INTERNET-DRAFT S. Santesson (Microsoft)
Updates: 2246, 4346
Intended Category: Standards track
Expires September 2006 March 2006
TLS Handshake Message for Supplemental Data
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Abstract
This specification specifies a TLS handshake message for exchange of
supplemental application data. TLS hello message extensions are used
to determine which supplemental data types are supported by both the
TLS client and the TLS server. Then, the supplemental data handshake
message is used to exchange the data. Other documents will define
the syntax of these extensions and the syntax of the associated
supplemental data types.
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1. Introduction
Recent standards activities have proposed different mechanisms for
transmitting supplemental application data in the TLS handshake
message. For example, recent proposals transfer data that is not
processed by the TLS protocol itself, but assist the TLS-protected
application in the authentication and authorization decisions. One
proposal transfers user name hints for locating credentials, and
another proposal transfers attribute certificates and SAML assertions
for authorization checks.
In order to avoid definition of multiple handshake messages, one for
each new type of application specific supplemental data, this
specification defines a new handshake message type that bundles all
such data objects together and sends them in a single handshake
message.
1.1 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [STDWORDS].
The syntax for the supplemental_data handshake message is defined
using the TLS Presentation Language, which is specified in Section 4
of [N2].
2 Supplemental Data Handshake Message
The new supplemental_data handshake message type is defined to
accommodate communication of supplemental data objects as agreed
during the exchange of extensions in the client and server hello
messages. See RFC 2246 (TLS 1.0) [N2] and RFC 4346 (TLS 1.1) [N3]
for other handshake message types.
enum {
supplemental_data(TBD), (255)
} HandshakeType;
struct {
HandshakeType msg_type; /* handshake type */
uint24 length; /* octets in message */
select (HandshakeType) {
case supplemental_data: SupplementalData;
} body;
} Handshake;
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struct {
SupplementalDataEntry supp_data<1..2^24-1>;
} SupplementalData;
struct {
SupplementalDataType supp_data_type;
select(SupplementalDataType) { }
} SupplementalDataEntry;
enum {
(65535)
} SupplementalDataType;
If present, the SupplementalData handshake message MUST contain a non
empty SupplementalDataEntry structure carrying data associated with
at least one defined SupplementalDataType. An explicit agreement
that governs presence of any associated data MUST be concluded
between client and server for each SupplementalDataType. This
agreement MUST be concluded through the use of TLS extensions in the
client and server hello messages.
Other documents will specify specific SupplementalDataType and their
associated data syntax and processing. These same specifications
must also specify the client and server hello message extensions that
are used to negotiate the support for the specified supplemental data
type. This document simply specifies the TLS Handshake Protocol
message that will carry the supplemental data objects.
Different situations require the transfer of supplemental data from
the client to the server, require the transfer of supplemental data
from server to the client, or require the transfer of supplemental
data from the client to the server as well as the transfer from the
server to the client. All three situations are fully supported.
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4 Message flow
The SupplementalData handshake message, if exchanged, MUST be sent as
the first handshake message as illustrated in Figure 1 below.
Client Server
ClientHello (with extensions) -------->
ServerHello(with extensions)
SupplementalData*
Certificate*
ServerKeyExchange*
CertificateRequest*
<-------- ServerHelloDone
SupplementalData*
Certificate*
ClientKeyExchange
CertificateVerify*
[ChangeCipherSpec]
Finished -------->
[ChangeCipherSpec]
<-------- Finished
Application Data <-------> Application Data
* Indicates optional or situation-dependent messages.
Figure 1. Message flow with SupplementalData
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5 Security Considerations
Each SupplementalDataType included in the handshake message defined
in this specification introduces its own unique set of security
properties and related considerations. Security considerations must
therefore be defined in each document that defines a supplemetal data
type.
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6 Normative References
[N1] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[N2] T. Dierks, C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[N3] T. Dierks, E. Rescorla, "The TLS Protocol Version 1.1",
RFC 4346, January 2006.
[N4] S. Blake-Wilson, M. Nystrom, D. Hopwood, J. Mikkelsen,
T. Wright, "Transport Layer Security (TLS) Extensions",
RFC 4366, February 2006.
7 IANA Considerations
IANA needs to establish a registry for TLS Supplemental Data Formats.
TLS Authorization Data Format identifiers with values in the
inclusive range 0-16385 (decimal) are assigned via RFC 2434 [IANA]
Standards Action. Values from the inclusive range 16385-65279
(decimal) are assigned via RFC 2434 Specification Required. Values
from the inclusive range 65280-65535 (decimal) are reserved for RFC
2434 Private Use.
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Author's Address
Stefan Santesson
Microsoft
Finlandsgatan 30
164 93 KISTA
Sweden
EMail: stefans(at)microsoft.com
Acknowledgements
The fundamental architectural idea for the supplemental data
handshake message was provided by Russ Housley and Eric Rescorla.
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Disclaimer
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Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
Expires September 2006
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