draft-ietf-tls-ticketrequests-02.txt		draft-ietf-tls-ticketrequests-03.txt
	Network Working Group T. Pauly		Network Working Group T. Pauly
	Internet-Draft Apple Inc.		Internet-Draft Apple Inc.
	Intended status: Informational D. Schinazi		Intended status: Informational D. Schinazi
	Expires: March 30, 2020 Google LLC		Expires: April 20, 2020 Google LLC
	C. Wood		C. Wood
	Apple Inc.		Apple Inc.
	September 27, 2019		October 18, 2019
	TLS Ticket Requests		TLS Ticket Requests
	draft-ietf-tls-ticketrequests-02		draft-ietf-tls-ticketrequests-03
	Abstract		Abstract
	TLS session tickets enable stateless connection resumption for		TLS session tickets enable stateless connection resumption for
	clients without server-side, per-client state. Servers vend an		clients without server-side, per-client state. Servers vend an
	arbitrary number of session tickets to clients, at their discretion,		arbitrary number of session tickets to clients, at their discretion,
	upon connection establishment. Clients store and use tickets when		upon connection establishment. Clients store and use tickets when
	resuming future connections. This document describes a mechanism by		resuming future connections. This document describes a mechanism by
	which clients may specify the desired number of tickets needed for		which clients can specify the desired number of tickets needed for
	future connections. This extension aims to provide a means for		future connections. This extension aims to provide a means for
	servers to determine the number of tickets to generate in order to		servers to determine the number of tickets to generate in order to
	reduce ticket waste, while simultaneously priming clients for future		reduce ticket waste, while simultaneously priming clients for future
	connection attempts.		connection attempts.
	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 https://datatracker.ietf.org/drafts/current/.		Drafts is at https://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 March 30, 2020.		This Internet-Draft will expire on April 20, 2020.
	Copyright Notice		Copyright Notice
	Copyright (c) 2019 IETF Trust and the persons identified as the		Copyright (c) 2019 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
	(https://trustee.ietf.org/license-info) in effect on the date of		(https://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 31 ¶		skipping to change at page 2, line 31 ¶
	4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4		4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
	5. Security Considerations . . . . . . . . . . . . . . . . . . . 5		5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
	6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5		6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
	7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5		7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
	7.1. Normative References . . . . . . . . . . . . . . . . . . 5		7.1. Normative References . . . . . . . . . . . . . . . . . . 5
	7.2. Informative References . . . . . . . . . . . . . . . . . 6		7.2. Informative References . . . . . . . . . . . . . . . . . 6
	Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6		Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
	1. Introduction		1. Introduction
	As per [RFC5077], and as described in [RFC8446], TLS servers send		As per [RFC5077], and as described in [RFC8446], TLS servers vend
	clients an arbitrary number of session tickets at their own		clients an arbitrary number of session tickets at their own
	discretion in NewSessionTicket messages. There are two limitations		discretion in NewSessionTicket messages. There are two limitations
	with this design. First, servers choose some (often hard-coded)		with this design. First, servers choose some (often hard-coded)
	number of tickets vended per connection. Second, clients do not have		number of tickets vended per connection. Second, clients do not have
	a way of expressing their desired number of tickets, which may impact		a way of expressing their desired number of tickets, which can impact
	future connection establishment. For example, clients may open		future connection establishment. For example, clients can open
	multiple TLS connections to the same server for HTTP, or may race TLS		multiple TLS connections to the same server for HTTP, or race TLS
	connections across different network interfaces. The latter is		connections across different network interfaces. The latter is
	especially useful in transport systems that implement Happy Eyeballs		especially useful in transport systems that implement Happy Eyeballs
	[RFC8305]. Since clients control connection concurrency and		[RFC8305]. Since clients control connection concurrency and
	resumption, a standard mechanism for requesting more than one ticket		resumption, a standard mechanism for requesting more than one ticket
	is desirable.		is desirable.
	This document specifies a new TLS extension - "ticket_request" - that		This document specifies a new TLS extension - "ticket_request" - that
	may be used by clients to express their desired number of session		can be used by clients to express their desired number of session
	tickets. Servers may use this extension as a hint of the number of		tickets. Servers can use this extension as a hint of the number of
	NewSessionTicket messages to vend. This extension is only applicable		NewSessionTicket messages to vend. This extension is only applicable
	to TLS 1.3 [RFC8446], DTLS 1.3 [I-D.ietf-tls-dtls13], and future		to TLS 1.3 [RFC8446], DTLS 1.3 [I-D.ietf-tls-dtls13], and future
	versions thereof.		versions thereof.
	1.1. Requirements Language		1.1. Requirements Language
	The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",		The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
	"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and		"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
	"OPTIONAL" in this document are to be interpreted as described in		"OPTIONAL" in this document are to be interpreted as described in
	[RFC2119] [RFC8174] when, and only when, they appear in all capitals,		[RFC2119] [RFC8174] when, and only when, they appear in all capitals,
	skipping to change at page 3, line 27 ¶		skipping to change at page 3, line 27 ¶
	o Parallel HTTP connections: To minimize ticket reuse while still		o Parallel HTTP connections: To minimize ticket reuse while still
	improving performance, it may be useful to use multiple, distinct		improving performance, it may be useful to use multiple, distinct
	tickets when opening parallel connections. Clients must therefore		tickets when opening parallel connections. Clients must therefore
	bound the number of parallel connections they initiate by the		bound the number of parallel connections they initiate by the
	number of tickets in their possession, or risk ticket re-use.		number of tickets in their possession, or risk ticket re-use.
	o Connection racing: Happy Eyeballs V2 [RFC8305] describes		o Connection racing: Happy Eyeballs V2 [RFC8305] describes
	techniques for performing connection racing. The Transport		techniques for performing connection racing. The Transport
	Services Architecture implementation from [TAPS] also describes		Services Architecture implementation from [TAPS] also describes
	how connections may race across interfaces and address families.		how connections can race across interfaces and address families.
	In cases where clients have early data to send and want to		In cases where clients have early data to send and want to
	minimize or avoid ticket re-use, unique tickets for each unique		minimize or avoid ticket re-use, unique tickets for each unique
	connection attempt are useful. Moreover, as some servers may		connection attempt are useful. Moreover, as some servers may
	implement single-use tickets (and even session ticket encryption		implement single-use tickets (and even session ticket encryption
	keys), distinct tickets will be needed to prevent premature ticket		keys), distinct tickets will be needed to prevent premature ticket
	invalidation by racing.		invalidation by racing.
	o Connection priming: In some systems, connections may be primed or		o Connection priming: In some systems, connections can be primed or
	bootstrapped by a centralized service or daemon for faster		bootstrapped by a centralized service or daemon for faster
	connection establishment. Requesting tickets on demand allows		connection establishment. Requesting tickets on demand allows
	such services to vend tickets to clients to use for accelerated		such services to vend tickets to clients to use for accelerated
	handshakes with early data. (Note that if early data is not		handshakes with early data. (Note that if early data is not
	needed by these connections, this method SHOULD NOT be used.		needed by these connections, this method SHOULD NOT be used.
	Fresh handshakes SHOULD be performed instead.)		Fresh handshakes SHOULD be performed instead.)
	o Less ticket waste: Currently, TLS servers use application-		o Less ticket waste: Currently, TLS servers use application-
	specific, and often implementation-specific, logic to determine		specific, and often implementation-specific, logic to determine
	how many tickets to issue. By moving the burden of ticket count		how many tickets to issue. By moving the burden of ticket count
	to clients, servers do not generate wasteful tickets for clients.		to clients, servers do not generate wasteful tickets. As an
	Moreover, as ticket generation may involve expensive computation,		example, clients might only request one ticket during resumption.
	e.g., public key cryptographic operations, avoiding waste is		Moreover, as ticket generation might involve expensive
	desirable.		computation, e.g., public key cryptographic operations, avoiding
			waste is desirable.
	o Decline resumption: Clients may indicate they have no intention of		o Decline resumption: Clients can indicate they have no intention of
	resuming connections by sending a ticket request with count of		resuming connections by sending a ticket request with count of
	zero.		zero.
	3. Ticket Requests		3. Ticket Requests
	Clients may indicate to servers their desired number of tickets for a		Clients can indicate to servers their desired number of tickets for a
	single connection via the following "ticket_request" extension:		single connection via the following "ticket_request" extension:
	enum {		enum {
	ticket_request(TBD), (65535)		ticket_request(TBD), (65535)
	} ExtensionType;		} ExtensionType;
	Clients may send this extension in ClientHello. It contains the		Clients MAY send this extension in ClientHello. It contains the
	following structure:		following structure:
	struct {		struct {
	uint8 count;		uint8 count;
	} TicketRequestContents;		} TicketRequestContents;
	count The number of tickets desired by the client.		count The number of tickets desired by the client.
	A supporting server MAY vend TicketRequestContents.count		A supporting server MAY use TicketRequestContents.count when
	NewSessionTicket messages to a requesting client, and SHOULD NOT send		determining how many NewSessionTicket messages to send to a
	more than TicketRequestContents.count NewSessionTicket messages to a		requesting client, and SHOULD place a limit on the number of tickets
	requesting client. Servers SHOULD place a limit on the number of		sent. The number of NewSessionTicket messages sent SHOULD be the
	tickets they are willing to vend to clients. Thus, the number of		minimum of the server's self-imposed limit and
	NewSessionTicket messages sent should be the minimum of the server's		TicketRequestContents.count.
	self-imposed limit and TicketRequestContents.count. Servers MUST NOT
	send more than 255 tickets to clients.
	Servers that support ticket requests MUST NOT echo "ticket_request"		Servers that support ticket requests MUST NOT echo "ticket_request"
	in the EncryptedExtensions message. A client MUST abort the		in the EncryptedExtensions message. A client MUST abort the
	connection with an "illegal_parameter" alert if the "ticket_request"		connection with an "illegal_parameter" alert if the "ticket_request"
	extension is present in the EncryptedExtensions message.		extension is present in the EncryptedExtensions message.
	Clients MUST NOT change the value of TicketRequestContents.count in		If a client receives a HelloRetryRequest, the presence (or absence)
	second ClientHello messages sent in response to a HelloRetryRequest.		of the "ticket_request" extension MUST be maintained in the second
			ClientHello message. Moreover, if this extension is present, a
			client MUST NOT change the value of TicketRequestContents.count in
			the second ClientHello message.
	4. IANA Considerations		4. IANA Considerations
	IANA is requested to Create an entry, ticket_request(TBD), in the		IANA is requested to Create an entry, ticket_request(TBD), in the
	existing registry for ExtensionType (defined in [RFC8446]), with "TLS		existing registry for ExtensionType (defined in [RFC8446]), with "TLS
	1.3" column values being set to "CH", and "Recommended" column being		1.3" column values being set to "CH", and "Recommended" column being
	set to "Yes".		set to "Yes".
	5. Security Considerations		5. Security Considerations
	Ticket re-use is a security and privacy concern. Moreover, clients		Ticket re-use is a security and privacy concern. Moreover, clients
	must take care when pooling tickets as a means of avoiding or		must take care when pooling tickets as a means of avoiding or
	amortizing handshake costs. If servers do not rotate session ticket		amortizing handshake costs. If servers do not rotate session ticket
	encryption keys frequently, clients may be encouraged to obtain and		encryption keys frequently, clients may be encouraged to obtain and
	use tickets beyond common lifetime windows of, e.g., 24 hours.		use tickets beyond common lifetime windows of, e.g., 24 hours.
	Despite ticket lifetime hints provided by servers, clients SHOULD		Despite ticket lifetime hints provided by servers, clients SHOULD
	dispose of pooled tickets after some reasonable amount of time that		dispose of pooled tickets after some reasonable amount of time that
	mimics the ticket rotation period.		mimics the ticket rotation period.
			Servers that do not enforce a limit on the number of NewSessionTicket
			messages sent in response to a "ticket_request" extension could leave
			themselves open to DoS attacks, especially if ticket creation is
			expensive.
	6. Acknowledgments		6. Acknowledgments
	The authors would like to thank David Benjamin, Eric Rescorla, Nick		The authors would like to thank David Benjamin, Eric Rescorla, Nick
	Sullivan, Martin Thomson, and other members of the TLS Working Group		Sullivan, Martin Thomson, Hubert Kario, and other members of the TLS
	for discussions on earlier versions of this draft.		Working Group for discussions on earlier versions of this draft.
	7. References		7. References
	7.1. Normative References		7.1. Normative References
	[I-D.ietf-tls-dtls13]		[I-D.ietf-tls-dtls13]
	Rescorla, E., Tschofenig, H., and N. Modadugu, "The		Rescorla, E., Tschofenig, H., and N. Modadugu, "The
	Datagram Transport Layer Security (DTLS) Protocol Version		Datagram Transport Layer Security (DTLS) Protocol Version
	1.3", draft-ietf-tls-dtls13-32 (work in progress), July		1.3", draft-ietf-tls-dtls13-33 (work in progress), October
	2019.		2019.
	[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,		Requirement Levels", BCP 14, RFC 2119,
	DOI 10.17487/RFC2119, March 1997,		DOI 10.17487/RFC2119, March 1997,
	<https://www.rfc-editor.org/info/rfc2119>.		<https://www.rfc-editor.org/info/rfc2119>.
	[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,		[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
	"Transport Layer Security (TLS) Session Resumption without		"Transport Layer Security (TLS) Session Resumption without
	Server-Side State", RFC 5077, DOI 10.17487/RFC5077,		Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
End of changes. 19 change blocks.
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