Internet DRAFT - draft-wood-tls-ticketrequests
draft-wood-tls-ticketrequests
Network Working Group T. Pauly
Internet-Draft D. Schinazi
Intended status: Informational C. Wood
Expires: April 16, 2019 Apple Inc.
October 13, 2018
TLS Ticket Requests
draft-wood-tls-ticketrequests-01
Abstract
TLS session tickets enable stateless connection resumption for
clients without server-side per-client state. Servers vend session
tickets to clients, at their discretion, upon connection
establishment. Clients store and use tickets when resuming future
connections. Moreover, clients should use tickets at most once for
session resumption, especially if such keying material protects early
application data. Single-use tickets bound the number of parallel
connections a client may initiate by the number of tickets received
from a given server. To address this limitation, this document
describes a mechanism by which clients may specify the desired number
of tickets needed for future connections.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on April 16, 2019.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Ticket Requests . . . . . . . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 4
7. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
As per [RFC5077], and as described in [RFC8446], TLS servers send
clients session tickets at their own discretion in NewSessionTicket
messages. Clients are in complete control of how many tickets they
may use when establishing future and subsequent connections. For
example, clients may open multiple TLS connections to the same server
for HTTP, or may race TLS connections across different network
interfaces. The latter is especially useful in transport systems
that implement Happy Eyeballs [RFC8305]. Since connection
concurrency and resumption is controlled by clients, a standard
mechanism to request more than one ticket is desirable.
This document specifies a new TLS extension - ticket_request - that
may be used by clients to express their desired number of session
tickets. Servers may use this extension as a hint of the number of
NewSessionTicket messages to vend. This extension is only applicable
to TLS 1.3 [RFC8446] and future versions of TLS.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119] [RFC8174] when, and only when, they appear in all capitals,
as shown here.
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2. Use Cases
The ability to request one or more tickets is useful for a variety of
purposes:
o Parallel HTTP connections: To minimize ticket reuse while still
improving performance, it may be useful to use multiple, distinct
tickets when opening parallel connections. Clients must therefore
bound the number of parallel connections they initiate by the
number of tickets in their possession, or risk ticket re-use.
o Connection racing: Happy Eyeballs V2 [RFC8305] describes
techniques for performing connection racing. The Transport
Services Architecture implementation from [I-D.ietf-taps-impl]
also describes how connections may race across interfaces and
address families. In cases where clients have early data to send
and want to minimize or avoid ticket re-use, unique tickets for
each unique connection attempt are useful. Moreover, as some
servers may implement single-use tickets (and even session ticket
encryption keys), distinct tickets will be needed to prevent
premature ticket invalidation by racing.
o Connection priming: In some systems, connections may be primed or
bootstrapped by a centralized service or daemon for faster
connection establishment. Requesting tickets on demand allows
such services to vend tickets to clients to use for accelerated
handshakes with early data. (Note that if early data is not
needed by these connections, this method SHOULD NOT be used.
Fresh handshakes SHOULD be performed instead.)
o Less ticket waste: Currently, TLS servers use application-
specific, and often implementation-specific, logic to determine
how many tickets to issue. By moving the burden of ticket count
to clients, servers do not generate wasteful tickets for clients.
Moreover, as ticket generation may involve expensive computation,
e.g., public key cryptographic operations, avoiding waste is
desirable.
3. Ticket Requests
Clients may indicate to servers their desired number of tickets via
the following "ticket_request" extension:
enum {
ticket_request(TBD), (65535)
} ExtensionType;
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Clients may send this extension in ClientHello. It contains the
following structure:
struct {
uint8 count;
} TicketRequestContents;
count The number of tickets desired by the client.
A supporting server MAY vend TicketRequestContents.count
NewSessionTicket messages to a requesting client, and SHOULD NOT send
more than TicketRequestContents.count NewSessionTicket messages to a
requesting client. Servers SHOULD place a limit on the number of
tickets they are willing to vend to clients. Thus, the number of
NewSessionTicket messages sent should be the minimum of the server's
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"
in the EncryptedExtensions.
4. IANA Considerations
IANA is requested to Create an entry, ticket_requests(TBD), in the
existing registry for ExtensionType (defined in [RFC8446]), with "TLS
1.3" column values being set to "CH", and "Recommended" column being
set to "Yes".
5. Security Considerations
Ticket re-use is a security and privacy concern. Moreover, ticket
pooling as a means of avoiding or amortizing handshake costs must be
used carefully. If servers do not rotate session ticket encryption
keys frequently, clients may be encouraged to obtain and use tickets
beyond common lifetime windows of, e.g., 24 hours. Despite ticket
lifetime hints provided by servers, clients SHOULD dispose of pooled
tickets after some reasonable amount of time that mimics the ticket
rotation period.
6. Acknowledgments
The authors would like to thank David Benjamin, Eric Rescorla, Nick
Sullivan, and Martin Thomson for discussions on earlier versions of
this draft.
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7. Normative References
[I-D.ietf-taps-impl]
Brunstrom, A., Pauly, T., Enghardt, T., Grinnemo, K.,
Jones, T., Tiesel, P., Perkins, C., and M. Welzl,
"Implementing Interfaces to Transport Services", draft-
ietf-taps-impl-01 (work in progress), July 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
[RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig,
"Transport Layer Security (TLS) Session Resumption without
Server-Side State", RFC 5077, DOI 10.17487/RFC5077,
January 2008, <https://www.rfc-editor.org/info/rfc5077>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2:
Better Connectivity Using Concurrency", RFC 8305,
DOI 10.17487/RFC8305, December 2017, <https://www.rfc-
editor.org/info/rfc8305>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
Authors' Addresses
Tommy Pauly
Apple Inc.
One Apple Park Way
Cupertino, California 95014
United States of America
Email: tpauly@apple.com
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David Schinazi
Apple Inc.
One Apple Park Way
Cupertino, California 95014
United States of America
Email: dschinazi@apple.com
Christopher A. Wood
Apple Inc.
One Apple Park Way
Cupertino, California 95014
United States of America
Email: cawood@apple.com
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