Network Working Group R. Seggelmann
Internet-Draft M. Tuexen
Intended status: Standards Track Muenster Univ. of Appl. Sciences
Expires: June 4, 2012 M. Williams
December 2, 2011
Transport Layer Security (TLS) and Datagram Transport Layer Security
(DTLS) Heartbeat Extension
draft-ietf-tls-dtls-heartbeat-04.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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 4, 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
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publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
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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 . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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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 [I-D.ietf-tls-rfc4347-bis] and
their adaptations to specific transport protocols 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 that has indicated peer_not_allowed_to_send receives a
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HeartbeatRequest message, the endpoint 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;
A HeartbeatRequest message can arrive almost at any time during the
lifetime of a connection. Whenever a HeartbeatRequest message is
received, it SHOULD be answered with a corresponding
HeartbeatResponse message.
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 DTLS retransmission
timer for it. The receiving peer SHOULD discard it silently, if it
arrives during the handshake. In case of DTLS, 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 [I-D.ietf-tls-rfc4347-bis]. 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 some amount of
time, the DTLS/TLS connection MAY be terminated by the application
that initiated the sending of the HeartbeatRequest message.
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 random content which MUST be ignored by the
receiver. The length of a HeartbeatMessage is TLSPlaintext.length
for TLS and DTLSPlaintext.length for DTLS. Furthermore the length
of the type field is 1 byte and the length of the payload_length
is 2. Therefore, the padding_length is TLSPlaintext.length -
payload_length - 3 for TLS and DTLSPlaintext.length -
payload_length - 3 for DTLS. The padding_length MUST be at least
16.
The sender of a HeartbeatMessage MUST use a random padding of at
least 16 bytes. The padding of a received HeartbeatMessage message
MUST be ignored.
If the payload_length of a received HeartbeatMessage is too large,
the received HeartbeatMessage MUST be discarded silently.
When a HeartbeatRequest message is received and sending a
HeartbeatResponse is not prohibited as described elsewhere in this
document, the receiver MUST send a corresponding HeartbeatResponse
message carrying an exact copy of the payload of the received
HeartbeatRequest.
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. Use Cases
Each endpoint sends HeartbeatRequest messages at a rate and with the
padding required for the particular use case. The endpoint should
not expect its peer to send HeartbeatRequests. The directions are
independent.
5.1. Path MTU Discovery
DTLS performs path MTU discovery as described in Section 4.1.1.1 of
[I-D.ietf-tls-rfc4347-bis]. 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].
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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 a check at a much higher rate than the TCP keep-alive
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. This idle period
SHOULD to be configurable up to a period of multiple minutes and down
to a period of one second. A default value for the idle period
SHOULD be configurable but it SHOULD also be tunable on a per peer
basis.
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 Expert
Review 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
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255 should be reserved. This registry uses the Expert Review 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 [I-D.ietf-tls-rfc4347-bis] and
[RFC5246].
8. Acknowledgments
The authors wish to thank Pasi Eronen, Adrian Farrel, Stephen
Farrell, Adam Langley, Nikos Mavrogiannopoulos, Tom Petch, Eric
Rescorla, Peter Saint-Andre, and Juho Vaehae-Herttua for their
invaluable comments.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
[I-D.ietf-tls-rfc4347-bis]
Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security version 1.2", draft-ietf-tls-rfc4347-bis-06 (work
in progress), July 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
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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.
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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