< draft-ietf-tls-cached-info-10.txt		draft-ietf-tls-cached-info-11.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 16, 2012 Nokia Siemens Networks		Expires: June 28, 2012 Nokia Siemens Networks
	December 14, 2011		December 26, 2011
	Transport Layer Security (TLS) Cached Information Extension		Transport Layer Security (TLS) Cached Information Extension
	draft-ietf-tls-cached-info-10.txt		draft-ietf-tls-cached-info-11.txt
	Abstract		Abstract
	This document defines a Transport Layer Security (TLS) extension for		Transport Layer Security (TLS) handshakes often include fairly static
	cached information. This extension allows the TLS client to inform a		information, such as the server certificate and a list of trusted
	server of cached information from previous TLS handshakes, allowing		Certification Authorities (CAs). This information can be of
	the server to omit sending cached static information to the client		considerable size, particularly if the server certificate is bundled
	during the TLS handshake protocol exchange.		with a complete certificate path (including all intermediary
			certificates up to the trust anchor public key).
			This document defines an extension that omits the exchange of already
			available information. The TLS client informs a server of cached
			information, for example from a previous TLS handshake, allowing the
			server to omit the already available information.
	Status of this Memo		Status of this Memo
	This Internet-Draft is submitted in full conformance with the		This Internet-Draft is submitted in full conformance with the
	provisions of BCP 78 and BCP 79.		provisions of BCP 78 and BCP 79.
	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 16, 2012.		This Internet-Draft will expire on June 28, 2012.
	Copyright Notice		Copyright Notice
	Copyright (c) 2011 IETF Trust and the persons identified as the		Copyright (c) 2011 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
	skipping to change at page 2, line 11 ¶		skipping to change at page 2, line 17 ¶
	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. Extension Exchange . . . . . . . . . . . . . . . . . . . . . . 7		4. Exchange Specification . . . . . . . . . . . . . . . . . . . . 7
	4.1. Cached Information . . . . . . . . . . . . . . . . . . . . 7		4.1. Fingerprint of the Certificate Chain . . . . . . . . . . . 7
	4.2. Reconnaissance . . . . . . . . . . . . . . . . . . . . . . 7		4.2. Fingerprint for Trusted CAs . . . . . . . . . . . . . . . 8
	5. Cached Information Substitution . . . . . . . . . . . . . . . 8		5. Security Considerations . . . . . . . . . . . . . . . . . . . 10
	5.1. Substitution Syntax for certificate_chain . . . . . . . . 8		6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
	5.2. Substitution Syntax for trusted_cas . . . . . . . . . . . 9		6.1. New Entry to the TLS ExtensionType Registry . . . . . . . 11
	6. Security Considerations . . . . . . . . . . . . . . . . . . . 10		6.2. New Registry for CachedInformationType . . . . . . . . . . 11
	7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11		6.3. New Registry for HashAlgorithm . . . . . . . . . . . . . . 11
	8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12		7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 12
	9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13		8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
	9.1. Normative References . . . . . . . . . . . . . . . . . . . 13		8.1. Normative References . . . . . . . . . . . . . . . . . . . 13
	9.2. Informative References . . . . . . . . . . . . . . . . . . 13		8.2. Informative References . . . . . . . . . . . . . . . . . . 13
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
	1. Introduction		1. Introduction
	TLS handshakes often include fairly static information such as server		Transport Layer Security (TLS) handshakes often include fairly static
	certificate and a list of trusted Certification Authorities (CAs).		information, such as the server certificate and a list of trusted
	Static information such as a server certificate can be of		Certification Authorities (CAs). This information can be of
	considerable size. This is the case in particular if the server		considerable size, particularly if the server certificate is bundled
	certificate is bundled with a complete certificate path, including		with a complete certificate path (including all intermediary
	all intermediary certificates up to the trust anchor public key.		certificates up to the trust anchor public key).
	Significant benefits can be achieved in low bandwidth and high		Optimizing the exchange of information to a minimum helps to improve
	latency networks, in particular if the communication channel also has		performance in environments where devices are connected to a network
	a relatively high rate of transmission errors, if a known and		with characteristics like low bandwidth, high latency and high loss
	previously cached server certificate path can be omitted from the TLS		rate. These types of networks exist, for example, when smart objects
	handshake.		are connected using a low power IEEE 802.15.4 radio. For more
			information about the challenges with smart object deployments please
			see [I-D.iab-smart-object-workshop].
	This specification defines the Cached Information TLS extension,		This specification defines a TLS extension that allows a client and a
	which may be used by a client and a server to exclude transmission of		server to exclude transmission of cached information from the TLS
	cached information from the TLS handshake.		handshake.
	2. Terminology		2. Terminology
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 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
	A new extension type (cached_information(TBD)) is defined and used in		This document defines a new extension type (cached_information(TBD)),
	both the client hello and server hello messages. The extension type		which is used in client hello and server hello messages. The
	is specified as follows.		extension type is specified as follows.
	enum {		enum {
	cached_information(TBD), (65535)		cached_information(TBD), (65535)
	} ExtensionType;		} ExtensionType;
	The extension_data field of this extension, when included in the		The extension_data field of this extension, when included in the
	client hello, SHALL contain CachedInformation according to the		client hello, MUST contain the CachedInformation structure.
	following structure:
	enum {		enum {
	certificate_chain(1), trusted_cas(2), (255)		certificate_chain(1), trusted_cas(2) (255)
	} CachedInformationType;		} CachedInformationType;
	struct {		struct {
	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 CachedInformationType identifies certificate_chain, then		When the CachedInformationType identifies a certificate_chain, then
	hash_value MUST include a hash calculated over the certificate_list		the hash_value field MUST include a hash calculated over the
	element of a server side Certificate message, excluding the three		certificate_list element of a server side Certificate message,
	length bytes of the certificate_list vector.		excluding the three length bytes of the certificate_list vector.
	When CachedInformationType identifies trusted_cas, then hash_value		When the CachedInformationType identifies a trusted_cas, then the
	MUST include a hash calculated over the certificate_authorities		hash_value MUST include a hash calculated over the
	element of a server side CertificateRequest message, excluding the		certificate_authorities element of a server side CertificateRequest
	two length bytes of the certificate_authorities vector.		message, excluding the two length bytes of the
			certificate_authorities vector.
	The hash algorithm used to calculate hash values SHALL be the hash		The hash algorithm used to calculate hash values is conveyed in the
	algorithm that was used to generate the Finished message in the		'hash' field of the CachedObject element. This document defines the
	handshake exchange from which the hashed information was cached.		following hash algorithms:
	Hash algorithm identifiers are defined in the RFC 5246 [RFC5246]
	HashAlgorithm registry.
	Other specifications MAY define more CachedInformationType types.		o SHA-1: NIST FIPS PUB 180-3 [SHA]
			o SHA-224: RFC 3874 [RFC3874]
	4. Extension Exchange		o SHA-256: NIST FIPS PUB 180-3 [SHA]
	4.1. Cached Information		o SHA-384: NIST FIPS PUB 180-3 [SHA]
	Clients MAY include a "cached_information" extension in the		o SHA-512: NIST FIPS PUB 180-3 [SHA]
	(extended) client hello, which MAY contain zero or more cached
	objects (CachedObject).
	Servers that receive an extended client hello containing a		This document establishes a registry for CachedInformationType types
	"cached_information" extension MAY indicate that they support cached		and additional values can be added following the policy described in
	information objects by including a cached_information extension in		Section 6.
	their (extended) server hello.
	A cached_information extension provided in the server hello has the		4. Exchange Specification
	following semantics:
	o An empty cached_information extension indicates that the server		Clients supporting this extension MAY include the
	supports information caching but provides no information about		"cached_information" extension in the (extended) client hello, which
	what information types it supports.		MAY contain zero or more CachedObject attributes.
	o A non-empty cached information extension indicates that the server		Server supporting this extension MAY include the "cached_information"
	supports caching of each present CachedObject that matches the		extension in the (extended) server hello, which MAY contain one or
	specified hash value. The server MAY support other cached objects		more CachedObject attributes. By returning the "cached_information"
	that are not present in the extension.		extension the server indicates that it supports caching of each
			present CachedObject that matches the specified hash value. The
			server MAY support other cached objects that are not present in the
			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.		[I-D.ietf-tls-rfc4366-bis] value.
	4.2. Reconnaissance
	A client MAY include an empty cached_information extension (with
	empty extension_data field) in its (extended) client hello to query
	whether the server supports cached information.
	Upon receiving an empty cached_information extension, a server MAY
	indicate that it supports cached information in handshakes by
	including a cached_information extension in its (extended) server
	hello according to any of the available options in Section 4.1.
	5. Cached Information Substitution
	Following a successful exchange of "cached_information" extensions,		Following a successful exchange of "cached_information" extensions,
	the server MAY substitute cached information in the handshake		the server MAY send fingerprints of the cached information in the
	exchange with a matching CachedObject from the client hello		handshake exchange as a replacement for the exchange of the full
	"cached_information" extension.		data. Section 4.1 and Section 4.2 defines the syntax of the
			fingerprinted information.
	A substitution syntax that defines how the CachedObject structure is
	carried in the handshake message MUST be defined for each
	CachedInformationType in a way that does not violate the syntax of
	the handshake message. The substitution syntax for
	certificate_chain(1) and trusted_cas(2) is provided below.
	The handshake protocol SHALL proceed using the cached information as		The handshake protocol MUST proceed using the information as if it
	if it was provided in the handshake protocol. The Finished message		was provided in the handshake protocol. The Finished message MUST be
	SHALL be calculated over the actual data exchanged in the handshake		calculated over the actual data exchanged in the handshake protocol.
	protocol. That is, the Finished message will be calculated over the		That is, the Finished message will be calculated over the hash values
	hash values of cached information objects and not over the cached		of cached information objects and not over the cached information
	information that were omitted from transmission.		that were omitted from transmission.
	The server MUST NOT include more than one CachedObject as		The server MUST NOT include more than one fingerprint for a single
	substitution for the cached information.		information element, i.e., at maximum only one CachedObject structure
			per replaced information is provided.
	5.1. Substitution Syntax for certificate_chain		4.1. Fingerprint of the Certificate Chain
	When an object of type certificate_chain is provided in the client		When an object of type 'certificate_chain' is provided in the client
	hello, the server MAY substitute the cached information with a		hello, the server MAY send a fingerprint instead of the complete
	matching hash value received from the client by expanding the		certificate chain as shown below.
	Certificate handshake message as follows.
	Original handshake message syntax defined in RFC 5246 [RFC5246]:		The original handshake message syntax is defined in RFC 5246
			[RFC5246] and has the following structure:
	opaque ASN.1Cert<1..2^24-1>;		opaque ASN.1Cert<1..2^24-1>;
	struct {		struct {
	ASN.1Cert certificate_list<0..2^24-1>;		ASN.1Cert certificate_list<0..2^24-1>;
	} Certificate;		} Certificate;
	Substitution syntax is defined by expanding the syntax of the opaque		By using the extension defined in this document the following
	ASN.1Cert structure:		information is sent:
	CachedObject ASN.1Cert<1..2^24-1>;		struct {
			CachedObject ASN.1Cert<1..2^24-1>;
			} Certificate;
	5.2. Substitution Syntax for trusted_cas		The opaque ASN.1Cert structure is replaced with the CachedObject
			structure defined in this document.
	When a hash for an object of type trusted_cas is provided in the		Note: [I-D.wouters-tls-oob-pubkey] allows a PKIX certificate
	client hello, the server MAY substitute the cached information with a		containing only the SubjectPublicKeyInfo instead of the full
	matching hash value received from the client by expanding the		information typically found in a certificate. Hence, when this
	CertificateRequest handshake message as follows.		specification is used in combination with
			[I-D.wouters-tls-oob-pubkey] and the negotiated certificate type is
			RawPublicKey then the TLS server sends the hashed Certificate element
			that contains a ASN.1Cert with the mentioned raw public key.
	Original handshake message syntax defined in RFC 5246 [RFC5246]:		4.2. Fingerprint for Trusted CAs
			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
			complete certificate authorities information as shown below.
			The original handshake message syntax is defined in RFC 5246
			[RFC5246] and has the following structure:
	opaque DistinguishedName<1..2^16-1>;		opaque DistinguishedName<1..2^16-1>;
	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>;
	DistinguishedName certificate_authorities<0..2^16-1>;		DistinguishedName certificate_authorities<0..2^16-1>;
	} CertificateRequest		} CertificateRequest;
	The substitution syntax is defined by expanding the syntax of the		By using the extension defined in this document the following
	opaque DistinguishedName structure:		information is sent:
	CachedObject DistinguishedName<1..2^16-1>;		struct {
			ClientCertificateType certificate_types<1..2^8-1>;
			SignatureAndHashAlgorithm
			supported_signature_algorithms<2^16-1>;
			CachedObject DistinguishedName<1..2^16-1>;
			} CertificateRequest;
	6. Security Considerations		The opaque DistinguishedName structure is replaced with the
			CachedObject structure defined in this document.
			5. Security Considerations
	The hash algorithm used in this specification is required to have		The hash algorithm used in this specification is required to have
	reasonable random properties in order to provide reasonably unique		reasonable random properties in order to provide reasonably unique
	identifiers. There is no clearly identified requirement that this		identifiers. There is no requirement that this hash algorithm must
	hash algorithm must have strong collision resistance. However since		have strong collision resistance.
	the hash algorithm is used to represent data in the finished
	calculation, the security properties of the finished calculation will
	change if a weaker hash algorithm is used to represent cached
	information compared with the hash algorithm used to calculate the
	finished message.
	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 en unencrypted
	handshake.		handshake.
	7. IANA Considerations		6. IANA Considerations
	1) Create an entry, cached_information(TBD), in the existing registry		6.1. New Entry to the TLS ExtensionType Registry
	for ExtensionType (defined in RFC 5246 [RFC5246]).
	2) Establish a registry for TLS CachedInformationType values. The		IANA is requested to add an entry to the existing TLS ExtensionType
	first entries in the registry are certificate_chain(1) and		registry, defined in RFC 5246 [RFC5246], for cached_information(TBD)
	trusted_cas(2). TLS CachedInformationType values in the inclusive		defined in this document.
	range 0-63 (decimal) are assigned via RFC 5226 [RFC5226] Standards
	Action. Values from the inclusive range 64-223 (decimal) are
	assigned via RFC 5226 Specification Required. Values from the
	inclusive range 224-255 (decimal) are reserved for RFC 5226 Private
	Use.
	8. Acknowledgments		6.2. New Registry for CachedInformationType
			IANA is requested to establish a registry for TLS
			CachedInformationType values. The first entries in the registry are
			o certificate_chain(1)
			o trusted_cas(2)
			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
			6.3. New Registry for HashAlgorithm
			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
			7. Acknowledgments
	The author acknowledges input from many members of the TLS working		The author acknowledges input from many members of the TLS working
	group.		group.
	9. References		We would like to thank Paul Wouters for his feedback and Nikos
			Mavrogiannopoulos for his document review in December 2011.
	9.1. Normative References		8. References
			8.1. Normative References
	[I-D.ietf-tls-rfc4366-bis]		[I-D.ietf-tls-rfc4366-bis]
	3rd, D., "Transport Layer Security (TLS) Extensions:		3rd, D., "Transport Layer Security (TLS) Extensions:
	Extension Definitions", draft-ietf-tls-rfc4366-bis-12		Extension Definitions", draft-ietf-tls-rfc4366-bis-12
	(work in progress), September 2010.		(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",
			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.
	9.2. Informative References		[SHA] "Federal Information Processing Standards Publication
			(FIPS PUB) 180-3, Secure Hash Standard (SHS)",
			October 2008.
			8.2. Informative References
			[I-D.iab-smart-object-workshop]
			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]
			Wouters, P., Gilmore, J., Weiler, S., Kivinen, T., and H.
			Tschofenig, "TLS out-of-band public key validation",
			draft-wouters-tls-oob-pubkey-02 (work in progress),
			November 2011.
	[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.
	Authors' Addresses		Authors' Addresses
	Stefan Santesson		Stefan Santesson
	3xA Security AB		3xA Security AB
	Scheelev. 17		Scheelev. 17
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