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 * RSA low level APIs are deprecated for public use, but still ok for
14 #include "internal/deprecated.h"
17 #include "internal/cryptlib.h"
18 #include <openssl/bn.h>
19 #include <openssl/rsa.h>
20 #include <openssl/rand.h>
21 #include "internal/constant_time.h"
23 int RSA_padding_add_SSLv23(unsigned char *to, int tlen,
24 const unsigned char *from, int flen)
29 if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
30 RSAerr(RSA_F_RSA_PADDING_ADD_SSLV23,
31 RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
35 p = (unsigned char *)to;
38 *(p++) = 2; /* Public Key BT (Block Type) */
40 /* pad out with non-zero random data */
41 j = tlen - 3 - 8 - flen;
43 if (RAND_bytes(p, j) <= 0)
45 for (i = 0; i < j; i++) {
48 if (RAND_bytes(p, 1) <= 0)
58 memcpy(p, from, (unsigned int)flen);
63 * Copy of RSA_padding_check_PKCS1_type_2 with a twist that rejects padding
64 * if nul delimiter is not preceded by 8 consecutive 0x03 bytes. It also
65 * preserves error code reporting for backward compatibility.
67 int RSA_padding_check_SSLv23(unsigned char *to, int tlen,
68 const unsigned char *from, int flen, int num)
71 /* |em| is the encoded message, zero-padded to exactly |num| bytes */
72 unsigned char *em = NULL;
73 unsigned int good, found_zero_byte, mask, threes_in_row;
74 int zero_index = 0, msg_index, mlen = -1, err;
76 if (tlen <= 0 || flen <= 0)
79 if (flen > num || num < RSA_PKCS1_PADDING_SIZE) {
80 RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, RSA_R_DATA_TOO_SMALL);
84 em = OPENSSL_malloc(num);
86 RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, ERR_R_MALLOC_FAILURE);
90 * Caller is encouraged to pass zero-padded message created with
91 * BN_bn2binpad. Trouble is that since we can't read out of |from|'s
92 * bounds, it's impossible to have an invariant memory access pattern
93 * in case |from| was not zero-padded in advance.
95 for (from += flen, em += num, i = 0; i < num; i++) {
96 mask = ~constant_time_is_zero(flen);
102 good = constant_time_is_zero(em[0]);
103 good &= constant_time_eq(em[1], 2);
104 err = constant_time_select_int(good, 0, RSA_R_BLOCK_TYPE_IS_NOT_02);
107 /* scan over padding data */
110 for (i = 2; i < num; i++) {
111 unsigned int equals0 = constant_time_is_zero(em[i]);
113 zero_index = constant_time_select_int(~found_zero_byte & equals0,
115 found_zero_byte |= equals0;
117 threes_in_row += 1 & ~found_zero_byte;
118 threes_in_row &= found_zero_byte | constant_time_eq(em[i], 3);
122 * PS must be at least 8 bytes long, and it starts two bytes into |em|.
123 * If we never found a 0-byte, then |zero_index| is 0 and the check
126 good &= constant_time_ge(zero_index, 2 + 8);
127 err = constant_time_select_int(mask | good, err,
128 RSA_R_NULL_BEFORE_BLOCK_MISSING);
131 good &= constant_time_ge(threes_in_row, 8);
132 err = constant_time_select_int(mask | good, err,
133 RSA_R_SSLV3_ROLLBACK_ATTACK);
137 * Skip the zero byte. This is incorrect if we never found a zero-byte
138 * but in this case we also do not copy the message out.
140 msg_index = zero_index + 1;
141 mlen = num - msg_index;
144 * For good measure, do this check in constant time as well.
146 good &= constant_time_ge(tlen, mlen);
147 err = constant_time_select_int(mask | good, err, RSA_R_DATA_TOO_LARGE);
150 * Move the result in-place by |num|-RSA_PKCS1_PADDING_SIZE-|mlen| bytes to the left.
151 * Then if |good| move |mlen| bytes from |em|+RSA_PKCS1_PADDING_SIZE to |to|.
152 * Otherwise leave |to| unchanged.
153 * Copy the memory back in a way that does not reveal the size of
154 * the data being copied via a timing side channel. This requires copying
155 * parts of the buffer multiple times based on the bits set in the real
156 * length. Clear bits do a non-copy with identical access pattern.
157 * The loop below has overall complexity of O(N*log(N)).
159 tlen = constant_time_select_int(constant_time_lt(num - RSA_PKCS1_PADDING_SIZE, tlen),
160 num - RSA_PKCS1_PADDING_SIZE, tlen);
161 for (msg_index = 1; msg_index < num - RSA_PKCS1_PADDING_SIZE; msg_index <<= 1) {
162 mask = ~constant_time_eq(msg_index & (num - RSA_PKCS1_PADDING_SIZE - mlen), 0);
163 for (i = RSA_PKCS1_PADDING_SIZE; i < num - msg_index; i++)
164 em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);
166 for (i = 0; i < tlen; i++) {
167 mask = good & constant_time_lt(i, mlen);
168 to[i] = constant_time_select_8(mask, em[i + RSA_PKCS1_PADDING_SIZE], to[i]);
171 OPENSSL_clear_free(em, num);
172 RSAerr(RSA_F_RSA_PADDING_CHECK_SSLV23, err);
173 err_clear_last_constant_time(1 & good);
175 return constant_time_select_int(good, mlen, -1);