1/*
2 * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (the "License"). You may not use
5 * this file except in compliance with the License. You can obtain a copy
6 * in the file LICENSE in the source distribution or at
7 * https://www.openssl.org/source/license.html
8 */
9
10#include <stdio.h>
11#include "internal/cryptlib.h"
12#include <openssl/bn.h>
13#include <openssl/rsa.h>
14#include <openssl/rand.h>
15#include "internal/constant_time.h"
16
17int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
18 const unsigned char *from, int flen)
19{
20 int i, j;
21 unsigned char *p;
22
23 if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
24 RSAerr(RSA_F_RSA_PADDING_ADD_SSLV23,
25 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
26 return 0;
27 }
28
29 p = (unsigned char *)to;
30
31 *(p++) = 0;
32 *(p++) = 2; /* Public Key BT (Block Type) */
33
34 /* pad out with non-zero random data */
35 j = tlen - 3 - 8 - flen;
36
37 if (RAND_bytes(p, j) <= 0)
38 return 0;
39 for (i = 0; i < j; i++) {
40 if (*p == '\0')
41 do {
42 if (RAND_bytes(p, 1) <= 0)
43 return 0;
44 } while (*p == '\0');
45 p++;
46 }
47
48 memset(p, 3, 8);
49 p += 8;
50 *(p++) = '\0';
51
52 memcpy(p, from, (unsigned int)flen);
53 return 1;
54}
55
56/*
57 * Copy of RSA_padding_check_PKCS1_type_2 with a twist that rejects padding
58 * if nul delimiter is not preceded by 8 consecutive 0x03 bytes. It also
59 * preserves error code reporting for backward compatibility.
60 */
61int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
62 const unsigned char *from, int flen, int num)
63{
64 int i;
65 /* |em| is the encoded message, zero-padded to exactly |num| bytes */
66 unsigned char *em = NULL;
67 unsigned int good, found_zero_byte, mask, threes_in_row;
68 int zero_index = 0, msg_index, mlen = -1, err;
69
70 if (tlen <= 0 || flen <= 0)
71 return -1;
72
73 if (flen > num || num < RSA_PKCS1_PADDING_SIZE) {
74 RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
75 return -1;
76 }
77
78 em = OPENSSL_malloc(num);
79 if (em == NULL) {
80 RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, ERR_R_MALLOC_FAILURE);
81 return -1;
82 }
83 /*
84 * Caller is encouraged to pass zero-padded message created with
85 * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
86 * bounds, it's impossible to have an invariant memory access pattern
87 * in case |from| was not zero-padded in advance.
88 */
89 for (from += flen, em += num, i = 0; i < num; i++) {
90 mask = ~constant_time_is_zero(flen);
91 flen -= 1 & mask;
92 from -= 1 & mask;
93 *--em = *from & mask;
94 }
95
96 good = constant_time_is_zero(em[0]);
97 good &= constant_time_eq(em[1], 2);
98 err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);
99 mask = ~good;
100
101 /* scan over padding data */
102 found_zero_byte = 0;
103 threes_in_row = 0;
104 for (i = 2; i < num; i++) {
105 unsigned int equals0 = constant_time_is_zero(em[i]);
106
107 zero_index = constant_time_select_int(~found_zero_byte & equals0,
108 i, zero_index);
109 found_zero_byte |= equals0;
110
111 threes_in_row += 1 & ~found_zero_byte;
112 threes_in_row &= found_zero_byte | constant_time_eq(em[i], 3);
113 }
114
115 /*
116 * PS must be at least 8 bytes long, and it starts two bytes into |em|.
117 * If we never found a 0-byte, then |zero_index| is 0 and the check
118 * also fails.
119 */
120 good &= constant_time_ge(zero_index, 2 + 8);
121 err = constant_time_select_int(mask | good, err,
122 RSA_R_NULL_BEFORE_BLOCK_MISSING);
123 mask = ~good;
124
125 good &= constant_time_ge(threes_in_row, 8);
126 err = constant_time_select_int(mask | good, err,
127 RSA_R_SSLV3_ROLLBACK_ATTACK);
128 mask = ~good;
129
130 /*
131 * Skip the zero byte. This is incorrect if we never found a zero-byte
132 * but in this case we also do not copy the message out.
133 */
134 msg_index = zero_index + 1;
135 mlen = num - msg_index;
136
137 /*
138 * For good measure, do this check in constant time as well.
139 */
140 good &= constant_time_ge(tlen, mlen);
141 err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);
142
143 /*
144 * Move the result in-place by |num|-RSA_PKCS1_PADDING_SIZE-|mlen| bytes to the left.
145 * Then if |good| move |mlen| bytes from |em|+RSA_PKCS1_PADDING_SIZE to |to|.
146 * Otherwise leave |to| unchanged.
147 * Copy the memory back in a way that does not reveal the size of
148 * the data being copied via a timing side channel. This requires copying
149 * parts of the buffer multiple times based on the bits set in the real
150 * length. Clear bits do a non-copy with identical access pattern.
151 * The loop below has overall complexity of O(N*log(N)).
152 */
153 tlen = constant_time_select_int(constant_time_lt(num - RSA_PKCS1_PADDING_SIZE, tlen),
154 num - RSA_PKCS1_PADDING_SIZE, tlen);
155 for (msg_index = 1; msg_index < num - RSA_PKCS1_PADDING_SIZE; msg_index <<= 1) {
156 mask = ~constant_time_eq(msg_index & (num - RSA_PKCS1_PADDING_SIZE - mlen), 0);
157 for (i = RSA_PKCS1_PADDING_SIZE; i < num - msg_index; i++)
158 em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);
159 }
160 for (i = 0; i < tlen; i++) {
161 mask = good & constant_time_lt(i, mlen);
162 to[i] = constant_time_select_8(mask, em[i + RSA_PKCS1_PADDING_SIZE], to[i]);
163 }
164
165 OPENSSL_clear_free(em, num);
166 RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, err);
167 err_clear_last_constant_time(1 & good);
168
169 return constant_time_select_int(good, mlen, -1);
170}
171