Network Working Group R. Seggelmann
Internet-Draft M. Tuexen
Intended status: Standards Track Muenster Univ. of Applied Sciences
Expires: February 22, 2010 M. Williams
August 21, 2009
Transport Layer Security and Datagram Transport Layer Security Heartbeat
Extension
draft-seggelmann-tls-dtls-heartbeat-01.txt
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Abstract
This document describes the Heartbeat Extension for the Transport
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Layer Security (TLS) and Datagram Transport Layer Security (DTLS)
protocol.
The Heartbeat Extension provides a new protocol for TLS/DTLS allowing
the usage of keep-alive functionality without performing a
renegotiation and a basis for PMTU discovery for DTLS.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Heartbeat Hello Extension . . . . . . . . . . . . . . . . . . . 3
3. Heartbeat Protocol . . . . . . . . . . . . . . . . . . . . . . 4
4. Heartbeat Request and Response Messages . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 5
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
8.1. Normative References . . . . . . . . . . . . . . . . . . . 5
8.2. Informative References . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
1.1. Overview
This document describes the Heartbeat Extension for the Transport
Layer Security (TLS) and Datagram Transport Layer Security (DTLS)
protocols, as defined in [RFC5246] and [RFC4347].
DTLS is designed to secure traffic running on top of unreliable
transport protocols. Such protocols have usually no session
management. The only mechanism available at the DTLS layer to figure
out if a peer is still alive is performing a costly renegotiation.
If the application uses unidirectional traffic there is no other way.
Furthermore, DTLS needs to perform PMTU discovery but has no specific
message type to realize it without affecting user message transfer.
TLS is based on reliable protocols but there is not necessarily a
feature available to keep the connection alive without continuous
data transfer.
The Heartbeat Extension as described in this document overcomes these
limitations. The user can use the new HeartbeatRequest message which
has to be answered by the peer with a HeartbeartResponse immediately.
To perform PMTU discovery HeartbeatRequest messages containing
padding can be used as described in [RFC4821] for SCTP using the PAD-
chunk defined in [RFC4820].
1.2. Conventions
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 [RFC2119].
2. Heartbeat Hello Extension
The support of Heartbeats is indicated with Hello Extensions. A peer
can not only indicate that its implementation supports Heartbeats, it
can also choose whether it is willed to receive and respond or only
to send them. This decision can be changed with every renegotiation.
HeartbeatRequests MUST NOT be sent to a peer denying acceptance.
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enum {
peer_allowed_to_send(1),
peer_not_allowed_to_send(2),
(255)
} HeartbeatMode;
struct {
HeartbeatMode mode;
} HeartbeatExtension;
3. Heartbeat Protocol
The Heartbeat protocol is a new protocol on top of the Record Layer.
The protocol itself consists of two message types, HeartbeatRequest
and HeartbeatResponse.
enum {
heartbeat_request(1),
heartbeat_response(2),
(255)
} HeartbeatMessageType;
Like the ChangeCipherSpec, a HeartbeatRequest can arrive at any time
during the lifetime of a connection. Whenever a HeartbeatRequest is
received, it has to be answered with a corresponding
HeartbeatResponse message immediately.
However, a HeartbeatRequest message SHOULD NOT be sent during
handshakes and there MUST NOT be more than one HeartbeatRequest
message in flight at a time.
When using DTLS, HeartbeatRequest messages MUST be retransmitted
using the simple timeout and retransmission scheme DTLS uses for
flights. In particular, after a number of retransmissions without
receiving a corresponding HeartbeatResponse message having the
expected payload the DTLS connection SHOULD be terminated. The
threshold used for this SHOULD be the same as for DTLS handshake
messages.
When using TLS, HeartbeatRequest messages only need to be sent once.
The transport layer will handle retransmissions. If no corresponding
HeartbeatResponse message has been received after a user configured
amount of time, the TLS connection SHOULD be terminated.
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4. Heartbeat Request and Response Messages
The Heartbeat protocol messages consist of their type and an
arbitrary payload and padding.
struct {
HeartbeatMessageType type;
opaque payload<0..2^14-5>;
opaque padding<0..2^14-5>;
} HeartbeatMessage;
The length of payload and padding in total MUST NOT exceed 2^14-5
bytes.
When a HeartbeatRequest message is received, a corresponding
HeartbeatResponse message MUST be sent carrying an exact copy of the
payload of the HeartbeatRequest. The padding MUST NOT be included in
the HeartbeatResponse message, i.e. the padding field has a length of
zero.
If a received HeartbeatResponse message does not contain the expected
payload the message MUST be discarded silently. If it does contain
the expected payload the retransmission timer MUST be stopped.
5. IANA Considerations
The extension, content and message types have to be assigned by IANA.
6. Security Considerations
This document does not add any additional security considerations in
addition to the ones given in [RFC4347] and [RFC5246].
7. Acknowledgments
The authors wish to thank Eric Rescorla, and Pasi Eronen for their
invaluable comments.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008.
[RFC4347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security", RFC 4347, April 2006.
8.2. Informative References
[RFC4820] Tuexen, M., Stewart, R., and P. Lei, "Padding Chunk and
Parameter for the Stream Control Transmission Protocol
(SCTP)", RFC 4820, March 2007.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, March 2007.
Authors' Addresses
Robin Seggelmann
Muenster Univ. of Applied Sciences
Stegerwaldstr. 39
48565 Steinfurt
Germany
Email: seggelmann@fh-muenster.de
Michael Tuexen
Muenster Univ. of Applied Sciences
Stegerwaldstr. 39
48565 Steinfurt
Germany
Email: tuexen@fh-muenster.de
Michael Williams
Email: michael.glenn.williams@gmail.com
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