draft-ietf-tls-cached-info-23.txt		rfc7924.txt
	TLS S. Santesson		Internet Engineering Task Force (IETF) S. Santesson
	Internet-Draft 3xA Security AB		Request for Comments: 7924 3xA Security AB
	Intended status: Standards Track H. Tschofenig		Category: Standards Track H. Tschofenig
	Expires: November 12, 2016 ARM Ltd.		ISSN: 2070-1721 ARM Ltd.
	May 11, 2016		July 2016
	Transport Layer Security (TLS) Cached Information Extension		Transport Layer Security (TLS) Cached Information Extension
	draft-ietf-tls-cached-info-23.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 chain (i.e., the certificates of		with a complete certificate chain (i.e., the certificates of
	intermediate CAs up to the root CA).		intermediate CAs up to the root CA).
	This document defines an extension that allows a TLS client to inform		This document defines an extension that allows a TLS client to inform
	a server of cached information, allowing the server to omit already		a server of cached information, thereby enabling the server to omit
	available information.		already available information.
	Status of This Memo		Status of This Memo
	This Internet-Draft is submitted in full conformance with the		This is an Internet Standards Track document.
	provisions of BCP 78 and BCP 79.
	Internet-Drafts are working documents of the Internet Engineering
	Task Force (IETF). Note that other groups may also distribute
	working documents as Internet-Drafts. The list of current Internet-
	Drafts is at http://datatracker.ietf.org/drafts/current/.
	Internet-Drafts are draft documents valid for a maximum of six months		This document is a product of the Internet Engineering Task Force
	and may be updated, replaced, or obsoleted by other documents at any		(IETF). It represents the consensus of the IETF community. It has
	time. It is inappropriate to use Internet-Drafts as reference		received public review and has been approved for publication by the
	material or to cite them other than as "work in progress."		Internet Engineering Steering Group (IESG). Further information on
			Internet Standards is available in Section 2 of RFC 7841.
	This Internet-Draft will expire on November 12, 2016.		Information about the current status of this document, any errata,
			and how to provide feedback on it may be obtained at
			http://www.rfc-editor.org/info/rfc7924.
	Copyright Notice		Copyright Notice
	Copyright (c) 2016 IETF Trust and the persons identified as the		Copyright (c) 2016 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
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	(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 . . . . . . . . . . . . . . . . . . . . . . . . 3
	2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3		2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
	3. Cached Information Extension . . . . . . . . . . . . . . . . 3		3. Cached Information Extension . . . . . . . . . . . . . . . . 3
	4. Exchange Specification . . . . . . . . . . . . . . . . . . . 5		4. Exchange Specification . . . . . . . . . . . . . . . . . . . 5
	4.1. Server Certificate Message . . . . . . . . . . . . . . . 5		4.1. Server Certificate Message . . . . . . . . . . . . . . . 6
	4.2. CertificateRequest Message . . . . . . . . . . . . . . . 6		4.2. CertificateRequest Message . . . . . . . . . . . . . . . 7
	5. Fingerprint Calculation . . . . . . . . . . . . . . . . . . . 7		5. Fingerprint Calculation . . . . . . . . . . . . . . . . . . . 7
	6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 8		6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
	7. Security Considerations . . . . . . . . . . . . . . . . . . . 9		7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
	8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10		8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
	8.1. New Entry to the TLS ExtensionType Registry . . . . . . . 10		8.1. New Entry to the TLS ExtensionType Registry . . . . . . . 10
	8.2. New Registry for CachedInformationType . . . . . . . . . 10		8.2. New Registry for CachedInformationType . . . . . . . . . 11
	9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10		9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
	10. References . . . . . . . . . . . . . . . . . . . . . . . . . 11		9.1. Normative References . . . . . . . . . . . . . . . . . . 11
	10.1. Normative References . . . . . . . . . . . . . . . . . . 11		9.2. Informative References . . . . . . . . . . . . . . . . . 12
	10.2. Informative References . . . . . . . . . . . . . . . . . 11		Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . 13
	Appendix A. Example . . . . . . . . . . . . . . . . . . . . . . 12		Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 18
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
	1. Introduction		1. Introduction
	Reducing the amount of information exchanged during a Transport Layer		Reducing the amount of information exchanged during a Transport Layer
	Security handshake to a minimum helps to improve performance in		Security handshake to a minimum helps to improve performance in
	environments where devices are connected to a network with a low		environments where devices are connected to a network with a low
	bandwidth, and lossy radio technology. With Internet of Things such		bandwidth and lossy radio technology. With the Internet of Things,
	environments exist, for example, when devices use IEEE 802.15.4 or		such environments exist, for example, when devices use IEEE 802.15.4,
	Bluetooth Smart. For more information about the challenges with		Bluetooth Low Energy, or low power wide area networks. For more
	smart object deployments please see [RFC6574].		information about the challenges with smart object deployments,
			please 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 information cached in an earlier TLS		server to exclude transmission information cached in an earlier TLS
	handshake.		handshake.
	A typical example exchange may therefore look as follows. First, the		A typical example exchange may therefore look as follows. First, the
	client and the server executes the full TLS handshake. The client		client and the server execute the full TLS handshake. The client
	then caches the certificate provided by the server. When the TLS		then caches the certificate provided by the server. When the TLS
	client connects to the TLS server some time in the future, without		client connects to the TLS server some time in the future, without
	using session resumption, it then attaches the cached_info extension		using session resumption, it then attaches the "cached_info"
	defined in this document to the client hello message to indicate that		extension defined in this document to the ClientHello message to
	it had cached the certificate, and it provides the fingerprint of it.		indicate that it has cached the certificate, and it provides the
	If the server's certificate has not changed then the TLS server does		fingerprint of it. If the server's certificate has not changed, then
	not need to send its certificate and the corresponding certificate		the TLS server does not need to send its certificate and the
	chain again. In case information has changed, which can be seen from		corresponding certificate chain again. In case information has
	the fingerprint provided by the client, the certificate payload is		changed, which can be seen from the fingerprint provided by the
	transmitted to the client to allow the client to update the cache.		client, the certificate payload is transmitted to the client to allow
			the client to update the cache.
	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].
	This document refers to the TLS protocol but the description is		This document refers to the TLS protocol, but the description is
	equally applicable to DTLS as well.		equally applicable to Datagram Transport Layer Security (DTLS) as
			well.
	3. Cached Information Extension		3. Cached Information Extension
	This document defines a new extension type (cached_info(TBD)), which		This document defines a new extension type (cached_info(25)), which
	is used in client hello and server hello messages. The extension		is used in ClientHello and ServerHello messages. The extension type
	type is specified as follows.		is specified as follows.
	enum {		enum {
	cached_info(TBD), (65535)		cached_info(25), (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, MUST contain the CachedInformation structure. The		ClientHello, MUST contain the CachedInformation structure. The
	client MAY send multiple CachedObjects of the same		client MAY send multiple CachedObjects of the same
	CachedInformationType. This may, for example, be the case when the		CachedInformationType. This may, for example, be the case when the
	client has cached multiple certificates from a server.		client has cached multiple certificates from a server.
	enum {		enum {
	cert(1), cert_req(2) (255)		cert(1), cert_req(2) (255)
	} CachedInformationType;		} CachedInformationType;
	struct {		struct {
	select (type) {		select (type) {
	skipping to change at page 4, line 25 ¶		skipping to change at page 4, line 31 ¶
	CachedInformationType type;		CachedInformationType type;
	} body;		} body;
	} CachedObject;		} CachedObject;
	struct {		struct {
	CachedObject cached_info<1..2^16-1>;		CachedObject cached_info<1..2^16-1>;
	} CachedInformation;		} CachedInformation;
	This document defines the following two types:		This document defines the following two types:
	'cert' Type for not sending the complete Server Certificate Message:		'cert' type for not sending the complete server certificate message:
	With the type field set to 'cert', the client MUST include the		With the type field set to 'cert', the client MUST include the
	fingerprint of the Certificate message in the hash_value field.		fingerprint of the Certificate message in the hash_value field.
	For this type the fingerprint MUST be calculated using the		For this type, the fingerprint MUST be calculated using the
	procedure described in Section 5 with the Certificate message as		procedure described in Section 5 with the Certificate message as
	input data.		input data.
	'cert_req' Type for not sending the complete CertificateRequest		'cert_req' Type for not sending the complete CertificateRequest
	Message:		Message:
	With the type set to 'cert_req', the client MUST include the		With the type set to 'cert_req', the client MUST include the
	fingerprint of the CertificateRequest message in the hash_value		fingerprint of the CertificateRequest message in the hash_value
	field. For this type the fingerprint MUST be calculated using the		field. For this type, the fingerprint MUST be calculated using
	procedure described in Section 5 with the CertificateRequest		the procedure described in Section 5 with the CertificateRequest
	message as input data.		message as input data.
	New cached info types can be added following the policy described in		New cached info types can be added following the policy described in
	the IANA considerations section, see Section 8. New message digest		the IANA Considerations (Section 8). New message digest algorithms
	algorithms for use with these types can also be added by registering		for use with these types can also be added by registering a new type
	a new type that makes use of the updated message digest algorithm.		that makes use of the updated message digest algorithm. For
	For practical reasons we recommend to re-use hash algorithms already		practical reasons, we recommend reusing hash algorithms already
	available with TLS ciphersuites to avoid additional code and to keep		available with TLS ciphersuites. To avoid additional code and to
	the collision probably low new hash algorithms MUST NOT have a		keep the collision probability low, new hash algorithms MUST NOT have
	collision resistance worse than SHA-256.		a collision resistance worse than SHA-256.
	4. Exchange Specification		4. Exchange Specification
	Clients supporting this extension MAY include the "cached_info"		Clients supporting this extension MAY include the "cached_info"
	extension in the (extended) client hello. If the client includes the		extension in the (extended) ClientHello. If the client includes the
	extension then it MUST contain one or more CachedObject attributes.		extension, then it MUST contain one or more CachedObject attributes.
	A server supporting this extension MAY include the "cached_info"		A server supporting this extension MAY include the "cached_info"
	extension in the (extended) server hello. By returning the		extension in the (extended) ServerHello. By returning the
	"cached_info" extension the server indicates that it supports the		"cached_info" extension, the server indicates that it supports the
	cached info types. For each indicated cached info type the server		cached info types. For each indicated cached info type, the server
	MUST alter the transmission of respective payloads, according to the		MUST alter the transmission of respective payloads, according to the
	rules outlined with each type. If the server includes the extension		rules outlined with each type. If the server includes the extension,
	it MUST only include CachedObjects of a type also supported by the		it MUST only include CachedObjects of a type also supported by the
	client (as expressed in the client hello). For example, if a client		client (as expressed in the ClientHello). For example, if a client
	indicates support for 'cert' and 'cert_req' then the server cannot		indicates support for 'cert' and 'cert_req', then the server cannot
	respond with a "cached_info" attribute containing support for ('foo-		respond with a "cached_info" attribute containing support for
	bar').		('foo-bar').
	Since the client includes a fingerprint of information it cached (for		Since the client includes a fingerprint of information it cached (for
	each indicated type) the server is able to determine whether cached		each indicated type), the server is able to determine whether cached
	information is stale. If the server supports this specification and		information is stale. If the server supports this specification and
	notices a mismatch between the data cached by the client and its own		notices a mismatch between the data cached by the client and its own
	information then the server MUST include the information in full and		information, then the server MUST include the information in full and
	MUST NOT list the respective type in the "cached_info" extension.		MUST NOT list the respective type in the "cached_info" extension.
	Note: If a server is part of a hosting environment then the client		Note: If a server is part of a hosting environment, then the client
	may have cached multiple data items for a single server. To allow		may have cached multiple data items for a single server. To allow
	the client to select the appropriate information from the cache it is		the client to select the appropriate information from the cache, it
	RECOMMENDED that the client utilizes the Server Name Indication		is RECOMMENDED that the client utilizes the Server Name Indication
	extension [RFC6066].		(SNI) extension [RFC6066].
	Following a successful exchange of the "cached_info" extension in the		Following a successful exchange of the "cached_info" extension in the
	client and server hello, the server alters sending the corresponding		ClientHello and ServerHello, the server alters sending the
	handshake message. How information is altered from the handshake		corresponding handshake message. How information is altered from the
	messages is defined in Section 4.1, and in Section 4.2 for the types		handshake messages and for the types defined in this specification is
	defined in this specification.		defined in Sections 4.1 and 4.2, respectively.
	Appendix A shows an example hash calculation and Section 6 shows an		Appendix A shows an example hash calculation, and Section 6
	example protocol exchange.		illustrates an example protocol exchange.
	4.1. Server Certificate Message		4.1. Server Certificate Message
	When a ClientHello message contains the "cached_info" extension with		When a ClientHello message contains the "cached_info" extension with
	a type set to 'cert' then the server MAY send the Certificate message		a type set to 'cert', then the server MAY send the Certificate
	shown in Figure 1 under the following conditions:		message shown in Figure 1 under the following conditions:
	o The server software implements the "cached_info" extension defined		o The server software implements the "cached_info" extension defined
	in this specification.		in this specification.
	o The 'cert' cached info extension is enabled (for example, a policy		o The 'cert' "cached_info" extension is enabled (for example, a
	allows the use of this extension).		policy allows the use of this extension).
	o The server compared the value in the hash_value field of the		o The server compared the value in the hash_value field of the
	client-provided "cached_info" extension with the fingerprint of		client-provided "cached_info" extension with the fingerprint of
	the Certificate message it normally sends to clients. This check		the Certificate message it normally sends to clients. This check
	ensures that the information cached by the client is current. The		ensures that the information cached by the client is current. The
	procedure for calculating the fingerprint is described in		procedure for calculating the fingerprint is described in
	Section 5.		Section 5.
	The original Certificate handshake message syntax is defined in		The original certificate handshake message syntax is defined in
	[RFC5246] and has been extended with [RFC7250]. RFC 7250 allows the		[RFC5246] and has been extended with [RFC7250]. RFC 7250 allows the
	certificate payload to contain only the SubjectPublicKeyInfo instead		certificate payload to contain only the SubjectPublicKeyInfo instead
	of the full information typically found in a certificate. Hence,		of the full information typically found in a certificate. Hence,
	when this specification is used in combination with [RFC7250] and the		when this specification is used in combination with [RFC7250] and the
	negotiated certificate type is a raw public key then the TLS server		negotiated certificate type is a raw public key, then the TLS server
	omits sending a Certificate payload that contains an ASN.1		omits sending a certificate payload that contains an ASN.1
	Certificate structure with the included SubjectPublicKeyInfo rather		certificate structure with the included SubjectPublicKeyInfo rather
	than the full certificate chain. As such, this extension is		than the full certificate chain. As such, this extension is
	compatible with the raw public key extension defined in RFC 7250.		compatible with the raw public key extension defined in RFC 7250.
	Note: We assume that the server implementation is able to select the		Note: We assume that the server implementation is able to select the
	appropriate certificate or SubjectPublicKeyInfo from the received		appropriate certificate or SubjectPublicKeyInfo from the received
	hash value. If the SNI extension is used by the client then the		hash value. If the SNI extension is used by the client, then the
	server has additional information to guide the selection of the		server has additional information to guide the selection of the
	appropriate cached info.		appropriate cached info.
	When the cached info specification is used then a modified version of		When the cached info specification is used, then a modified version
	the Certificate message is exchanged. The modified structure is		of the Certificate message is exchanged. The modified structure is
	shown in Figure 1.		shown in Figure 1.
	struct {		struct {
	opaque hash_value<1..255>;		opaque hash_value<1..255>;
	} Certificate;		} Certificate;
	Figure 1: Cached Info Certificate Message.		Figure 1: Cached Info Certificate Message
	4.2. CertificateRequest Message		4.2. CertificateRequest Message
	When a fingerprint for an object of type 'cert_req' is provided in		When a fingerprint for an object of type 'cert_req' is provided in
	the client hello, the server MAY send the CertificateRequest message		the ClientHello, the server MAY send the CertificateRequest message
	shown in Figure 2 message under the following conditions:		shown in Figure 2 under the following conditions:
	o The server software implements the "cached_info" extension defined		o The server software implements the "cached_info" extension defined
	in this specification.		in this specification.
	o The 'cert_req' cached info extension is enabled (for example, a		o The 'cert_req' "cached_info" extension is enabled (for example, a
	policy allows the use of this extension).		policy allows the use of this extension).
	o The server compared the value in the hash_value field of the		o The server compared the value in the hash_value field of the
	client-provided "cached_info" extension with the fingerprint of		client-provided "cached_info" extension with the fingerprint of
	the CertificateRequest message it normally sends to clients. This		the CertificateRequest message it normally sends to clients. This
	check ensures that the information cached by the client is		check ensures that the information cached by the client is
	current. The procedure for calculating the fingerprint is		current. The procedure for calculating the fingerprint is
	described in Section 5.		described in Section 5.
	o The server wants to request a certificate from the client.		o The server wants to request a certificate from the client.
	The original CertificateRequest handshake message syntax is defined		The original CertificateRequest handshake message syntax is defined
	in [RFC5246]. The modified structure of the CertificateRequest		in [RFC5246]. The modified structure of the CertificateRequest
	message is shown in Figure 2.		message is shown in Figure 2.
	struct {		struct {
	opaque hash_value<1..255>;		opaque hash_value<1..255>;
	} CertificateRequest;		} CertificateRequest;
	Figure 2: Cached Info CertificateRequest Message.		Figure 2: Cached Info CertificateRequest Message
	The CertificateRequest payload is the input parameter to the		The CertificateRequest payload is the input parameter to the
	fingerprint calculation described in Section 5.		fingerprint calculation described in Section 5.
	5. Fingerprint Calculation		5. Fingerprint Calculation
	The fingerprint for the two cached info objects defined in this		The fingerprint for the two cached info objects defined in this
	document MUST be computed as follows:		document MUST be computed as follows:
	1. Compute the SHA-256 [RFC6234] hash of the input data. The input		1. Compute the SHA-256 [RFC6234] hash of the input data. The input
	data depends on the cached info type. This document defines two		data depends on the cached info type. This document defines two
	cached info types, described in Section 4.1 and in Section 4.2.		cached info types, described in Sections 4.1 and in 4.2. Note
	Note that the computed hash only covers the input data structure		that the computed hash only covers the input data structure (and
	(and not any type and length information of the record layer).		not any type and length information of the record layer).
	Appendix A shows an example.		Appendix A shows an example.
	2. Use the output of the SHA-256 hash.		2. Use the output of the SHA-256 hash.
	The purpose of the fingerprint provided by the client is to help the		The purpose of the fingerprint provided by the client is to help the
	server select the correct information. For example, in case of the		server select the correct information. For example, in case of a
	certificate message the fingerprint identifies the server certificate		Certificate message, the fingerprint identifies the server
	(and the corresponding private key) for use for with the rest of the		certificate (and the corresponding private key) for use with the rest
	handshake. Servers may have more than one certificate and therefore		of the handshake. Servers may have more than one certificate, and
	a hash needs to be long enough to keep the probably of hash		therefore a hash needs to be long enough to keep the probably of hash
	collisions low. On the other hand, the cached info design aims to		collisions low. On the other hand, the cached info design aims to
	reduce the amount of data being exchanged. The security of the		reduce the amount of data being exchanged. The security of the
	handshake depends on the private key and not on the size of the		handshake depends on the private key and not on the size of the
	fingerprint. Hence, the fingerprint is a way to prevent the server		fingerprint. Hence, the fingerprint is a way to prevent the server
	from accidentally selecting the wrong information. If an attacker		from accidentally selecting the wrong information. If an attacker
	injects an incorrect fingerprint then two outcomes are possible: (1)		injects an incorrect fingerprint, then two outcomes are possible: (1)
	The fingerprint does not relate to any cached state and the server		the fingerprint does not relate to any cached state and the server
	has to fall back to a full exchange. (2) If the attacker manages to		has to fall back to a full exchange, and (2) if the attacker manages
	inject a fingerprint that refers to data the client has not cached		to inject a fingerprint that refers to data the client has not
	then the exchange will fail later when the client continues with the		cached, then the exchange will fail later when the client continues
	handshake and aims to verify the digital signature. The signature		with the handshake and aims to verify the digital signature. The
	verification will fail since the public key cached by the client will		signature verification will fail since the public key cached by the
	not correspond to the private key that was used by server to sign the		client will not correspond to the private key that was used by the
	message.		server to sign the message.
	6. Example		6. Example
	In the regular, full TLS handshake exchange, shown in Figure 3, the		In the regular, full TLS handshake exchange, shown in Figure 3, the
	TLS server provides its certificate in the Certificate payload to the		TLS server provides its certificate in the certificate payload to the
	client, see step (1). This allows the client to store the		client; see step (1). This allows the client to store the
	certificate for future use. After some time the TLS client again		certificate for future use. After some time, the TLS client again
	interacts with the same TLS server and makes use of the TLS cached		interacts with the same TLS server and makes use of the TLS
	info extension, as shown in Figure 4. The TLS client indicates		"cached_info" extension, as shown in Figure 4. The TLS client
	support for this specification via the "cached_info" extension, see		indicates support for this specification via the "cached_info"
	step (2), and indicates that it has stored the certificate from the		extension, see step (2), and indicates that it has stored the
	earlier exchange (by indicating the 'cert' type). With step (3) the		certificate from the earlier exchange (by indicating the 'cert'
	TLS server acknowledges the supports of the 'cert' type and by		type). With step (3), the TLS server acknowledges the support of the
	including the value in the server hello informs the client that the		'cert' type and by including the value in the ServerHello, it informs
	content of the certificate payload contains the fingerprint of the		the client that the content of the certificate payload contains the
	certificate instead of the RFC 5246-defined payload of the		fingerprint of the certificate instead of the payload, defined in RFC
	certificate message in step (4).		5246, of the Certificate message; see step (4).
	ClientHello ->		ClientHello ->
	<- ServerHello		<- ServerHello
	Certificate* // (1)		Certificate* // (1)
	ServerKeyExchange*		ServerKeyExchange*
	CertificateRequest*		CertificateRequest*
	ServerHelloDone		ServerHelloDone
	Certificate*		Certificate*
	ClientKeyExchange		ClientKeyExchange
	CertificateVerify*		CertificateVerify*
	[ChangeCipherSpec]		[ChangeCipherSpec]
	Finished ->		Finished ->
	<- [ChangeCipherSpec]		<- [ChangeCipherSpec]
	Finished		Finished
	Application Data <-------> Application Data		Application Data <-------> Application Data
	Figure 3: Example Message Exchange: Initial (full) Exchange.		Figure 3: Example Message Exchange: Initial (Full) Exchange
	ClientHello		ClientHello
	cached_info=(cert) -> // (2)		cached_info=(cert) -> // (2)
	<- ServerHello		<- ServerHello
	cached_info=(cert) (3)		cached_info=(cert) (3)
	Certificate (4)		Certificate (4)
	ServerKeyExchange*		ServerKeyExchange*
	ServerHelloDone		ServerHelloDone
	ClientKeyExchange		ClientKeyExchange
	CertificateVerify*		CertificateVerify*
	[ChangeCipherSpec]		[ChangeCipherSpec]
	Finished ->		Finished ->
	<- [ChangeCipherSpec]		<- [ChangeCipherSpec]
	Finished		Finished
	Application Data <-------> Application Data		Application Data <-------> Application Data
	Figure 4: Example Message Exchange: TLS Cached Extension Usage.		Figure 4: Example Message Exchange: TLS Cached Extension Usage
	7. Security Considerations		7. Security Considerations
	This specification defines a mechanism to reference stored state		This specification defines a mechanism to reference stored state
	using a fingerprint. Sending a fingerprint of cached information in		using a fingerprint. Sending a fingerprint of cached information in
	an unencrypted handshake, as the client and server hello is, may		an unencrypted handshake, as the ClientHello and ServerHello does,
	allow an attacker or observer to correlate independent TLS exchanges.		may allow an attacker or observer to correlate independent TLS
	While some information elements used in this specification, such as		exchanges. While some information elements used in this
	server certificates, are public objects and usually do not contain		specification, such as server certificates, are public objects and
	sensitive information, other not yet defined types may. Those who		usually do not contain sensitive information, other types that are
	implement and deploy this specification should therefore make an		not yet defined may. Those who implement and deploy this
	informed decision whether the cached information is inline with their		specification should therefore make an informed decision whether the
	security and privacy goals. In case of concerns, it is advised to		cached information is in line with their security and privacy goals.
	avoid sending the fingerprint of the data objects in clear.		In case of concerns, it is advised to avoid sending the fingerprint
			of the data objects in clear.
	The use of the cached info extension allows the server to send		The use of the "cached_info" extension allows the server to send
	significantly smaller TLS messages. Consequently, these omitted		significantly smaller TLS messages. Consequently, these omitted
	parts of the messages are not included in the transcript of the		parts of the messages are not included in the transcript of the
	handshake in the TLS Finish message. However, since the client and		handshake in the TLS Finish message. However, since the client and
	the server communicate the hash values of the cached data in the		the server communicate the hash values of the cached data in the
	initial handshake messages the fingerprints are included in the TLS		initial handshake messages, the fingerprints are included in the TLS
	Finish message.		Finish message.
	Clients MUST ensure that they only cache information from legitimate		Clients MUST ensure that they only cache information from legitimate
	sources. For example, when the client populates the cache from a TLS		sources. For example, when the client populates the cache from a TLS
	exchange then it must only cache information after the successful		exchange, then it must only cache information after the successful
	completion of a TLS exchange to ensure that an attacker does not		completion of a TLS exchange to ensure that an attacker does not
	inject incorrect information into the cache. Failure to do so allows		inject incorrect information into the cache. Failure to do so allows
	for man-in-the-middle attacks.		for man-in-the-middle attacks.
	Security considerations for the fingerprint calculation are discussed		Security considerations for the fingerprint calculation are discussed
	in Section 5.		in Section 5.
	8. IANA Considerations		8. IANA Considerations
	8.1. New Entry to the TLS ExtensionType Registry		8.1. New Entry to the TLS ExtensionType Registry
	IANA is requested to add an entry to the existing TLS ExtensionType		IANA has added an entry to the existing TLS "ExtensionType Values"
	registry, defined in [RFC5246], for cached_info(TBD) defined in this		registry, defined in [RFC5246], for cached_info(25) defined in this
	document.		document.
	8.2. New Registry for CachedInformationType		8.2. New Registry for CachedInformationType
	IANA is requested to establish a registry for TLS		IANA has established a registry titled "TLS CachedInformationType
	CachedInformationType values. The first entries in the registry are		Values". The entries in the registry are:
	o cert(1)
	o cert_req(2)		Value Description
			----- -----------
			0 Reserved
			1 cert
			2 cert_req
			224-255 Reserved for Private Use
	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 [RFC5226], is as follows:		terminology defined in [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		9. References
	9. Acknowledgments
	We would like to thank the following persons for your detailed
	document reviews:
	o Paul Wouters and Nikos Mavrogiannopoulos (December 2011)
	o Rob Stradling (February 2012)
	o Ondrej Mikle (March 2012)
	o Ilari Liusvaara, Adam Langley, and Eric Rescorla (July 2014)
	o Sean Turner (August 2014)
	o Martin Thomson (August 2015)
	o Jouni Korhonen (November 2015)
	o Matt Miller (December 2015)
	We would also to thank Martin Thomson, Karthikeyan Bhargavan, Sankalp
	Bagaria and Eric Rescorla for their feedback regarding the
	fingerprint calculation.
	Finally, we would like to thank the TLS working group chairs, Sean
	Turner and Joe Salowey, as well as the responsible security area
	director, Stephen Farrell, for their support and their reviews.
	10. References
	10.1. Normative References		9.1. Normative References
	[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, DOI 10.17487/		Requirement Levels", BCP 14, RFC 2119,
	RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<http://www.rfc-editor.org/info/rfc2119>.		<http://www.rfc-editor.org/info/rfc2119>.
	[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, DOI 10.17487/		(TLS) Protocol Version 1.2", RFC 5246,
	RFC5246, August 2008,		DOI 10.17487/RFC5246, August 2008,
	<http://www.rfc-editor.org/info/rfc5246>.		<http://www.rfc-editor.org/info/rfc5246>.
	[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)		[RFC6066] Eastlake 3rd, D., "Transport Layer Security (TLS)
	Extensions: Extension Definitions", RFC 6066, DOI		Extensions: Extension Definitions", RFC 6066,
	10.17487/RFC6066, January 2011,		DOI 10.17487/RFC6066, January 2011,
	<http://www.rfc-editor.org/info/rfc6066>.		<http://www.rfc-editor.org/info/rfc6066>.
	[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms		[RFC6234] Eastlake 3rd, D. and T. Hansen, "US Secure Hash Algorithms
	(SHA and SHA-based HMAC and HKDF)", RFC 6234, DOI		(SHA and SHA-based HMAC and HKDF)", RFC 6234,
	10.17487/RFC6234, May 2011,		DOI 10.17487/RFC6234, May 2011,
	<http://www.rfc-editor.org/info/rfc6234>.		<http://www.rfc-editor.org/info/rfc6234>.
	10.2. Informative References		9.2. Informative References
	[ASN.1-Dump]		[ASN.1-Dump]
	Gutmann, P., "ASN.1 Object Dump Program", February 2013,		Gutmann, P., "ASN.1 Object Dump Program", November 2010,
	<http://www.cs.auckland.ac.nz/~pgut001/>.		<http://manpages.ubuntu.com/manpages/precise/man1/
			dumpasn1.1.html>.
	[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,
	DOI 10.17487/RFC5226, May 2008,		DOI 10.17487/RFC5226, May 2008,
	<http://www.rfc-editor.org/info/rfc5226>.		<http://www.rfc-editor.org/info/rfc5226>.
	[RFC6574] Tschofenig, H. and J. Arkko, "Report from the Smart Object		[RFC6574] Tschofenig, H. and J. Arkko, "Report from the Smart Object
	Workshop", RFC 6574, DOI 10.17487/RFC6574, April 2012,		Workshop", RFC 6574, DOI 10.17487/RFC6574, April 2012,
	<http://www.rfc-editor.org/info/rfc6574>.		<http://www.rfc-editor.org/info/rfc6574>.
	[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,		[RFC7250] Wouters, P., Ed., Tschofenig, H., Ed., Gilmore, J.,
	Weiler, S., and T. Kivinen, "Using Raw Public Keys in		Weiler, S., and T. Kivinen, "Using Raw Public Keys in
	Transport Layer Security (TLS) and Datagram Transport		Transport Layer Security (TLS) and Datagram Transport
	Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,		Layer Security (DTLS)", RFC 7250, DOI 10.17487/RFC7250,
	June 2014, <http://www.rfc-editor.org/info/rfc7250>.		June 2014, <http://www.rfc-editor.org/info/rfc7250>.
	Appendix A. Example		Appendix A. Example
	Consider a certificate containing an NIST P256 elliptic curve public		Consider a certificate containing a NIST P256 elliptic curve public
	key displayed using Peter Gutmann's ASN.1 decoder [ASN.1-Dump] in		key displayed using Peter Gutmann's ASN.1 decoder [ASN.1-Dump] in
	Figure 5.		Figure 5.
	0 556: SEQUENCE {		0 556: SEQUENCE {
	4 434: SEQUENCE {		4 434: SEQUENCE {
	8 3: [0] {		8 3: [0] {
	10 1: INTEGER 2		10 1: INTEGER 2
	: }		: }
	13 1: INTEGER 13		13 1: INTEGER 13
	16 10: SEQUENCE {		16 10: SEQUENCE {
	skipping to change at page 14, line 50 ¶		skipping to change at page 16, line 4 ¶
	: }		: }
	442 10: SEQUENCE {		442 10: SEQUENCE {
	444 8: OBJECT IDENTIFIER ecdsaWithSHA256 (1 2 840 10045 4 3 2)		444 8: OBJECT IDENTIFIER ecdsaWithSHA256 (1 2 840 10045 4 3 2)
	: }		: }
	454 104: BIT STRING, encapsulates {		454 104: BIT STRING, encapsulates {
	457 101: SEQUENCE {		457 101: SEQUENCE {
	459 48: INTEGER		459 48: INTEGER
	: 4A 65 0D 7B 20 83 A2 99 B9 A8 0F FC 8D EE 8F 3D		: 4A 65 0D 7B 20 83 A2 99 B9 A8 0F FC 8D EE 8F 3D
	: BB 70 4C 96 03 AC 8E 78 70 DD F2 0E A0 B2 16 CB		: BB 70 4C 96 03 AC 8E 78 70 DD F2 0E A0 B2 16 CB
	: 65 8E 1A C9 3F 2C 61 7E F8 3C EF AD 1C EE 36 20		: 65 8E 1A C9 3F 2C 61 7E F8 3C EF AD 1C EE 36 20
	509 49: INTEGER		509 49: INTEGER
	: 00 9D F2 27 A6 D5 74 B8 24 AE E1 6A 3F 31 A1 CA		: 00 9D F2 27 A6 D5 74 B8 24 AE E1 6A 3F 31 A1 CA
	: 54 2F 08 D0 8D EE 4F 0C 61 DF 77 78 7D B4 FD FC		: 54 2F 08 D0 8D EE 4F 0C 61 DF 77 78 7D B4 FD FC
	: 42 49 EE E5 B2 6A C2 CD 26 77 62 8E 28 7C 9E 57		: 42 49 EE E5 B2 6A C2 CD 26 77 62 8E 28 7C 9E 57
	: 45		: 45
	: }		: }
	: }		: }
	: }		: }
	Figure 5: ASN.1-based Certificate: Example.		Figure 5: ASN.1-Based Certificate: Example
	To include the certificate shown in Figure 5 in a TLS/DTLS		To include the certificate shown in Figure 5 in a TLS/DTLS
	Certificate message it is prepended with a message header. This		Certificate message, it is prepended with a message header. This
	Certificate message header in our example is 0b 00 02 36 00 02 33 00		Certificate message header in our example is 0b 00 02 36 00 02 33 00
	02 00 02 30, which indicates:		02 00 02 30, which indicates:
	Message Type: 0b -- 1 byte type field indicating a Certificate		Message Type: 0b -- 1-byte type field indicating a Certificate
	message		message
	Length: 00 02 36 -- 3 byte length field indicating a 566 bytes		Length: 00 02 36 -- 3-byte length field indicating a 566-byte
	payload		payload
	Certificates Length: 00 02 33 -- 3 byte length field indicating 563		Certificates Length: 00 02 33 -- 3-byte length field indicating 563
	bytes for the entire certificates_list structure, which may		bytes for the entire certificates_list structure, which may
	contain multiple certificates. In our example only one		contain multiple certificates. In our example, only one
	certificate is included.		certificate is included.
	Certificate Length: 00 02 30 -- 3 byte length field indicating 560		Certificate Length: 00 02 30 -- 3-byte length field indicating 560
	bytes of the actual certificate following immediately afterwards.		bytes of the actual certificate following immediately afterwards.
	In our example, this is the certificate content with 30 82 02 ....		In our example, this is the certificate content with 30 82 02 ....
	9E 57 45 shown in Figure 6.		9E 57 45 shown in Figure 6.
	The hex encoding of the ASN.1 encoded certificate payload shown in		The hex encoding of the ASN.1-encoded certificate payload shown in
	Figure 5 leads to the following encoding.		Figure 5 leads to the following encoding.
	30 82 02 2C 30 82 01 B2 A0 03 02 01 02 02 01 0D		30 82 02 2C 30 82 01 B2 A0 03 02 01 02 02 01 0D
	30 0A 06 08 2A 86 48 CE 3D 04 03 02 30 3E 31 0B		30 0A 06 08 2A 86 48 CE 3D 04 03 02 30 3E 31 0B
	30 09 06 03 55 04 06 13 02 4E 4C 31 11 30 0F 06		30 09 06 03 55 04 06 13 02 4E 4C 31 11 30 0F 06
	03 55 04 0A 13 08 50 6F 6C 61 72 53 53 4C 31 1C		03 55 04 0A 13 08 50 6F 6C 61 72 53 53 4C 31 1C
	30 1A 06 03 55 04 03 13 13 50 6F 6C 61 72 73 73		30 1A 06 03 55 04 03 13 13 50 6F 6C 61 72 73 73
	6C 20 54 65 73 74 20 45 43 20 43 41 30 1E 17 0D		6C 20 54 65 73 74 20 45 43 20 43 41 30 1E 17 0D
	31 33 30 39 32 34 31 35 35 32 30 34 5A 17 0D 32		31 33 30 39 32 34 31 35 35 32 30 34 5A 17 0D 32
	33 30 39 32 32 31 35 35 32 30 34 5A 30 41 31 0B		33 30 39 32 32 31 35 35 32 30 34 5A 30 41 31 0B
	skipping to change at page 16, line 41 ¶		skipping to change at page 17, line 44 ¶
	72 73 73 6C 20 54 65 73 74 20 45 43 20 43 41 82		72 73 73 6C 20 54 65 73 74 20 45 43 20 43 41 82
	09 00 C1 43 E2 7E 62 43 CC E8 30 0A 06 08 2A 86		09 00 C1 43 E2 7E 62 43 CC E8 30 0A 06 08 2A 86
	48 CE 3D 04 03 02 03 68 00 30 65 02 30 4A 65 0D		48 CE 3D 04 03 02 03 68 00 30 65 02 30 4A 65 0D
	7B 20 83 A2 99 B9 A8 0F FC 8D EE 8F 3D BB 70 4C		7B 20 83 A2 99 B9 A8 0F FC 8D EE 8F 3D BB 70 4C
	96 03 AC 8E 78 70 DD F2 0E A0 B2 16 CB 65 8E 1A		96 03 AC 8E 78 70 DD F2 0E A0 B2 16 CB 65 8E 1A
	C9 3F 2C 61 7E F8 3C EF AD 1C EE 36 20 02 31 00		C9 3F 2C 61 7E F8 3C EF AD 1C EE 36 20 02 31 00
	9D F2 27 A6 D5 74 B8 24 AE E1 6A 3F 31 A1 CA 54		9D F2 27 A6 D5 74 B8 24 AE E1 6A 3F 31 A1 CA 54
	2F 08 D0 8D EE 4F 0C 61 DF 77 78 7D B4 FD FC 42		2F 08 D0 8D EE 4F 0C 61 DF 77 78 7D B4 FD FC 42
	49 EE E5 B2 6A C2 CD 26 77 62 8E 28 7C 9E 57 45		49 EE E5 B2 6A C2 CD 26 77 62 8E 28 7C 9E 57 45
	Figure 6: Hex Encoding of the Example Certificate.		Figure 6: Hex Encoding of the Example Certificate
	Applying the SHA-256 hash function to the Certificate message, which		Applying the SHA-256 hash function to the Certificate message, which
	is starts with 0b 00 02 and ends with 9E 57 45, produces		starts with 0b 00 02 and ends with 9E 57 45, produces
	0x086eefb4859adfe977defac494fff6b73033b4ce1f86b8f2a9fc0c6bf98605af.		0x086eefb4859adfe977defac494fff6b73033b4ce1f86b8f2a9fc0c6bf98605af.
			Acknowledgments
			We would like to thank the following persons for your detailed
			document reviews:
			o Paul Wouters and Nikos Mavrogiannopoulos (December 2011)
			o Rob Stradling (February 2012)
			o Ondrej Mikle (March 2012)
			o Ilari Liusvaara, Adam Langley, and Eric Rescorla (July 2014)
			o Sean Turner (August 2014)
			o Martin Thomson (August 2015)
			o Jouni Korhonen (November 2015)
			o Dave Garrett (December 2015)
			o Matt Miller (December 2015)
			o Anirudh Ramachandran (March 2016)
			We would also to thank Martin Thomson, Karthikeyan Bhargavan, Sankalp
			Bagaria, and Eric Rescorla for their feedback regarding the
			fingerprint calculation.
			Finally, we would like to thank the TLS working group chairs, Sean
			Turner and Joe Salowey, as well as the responsible Security Area
			Director, Stephen Farrell, for their support and their reviews.
	Authors' Addresses		Authors' Addresses
	Stefan Santesson		Stefan Santesson
	3xA Security AB		3xA Security AB
	Scheelev. 17		Forskningsbyn Ideon
	Lund 223 70		Lund 223 70
	Sweden		Sweden
	Email: sts@aaa-sec.com		Email: sts@aaa-sec.com
	Hannes Tschofenig		Hannes Tschofenig
	ARM Ltd.		ARM Ltd.
	Hall in Tirol 6060		Hall in Tirol 6060
	Austria		Austria
End of changes. 78 change blocks.
	207 lines changed or deleted		216 lines changed or added
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