Network Working Group S. Blake-Wilson
Request for Comments: 4366 BCI
Obsoletes: 3546 M. Nystrom
Updates: 4346 RSA Security
Category: Standards Track D. Hopwood
Independent Consultant
J. Mikkelsen
Transactionware
T. Wright
Vodafone
April 2006
Transport Layer Security (TLS) Extensions
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document describes extensions that may be used to add
functionality to Transport Layer Security (TLS). It provides both
generic extension mechanisms for the TLS handshake client and server
hellos, and specific extensions using these generic mechanisms.
The extensions may be used by TLS clients and servers. The
extensions are backwards compatible: communication is possible
between TLS clients that support the extensions and TLS servers that
do not support the extensions, and vice versa.
Blake-Wilson, et al. Standards Track [Page 1]RFC 4366 TLS Extensions April 2006Table of Contents
1. Introduction ....................................................3
1.1. Conventions Used in This Document ..........................5
2. General Extension Mechanisms ....................................5
2.1. Extended Client Hello ......................................5
2.2. Extended Server Hello ......................................6
2.3. Hello Extensions ...........................................6
2.4. Extensions to the Handshake Protocol .......................8
3. Specific Extensions .............................................8
3.1. Server Name Indication ....................................9
3.2. Maximum Fragment Length Negotiation ......................11
3.3. Client Certificate URLs ..................................12
3.4. Trusted CA Indication ....................................15
3.5. Truncated HMAC ............................................16
3.6. Certificate Status Request ................................17
4. Error Alerts ...................................................19
5. Procedure for Defining New Extensions ..........................20
6. Security Considerations ........................................21
6.1. Security of server_name ...................................22
6.2. Security of max_fragment_length ...........................22
6.3. Security of client_certificate_url ........................22
6.4. Security of trusted_ca_keys ...............................24
6.5. Security of truncated_hmac ................................24
6.6. Security of status_request ................................25
7. Internationalization Considerations ............................25
8. IANA Considerations ............................................25
9. Acknowledgements ...............................................27
10. Normative References ..........................................27
11. Informative References ........................................28
Blake-Wilson, et al. Standards Track [Page 2]RFC 4366 TLS Extensions April 20061. Introduction
This document describes extensions that may be used to add
functionality to Transport Layer Security (TLS). It provides both
generic extension mechanisms for the TLS handshake client and server
hellos, and specific extensions using these generic mechanisms.
TLS is now used in an increasing variety of operational environments,
many of which were not envisioned when the original design criteria
for TLS were determined. The extensions introduced in this document
are designed to enable TLS to operate as effectively as possible in
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