countermeasure against new Klima-Pokorny-Rosa atack (ef42d6a4) · Commits · CYBER - Cyber Security / TS 103 523 MSP / TLMSP / TLMSP OpenSSL

CHANGES

+5 −1

Original line number	Diff line number	Diff line
		@@ -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]

ssl/s3_srvr.c

+11 −13

Original line number	Diff line number	Diff line
		@@ -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=