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 | |
17 | int 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 | */ |
61 | int 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 | |