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Versions: (draft-seggelmann-tls-dtls-heartbeat) 00 01 02 03 04 RFC 6520

Network Working Group                                      R. Seggelmann
Internet-Draft                                                 M. Tuexen
Intended status: Standards Track        Muenster Univ. of Appl. Sciences
Expires: January 12, 2012                                    M. Williams
                                                           July 11, 2011


  Transport Layer Security (TLS) and Datagram Transport Layer Security
                       (DTLS) Heartbeat Extension
                  draft-ietf-tls-dtls-heartbeat-02.txt

Abstract

   This document describes the Heartbeat Extension for the Transport
   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 path maximum transmission unit (PMTU)
   discovery for DTLS.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 12, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Heartbeat Hello Extension . . . . . . . . . . . . . . . . . . . 3
   3.  Heartbeat Protocol  . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Heartbeat Request and Response Messages . . . . . . . . . . . . 5
   5.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 7
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     9.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     9.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8






























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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] and their adoptions
   to specific transport protocol as described in [RFC3436], [RFC5238],
   and [RFC6083].

   DTLS is designed to secure traffic running on top of unreliable
   transport protocols.  Usually such protocols have 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 path maximum transmission unit
   (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 probe packets as described in [RFC4821].

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 willing to receive HeartbeatRequest
   messages and respond with HeartbeatResponse messages or only to send
   HeartbeatRequest messages.  The former is indicated by using
   peer_allowed_to_send as the HeartbeatMode, the latter is indicated by
   using peer_not_allowed_to_send as the Heartbeat mode.  This decision
   can be changed with every renegotiation.  HeartbeatRequest messages
   MUST NOT be sent to a peer indicating peer_not_allowed_to_send.  If
   an endpoint has indicated peer_not_allowed_to_send and receives a



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   HeartbeatRequest message SHOULD drop the message silently and MAY
   send an unexpected_message Alert message.

   The format of the Heartbeat Hello Extension is defined by:

   enum {
      peer_allowed_to_send(1),
      peer_not_allowed_to_send(2),
      (255)
   } HeartbeatMode;

   struct {
      HeartbeatMode mode;
   } HeartbeatExtension;

   Upon reception of an unknown mode, an error Alert message using
   illegal_parameter as its AlertDescription MUST be sent in response.


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 message, a HeartbeatRequest message can
   arrive at any time during the lifetime of a connection.  Whenever a
   HeartbeatRequest message is received, it has to be answered with a
   corresponding HeartbeatResponse message immediately.

   However, a HeartbeatRequest message SHOULD NOT be sent during
   handshakes.  If a handshake is initiated while a HeartbeatRequest is
   still in flight, the sending peer MUST stop the retransmission timer
   for it.  The receiving peer SHOULD discard it silently, if it arrives
   during or after the handshake.  HeartbeatRequest messages from older
   epochs SHOULD be discarded.

   There MUST NOT be more than one HeartbeatRequest message in flight at
   a time.  A HeartbeatRequest message is considered to be in flight
   until the corresponding HeartbeatResponse message is received, or
   until the retransmit timer expires.




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   When using an unreliable transport protocol like DCCP or UDP,
   HeartbeatRequest messages MUST be retransmitted using the simple
   timeout and retransmission scheme DTLS uses for flights as described
   in Section 4.2.4 of [RFC4347].  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.  Please note, that after the timer
   supervising a HeartbeatRequest messages expires, this message is no
   longer considered in flight.  Therefore the HeartbeatRequest message
   is eligible for retransmission.  The retransmission scheme in
   combination with the restriction that only one HeartbeatRequest is
   allowed to be in flight ensures that the congestion control is
   handled appropriately in case of the transport protocol not providing
   one, like in the case of DTLS over UDP.

   When using a reliable transport protocol like SCTP or TCP,
   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 DTLS/TLS connection SHOULD be terminated.


4.  Heartbeat Request and Response Messages

   The Heartbeat protocol messages consist of their type and an
   arbitrary payload and padding.

   struct {
      HeartbeatMessageType type;
      uint16 payload_length;
      opaque payload[HeartbeatMessage.payload_length];
      opaque padding[padding_length];
   } HeartbeatMessage;

   The length of a HeartbeatMessage in total MUST NOT exceed 2^14 or
   max_fragment_length when negotiated as defined in [RFC6066].

   type:  The message type, either heartbeat_request or
      heartbeat_response.

   payload_length:  The length of the payload.

   payload:  The payload consists of arbitrary content.







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   padding:  The padding is additional arbitrary content which MUST be
      ignored by the receiver.  The padding_length is
      TLSPlaintext.length - payload_length - 3 with TLS and
      DTLSPlaintext.length - payload_length - 3 with DTLS.

   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 of the received
   HeartbeatRequest message MUST be ignored.  It MUST NOT be included in
   the HeartbeatResponse message, i.e. the padding field of the
   HeartbeatResponse message MUST have 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.

   If payload_length is either shorter than expected and thus indicates
   padding in a HeartbeatResponse or exceeds the actual message length
   in any message type, an error Alert message using illegal_parameter
   as its AlertDescription MUST be sent in response.


5.  Use Cases

5.1.  Path MTU Discovery

   DTLS performs path MTU discovery as described in Section 4.1.1.1 of
   [RFC4347].  A detailed description how to perform path MTU discovery
   is given in [RFC4821].  The necessary probe packets are the
   HeartbeatRequest messages.

   This method using HeartbeatRequest messages for DTLS is similar to
   the one for the Stream Control Transmission Protocol (SCTP) using the
   padding chunk (PAD-chunk) defined in [RFC4820].

5.2.  Liveliness check

   Sending HeartbeatRequest messages allows the sender to make sure that
   it can reach the peer and the peer is alive.  Even in case of TLS/TCP
   this allows this check at a much higher rate than the TCP keepalive
   feature would allow.

   Besides making sure that the peer is still reachable, sending
   HeartbeatRequest messages refreshes the NAT state of all involved
   NATs.

   HeartbeatRequest messages SHOULD only be sent after an idle period
   that is at least multiple round trip times long.



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6.  IANA Considerations

   [NOTE to RFC-Editor:

      "RFCXXXX" is to be replaced by the RFC number you assign this
      document.

   ]

   IANA needs to assign the heartbeat content type (value TBD) from the
   TLS ContentType Registry as specified in [RFC5246].  The reference
   should be RFCXXXX.

   IANA needs to maintain a new registry for Heartbeat Message Types.
   The message types are numbers in the range from 0 to 255 (decimal).
   Initially IANA needs to assign the heartbeat_request (suggested value
   1) and the heartbeat_response (suggested value 2) message type.  The
   values 0 and 255 should be reserved.  This registry uses the
   Specification Required policy as described in [RFC5226].  The
   reference should be RFCXXXX.

   IANA needs to assign the heartbeat extension type (value TBD) from
   the TLS Extension Type Registry as specified in [RFC5246].  The
   reference should be RFCXXXX.

   IANA needs to maintain a new registry for Heartbeat Modes.  The modes
   are numbers in the range from 0 to 255 (decimal).  Initially IANA
   needs to assign the peer_allowed_to_send (suggested value 1) and the
   peer_not_allowed_to_send (suggested value 2) modes.  The values 0 and
   255 should be reserved.  This registry uses the Specification
   Required policy as described in [RFC5226].  The reference should be
   RFCXXXX.


7.  Security Considerations

   This document does not add any additional security considerations in
   addition to the ones given in [RFC4347] and [RFC5246].


8.  Acknowledgments

   The authors wish to thank Pasi Eronen, Adam Langley, Tom Petch, Eric
   Rescorla, Peter Saint-Andre, and Juho Vaehae-Herttua for their
   invaluable comments.


9.  References



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9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security", RFC 4347, April 2006.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

   [RFC6066]  Eastlake, D., "Transport Layer Security (TLS) Extensions:
              Extension Definitions", RFC 6066, January 2011.

9.2.  Informative References

   [RFC3436]  Jungmaier, A., Rescorla, E., and M. Tuexen, "Transport
              Layer Security over Stream Control Transmission Protocol",
              RFC 3436, December 2002.

   [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.

   [RFC5238]  Phelan, T., "Datagram Transport Layer Security (DTLS) over
              the Datagram Congestion Control Protocol (DCCP)",
              RFC 5238, May 2008.

   [RFC6083]  Tuexen, M., Seggelmann, R., and E. Rescorla, "Datagram
              Transport Layer Security (DTLS) for Stream Control
              Transmission Protocol (SCTP)", RFC 6083, January 2011.













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Authors' Addresses

   Robin Seggelmann
   Muenster University of Applied Sciences
   Stegerwaldstr. 39
   48565 Steinfurt
   DE

   Email: seggelmann@fh-muenster.de


   Michael Tuexen
   Muenster University of Applied Sciences
   Stegerwaldstr. 39
   48565 Steinfurt
   DE

   Email: tuexen@fh-muenster.de


   Michael Williams

   Email: michael.glenn.williams@gmail.com




























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