Keying Material Exporters for Transport Layer Security (TLS)
RFC 5705
Internet Engineering Task Force (IETF) E. Rescorla
Request for Comments: 5705 RTFM, Inc.
Category: Standards Track March 2010
ISSN: 2070-1721
Keying Material Exporters for Transport Layer Security (TLS)
Abstract
A number of protocols wish to leverage Transport Layer Security (TLS)
to perform key establishment but then use some of the keying material
for their own purposes. This document describes a general mechanism
for allowing that.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
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/5705.
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Rescorla Standards Track [Page 1]
RFC 5705 TLS Exporters March 2010
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used In This Document . . . . . . . . . . . . . . . 3
3. Binding to Application Contexts . . . . . . . . . . . . . . . . 3
4. Exporter Definition . . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . . 7
1. Introduction
Note: The mechanism described in this document was previously known
as "TLS Extractors" but was changed to avoid a name conflict
with the use of the term "Extractor" in the cryptographic
community.
A number of protocols wish to leverage Transport Layer Security (TLS)
[RFC5246] or Datagram TLS (DTLS) [RFC4347] to perform key
establishment but then use some of the keying material for their own
purposes. A typical example is DTLS-SRTP [DTLS-SRTP], a key
management scheme for the Secure Real-time Transport Protocol (SRTP)
that uses DTLS to perform a key exchange and negotiate the SRTP
[RFC3711] protection suite and then uses the DTLS master_secret to
generate the SRTP keys.
These applications imply a need to be able to export keying material
(later called Exported Keying Material or EKM) from TLS/DTLS to an
application or protocol residing at an upper layer, and to securely
agree on the upper-layer context where the keying material will be
used. The mechanism for exporting the keying material has the
following requirements:
o Both client and server need to be able to export the same EKM
value.
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RFC 5705 TLS Exporters March 2010
o EKM values should be indistinguishable from random data to
attackers who don't know the master_secret.
o It should be possible to export multiple EKM values from the same
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