countermeasure against new Klima-Pokorny-Rosa atack
diff --git a/CHANGES b/CHANGES
index bf9d55c..ea29f5a 100644
--- a/CHANGES
+++ b/CHANGES
@@ -460,6 +460,16 @@
Changes between 0.9.7a and 0.9.7b [xx XXX 2003]
+ *) Countermeasure against the Klima-Pokorny-Rosa extension of
+ Bleichbacher's attack on PKCS #1 v1.5 padding: treat
+ a protocol version number mismatch like a decryption error
+ in ssl3_get_client_key_exchange (ssl/s3_srvr.c).
+ [Bodo Moeller]
+
+yet to be integrated into this CVS branch:
+- RSA blinding changes
+- Geoff's ENGINE_set_default() fix
+
*) Target "mingw" now allows native Windows code to be generated in
the Cygwin environment as well as with the MinGW compiler.
[Ulf Moeller]
diff --git a/ssl/s3_srvr.c b/ssl/s3_srvr.c
index a2f5b84..084b9cf 100644
--- a/ssl/s3_srvr.c
+++ b/ssl/s3_srvr.c
@@ -1684,7 +1684,7 @@
if (i != SSL_MAX_MASTER_KEY_LENGTH)
{
al=SSL_AD_DECODE_ERROR;
- SSLerr(SSL_F_SSL3_GET_CLIENT_KEY_EXCHANGE,SSL_R_BAD_RSA_DECRYPT);
+ /* SSLerr(SSL_F_SSL3_GET_CLIENT_KEY_EXCHANGE,SSL_R_BAD_RSA_DECRYPT); */
}
if ((al == -1) && !((p[0] == (s->client_version>>8)) && (p[1] == (s->client_version & 0xff))))
@@ -1700,30 +1700,29 @@
(p[0] == (s->version>>8)) && (p[1] == (s->version & 0xff))))
{
al=SSL_AD_DECODE_ERROR;
- SSLerr(SSL_F_SSL3_GET_CLIENT_KEY_EXCHANGE,SSL_R_BAD_PROTOCOL_VERSION_NUMBER);
- goto f_err;
+ /* SSLerr(SSL_F_SSL3_GET_CLIENT_KEY_EXCHANGE,SSL_R_BAD_PROTOCOL_VERSION_NUMBER); */
+
+ /* 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" -- an alert would
+ * reveal that the plaintext corresponding to some ciphertext
+ * made up by the adversary is properly formatted except
+ * that the version number is wrong. To avoid such attacks,
+ * we should treat this just like any other decryption error. */
+ p[0] = (char)(int) "CAN-2003-0131 patch 2003-03-20";
}
}
if (al != -1)
{
-#if 0
- goto f_err;
-#else
/* Some decryption failure -- use random value instead as countermeasure
* against Bleichenbacher's attack on PKCS #1 v1.5 RSA padding
- * (see RFC 2246, section 7.4.7.1).
- * But note that due to length and protocol version checking, the
- * attack is impractical anyway (see section 5 in D. Bleichenbacher:
- * "Chosen Ciphertext Attacks Against Protocols Based on the RSA
- * Encryption Standard PKCS #1", CRYPTO '98, LNCS 1462, pp. 1-12).
- */
+ * (see RFC 2246, section 7.4.7.1). */
ERR_clear_error();
i = SSL_MAX_MASTER_KEY_LENGTH;
p[0] = s->client_version >> 8;
p[1] = s->client_version & 0xff;
RAND_pseudo_bytes(p+2, i-2); /* should be RAND_bytes, but we cannot work around a failure */
-#endif
}
s->session->master_key_length=
