-/* crypto/rsa/rsa_pk1.c */
-/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
- * All rights reserved.
+/*
+ * Copyright 1995-2020 The OpenSSL Project Authors. All Rights Reserved.
*
- * This package is an SSL implementation written
- * by Eric Young (eay@cryptsoft.com).
- * The implementation was written so as to conform with Netscapes SSL.
- *
- * This library is free for commercial and non-commercial use as long as
- * the following conditions are aheared to. The following conditions
- * apply to all code found in this distribution, be it the RC4, RSA,
- * lhash, DES, etc., code; not just the SSL code. The SSL documentation
- * included with this distribution is covered by the same copyright terms
- * except that the holder is Tim Hudson (tjh@cryptsoft.com).
- *
- * Copyright remains Eric Young's, and as such any Copyright notices in
- * the code are not to be removed.
- * If this package is used in a product, Eric Young should be given attribution
- * as the author of the parts of the library used.
- * This can be in the form of a textual message at program startup or
- * in documentation (online or textual) provided with the package.
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- * 1. Redistributions of source code must retain the copyright
- * notice, this list of conditions and the following disclaimer.
- * 2. Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in the
- * documentation and/or other materials provided with the distribution.
- * 3. All advertising materials mentioning features or use of this software
- * must display the following acknowledgement:
- * "This product includes cryptographic software written by
- * Eric Young (eay@cryptsoft.com)"
- * The word 'cryptographic' can be left out if the rouines from the library
- * being used are not cryptographic related :-).
- * 4. If you include any Windows specific code (or a derivative thereof) from
- * the apps directory (application code) you must include an acknowledgement:
- * "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"
- *
- * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND
- * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
- * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
- * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
- * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
- * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
- * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
- * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
- * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
- * SUCH DAMAGE.
- *
- * The licence and distribution terms for any publically available version or
- * derivative of this code cannot be changed. i.e. this code cannot simply be
- * copied and put under another distribution licence
- * [including the GNU Public Licence.]
+ * Licensed under the Apache License 2.0 (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
*/
-#define OPENSSL_FIPSAPI
+/*
+ * RSA low level APIs are deprecated for public use, but still ok for
+ * internal use.
+ */
+#include "internal/deprecated.h"
-#include "constant_time_locl.h"
+#include "internal/constant_time.h"
#include <stdio.h>
-#include "cryptlib.h"
#include <openssl/bn.h>
#include <openssl/rsa.h>
#include <openssl/rand.h>
+/* Just for the SSL_MAX_MASTER_KEY_LENGTH value */
+#include <openssl/ssl.h>
+#include "internal/cryptlib.h"
+#include "crypto/rsa.h"
+#include "rsa_local.h"
int RSA_padding_add_PKCS1_type_1(unsigned char *to, int tlen,
- const unsigned char *from, int flen)
- {
- int j;
- unsigned char *p;
-
- if (flen > (tlen-RSA_PKCS1_PADDING_SIZE))
- {
- RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_TYPE_1,RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
- return(0);
- }
-
- p=(unsigned char *)to;
-
- *(p++)=0;
- *(p++)=1; /* Private Key BT (Block Type) */
-
- /* pad out with 0xff data */
- j=tlen-3-flen;
- memset(p,0xff,j);
- p+=j;
- *(p++)='\0';
- memcpy(p,from,(unsigned int)flen);
- return(1);
- }
+ const unsigned char *from, int flen)
+{
+ int j;
+ unsigned char *p;
+
+ if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
+ RSAerr(RSA_F_RSA_PADDING_ADD_PKCS1_TYPE_1,
+ RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
+ return 0;
+ }
+
+ p = (unsigned char *)to;
+
+ *(p++) = 0;
+ *(p++) = 1; /* Private Key BT (Block Type) */
+
+ /* pad out with 0xff data */
+ j = tlen - 3 - flen;
+ memset(p, 0xff, j);
+ p += j;
+ *(p++) = '\0';
+ memcpy(p, from, (unsigned int)flen);
+ return 1;
+}
int RSA_padding_check_PKCS1_type_1(unsigned char *to, int tlen,
- const unsigned char *from, int flen, int num)
- {
- int i,j;
- const unsigned char *p;
-
- p=from;
- if ((num != (flen+1)) || (*(p++) != 01))
- {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,RSA_R_BLOCK_TYPE_IS_NOT_01);
- return(-1);
- }
-
- /* scan over padding data */
- j=flen-1; /* one for type. */
- for (i=0; i<j; i++)
- {
- if (*p != 0xff) /* should decrypt to 0xff */
- {
- if (*p == 0)
- { p++; break; }
- else {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,RSA_R_BAD_FIXED_HEADER_DECRYPT);
- return(-1);
- }
- }
- p++;
- }
-
- if (i == j)
- {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,RSA_R_NULL_BEFORE_BLOCK_MISSING);
- return(-1);
- }
-
- if (i < 8)
- {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,RSA_R_BAD_PAD_BYTE_COUNT);
- return(-1);
- }
- i++; /* Skip over the '\0' */
- j-=i;
- if (j > tlen)
- {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,RSA_R_DATA_TOO_LARGE);
- return(-1);
- }
- memcpy(to,p,(unsigned int)j);
-
- return(j);
- }
+ const unsigned char *from, int flen,
+ int num)
+{
+ int i, j;
+ const unsigned char *p;
+
+ p = from;
+
+ /*
+ * The format is
+ * 00 || 01 || PS || 00 || D
+ * PS - padding string, at least 8 bytes of FF
+ * D - data.
+ */
+
+ if (num < RSA_PKCS1_PADDING_SIZE)
+ return -1;
+
+ /* Accept inputs with and without the leading 0-byte. */
+ if (num == flen) {
+ if ((*p++) != 0x00) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
+ RSA_R_INVALID_PADDING);
+ return -1;
+ }
+ flen--;
+ }
+
+ if ((num != (flen + 1)) || (*(p++) != 0x01)) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
+ RSA_R_BLOCK_TYPE_IS_NOT_01);
+ return -1;
+ }
+
+ /* scan over padding data */
+ j = flen - 1; /* one for type. */
+ for (i = 0; i < j; i++) {
+ if (*p != 0xff) { /* should decrypt to 0xff */
+ if (*p == 0) {
+ p++;
+ break;
+ } else {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
+ RSA_R_BAD_FIXED_HEADER_DECRYPT);
+ return -1;
+ }
+ }
+ p++;
+ }
+
+ if (i == j) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
+ RSA_R_NULL_BEFORE_BLOCK_MISSING);
+ return -1;
+ }
+
+ if (i < 8) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1,
+ RSA_R_BAD_PAD_BYTE_COUNT);
+ return -1;
+ }
+ i++; /* Skip over the '\0' */
+ j -= i;
+ if (j > tlen) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_1, RSA_R_DATA_TOO_LARGE);
+ return -1;
+ }
+ memcpy(to, p, (unsigned int)j);
+
+ return j;
+}
+
+int ossl_rsa_padding_add_PKCS1_type_2_ex(OPENSSL_CTX *libctx, unsigned char *to,
+ int tlen, const unsigned char *from,
+ int flen)
+{
+ int i, j;
+ unsigned char *p;
+
+ if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
+ RSAerr(0, 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 - flen;
+
+ if (RAND_bytes_ex(libctx, p, j) <= 0)
+ return 0;
+ for (i = 0; i < j; i++) {
+ if (*p == '\0')
+ do {
+ if (RAND_bytes_ex(libctx, p, 1) <= 0)
+ return 0;
+ } while (*p == '\0');
+ p++;
+ }
+
+ *(p++) = '\0';
+
+ memcpy(p, from, (unsigned int)flen);
+ return 1;
+}
int RSA_padding_add_PKCS1_type_2(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_PKCS1_TYPE_2,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-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++;
- }
-
- *(p++)='\0';
-
- memcpy(p,from,(unsigned int)flen);
- return(1);
- }
+ const unsigned char *from, int flen)
+{
+ return ossl_rsa_padding_add_PKCS1_type_2_ex(NULL, to, tlen, from, flen);
+}
int RSA_padding_check_PKCS1_type_2(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;
- int zero_index = 0, msg_index, mlen = -1;
-
- if (tlen < 0 || flen < 0)
- return -1;
-
- /* PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography
- * Standard", section 7.2.2. */
-
- if (flen > num)
- goto err;
-
- if (num < 11)
- goto err;
-
- em = OPENSSL_malloc(num);
- if (em == NULL)
- {
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, ERR_R_MALLOC_FAILURE);
- return -1;
- }
- memset(em, 0, num);
- /*
- * Always do this zero-padding copy (even when num == flen) to avoid
- * leaking that information. The copy still leaks some side-channel
- * information, but it's impossible to have a fixed memory access
- * pattern since we can't read out of the bounds of |from|.
- *
- * TODO(emilia): Consider porting BN_bn2bin_padded from BoringSSL.
- */
- memcpy(em + num - flen, from, flen);
-
- good = constant_time_is_zero(em[0]);
- good &= constant_time_eq(em[1], 2);
-
- found_zero_byte = 0;
- for (i = 2; i < num; i++)
- {
- unsigned int equals0 = constant_time_is_zero(em[i]);
- zero_index = constant_time_select_int(~found_zero_byte & equals0, i, zero_index);
- found_zero_byte |= equals0;
- }
-
- /*
- * PS must be at least 8 bytes long, and it starts two bytes into |em|.
- * If we never found a 0-byte, then |zero_index| is 0 and the check
- * also fails.
- */
- good &= constant_time_ge((unsigned int)(zero_index), 2 + 8);
-
- /* 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; it could
- * leak something if |tlen| was assuming valid padding. */
- good &= constant_time_ge((unsigned int)(tlen), (unsigned int)(mlen));
-
- /*
- * We can't continue in constant-time because we need to copy the result
- * and we cannot fake its length. This unavoidably leaks timing
- * information at the API boundary.
- * TODO(emilia): this could be addressed at the call site,
- * see BoringSSL commit 0aa0767340baf925bda4804882aab0cb974b2d26.
- */
- if (!good)
- {
- mlen = -1;
- goto err;
- }
-
- memcpy(to, em + msg_index, mlen);
-
-err:
- if (em != NULL)
- OPENSSL_free(em);
- if (mlen == -1)
- RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, RSA_R_PKCS_DECODING_ERROR);
- return mlen;
- }
+ 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;
+ int zero_index = 0, msg_index, mlen = -1;
+
+ if (tlen <= 0 || flen <= 0)
+ return -1;
+
+ /*
+ * PKCS#1 v1.5 decryption. See "PKCS #1 v2.2: RSA Cryptography Standard",
+ * section 7.2.2.
+ */
+
+ if (flen > num || num < RSA_PKCS1_PADDING_SIZE) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,
+ RSA_R_PKCS_DECODING_ERROR);
+ return -1;
+ }
+
+ em = OPENSSL_malloc(num);
+ if (em == NULL) {
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, 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;
+ }
+
+ good = constant_time_is_zero(em[0]);
+ good &= constant_time_eq(em[1], 2);
+
+ /* scan over padding data */
+ found_zero_byte = 0;
+ for (i = 2; i < num; i++) {
+ unsigned int equals0 = constant_time_is_zero(em[i]);
+
+ zero_index = constant_time_select_int(~found_zero_byte & equals0,
+ i, zero_index);
+ found_zero_byte |= equals0;
+ }
+
+ /*
+ * PS must be at least 8 bytes long, and it starts two bytes into |em|.
+ * 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);
+
+ /*
+ * 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);
+
+ /*
+ * Move the result in-place by |num|-RSA_PKCS1_PADDING_SIZE-|mlen| bytes to the left.
+ * Then if |good| move |mlen| bytes from |em|+RSA_PKCS1_PADDING_SIZE to |to|.
+ * Otherwise leave |to| unchanged.
+ * Copy the memory back in a way that does not reveal the size of
+ * the data being copied via a timing side channel. This requires copying
+ * parts of the buffer multiple times based on the bits set in the real
+ * length. Clear bits do a non-copy with identical access pattern.
+ * The loop below has overall complexity of O(N*log(N)).
+ */
+ tlen = constant_time_select_int(constant_time_lt(num - RSA_PKCS1_PADDING_SIZE, tlen),
+ num - RSA_PKCS1_PADDING_SIZE, tlen);
+ for (msg_index = 1; msg_index < num - RSA_PKCS1_PADDING_SIZE; msg_index <<= 1) {
+ mask = ~constant_time_eq(msg_index & (num - RSA_PKCS1_PADDING_SIZE - mlen), 0);
+ for (i = RSA_PKCS1_PADDING_SIZE; i < num - msg_index; i++)
+ em[i] = constant_time_select_8(mask, em[i + msg_index], em[i]);
+ }
+ for (i = 0; i < tlen; i++) {
+ mask = good & constant_time_lt(i, mlen);
+ to[i] = constant_time_select_8(mask, em[i + RSA_PKCS1_PADDING_SIZE], to[i]);
+ }
+
+ OPENSSL_clear_free(em, num);
+#ifndef FIPS_MODULE
+ /*
+ * This trick doesn't work in the FIPS provider because libcrypto manages
+ * the error stack. Instead we opt not to put an error on the stack at all
+ * in case of padding failure in the FIPS provider.
+ */
+ RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2, RSA_R_PKCS_DECODING_ERROR);
+ err_clear_last_constant_time(1 & good);
+#endif
+
+ return constant_time_select_int(good, mlen, -1);
+}
+
+/*
+ * ossl_rsa_padding_check_PKCS1_type_2_TLS() checks and removes the PKCS1 type 2
+ * padding from a decrypted RSA message in a TLS signature. The result is stored
+ * in the buffer pointed to by |to| which should be |tlen| bytes long. |tlen|
+ * must be at least SSL_MAX_MASTER_KEY_LENGTH. The original decrypted message
+ * should be stored in |from| which must be |flen| bytes in length and padded
+ * such that |flen == RSA_size()|. The TLS protocol version that the client
+ * originally requested should be passed in |client_version|. Some buggy clients
+ * can exist which use the negotiated version instead of the originally
+ * requested protocol version. If it is necessary to work around this bug then
+ * the negotiated protocol version can be passed in |alt_version|, otherwise 0
+ * should be passed.
+ *
+ * If the passed message is publicly invalid or some other error that can be
+ * treated in non-constant time occurs then -1 is returned. On success the
+ * length of the decrypted data is returned. This will always be
+ * SSL_MAX_MASTER_KEY_LENGTH. If an error occurs that should be treated in
+ * constant time then this function will appear to return successfully, but the
+ * decrypted data will be randomly generated (as per
+ * https://tools.ietf.org/html/rfc5246#section-7.4.7.1).
+ */
+int ossl_rsa_padding_check_PKCS1_type_2_TLS(OPENSSL_CTX *libctx,
+ unsigned char *to, size_t tlen,
+ const unsigned char *from,
+ size_t flen, int client_version,
+ int alt_version)
+{
+ unsigned int i, good, version_good;
+ unsigned char rand_premaster_secret[SSL_MAX_MASTER_KEY_LENGTH];
+
+ /*
+ * If these checks fail then either the message in publicly invalid, or
+ * we've been called incorrectly. We can fail immediately.
+ */
+ if (flen < RSA_PKCS1_PADDING_SIZE + SSL_MAX_MASTER_KEY_LENGTH
+ || tlen < SSL_MAX_MASTER_KEY_LENGTH) {
+ ERR_raise(ERR_LIB_RSA, RSA_R_PKCS_DECODING_ERROR);
+ return -1;
+ }
+
+ /*
+ * Generate a random premaster secret to use in the event that we fail
+ * to decrypt.
+ */
+ if (RAND_priv_bytes_ex(libctx, rand_premaster_secret,
+ sizeof(rand_premaster_secret)) <= 0) {
+ ERR_raise(ERR_LIB_RSA, ERR_R_INTERNAL_ERROR);
+ return -1;
+ }
+
+ good = constant_time_is_zero(from[0]);
+ good &= constant_time_eq(from[1], 2);
+
+ /* Check we have the expected padding data */
+ for (i = 2; i < flen - SSL_MAX_MASTER_KEY_LENGTH - 1; i++)
+ good &= ~constant_time_is_zero_8(from[i]);
+ good &= constant_time_is_zero_8(from[flen - SSL_MAX_MASTER_KEY_LENGTH - 1]);
+
+
+ /*
+ * If the version in the decrypted pre-master secret is correct then
+ * version_good will be 0xff, otherwise it'll be zero. The
+ * Klima-Pokorny-Rosa extension of Bleichenbacher's attack
+ * (http://eprint.iacr.org/2003/052/) exploits the version number
+ * check as a "bad version oracle". Thus version checks are done in
+ * constant time and are treated like any other decryption error.
+ */
+ version_good =
+ constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH],
+ (client_version >> 8) & 0xff);
+ version_good &=
+ constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH + 1],
+ client_version & 0xff);
+
+ /*
+ * The premaster secret must contain the same version number as the
+ * ClientHello to detect version rollback attacks (strangely, the
+ * protocol does not offer such protection for DH ciphersuites).
+ * However, buggy clients exist that send the negotiated protocol
+ * version instead if the server does not support the requested
+ * protocol version. If SSL_OP_TLS_ROLLBACK_BUG is set then we tolerate
+ * such clients. In that case alt_version will be non-zero and set to
+ * the negotiated version.
+ */
+ if (alt_version > 0) {
+ unsigned int workaround_good;
+
+ workaround_good =
+ constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH],
+ (alt_version >> 8) & 0xff);
+ workaround_good &=
+ constant_time_eq(from[flen - SSL_MAX_MASTER_KEY_LENGTH + 1],
+ alt_version & 0xff);
+ version_good |= workaround_good;
+ }
+
+ good &= version_good;
+
+
+ /*
+ * Now copy the result over to the to buffer if good, or random data if
+ * not good.
+ */
+ for (i = 0; i < SSL_MAX_MASTER_KEY_LENGTH; i++) {
+ to[i] =
+ constant_time_select_8(good,
+ from[flen - SSL_MAX_MASTER_KEY_LENGTH + i],
+ rand_premaster_secret[i]);
+ }
+
+ /*
+ * We must not leak whether a decryption failure occurs because of
+ * Bleichenbacher's attack on PKCS #1 v1.5 RSA padding (see RFC 2246,
+ * section 7.4.7.1). The code follows that advice of the TLS RFC and
+ * generates a random premaster secret for the case that the decrypt
+ * fails. See https://tools.ietf.org/html/rfc5246#section-7.4.7.1
+ * So, whether we actually succeeded or not, return success.
+ */
+
+ return SSL_MAX_MASTER_KEY_LENGTH;
+}