    good &= constant_time_ge(zero_index, 2 + 8);
168    err = constant_time_select_int(mask | good, err,
169                                   RSA_R_NULL_BEFORE_BLOCK_MISSING);
170    mask = ~good;
171
172    good &= constant_time_lt(threes_in_row, 8);
173    err = constant_time_select_int(mask | good, err,
174                                   RSA_R_SSLV3_ROLLBACK_ATTACK);
175    mask = ~good;
176
177    /*
178     * Skip the zero byte. This is incorrect if we never found a zero-byte
179     * but in this case we also do not copy the message out.
180     */
181    msg_index = zero_index + 1;
182    mlen = num - msg_index;
183
184    /*
185     * For good measure, do this check in constant time as well.
186     */
187    good &= constant_time_ge(tlen, mlen);
188    err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);
189
190    /*
191     * Even though we can't fake result's length, we can pretend copying
192     * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |num|
193     * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,
194     * where |mlen'| is "saturated" |mlen| value. Deducing information
195     * about failure or |mlen| would take attacker's ability to observe
196     * memory access pattern with byte granularity *as it occurs*. It
197     * should be noted that failure is indistinguishable from normal
198     * operation if |tlen| is fixed by protocol.
199     */
200    tlen = constant_time_select_int(constant_time_lt(num, tlen), num, tlen);
201    msg_index = constant_time_select_int(good, msg_index, num - tlen);
202    mlen = num - msg_index;
203    for (from += msg_index, mask = good, i = 0; i < tlen; i++) {
204        unsigned int equals = constant_time_eq(i, mlen);
205
206        from -= tlen & equals;  /* if (i == mlen) rewind   */
207        mask &= mask ^ equals;  /* if (i == mlen) mask = 0 */
208        to[i] = constant_time_select_8(mask, from[i], to[i]);
209    }
210
211    OPENSSL_cleanse(em, num);
212    OPENSSL_free(em);
213    RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, err);
214    err_clear_last_constant_time(1 & good);
215
216    return constant_time_select_int(good, mlen, -1);
217}
218