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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

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
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Copyright Notice

   Copyright (c) 2009 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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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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