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-rw-r--r--ssl/s2_srvr.c104
1 files changed, 51 insertions, 53 deletions
diff --git a/ssl/s2_srvr.c b/ssl/s2_srvr.c
index 19bb48c9cd46..4289272b73d3 100644
--- a/ssl/s2_srvr.c
+++ b/ssl/s2_srvr.c
@@ -111,6 +111,7 @@
#include "ssl_locl.h"
#ifndef OPENSSL_NO_SSL2
+#include "../crypto/constant_time_locl.h"
# include <stdio.h>
# include <openssl/bio.h>
# include <openssl/rand.h>
@@ -372,12 +373,15 @@ int ssl2_accept(SSL *s)
static int get_client_master_key(SSL *s)
{
int is_export, i, n, keya;
- unsigned int ek;
+ unsigned int num_encrypted_key_bytes, key_length;
unsigned long len;
unsigned char *p;
const SSL_CIPHER *cp;
const EVP_CIPHER *c;
const EVP_MD *md;
+ unsigned char rand_premaster_secret[SSL_MAX_MASTER_KEY_LENGTH];
+ unsigned char decrypt_good;
+ size_t j;
p = (unsigned char *)s->init_buf->data;
if (s->state == SSL2_ST_GET_CLIENT_MASTER_KEY_A) {
@@ -465,12 +469,6 @@ static int get_client_master_key(SSL *s)
return (0);
}
- if (s->session->cipher->algorithm2 & SSL2_CF_8_BYTE_ENC) {
- is_export = 1;
- ek = 8;
- } else
- ek = 5;
-
/*
* The format of the CLIENT-MASTER-KEY message is
* 1 byte message type
@@ -484,12 +482,27 @@ static int get_client_master_key(SSL *s)
*
* If the cipher is an export cipher, then the encrypted key bytes
* are a fixed portion of the total key (5 or 8 bytes). The size of
- * this portion is in |ek|. If the cipher is not an export cipher,
- * then the entire key material is encrypted (i.e., clear key length
- * must be zero).
+ * this portion is in |num_encrypted_key_bytes|. If the cipher is not an
+ * export cipher, then the entire key material is encrypted (i.e., clear
+ * key length must be zero).
*/
- if ((!is_export && s->s2->tmp.clear != 0) ||
- (is_export && s->s2->tmp.clear + ek != (unsigned int)EVP_CIPHER_key_length(c))) {
+ key_length = (unsigned int)EVP_CIPHER_key_length(c);
+ if (key_length > SSL_MAX_MASTER_KEY_LENGTH) {
+ ssl2_return_error(s, SSL2_PE_UNDEFINED_ERROR);
+ SSLerr(SSL_F_GET_CLIENT_MASTER_KEY, ERR_R_INTERNAL_ERROR);
+ return -1;
+ }
+
+ if (s->session->cipher->algorithm2 & SSL2_CF_8_BYTE_ENC) {
+ is_export = 1;
+ num_encrypted_key_bytes = 8;
+ } else if (is_export) {
+ num_encrypted_key_bytes = 5;
+ } else {
+ num_encrypted_key_bytes = key_length;
+ }
+
+ if (s->s2->tmp.clear + num_encrypted_key_bytes != key_length) {
ssl2_return_error(s, SSL2_PE_UNDEFINED_ERROR);
SSLerr(SSL_F_GET_CLIENT_MASTER_KEY,SSL_R_BAD_LENGTH);
return -1;
@@ -499,64 +512,49 @@ static int get_client_master_key(SSL *s)
* Decryption can't be expanding, so if we don't have enough encrypted
* bytes to fit the key in the buffer, stop now.
*/
- if ((is_export && s->s2->tmp.enc < ek) ||
- (!is_export && s->s2->tmp.enc < (unsigned int)EVP_CIPHER_key_length(c))) {
+ if (s->s2->tmp.enc < num_encrypted_key_bytes) {
ssl2_return_error(s,SSL2_PE_UNDEFINED_ERROR);
SSLerr(SSL_F_GET_CLIENT_MASTER_KEY,SSL_R_LENGTH_TOO_SHORT);
return -1;
}
+ /*
+ * 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
+ */
+
+ /*
+ * should be RAND_bytes, but we cannot work around a failure.
+ */
+ if (RAND_pseudo_bytes(rand_premaster_secret,
+ (int)num_encrypted_key_bytes) <= 0)
+ return 0;
+
i = ssl_rsa_private_decrypt(s->cert, s->s2->tmp.enc,
&(p[s->s2->tmp.clear]),
&(p[s->s2->tmp.clear]),
(s->s2->ssl2_rollback) ? RSA_SSLV23_PADDING :
RSA_PKCS1_PADDING);
-
- /* bad decrypt */
-# if 1
+ ERR_clear_error();
/*
* If a bad decrypt, continue with protocol but with a random master
* secret (Bleichenbacher attack)
*/
- if ((i < 0) || ((!is_export && i != EVP_CIPHER_key_length(c))
- || (is_export && i != (int)ek))) {
- ERR_clear_error();
- if (is_export)
- i = ek;
- else
- i = EVP_CIPHER_key_length(c);
- if (RAND_pseudo_bytes(&p[s->s2->tmp.clear], i) <= 0)
- return 0;
- }
-# else
- if (i < 0) {
- error = 1;
- SSLerr(SSL_F_GET_CLIENT_MASTER_KEY, SSL_R_BAD_RSA_DECRYPT);
- }
- /* incorrect number of key bytes for non export cipher */
- else if ((!is_export && (i != EVP_CIPHER_key_length(c)))
- || (is_export && ((i != ek) || (s->s2->tmp.clear + i !=
- EVP_CIPHER_key_length(c))))) {
- error = 1;
- SSLerr(SSL_F_GET_CLIENT_MASTER_KEY, SSL_R_WRONG_NUMBER_OF_KEY_BITS);
- }
- if (error) {
- ssl2_return_error(s, SSL2_PE_UNDEFINED_ERROR);
- return (-1);
+ decrypt_good = constant_time_eq_int_8(i, (int)num_encrypted_key_bytes);
+ for (j = 0; j < num_encrypted_key_bytes; j++) {
+ p[s->s2->tmp.clear + j] =
+ constant_time_select_8(decrypt_good, p[s->s2->tmp.clear + j],
+ rand_premaster_secret[j]);
}
-# endif
- if (is_export)
- i = EVP_CIPHER_key_length(c);
+ s->session->master_key_length = (int)key_length;
+ memcpy(s->session->master_key, p, key_length);
+ OPENSSL_cleanse(p, key_length);
- if (i > SSL_MAX_MASTER_KEY_LENGTH) {
- ssl2_return_error(s, SSL2_PE_UNDEFINED_ERROR);
- SSLerr(SSL_F_GET_CLIENT_MASTER_KEY, ERR_R_INTERNAL_ERROR);
- return -1;
- }
- s->session->master_key_length = i;
- memcpy(s->session->master_key, p, (unsigned int)i);
- return (1);
+ return 1;
}
static int get_client_hello(SSL *s)