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/*
* Copyright 1995-2021 The OpenSSL Project Authors. All Rights Reserved.
*
* 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
*/
/*
* RSA low level APIs are deprecated for public use, but still ok for
* internal use.
*/
#include "internal/deprecated.h"
#include "internal/constant_time.h"
#include <stdio.h>
#include <openssl/bn.h>
#include <openssl/rsa.h>
#include <openssl/rand.h>
/* Just for the SSL_MAX_MASTER_KEY_LENGTH value */
#include <openssl/prov_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)) {
ERR_raise(ERR_LIB_RSA, 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;
/*
* 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) {
ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_PADDING);
return -1;
}
flen--;
}
if ((num != (flen + 1)) || (*(p++) != 0x01)) {
ERR_raise(ERR_LIB_RSA, 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 {
ERR_raise(ERR_LIB_RSA, RSA_R_BAD_FIXED_HEADER_DECRYPT);
return -1;
}
}
p++;
}
if (i == j) {
ERR_raise(ERR_LIB_RSA, RSA_R_NULL_BEFORE_BLOCK_MISSING);
return -1;
}
if (i < 8) {
ERR_raise(ERR_LIB_RSA, RSA_R_BAD_PAD_BYTE_COUNT);
return -1;
}
i++; /* Skip over the '\0' */
j -= i;
if (j > tlen) {
ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE);
return -1;
}
memcpy(to, p, (unsigned int)j);
return j;
}
int ossl_rsa_padding_add_PKCS1_type_2_ex(OSSL_LIB_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)) {
ERR_raise(ERR_LIB_RSA, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
return 0;
} else if (flen < 0) {
ERR_raise(ERR_LIB_RSA, RSA_R_INVALID_LENGTH);
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) <= 0)
return 0;
for (i = 0; i < j; i++) {
if (*p == '\0')
do {
if (RAND_bytes_ex(libctx, p, 1, 0) <= 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)
{
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, 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) {
ERR_raise(ERR_LIB_RSA, RSA_R_PKCS_DECODING_ERROR);
return -1;
}
em = OPENSSL_malloc(num);
if (em == NULL) {
ERR_raise(ERR_LIB_RSA, 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.
*/
ERR_raise(ERR_LIB_RSA, 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(OSSL_LIB_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) <= 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;
}
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