aboutsummaryrefslogtreecommitdiffstats
path: root/crypto/rsa/rsa_ssl.c
blob: c5654595fb2f30fabf955856dcac02cb814f6200 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
/*
 * Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
 *
 * Licensed under the OpenSSL license (the "License").  You may not use
 * this file except in compliance with the License.  You can obtain a copy
 * in the file LICENSE in the source distribution or at
 * https://www.openssl.org/source/license.html
 */

#include <stdio.h>
#include "internal/cryptlib.h"
#include <openssl/bn.h>
#include <openssl/rsa.h>
#include <openssl/rand.h>
#include "internal/constant_time_locl.h"

int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
                           const unsigned char *from, int flen)
{
    int i, j;
    unsigned char *p;

    if (flen > (tlen - 11)) {
        RSAerr(RSA_F_RSA_PADDING_ADD_SSLV23,
               RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
        return 0;
    }

    p = (unsigned char *)to;

    *(p++) = 0;
    *(p++) = 2;                 /* Public Key BT (Block Type) */

    /* pad out with non-zero random data */
    j = tlen - 3 - 8 - flen;

    if (RAND_bytes(p, j) <= 0)
        return 0;
    for (i = 0; i < j; i++) {
        if (*p == '\0')
            do {
                if (RAND_bytes(p, 1) <= 0)
                    return 0;
            } while (*p == '\0');
        p++;
    }

    memset(p, 3, 8);
    p += 8;
    *(p++) = '\0';

    memcpy(p, from, (unsigned int)flen);
    return 1;
}

/*
 * Copy of RSA_padding_check_PKCS1_type_2 with a twist that rejects padding
 * if nul delimiter is preceded by 8 consecutive 0x03 bytes. It also
 * preserves error code reporting for backward compatibility.
 */
int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
                             const unsigned char *from, int flen, int num)
{
    int i;
    /* |em| is the encoded message, zero-padded to exactly |num| bytes */
    unsigned char *em = NULL;
    unsigned int good, found_zero_byte, mask, threes_in_row;
    int zero_index = 0, msg_index, mlen = -1, err;

    if (flen < 10) {
        RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
        return -1;
    }

    em = OPENSSL_malloc(num);
    if (em == NULL) {
        RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, ERR_R_MALLOC_FAILURE);
        return -1;
    }
    /*
     * Caller is encouraged to pass zero-padded message created with
     * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
     * bounds, it's impossible to have an invariant memory access pattern
     * in case |from| was not zero-padded in advance.
     */
    for (from += flen, em += num, i = 0; i < num; i++) {
        mask = ~constant_time_is_zero(flen);
        flen -= 1 & mask;
        from -= 1 & mask;
        *--em = *from & mask;
    }
    from = em;

    good = constant_time_is_zero(from[0]);
    good &= constant_time_eq(from[1], 2);
    err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);
    mask = ~good;

    /* scan over padding data */
    found_zero_byte = 0;
    threes_in_row = 0;
    for (i = 2; i < num; i++) {
        unsigned int equals0 = constant_time_is_zero(from[i]);

        zero_index = constant_time_select_int(~found_zero_byte & equals0,
                                              i, zero_index);
        found_zero_byte |= equals0;

        threes_in_row += 1 & ~found_zero_byte;
        threes_in_row &= found_zero_byte | constant_time_eq(from[i], 3);
    }

    /*
     * PS must be at least 8 bytes long, and it starts two bytes into |from|.
     * If we never found a 0-byte, then |zero_index| is 0 and the check
     * also fails.
     */
    good &= constant_time_ge(zero_index, 2 + 8);
    err = constant_time_select_int(mask | good, err,
                                   RSA_R_NULL_BEFORE_BLOCK_MISSING);
    mask = ~good;

    good &= constant_time_lt(threes_in_row, 8);
    err = constant_time_select_int(mask | good, err,
                                   RSA_R_SSLV3_ROLLBACK_ATTACK);
    mask = ~good;

    /*
     * Skip the zero byte. This is incorrect if we never found a zero-byte
     * but in this case we also do not copy the message out.
     */
    msg_index = zero_index + 1;
    mlen = num - msg_index;

    /*
     * For good measure, do this check in constant time as well.
     */
    good &= constant_time_ge(tlen, mlen);
    err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);

    /*
     * Even though we can't fake result's length, we can pretend copying
     * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |num|
     * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,
     * where |mlen'| is "saturated" |mlen| value. Deducing information
     * about failure or |mlen| would take attacker's ability to observe
     * memory access pattern with byte granularity *as it occurs*. It
     * should be noted that failure is indistinguishable from normal
     * operation if |tlen| is fixed by protocol.
     */
    tlen = constant_time_select_int(constant_time_lt(num, tlen), num, tlen);
    msg_index = constant_time_select_int(good, msg_index, num - tlen);
    mlen = num - msg_index;
    for (from += msg_index, mask = good, i = 0; i < tlen; i++) {
        unsigned int equals = constant_time_eq(i, mlen);

        from -= tlen & equals;  /* if (i == mlen) rewind   */
        mask &= mask ^ equals;  /* if (i == mlen) mask = 0 */
        to[i] = constant_time_select_8(mask, from[i], to[i]);
    }

    OPENSSL_clear_free(em, num);
    RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, err);
    err_clear_last_constant_time(1 & good);

    return constant_time_select_int(good, mlen, -1);
}