From: Bodo Möller <bodo@openssl.org>
Date: Wed, 19 Mar 2003 19:20:30 +0000 (+0000)
Subject: countermeasure against new Klima-Pokorny-Rosa atack
X-Git-Tag: OpenSSL_0_9_6j~12
X-Git-Url: https://git.librecmc.org/?a=commitdiff_plain;h=ef42d6a4eda7af66fcd8168bfb8f11f160f22913;p=oweals%2Fopenssl.git

countermeasure against new Klima-Pokorny-Rosa atack
---

diff --git a/CHANGES b/CHANGES
index b3f3ffb4d0..46916103b9 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,7 +4,11 @@
 
  Changes between 0.9.6i and 0.9.6j  [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]
 
  Changes between 0.9.6h and 0.9.6i  [19 Feb 2003]
 
diff --git a/ssl/s3_srvr.c b/ssl/s3_srvr.c
index 6b414cfa5c..3f4818e888 100644
--- a/ssl/s3_srvr.c
+++ b/ssl/s3_srvr.c
@@ -1425,7 +1425,7 @@ 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))))
@@ -1441,30 +1441,28 @@ 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. */
 				}
 			}
 
 		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=