Internet DRAFT - draft-vvv-tls-cross-sni-resumption
draft-vvv-tls-cross-sni-resumption
TLS Working Group V. Vasiliev
Internet-Draft Google
Intended status: Standards Track 12 July 2020
Expires: 13 January 2021
Transport Layer Security (TLS) Resumption across Server Names
draft-vvv-tls-cross-sni-resumption-00
Abstract
This document specifies a way for the parties in the Transport Layer
Security (TLS) protocol to indicate that an individual session ticket
can be used to perform resumption even if the Server Name of the new
connection does not match the Server Name of the original.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the TLS Working Group
mailing list (tls@ietf.org), which is archived at
https://mailarchive.ietf.org/arch/browse/tls/
(https://mailarchive.ietf.org/arch/browse/tls/).
Source for this draft and an issue tracker can be found at
https://github.com/vasilvv/tls-cross-sni-resumption
(https://github.com/vasilvv/tls-cross-sni-resumption).
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
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 13 January 2021.
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Copyright Notice
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document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. The Extension . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Security Considerations . . . . . . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
6.1. Normative References . . . . . . . . . . . . . . . . . . 4
6.2. Informative References . . . . . . . . . . . . . . . . . 5
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
Transport Layer Security protocol [RFC8446] allows the clients to use
an abbreviated handshake in cases where the client has previously
established a secure session with the same server. This mechanism is
known as "session resumption", and its positive impact on performance
makes it desirable to be able to use it as frequently as possible.
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Modern application-level protocols, HTTP in particular, often require
accessing multiple servers within a single workflow. Since the
identity of the server is established through its certificate, in the
ideal case, the resumption would be possible to all of the domains
for which the certificate is valid (see [PERF] for a survey of
potential practical impact of such approach). TLS, starting with
version 1.3, defines the SNI value to be a property of an individual
connection that is not retained across sessions ([RFC8446],
Section 4.2.11). However, in the absence of additional signals, it
discourages using a session ticket when the SNI value does not match
([RFC8446], Section 4.6.1), as there is normally no reason to assume
that all servers sharing the same certificate would also share the
same session keys. The extension defined in this document allows the
server to provide such a signal in-band.
2. Conventions and Definitions
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. The Extension
The server MAY send a resumption_across_names(TBD) extension in a
NewSessionTicket message. That extension SHALL have an empty body.
If the extension is sent, it indicates that the client MAY use the
ticket for any SNI value for which the certificate presented by the
server is valid. The server MUST handle the ticket correctly by
either resuming and using a new SNI provided by the client, or by
ignoring the ticket.
The server MAY send the extension if it reasonably believes that any
server for any identity presented in its certificate would be capable
of accepting that ticket. The server SHOULD NOT send the extension
otherwise, since, if the client follows the single-use ticket policy
recommended by [RFC8446], sending the ticket results in it being no
longer usable regardless of whether resumption has succeeded.
4. Security Considerations
This document does not alter any of the security requirements of
[RFC8446], but merely lifts a performance-motivated "SHOULD NOT"
recommendation from Section 4.6.1. Notably, it still relies on the
server certificate being re-validated against the new SNI at the
session resumption time.
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If a client certificate has been associated with the session, the
client MUST use the same policy on whether to present said
certificate to the server as if it were a new TLS session. For
instance, if the client would show a certificate choice prompt for
every individual domain it connects to, it MUST show that prompt for
the new host when performing cross-domain resumption.
Cross-domain resumption, like other similar mechanisms (e.g. cross-
domain HTTP connection reuse), can incentivize the server deployments
to create server certificates valid for a wider range of domains than
they would otherwise. However, any increase in the scope of a
certificate comes at a cost: the wider is the scope of the
certificate, the wider is the impact of the key compromise for that
certificate. In addition, creating a certificate that is valid for
multiple hostnames can lead to complications if some of those
hostnames change ownership, or otherwise require a different
operational domain.
5. IANA Considerations
IANA (will add/has added) the following entry to the "TLS
ExtensionType Values" table of the "Transport Layer Security (TLS)
Extensions" registry:
Value TBD
Extension Name resumption_across_names
TLS 1.3 NST
Recommended N
Reference This document
6. References
6.1. Normative References
[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>.
[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>.
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[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>.
6.2. Informative References
[PERF] Sy, E., Moennich, M., Mueller, T., Federrath, H., and M.
Fischer, "Enhanced Performance for the encrypted Web
through TLS Resumption across Hostnames", 7 February 2019,
<https://arxiv.org/pdf/1902.02531.pdf>.
Acknowledgments
Cross-name resumption has been previously implemented in the QUIC
Crypto protocol as a preloaded list of hostnames.
Erik Sy has previously proposed a similar mechanism for TLS, draft-
sy-tls-resumption-group (https://datatracker.ietf.org/doc/draft-sy-
tls-resumption-group/). This document incorporates ideas from that
draft.
This document has benefited from contributions and suggestions from
David Benjamin, Nick Harper, David Schinazi, Ryan Sleevi, Ian Swett
and many others.
Author's Address
Victor Vasiliev
Google
Email: vasilvv@google.com
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