/*
- * Copyright 1995-2018 The OpenSSL Project Authors. All Rights Reserved.
+ * Copyright 1995-2020 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
* https://www.openssl.org/source/license.html
*/
-#include "internal/constant_time_locl.h"
+/*
+ * 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 "internal/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)
* D - data.
*/
- if (num < 11)
+ if (num < RSA_PKCS1_PADDING_SIZE)
return -1;
/* Accept inputs with and without the leading 0-byte. */
return j;
}
-int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,
- const unsigned char *from, int flen)
+int rsa_padding_add_PKCS1_type_2_with_libctx(OPENSSL_CTX *libctx,
+ 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);
+ if (flen > (tlen - RSA_PKCS1_PADDING_SIZE)) {
+ RSAerr(0, RSA_R_DATA_TOO_LARGE_FOR_KEY_SIZE);
return 0;
}
/* pad out with non-zero random data */
j = tlen - 3 - flen;
- if (RAND_bytes(p, j) <= 0)
+ if (RAND_bytes_ex(libctx, p, j) <= 0)
return 0;
for (i = 0; i < j; i++) {
if (*p == '\0')
do {
- if (RAND_bytes(p, 1) <= 0)
+ if (RAND_bytes_ex(libctx, p, 1) <= 0)
return 0;
} while (*p == '\0');
p++;
return 1;
}
+int RSA_padding_add_PKCS1_type_2(unsigned char *to, int tlen,
+ const unsigned char *from, int flen)
+{
+ return rsa_padding_add_PKCS1_type_2_with_libctx(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)
unsigned int good, found_zero_byte, mask;
int zero_index = 0, msg_index, mlen = -1;
- if (tlen < 0 || flen < 0)
+ if (tlen <= 0 || flen <= 0)
return -1;
/*
* section 7.2.2.
*/
- if (flen > num || num < 11) {
+ if (flen > num || num < RSA_PKCS1_PADDING_SIZE) {
RSAerr(RSA_F_RSA_PADDING_CHECK_PKCS1_TYPE_2,
RSA_R_PKCS_DECODING_ERROR);
return -1;
from -= 1 & mask;
*--em = *from & mask;
}
- from = em;
- good = constant_time_is_zero(from[0]);
- good &= constant_time_eq(from[1], 2);
+ 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(from[i]);
+ unsigned int equals0 = constant_time_is_zero(em[i]);
zero_index = constant_time_select_int(~found_zero_byte & equals0,
i, zero_index);
}
/*
- * PS must be at least 8 bytes long, and it starts two bytes into |from|.
+ * 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(tlen, mlen);
/*
- * Even though we can't fake result's length, we can pretend copying
- * |tlen| bytes where |mlen| bytes would be real. Last |tlen| of |num|
- * bytes are viewed as circular buffer with start at |tlen|-|mlen'|,
- * where |mlen'| is "saturated" |mlen| value. Deducing information
- * about failure or |mlen| would take attacker's ability to observe
- * memory access pattern with byte granularity *as it occurs*. It
- * should be noted that failure is indistinguishable from normal
- * operation if |tlen| is fixed by protocol.
+ * 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, tlen), num, tlen);
- msg_index = constant_time_select_int(good, msg_index, num - tlen);
- mlen = num - msg_index;
- for (from += msg_index, mask = good, i = 0; i < tlen; i++) {
- unsigned int equals = constant_time_eq(i, mlen);
-
- from -= tlen & equals; /* if (i == mlen) rewind */
- mask &= mask ^ equals; /* if (i == mlen) mask = 0 */
- to[i] = constant_time_select_8(mask, from[i], to[i]);
+ 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);
}
+
+/*
+ * 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 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;
+}
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