draft-ietf-uta-tls-attacks-00.txt		draft-ietf-uta-tls-attacks-01.txt
	uta Y. Sheffer		uta Y. Sheffer
	Internet-Draft Porticor		Internet-Draft Porticor
	Intended status: Informational R. Holz		Intended status: Informational R. Holz
	Expires: September 28, 2014 TUM		Expires: December 26, 2014 TUM
	P. Saint-Andre		P. Saint-Andre
	&yet		&yet
	March 27, 2014		June 24, 2014
	Summarizing Current Attacks on TLS and DTLS		Summarizing Current Attacks on TLS and DTLS
	draft-ietf-uta-tls-attacks-00		draft-ietf-uta-tls-attacks-01
	Abstract		Abstract
	Over the last few years there have been several serious attacks on		Over the last few years there have been several serious attacks on
	TLS, including attacks on its most commonly used ciphers and modes of		TLS, including attacks on its most commonly used ciphers and modes of
	operation. This document summarizes these attacks, with the goal of		operation. This document summarizes these attacks, with the goal of
	motivating generic and protocol-specific recommendations on the usage		motivating generic and protocol-specific recommendations on the usage
	of TLS and DTLS.		of TLS and DTLS.
	Status of This Memo		Status of This Memo
	skipping to change at page 1, line 37		skipping to change at page 1, line 37
	Internet-Drafts are working documents of the Internet Engineering		Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute		Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-		working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.		Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	time. It is inappropriate to use Internet-Drafts as reference		time. It is inappropriate to use Internet-Drafts as reference
	material or to cite them other than as "work in progress."		material or to cite them other than as "work in progress."
	This Internet-Draft will expire on September 28, 2014.		This Internet-Draft will expire on December 26, 2014.
	Copyright Notice		Copyright Notice
	Copyright (c) 2014 IETF Trust and the persons identified as the		Copyright (c) 2014 IETF Trust and the persons identified as the
	document authors. All rights reserved.		document authors. All rights reserved.
	This document is subject to BCP 78 and the IETF Trust's Legal		This document is subject to BCP 78 and the IETF Trust's Legal
	Provisions Relating to IETF Documents		Provisions Relating to IETF Documents
	(http://trustee.ietf.org/license-info) in effect on the date of		(http://trustee.ietf.org/license-info) in effect on the date of
	publication of this document. Please review these documents		publication of this document. Please review these documents
	carefully, as they describe your rights and restrictions with respect		carefully, as they describe your rights and restrictions with respect
	to this document. Code Components extracted from this document must		to this document. Code Components extracted from this document must
	include Simplified BSD License text as described in Section 4.e of		include Simplified BSD License text as described in Section 4.e of
	the Trust Legal Provisions and are provided without warranty as		the Trust Legal Provisions and are provided without warranty as
	described in the Simplified BSD License.		described in the Simplified BSD License.
	Table of Contents		Table of Contents
	1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
	2. Attacks on TLS . . . . . . . . . . . . . . . . . . . . . . . 2		2. Attacks on TLS . . . . . . . . . . . . . . . . . . . . . . . 3
	2.1. BEAST . . . . . . . . . . . . . . . . . . . . . . . . . . . 3		2.1. SSL Stripping . . . . . . . . . . . . . . . . . . . . . . . 3
	2.2. Lucky Thirteen . . . . . . . . . . . . . . . . . . . . . . 3		2.2. BEAST . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2.3. Attacks on RC4 . . . . . . . . . . . . . . . . . . . . . . 3		2.3. Lucky Thirteen . . . . . . . . . . . . . . . . . . . . . . 3
	2.4. Compression Attacks: CRIME and BREACH . . . . . . . . . . . 3		2.4. Attacks on RC4 . . . . . . . . . . . . . . . . . . . . . . 3
	3. Security Considerations . . . . . . . . . . . . . . . . . . . 4		2.5. Compression Attacks: CRIME and BREACH . . . . . . . . . . . 4
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4		2.6. Certificate Attacks . . . . . . . . . . . . . . . . . . . . 4
	5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4		2.7. Diffe-Hellman Parameters . . . . . . . . . . . . . . . . . 4
	6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4		2.8. Denial of Service . . . . . . . . . . . . . . . . . . . . . 4
	6.1. Normative References . . . . . . . . . . . . . . . . . . . 4		3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
	6.2. Informative References . . . . . . . . . . . . . . . . . . 4		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
	Appendix A. Appendix: Change Log . . . . . . . . . . . . . . . . 5		5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
	A.1. draft-ietf-uta-tls-bcp-00 . . . . . . . . . . . . . . . . . 5		6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
	A.2. draft-sheffer-uta-tls-bcp-00 . . . . . . . . . . . . . . . 6		6.1. Normative References . . . . . . . . . . . . . . . . . . . 5
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6		6.2. Informative References . . . . . . . . . . . . . . . . . . 5
			Appendix A. Appendix: Change Log . . . . . . . . . . . . . . . . 7
			A.1. draft-ietf-uta-tls-bcp-01 . . . . . . . . . . . . . . . . . 7
			A.2. draft-ietf-uta-tls-bcp-00 . . . . . . . . . . . . . . . . . 7
			A.3. draft-sheffer-uta-tls-bcp-00 . . . . . . . . . . . . . . . 7
			Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
	1. Introduction		1. Introduction
	Over the last few years there have been several major attacks on TLS		Over the last few years there have been several major attacks on TLS
	[RFC5246], including attacks on its most commonly used ciphers and		[RFC5246], including attacks on its most commonly used ciphers and
	modes of operation. Details are given in Section 2, but suffice it		modes of operation. Details are given in Section 2, but suffice it
	to say that both AES-CBC and RC4, which together make up for most		to say that both AES-CBC and RC4, which together make up for most
	current usage, have been seriously attacked in the context of TLS.		current usage, have been seriously attacked in the context of TLS.
	This situation motivated the creation of the UTA working group, which		This situation motivated the creation of the UTA working group, which
	skipping to change at page 3, line 9		skipping to change at page 3, line 15
	2. Attacks on TLS		2. Attacks on TLS
	This section lists the attacks that motivated the current		This section lists the attacks that motivated the current
	recommendations. This is not intended to be an extensive survey of		recommendations. This is not intended to be an extensive survey of
	TLS's security.		TLS's security.
	While there are widely deployed mitigations for some of the attacks		While there are widely deployed mitigations for some of the attacks
	listed below, we believe that their root causes necessitate a more		listed below, we believe that their root causes necessitate a more
	systemic solution.		systemic solution.
	2.1. BEAST		2.1. SSL Stripping
			Various attacks attempt to remove the use of SSL/TLS altogether, by
			modifying HTTP traffic and HTML pages as they pass on the wire.
			These attacks are known collectively as SSL Stripping, and were first
			introduced by Moxie Marlinspike [SSL-Stripping]. In the context of
			Web traffic, these attacks are only effective if the client accesses
			a Web server using a mixture of HTTP and HTTPS.
			2.2. BEAST
	The BEAST attack [BEAST] uses issues with the TLS 1.0 implementation		The BEAST attack [BEAST] uses issues with the TLS 1.0 implementation
	of CBC (that is, the predictable initialization vector) to decrypt		of CBC (that is, the predictable initialization vector) to decrypt
	parts of a packet, and specifically shows how this can be used to		parts of a packet, and specifically to decrypt HTTP cookies when HTTP
	decrypt HTTP cookies when run over TLS.		is run over TLS.
	2.2. Lucky Thirteen		2.3. Lucky Thirteen
	A consequence of the MAC-then-encrypt design in all current versions		A consequence of the MAC-then-encrypt design in all current versions
	of TLS is the existence of padding oracle attacks [Padding-Oracle].		of TLS is the existence of padding oracle attacks [Padding-Oracle].
	A recent incarnation of these attacks is the Lucky Thirteen attack		A recent incarnation of these attacks is the Lucky Thirteen attack
	[CBC-Attack], a timing side-channel attack that allows the attacker		[CBC-Attack], a timing side-channel attack that allows the attacker
	to decrypt arbitrary ciphertext.		to decrypt arbitrary ciphertext.
	2.3. Attacks on RC4		2.4. Attacks on RC4
	The RC4 algorithm [RC4] has been used with TLS (and previously, SSL)		The RC4 algorithm [RC4] has been used with TLS (and previously, SSL)
	for many years. Attacks have also been known for a long time, e.g.		for many years. RC4 has long been known to have a variety of
	[RC4-Attack-FMS]. But recent attacks ([RC4-Attack],		cryptographic weaknesses, e.g. [RC4-Attack-Pau], [RC4-Attack-Man],
	[RC4-Attack-AlF]) have weakened this algorithm even more. See		[RC4-Attack-FMS]. Recent cryptanalysis results [RC4-Attack-AlF]
	[I-D.popov-tls-prohibiting-rc4] for more details.		exploit biases in the RC4 keystream to recover repeatedly encrypted
			plaintexts.
	2.4. Compression Attacks: CRIME and BREACH		These recent results are on the verge of becoming practically
			exploitable; currently they require 2^26 sessions or 13x2^30
			encryptions. As a result, RC4 can no longer be seen as providing a
			sufficient level of security for TLS sessions.
			2.5. Compression Attacks: CRIME and BREACH
	The CRIME attack [CRIME] allows an active attacker to decrypt		The CRIME attack [CRIME] allows an active attacker to decrypt
	cyphertext (specifically, cookies) when TLS is used with protocol-		ciphertext (specifically, cookies) when TLS is used with protocol-
	level compression.		level compression.
	The TIME attack [TIME] and the later BREACH attack [BREACH] both make		The TIME attack [TIME] and the later BREACH attack [BREACH] both make
	similar use of HTTP-level compression to decrypt secret data passed		similar use of HTTP-level compression to decrypt secret data passed
	in the HTTP response. We note that compression of the HTTP message		in the HTTP response. We note that compression of the HTTP message
	body is much more prevalent than compression at the TLS level.		body is much more prevalent than compression at the TLS level.
	The former attack can be mitigated by disabling TLS compression, as		The former attack can be mitigated by disabling TLS compression, as
	recommended below. We are not aware of mitigations at the protocol		recommended below. We are not aware of mitigations at the protocol
	level to the latter attack, and so application-level mitigations are		level to the latter attack, and so application-level mitigations are
	needed (see [BREACH]). For example, implementations of HTTP that use		needed (see [BREACH]). For example, implementations of HTTP that use
	CSRF tokens will need to randomize them even when the recommendations		CSRF tokens will need to randomize them even when the recommendations
	of [I-D.ietf-uta-tls-bcp] are adopted.		of [I-D.ietf-uta-tls-bcp] are adopted.
			2.6. Certificate Attacks
			There have been several practical attacks on TLS when used with RSA
			certificates (the most common use case). These include
			[Bleichenbacher98] and [Klima03]. While the Bleichenbacher attack
			has been mitigated in TLS 1.0, the Klima attack that relies on a
			version-check oracle is only mitigated by TLS 1.1.
			The use of RSA certificates often involves exploitable timing issues
			[Brumley03], unless the implementation takes care to explicitly
			eliminate them.
			2.7. Diffe-Hellman Parameters
			TLS allows to define ephemeral Diffie-Hellman and Elliptic Curve
			Diffie-Hellman parameters in its respective key exchange modes. This
			results in an outstanding attack, detailed in [Cross-Protocol]. In
			addition, clients that do not properly verify the received parameters
			are exposed to MITM attacks. Unfortunately the TLS protocol does not
			require this verification, see [RFC6989] for the IPsec analogy.
			2.8. Denial of Service
			Server CPU power has progressed over the years so that TLS can now be
			turned on by default. However the risk of malicious clients and
			coordinated groups of clients ("botnets") mounting denial of service
			attacks is still very real. TLS adds another vector for
			computational attacks, since a client can easily (with little
			computational effort) force the server to expend relatively large
			computational work. It is known that such attacks have in fact been
			mounted.
	3. Security Considerations		3. Security Considerations
	This document describes protocol attacks in an informational manner,		This document describes protocol attacks in an informational manner,
	and in itself does not have any security implications. Its companion		and in itself does not have any security implications. Its companion
	documents certainly do.		documents certainly do.
	4. IANA Considerations		4. IANA Considerations
	This document requires no IANA actions.		This document requires no IANA actions.
	5. Acknowledgements		5. Acknowledgements
	We would like to thank Stephen Farrell, Simon Josefsson, Yoav Nir,		We would like to thank Stephen Farrell, Simon Josefsson, Yoav Nir,
	Kenny Paterson, Patrick Pelletier, and Rich Salz for their review of		Kenny Paterson, Patrick Pelletier, Tom Ritter and Rich Salz for their
	a previous version of this document.		review of this document. We thank Andrei Popov for contributing text
			on RC4.
	The document was prepared using the lyx2rfc tool, created by Nico		The document was prepared using the lyx2rfc tool, created by Nico
	Williams.		Williams.
	6. References		6. References
	6.1. Normative References		6.1. Normative References
	[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security		[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
	(TLS) Protocol Version 1.2", RFC 5246, August 2008.		(TLS) Protocol Version 1.2", RFC 5246, August 2008.
	6.2. Informative References		6.2. Informative References
	[I-D.ietf-uta-tls-bcp]		[I-D.ietf-uta-tls-bcp]
	Sheffer, Y., Holz, R., and P. Saint-Andre,		Sheffer, Y., Holz, R., and P. Saint-Andre,
	"Recommendations for Secure Use of TLS and DTLS", draft-		"Recommendations for Secure Use of TLS and DTLS", draft-
	ietf-uta-tls-bcp-00 (work in progress), March 2014.		ietf-uta-tls-bcp-00 (work in progress), March 2014.
	[I-D.popov-tls-prohibiting-rc4]		[RFC6989] Sheffer, Y. and S. Fluhrer, "Additional Diffie-Hellman
	Popov, A., "Prohibiting RC4 Cipher Suites", draft-popov-		Tests for the Internet Key Exchange Protocol Version 2
	tls-prohibiting-rc4-01 (work in progress), October 2013.		(IKEv2)", RFC 6989, July 2013.
	[CBC-Attack]		[CBC-Attack]
	AlFardan, N. and K. Paterson, "Lucky Thirteen: Breaking		AlFardan, N. and K. Paterson, "Lucky Thirteen: Breaking
	the TLS and DTLS Record Protocols", IEEE Symposium on		the TLS and DTLS Record Protocols", IEEE Symposium on
	Security and Privacy , 2013.		Security and Privacy , 2013.
	[BEAST] Rizzo, J. and T. Duong, "Browser Exploit Against SSL/TLS",		[BEAST] Rizzo, J. and T. Duong, "Browser Exploit Against SSL/TLS",
	2011, <http://packetstormsecurity.com/files/105499/		2011, <http://packetstormsecurity.com/files/105499/
	Browser-Exploit-Against-SSL-TLS.html>.		Browser-Exploit-Against-SSL-TLS.html>.
	[CRIME] Rizzo, J. and T. Duong, "The CRIME Attack", EKOparty		[CRIME] Rizzo, J. and T. Duong, "The CRIME Attack", EKOparty
	Security Conference 2012, 2012.		Security Conference 2012, 2012.
	[BREACH] Prado, A., Harris, N., and Y. Gluck, "The BREACH Attack",		[BREACH] Prado, A., Harris, N., and Y. Gluck, "The BREACH Attack",
	2013, <http://breachattack.com/>.		2013, <http://breachattack.com/>.
	[TIME] Be'ery, T. and A. Shulman, "A Perfect CRIME? Only TIME		[TIME] Be'ery, T. and A. Shulman, "A Perfect CRIME? Only TIME
	Will Tell", Black Hat Europe 2013, 2013, <https://		Will Tell", Black Hat Europe 2013, 2013,
	media.blackhat.com/eu-13/briefings/Beery/bh-eu-13-a		<https://media.blackhat.com/eu-13/briefings/Beery/bh-
	-perfect-crime-beery-wp.pdf>.		eu-13-a-perfect-crime-beery-wp.pdf>.
	[RC4] Schneier, B., "Applied Cryptography: Protocols,		[RC4] Schneier, B., "Applied Cryptography: Protocols,
	Algorithms, and Source Code in C, 2nd Ed.", 1996.		Algorithms, and Source Code in C, 2nd Ed.", 1996.
	[RC4-Attack-FMS]		[RC4-Attack-FMS]
	Fluhrer, S., Mantin, I., and A. Shamir, "Weaknesses in the		Fluhrer, S., Mantin, I., and A. Shamir, "Weaknesses in the
	Key Scheduling Algorithm of RC4", Selected Areas in		Key Scheduling Algorithm of RC4", Selected Areas in
	Cryptography , 2001.		Cryptography , 2001.
	[RC4-Attack]
	ISOBE, T., OHIGASHI, T., WATANABE, Y., and M. MORII, "Full
	Plaintext Recovery Attack on Broadcast RC4", International
	Workshop on Fast Software Encryption , 2013.
	[RC4-Attack-AlF]		[RC4-Attack-AlF]
	AlFardan, N., Bernstein, D., Paterson, K., Poettering, B.,		AlFardan, N., Bernstein, D., Paterson, K., Poettering, B.,
	and J. Schuldt, "On the Security of RC4 in TLS", Usenix		and J. Schuldt, "On the Security of RC4 in TLS", Usenix
	Security Symposium 2013, 2013, <https://www.usenix.org/		Security Symposium 2013, 2013, <https://www.usenix.org/
	conference/usenixsecurity13/security-rc4-tls>.		conference/usenixsecurity13/security-rc4-tls>.
	[Attacks-iSec]		[Attacks-iSec]
	Sarkar, P. and S. Fitzgerald, "Attacks on SSL, a		Sarkar, P. and S. Fitzgerald, "Attacks on SSL, a
	comprehensive study of BEAST, CRIME, TIME, BREACH, Lucky13		comprehensive study of BEAST, CRIME, TIME, BREACH, Lucky13
	and RC4 biases", 8 2013, <https://www.isecpartners.com/		and RC4 biases", 8 2013, <https://www.isecpartners.com/
	media/106031/ssl_attacks_survey.pdf>.		media/106031/ssl_attacks_survey.pdf>.
	[Padding-Oracle]		[Padding-Oracle]
	Vaudenay, S., "Security Flaws Induced by CBC Padding		Vaudenay, S., "Security Flaws Induced by CBC Padding
	Applications to SSL, IPSEC, WTLS...", EUROCRYPT 2002,		Applications to SSL, IPSEC, WTLS...", EUROCRYPT 2002,
	2002, <http://www.iacr.org/cryptodb/archive/2002/EUROCRYPT		2002, <http://www.iacr.org/cryptodb/archive/2002/
	/2850/2850.pdf>.		EUROCRYPT/2850/2850.pdf>.
			[Cross-Protocol]
			Mavrogiannopoulos, N., Vercauteren, F., Velichkov, V., and
			B. Preneel, "A cross-protocol attack on the TLS protocol",
			2012, <http://doi.acm.org/10.1145/2382196.2382206>.
			[RC4-Attack-Pau]
			Paul, G. and S. Maitra, "Permutation after RC4 key
			scheduling reveals the secret key.", 2007,
			<http://dblp.uni-trier.de/db/conf/sacrypt/
			sacrypt2007.html#PaulM07>.
			[RC4-Attack-Man]
			Mantin, I. and A. Shamir, "A practical attack on broadcast
			RC4", 2001.
			[SSL-Stripping]
			Marlinspike, M., "SSL Stripping", February 2009,
			<http://www.thoughtcrime.org/software/sslstrip/>.
			[Bleichenbacher98]
			Bleichenbacher, D., "Chosen ciphertext attacks against
			protocols based on the RSA encryption standard pkcs1",
			1998.
			[Klima03] Klima, V., Pokorny, O., and T. Rosa, "Attacking RSA-based
			sessions in SSL/TLS", 2003.
			[Brumley03]
			Brumley, D. and D. Boneh, "Remote timing attacks are
			practical", 2003.
	Appendix A. Appendix: Change Log		Appendix A. Appendix: Change Log
	Note to RFC Editor: please remove this section before publication.		Note to RFC Editor: please remove this section before publication.
	A.1. draft-ietf-uta-tls-bcp-00		A.1. draft-ietf-uta-tls-bcp-01
			o Added SSL Stripping, attacks related to certificates, Diffie
			Hellman parameters and denial of service.
			o Expanded on RC4 attacks, thanks to Andrei Popov.
			A.2. draft-ietf-uta-tls-bcp-00
	o Initial WG version, with only updated references.		o Initial WG version, with only updated references.
	A.2. draft-sheffer-uta-tls-bcp-00		A.3. draft-sheffer-uta-tls-bcp-00
	o Initial version, extracted from draft-sheffer-tls-bcp-01.		o Initial version, extracted from draft-sheffer-tls-bcp-01.
	Authors' Addresses		Authors' Addresses
	Yaron Sheffer		Yaron Sheffer
	Porticor		Porticor
	29 HaHarash St.		29 HaHarash St.
	Hod HaSharon 4501303		Hod HaSharon 4501303
	Israel		Israel
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