< draft-ietf-tls-cached-info-11.txt		draft-ietf-tls-cached-info-12.txt >
	TLS S. Santesson		TLS S. Santesson
	Internet-Draft 3xA Security AB		Internet-Draft 3xA Security AB
	Intended status: Standards Track H. Tschofenig		Intended status: Standards Track H. Tschofenig
	Expires: June 28, 2012 Nokia Siemens Networks		Expires: January 16, 2013 Nokia Siemens Networks
	December 26, 2011		July 15, 2012
	Transport Layer Security (TLS) Cached Information Extension		Transport Layer Security (TLS) Cached Information Extension
	draft-ietf-tls-cached-info-11.txt		draft-ietf-tls-cached-info-12.txt
	Abstract		Abstract
	Transport Layer Security (TLS) handshakes often include fairly static		Transport Layer Security (TLS) handshakes often include fairly static
	information, such as the server certificate and a list of trusted		information, such as the server certificate and a list of trusted
	Certification Authorities (CAs). This information can be of		Certification Authorities (CAs). This information can be of
	considerable size, particularly if the server certificate is bundled		considerable size, particularly if the server certificate is bundled
	with a complete certificate path (including all intermediary		with a complete certificate path (including all intermediary
	certificates up to the trust anchor public key).		certificates up to the trust anchor public key).
	skipping to change at page 1, line 41 ¶		skipping to change at page 1, line 41 ¶
	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 June 28, 2012.		This Internet-Draft will expire on January 16, 2013.
	Copyright Notice		Copyright Notice
	Copyright (c) 2011 IETF Trust and the persons identified as the		Copyright (c) 2012 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 . . . . . . . . . . . . . . . . . . . . . . . . . 3		1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
	3. Cached Information Extension . . . . . . . . . . . . . . . . . 5		3. Cached Information Extension . . . . . . . . . . . . . . . . . 5
	4. Exchange Specification . . . . . . . . . . . . . . . . . . . . 7		4. Exchange Specification . . . . . . . . . . . . . . . . . . . . 7
	4.1. Fingerprint of the Certificate Chain . . . . . . . . . . . 7		4.1. Fingerprint of the Certificate Chain . . . . . . . . . . . 7
	4.2. Fingerprint for Trusted CAs . . . . . . . . . . . . . . . 8		4.2. Fingerprint for Trusted CAs . . . . . . . . . . . . . . . 8
	5. Security Considerations . . . . . . . . . . . . . . . . . . . 10		5. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
	6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11		6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
	6.1. New Entry to the TLS ExtensionType Registry . . . . . . . 11		7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
	6.2. New Registry for CachedInformationType . . . . . . . . . . 11		7.1. New Entry to the TLS ExtensionType Registry . . . . . . . 13
	6.3. New Registry for HashAlgorithm . . . . . . . . . . . . . . 11		7.2. New Registry for CachedInformationType . . . . . . . . . . 13
	7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12		8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 14
	8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13		9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
	8.1. Normative References . . . . . . . . . . . . . . . . . . . 13		9.1. Normative References . . . . . . . . . . . . . . . . . . . 15
	8.2. Informative References . . . . . . . . . . . . . . . . . . 13		9.2. Informative References . . . . . . . . . . . . . . . . . . 15
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
	1. Introduction		1. Introduction
	Transport Layer Security (TLS) handshakes often include fairly static		Transport Layer Security (TLS) handshakes often include fairly static
	information, such as the server certificate and a list of trusted		information, such as the server certificate and a list of trusted
	Certification Authorities (CAs). This information can be of		Certification Authorities (CAs). This information can be of
	considerable size, particularly if the server certificate is bundled		considerable size, particularly if the server certificate is bundled
	with a complete certificate path (including all intermediary		with a complete certificate path (including all intermediary
	certificates up to the trust anchor public key).		certificates up to the trust anchor public key).
	Optimizing the exchange of information to a minimum helps to improve		Optimizing the exchange of information to a minimum helps to improve
	performance in environments where devices are connected to a network		performance in environments where devices are connected to a network
	with characteristics like low bandwidth, high latency and high loss		with characteristics like low bandwidth, high latency and high loss
	rate. These types of networks exist, for example, when smart objects		rate. These types of networks exist, for example, when smart objects
	are connected using a low power IEEE 802.15.4 radio. For more		are connected using a low power IEEE 802.15.4 radio. For more
	information about the challenges with smart object deployments please		information about the challenges with smart object deployments please
	see [I-D.iab-smart-object-workshop].		see [RFC6574].
	This specification defines a TLS extension that allows a client and a		This specification defines a TLS extension that allows a client and a
	server to exclude transmission of cached information from the TLS		server to exclude transmission of cached information from the TLS
	handshake.		handshake.
			A typical example exchange may therefore look as follows. First, the
			TLS exchange executes the usual TLS handshake. It may decide to
			store the certificate provided by the server for a future exchange.
			When the TLS client then connects to the TLS server some time in the
			future, without using session resumption, it then attaches the
			cached_information extension defined in this document to the client
			hello message to indicate that it had cached the certificate, and it
			provides the fingerprint of it. If the server's certificate had not
			changed then the TLS server does not need to send the full
			certificate to the client again. In case the information had
			changed, the certificate payload is transmitted to the client to
			allow the client to update it's state information.
	2. Terminology		2. Terminology
	The key words "MUST", "MUST NOT", "REQUIRED", "MUST", "MUST NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "MUST", "MUST NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this		"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
	document are to be interpreted as described in [RFC2119].		document are to be interpreted as described in [RFC2119].
	3. Cached Information Extension		3. Cached Information Extension
	This document defines a new extension type (cached_information(TBD)),		This document defines a new extension type (cached_information(TBD)),
	which is used in client hello and server hello messages. The		which is used in client hello and server hello messages. The
	skipping to change at page 5, line 33 ¶		skipping to change at page 5, line 33 ¶
	CachedInformationType type;		CachedInformationType type;
	HashAlgorithm hash;		HashAlgorithm hash;
	opaque hash_value<1..255>;		opaque hash_value<1..255>;
	} CachedObject;		} CachedObject;
	struct {		struct {
	CachedObject cached_info<1..2^16-1>;		CachedObject cached_info<1..2^16-1>;
	} CachedInformation;		} CachedInformation;
	When the CachedInformationType identifies a certificate_chain, then		When the CachedInformationType identifies a certificate_chain, then
	the hash_value field MUST include a hash calculated over the		the hash_value field MUST include the hash calculated over the
	certificate_list element of a server side Certificate message,		certificate_list element of the Certificate payload provided by the
	excluding the three length bytes of the certificate_list vector.		TLS server in an earlier exchange, excluding the three length bytes
			of the certificate_list vector.
	When the CachedInformationType identifies a trusted_cas, then the		When the CachedInformationType identifies a trusted_cas, then the
	hash_value MUST include a hash calculated over the		hash_value MUST include a hash calculated over the
	certificate_authorities element of a server side CertificateRequest		certificate_authorities element of the CertificateRequest payload
	message, excluding the two length bytes of the		provided by the TLS server in an earlier exchange, excluding the two
	certificate_authorities vector.		length bytes of the certificate_authorities vector.
	The hash algorithm used to calculate hash values is conveyed in the		The hash algorithm used to calculate hash values is conveyed in the
	'hash' field of the CachedObject element. This document defines the		'hash' field of the CachedObject element. The list of registered
	following hash algorithms:		hash algorithms can be found in the TLS HashAlgorithm Registry, which
			was created by RFC 5246 [RFC5246]. The value zero (0) for 'none' is
	o SHA-1: NIST FIPS PUB 180-3 [SHA]		not an allowed choice for a hash algorithm and MUST NOT be used.
	o SHA-224: RFC 3874 [RFC3874]
	o SHA-256: NIST FIPS PUB 180-3 [SHA]
	o SHA-384: NIST FIPS PUB 180-3 [SHA]
	o SHA-512: NIST FIPS PUB 180-3 [SHA]
	This document establishes a registry for CachedInformationType types		This document establishes a registry for CachedInformationType types
	and additional values can be added following the policy described in		and additional values can be added following the policy described in
	Section 6.		Section 7.
	4. Exchange Specification		4. Exchange Specification
	Clients supporting this extension MAY include the		Clients supporting this extension MAY include the
	"cached_information" extension in the (extended) client hello, which		"cached_information" extension in the (extended) client hello, which
	MAY contain zero or more CachedObject attributes.		MAY contain zero or more CachedObject attributes.
	Server supporting this extension MAY include the "cached_information"		Server supporting this extension MAY include the "cached_information"
	extension in the (extended) server hello, which MAY contain one or		extension in the (extended) server hello, which MAY contain one or
	more CachedObject attributes. By returning the "cached_information"		more CachedObject attributes. By returning the "cached_information"
	extension the server indicates that it supports caching of each		extension the server indicates that it supports caching of each
	present CachedObject that matches the specified hash value. The		present CachedObject that matches the specified hash value. The
	server MAY support other cached objects that are not present in the		server MAY support other cached objects that are not present in the
	extension.		extension.
	Note: Clients may need the ability to cache different values		Note: Clients may need the ability to cache different values
	depending on other information in the Client Hello that modify what		depending on other information in the Client Hello that modify what
	values the server uses, in particular the Server Name Indication		values the server uses, in particular the Server Name Indication
	[I-D.ietf-tls-rfc4366-bis] value.		[RFC6066] value.
	Following a successful exchange of "cached_information" extensions,		Following a successful exchange of "cached_information" extensions,
	the server MAY send fingerprints of the cached information in the		the server MAY send fingerprints of the cached information in the
	handshake exchange as a replacement for the exchange of the full		handshake exchange as a replacement for the exchange of the full
	data. Section 4.1 and Section 4.2 defines the syntax of the		data. Section 4.1 and Section 4.2 defines the syntax of the
	fingerprinted information.		fingerprinted information.
	The handshake protocol MUST proceed using the information as if it		The handshake protocol MUST proceed using the information as if it
	was provided in the handshake protocol. The Finished message MUST be		was provided in the handshake protocol. The Finished message MUST be
	calculated over the actual data exchanged in the handshake protocol.		calculated over the actual data exchanged in the handshake protocol.
	skipping to change at page 8, line 21 ¶		skipping to change at page 8, line 21 ¶
	By using the extension defined in this document the following		By using the extension defined in this document the following
	information is sent:		information is sent:
	struct {		struct {
	CachedObject ASN.1Cert<1..2^24-1>;		CachedObject ASN.1Cert<1..2^24-1>;
	} Certificate;		} Certificate;
	The opaque ASN.1Cert structure is replaced with the CachedObject		The opaque ASN.1Cert structure is replaced with the CachedObject
	structure defined in this document.		structure defined in this document.
	Note: [I-D.wouters-tls-oob-pubkey] allows a PKIX certificate		Note: [I-D.ietf-tls-oob-pubkey] allows a PKIX certificate containing
	containing only the SubjectPublicKeyInfo instead of the full		only the SubjectPublicKeyInfo instead of the full information
	information typically found in a certificate. Hence, when this		typically found in a certificate. Hence, when this specification is
	specification is used in combination with		used in combination with [I-D.ietf-tls-oob-pubkey] and the negotiated
	[I-D.wouters-tls-oob-pubkey] and the negotiated certificate type is		certificate type is a raw public key then the TLS server sends the
	RawPublicKey then the TLS server sends the hashed Certificate element		hashed Certificate payload that contains a ASN.1Cert structure of the
	that contains a ASN.1Cert with the mentioned raw public key.		SubjectPublicKeyInfo.
	4.2. Fingerprint for Trusted CAs		4.2. Fingerprint for Trusted CAs
	When a hash for an object of type 'trusted_cas' is provided in the		When a hash for an object of type 'trusted_cas' is provided in the
	client hello, the server MAY send a fingerprint instead of the		client hello, the server MAY send a fingerprint instead of the
	complete certificate authorities information as shown below.		complete certificate authorities information as shown below.
	The original handshake message syntax is defined in RFC 5246		The original handshake message syntax is defined in RFC 5246
	[RFC5246] and has the following structure:		[RFC5246] and has the following structure:
	skipping to change at page 10, line 5 ¶		skipping to change at page 10, line 5 ¶
	struct {		struct {
	ClientCertificateType certificate_types<1..2^8-1>;		ClientCertificateType certificate_types<1..2^8-1>;
	SignatureAndHashAlgorithm		SignatureAndHashAlgorithm
	supported_signature_algorithms<2^16-1>;		supported_signature_algorithms<2^16-1>;
	CachedObject DistinguishedName<1..2^16-1>;		CachedObject DistinguishedName<1..2^16-1>;
	} CertificateRequest;		} CertificateRequest;
	The opaque DistinguishedName structure is replaced with the		The opaque DistinguishedName structure is replaced with the
	CachedObject structure defined in this document.		CachedObject structure defined in this document.
	5. Security Considerations		5. Example
	The hash algorithm used in this specification is required to have		Figure 1 illustrates an example exchange using the TLS cached info
	reasonable random properties in order to provide reasonably unique		extension. In the normal TLS handshake exchange shown in flow (A)
	identifiers. There is no requirement that this hash algorithm must		the TLS server provides its certificate in the Certificate payload to
	have strong collision resistance.		the client, see step [1]. This allows the client to store the
			certificate for future use. After some time the TLS client again
			interacts with the same TLS server and makes use of the TLS cached
			info extension, as shown in flow (B). The TLS client indicates
			support for this specification via the cached_information extension,
			see [2], and indicates that it has stored the certificate_chain from
			the earlier exchange. With [3] the TLS server indicates that it also
			supports this specification and informs the client that it also
			supports caching of other objects beyond the 'certificate_chain',
			namely 'trusted_cas' (also defined in this document), and the 'foo-
			bar' extension (i.e., an imaginary extension that yet needs to be
			defined). With [4] the TLS server provides the fingerprint of the
			certificate chain as described in Section 4.1.
			(A) Initial (full) Exchange
			client_hello ->
			<- server_hello,
			certificate, // [1]
			server_key_exchange,
			server_hello_done
			client_key_exchange,
			change_cipher_spec,
			finished ->
			<- change_cipher_spec,
			finished
			Application Data <-------> Application Data
			(B) TLS Cached Extension Usage
			client_hello,
			cached_information=(certificate_chain) -> // [2]
			<- server_hello,
			cached_information= // [3]
			(certificate_chain, trusted_cas, foo-bar)
			certificate, // [4]
			server_key_exchange,
			server_hello_done
			client_key_exchange,
			change_cipher_spec,
			finished ->
			<- change_cipher_spec,
			finished
			Application Data <-------> Application Data
			Figure 1: Example Message Exchange
			6. Security Considerations
			This specification defines a mechanism to reference stored state
			using a fingerprint. The hash algorithm used in this specification
			is required to have reasonable random properties in order to provide
			reasonably unique identifiers. There is no requirement that this
			hash algorithm must have strong collision resistance.
	Caching information in an encrypted handshake (such as a renegotiated		Caching information in an encrypted handshake (such as a renegotiated
	handshake) and sending a hash of that cached information in an		handshake) and sending a hash of that cached information in an
	unencrypted handshake might introduce integrity or data disclosure		unencrypted handshake might introduce integrity or data disclosure
	issues as it enables an attacker to identify if a known object (such		issues as it enables an attacker to identify if a known object (such
	as a known server certificate) has been used in previous encrypted		as a known server certificate) has been used in previous encrypted
	handshakes. Information object types defined in this specification,		handshakes. Information object types defined in this specification,
	such as server certificates, are public objects and usually not		such as server certificates, are public objects and usually not
	sensitive in this regard, but implementers should be aware if any		sensitive in this regard, but implementers should be aware if any
	cached information are subject to such security concerns and in such		cached information are subject to such security concerns and in such
	case SHOULD NOT send a hash over encrypted data in en unencrypted		case SHOULD NOT send a hash over encrypted data in unencrypted
	handshake.		handshake.
	6. IANA Considerations		7. IANA Considerations
	6.1. New Entry to the TLS ExtensionType Registry		7.1. New Entry to the TLS ExtensionType Registry
	IANA is requested to add an entry to the existing TLS ExtensionType		IANA is requested to add an entry to the existing TLS ExtensionType
	registry, defined in RFC 5246 [RFC5246], for cached_information(TBD)		registry, defined in RFC 5246 [RFC5246], for cached_information(TBD)
	defined in this document.		defined in this document.
	6.2. New Registry for CachedInformationType		7.2. New Registry for CachedInformationType
	IANA is requested to establish a registry for TLS		IANA is requested to establish a registry for TLS
	CachedInformationType values. The first entries in the registry are		CachedInformationType values. The first entries in the registry are
	o certificate_chain(1)		o certificate_chain(1)
	o trusted_cas(2)		o trusted_cas(2)
	The policy for adding new values to this registry, following the		The policy for adding new values to this registry, following the
	terminology defined in RFC 5226 [RFC5226], is as follows:		terminology defined in RFC 5226 [RFC5226], is as follows:
	o 0-63 (decimal): Standards Action		o 0-63 (decimal): Standards Action
	o 64-223 (decimal): Specification Required		o 64-223 (decimal): Specification Required
	o 224-255 (decimal): reserved for Private Use		o 224-255 (decimal): reserved for Private Use
	6.3. New Registry for HashAlgorithm		8. Acknowledgments
	IANA is requested to establish a registry for HashAlgorithm values
	and to populate the registry with an initial set of values listed in
	Section 3.
	The policy for adding new values to this registry, following the
	terminology defined in RFC 5226 [RFC5226], is as follows:
	o 0-63 (decimal): Standards Action
	o 64-223 (decimal): Specification Required
	o 224-255 (decimal): reserved for Private Use		We would like to thank the following persons for your detailed
			document reviews:
	7. Acknowledgments		o Paul Wouters and Nikos Mavrogiannopoulos (December 2011)
	The author acknowledges input from many members of the TLS working		o Rob Stradling (February 2012)
	group.
	We would like to thank Paul Wouters for his feedback and Nikos		o Ondrej Mikle in March 2012)
	Mavrogiannopoulos for his document review in December 2011.
	8. References		Additionally, we would like to thank the TLS working group chairs,
			Eric Rescorla and Joe Salowey, as well as the security area
			directors, Sean Turner and Stephen Farrell, for their feedback and
			support.
	8.1. Normative References		9. References
	[I-D.ietf-tls-rfc4366-bis]		9.1. Normative References
	3rd, D., "Transport Layer Security (TLS) Extensions:
	Extension Definitions", draft-ietf-tls-rfc4366-bis-12
	(work in progress), September 2010.
	[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate		[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
	Requirement Levels", BCP 14, RFC 2119, March 1997.		Requirement Levels", BCP 14, RFC 2119, March 1997.
	[RFC3874] Housley, R., "A 224-bit One-way Hash Function: SHA-224",		[RFC3874] Housley, R., "A 224-bit One-way Hash Function: SHA-224",
	RFC 3874, September 2004.		RFC 3874, September 2004.
	[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.
	[SHA] "Federal Information Processing Standards Publication		[RFC6066] Eastlake, D., "Transport Layer Security (TLS) Extensions:
	(FIPS PUB) 180-3, Secure Hash Standard (SHS)",		Extension Definitions", RFC 6066, January 2011.
	October 2008.
	8.2. Informative References
	[I-D.iab-smart-object-workshop]		9.2. Informative References
	Tschofenig, H. and J. Arkko, "Report from the
	'Interconnecting Smart Objects with the Internet'
	Workshop, 25th March 2011, Prague",
	draft-iab-smart-object-workshop-06 (work in progress),
	October 2011.
	[I-D.wouters-tls-oob-pubkey]		[I-D.ietf-tls-oob-pubkey]
	Wouters, P., Gilmore, J., Weiler, S., Kivinen, T., and H.		Wouters, P., Gilmore, J., Weiler, S., Kivinen, T., and H.
	Tschofenig, "TLS out-of-band public key validation",		Tschofenig, "TLS Out-of-Band Public Key Validation",
	draft-wouters-tls-oob-pubkey-02 (work in progress),		draft-ietf-tls-oob-pubkey-03 (work in progress),
	November 2011.		April 2012.
	[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an		[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
	IANA Considerations Section in RFCs", BCP 26, RFC 5226,		IANA Considerations Section in RFCs", BCP 26, RFC 5226,
	May 2008.		May 2008.
			[RFC6574] Tschofenig, H. and J. Arkko, "Report from the Smart Object
			Workshop", RFC 6574, April 2012.
	Authors' Addresses		Authors' Addresses
	Stefan Santesson		Stefan Santesson
	3xA Security AB		3xA Security AB
	Scheelev. 17		Scheelev. 17
	Lund 223 70		Lund 223 70
	Sweden		Sweden
	Email: sts@aaa-sec.com		Email: sts@aaa-sec.com
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