countermeasure against new Klima-Pokorny-Rosa atack
authorBodo Möller <bodo@openssl.org>
Wed, 19 Mar 2003 19:19:53 +0000 (19:19 +0000)
committerBodo Möller <bodo@openssl.org>
Wed, 19 Mar 2003 19:19:53 +0000 (19:19 +0000)
CHANGES
ssl/s3_srvr.c

diff --git a/CHANGES b/CHANGES
index bf9d55c..ea29f5a 100644 (file)
--- a/CHANGES
+++ b/CHANGES
 
  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] 
index a2f5b84..084b9cf 100644 (file)
@@ -1684,7 +1684,7 @@ static int ssl3_get_client_key_exchange(SSL *s)
                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 @@ static int ssl3_get_client_key_exchange(SSL *s)
                                (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=