2 * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
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
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_locl.h"
17 int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
18 const unsigned char *from, int flen)
23 if (flen > (tlen - 11)) {
24 RSAerr(RSA_F_RSA_PADDING_ADD_SSLV23,
25 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
29 p = (unsigned char *)to;
32 *(p++) = 2; /* Public Key BT (Block Type) */
34 /* pad out with non-zero random data */
35 j = tlen - 3 - 8 - flen;
37 if (RAND_bytes(p, j) <= 0)
39 for (i = 0; i < j; i++) {
42 if (RAND_bytes(p, 1) <= 0)
52 memcpy(p, from, (unsigned int)flen);
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.
61 int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
62 const unsigned char *from, int flen, int num)
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;
70 if (tlen <= 0 || flen <= 0)
73 if (flen > num || num < 11) {
74 RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
78 em = OPENSSL_malloc(num);
80 RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, ERR_R_MALLOC_FAILURE);
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.
89 for (from += flen, em += num, i = 0; i < num; i++) {
90 mask = ~constant_time_is_zero(flen);
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);
101 /* scan over padding data */
104 for (i = 2; i < num; i++) {
105 unsigned int equals0 = constant_time_is_zero(em[i]);
107 zero_index = constant_time_select_int(~found_zero_byte & equals0,
109 found_zero_byte |= equals0;
111 threes_in_row += 1 & ~found_zero_byte;
112 threes_in_row &= found_zero_byte | constant_time_eq(em[i], 3);
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
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);
125 good &= constant_time_ge(threes_in_row, 8);
126 err = constant_time_select_int(mask | good, err,
127 RSA_R_SSLV3_ROLLBACK_ATTACK);
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.
134 msg_index = zero_index + 1;
135 mlen = num - msg_index;
138 * For good measure, do this check in constant time as well.
140 good &= constant_time_ge(tlen, mlen);
141 err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);
144 * Even though we can't fake result's length, we can pretend copying
145 * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |num|
146 * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,
147 * where |mlen'| is "saturated" |mlen| value. Deducing information
148 * about failure or |mlen| would take attacker's ability to observe
149 * memory access pattern with byte granularity *as it occurs*. It
150 * should be noted that failure is indistinguishable from normal
151 * operation if |tlen| is fixed by protocol.
153 tlen = constant_time_select_int(constant_time_lt(num - 11, tlen),
155 msg_index = constant_time_select_int(good, msg_index, num - tlen);
156 mlen = num - msg_index;
157 for (mask = good, i = 0; i < tlen; i++) {
158 unsigned int equals = constant_time_eq(msg_index, num);
160 msg_index -= tlen & equals; /* rewind at EOF */
161 mask &= ~equals; /* mask = 0 at EOF */
162 to[i] = constant_time_select_8(mask, em[msg_index++], to[i]);
165 OPENSSL_clear_free(em, num);
166 RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, err);
167 err_clear_last_constant_time(1 & good);
169 return constant_time_select_int(good, mlen, -1);