wdiff draft-tschofenig-tls-dtls-rrc-00.txt draft-tschofenig-tls-dtls-rrc-01.txt

TLS T. Fossati
Internet-Draft H. Tschofenig, Ed.
Updates: 6347 (if approved) Arm Limited
Intended status: Standards Track July 08, 2019 March 2, 2020
Expires: January 9, September 3, 2020

Return Routability Check for DTLS 1.2 and DTLS 1.3
draft-tschofenig-tls-dtls-rrc-00
draft-tschofenig-tls-dtls-rrc-01

Abstract

This document specifies a return routability check for use in context
of the Connection ID (CID) construct for the Datagram Transport Layer
Security (DTLS) protocol versions 1.2 and 1.3.

Status of This Memo

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Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
3. Application Layer Return Routability Check . . . . . . . . . 3
4. The Return Routability Check Message . . . . . . . . . . . . 4
5. 3
4. RRC Example . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. 4
5. Security and Privacy Considerations . . . . . . . . . . . . . 7
7.
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8.
7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.
8. Normative References . . . . . . . . . . . . . . . . . . . . 7
Appendix A. History . . . . . . . . . . . . . . . . . . . . . . 9 8
Appendix B. Working Group Information . . . . . . . . . . . . . 9
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 9 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 8

1. Introduction

In "classical" DTLS, selecting a security context of an incoming DTLS
record is accomplished with the help of the 5-tuple, i.e. source IP
address, source port, transport protocol, destination IP address, and
destination port. Changes to this 5 tuple can happen for a variety
reasons over the lifetime of the DTLS session. In the IoT content context,
NAT rebinding is a common reason with sleepy devices. Other examples include
end host mobility and multi-homing. Without CID, if the source IP
address and/or source port changes during the lifetime of an ongoing
DTLS session then the receiver will be unable to locate the correct
security context. As a result, the DTLS handshake has to be re-run.
Of course, it is not necessary to re-run the full handshake if
session resumption is supported and negotiated.

A CID is an identifier carried in the record layer header of a DTLS
datagram that gives the receiver additional information for selecting
the appropriate security context. The CID mechanism has been
specified in [I-D.ietf-tls-dtls-connection-id] for DTLS 1.2 and in
[I-D.ietf-tls-dtls13] for DTLS 1.3.

Section 6 of [I-D.ietf-tls-dtls-connection-id] describes how the use
of CID increases the attack surface by providing both on-path adversary could intercept and modify
off-path attackers an opportunity for (D)DoS. It then goes on
describing the steps a DTLS principal must take when a record with a
CID is received that has a source IP address
(and the source port). Even if receiver checks the authenticity and
freshness of (and/or port) different
from the packet, one currently associated with the recipient is fooled into changing DTLS connection. However,
the
CID-to-IP/port association. This attack is possible because actual mechanism for ensuring that the
network and transport layer identifiers, such as source IP new peer address is
willing to receive and source port numbers, are not integrity protected and
authenticated by the process DTLS record layer. records is left open. This attack makes strong assumptions on the attacker's abilities, and
moreover it only misleads the peer until the next message gets
through un-intercepted.

A
document standardizes a return routability check (RRC) as part of the
DTLS protocol itself.

The return routability check is performed by the receiving peer
before the CID-to-IP address/port binding is updated in that peer's
session state database. This is done in order to provide a certain
degree of more
confidence to the receiving peer that the sending peer is reachable
at the indicated address and port.

Without such a return routability check, an adversary can redirect
traffic towards a third party or a black hole.

While an equivalent check can be performed at the application layer
(modulo the DTLS API exposing the address update event to the calling
application), it is advantageous to offer this functionality at the
DTLS layer. Section 3 describes the application layer procedure and
Section 4 specifies a new message to perform this return routability
check.

2. Conventions and Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.

This document assumes familiarity with the CID solutions format and protocol
defined for DTLS 1.2 [I-D.ietf-tls-dtls-connection-id] and for DTLS
1.3 [I-D.ietf-tls-dtls13].

3. Application Layer The Return Routability Check Message

When a record with CID is received that has the source address of the
enclosing UDP datagram different from the one previously associated
with that CID, the receiver MUST NOT update its view of the peer's IP
address and port number with the source specified in the UDP datagram
before cryptographically validating the enclosed record(s). This is
to ensure that a man-on-the-middle attacker that sends a datagram
with a different source address/port on an existing CID session does
not successfully manage to re-route any return traffic.

Furthermore, when using CID, anti-replay protection MUST be enabled.
This is to ensure that a man-on-the-middle attacker sending a
previously captured record with a modified source IP address and port
will not be able to successfully pass the above check (since the
datagram is very likely discarded on receipt - if it falls outside
the replay window).

The two countermeasures cannot complete stop a man-in-the-middle
attacker who performs a DoS on the sender or uses the receiver as as
backscatter source for a DDoS attack. For a more generic protection,
a return routability check is needed.

It is RECOMMENDED that implementations of the CID functionaliy
described in [I-D.ietf-tls-dtls-connection-id] and in
[I-D.ietf-tls-dtls13] added peer address update events to their APIs.
Applications can then use these events as triggers to record(s) but
instead perform an
application layer a return routability check, for example one that is
based on successful exchange of minimal amount of ping-pong traffic
with the peer.

4. The Return Routability Check Message check.

enum {
invalid(0),
change_cipher_spec(20),
alert(21),
handshake(22),
application_data(23),
heartbeat(24), /* RFC 6520 */
return_routability_check(TBD), /* NEW */
(255)
} ContentType;
struct {
opaque cookie<1..2^16-1>;
} Cookie;

struct {
Cookie cookie;
} return_routability_check;

The newly introduced return_routability_check message contains a
cookie. The semantic of the cookie is similar to the cookie used in
the HelloRetryRequest message defined in [RFC8446].

The return_routability_check message MUST be authenticated and
encrypted using the currently active security context.

The endpoint receiver that observes the peer's address and or port update MUST
stop sending any buffered application data (or limit the sending rate
to a TBD threshold) and initiate the return routability check that
proceeds as follows:

1. A cookie is placed in the return_routability_check message;

2. The message is sent to the observed new address and a timeout T
is started;

3. The peer endpoint, after successfully verifying the received
return_routability_check message echoes it back;

4. When the initiator receives and verifies the
return_routability_check message, it updates the peer address
binding;

5. If T expires, or the address confirmation fails, the peer address
binding is not updated.

After this point, any pending send operation is resumed to the bound
peer address.

struct {
opaque cookie<1..2^16-1>;
} Cookie;

struct {
Cookie cookie;
} return_routability_check;

4. RRC Example

The example shown in Figure 1 illustrates a client and a server
exchanging application payloads protected by DTLS with an
unilaterally used CIDs. At some point in the communication
interaction the IP address used by the client changes and, thanks to
the CID usage, the security context to interpret the record is
successfully located by the server. However, the server wants to
test the reachability of the client at his new IP address, to avoid
being abused (e.g., as an amplifier) by an attacker impersonating the
client.

Client Server
------ ------

Application Data ========>
<CID=100>
Src-IP=A
Dst-IP=Z
<======== Application Data
Src-IP=Z
Dst-IP=A

<<------------->>
<< Some >>
<< Time >>
<< Later >>
<<------------->>

Application Data ========>
<CID=100>
Src-IP=B
Dst-IP=Z

<<< Unverified IP
Address B >>

<-------- Return Routability Check
(cookie)
Src-IP=Z
Dst-IP=B

Return Routability Check -------->
(cookie)
Src-IP=B
Dst-IP=Z

<<< IP Address B
Verified >>

<======== Application Data
Src-IP=Z
Dst-IP=B

Figure 1: Return Routability Example

5. Security and Privacy Considerations

As all the datagrams in DTLS are authenticated, integrity and
confidentiality protected there is no risk that an attacker
undetectably modifies the contents of those packets. The IP
addresses in the IP header and the port numbers of the transport
layer are, however, not authenticated. With the introduction of the
CID, care must be taken to test reachability of a peer at a given IP
address and port.

Note that the return routability checks do not protect against third-
party
flooding of third-parties if the attacker is along the path, on-path, as the attacker
can
forward redirect the return routability checks to the real peer (even if
those datagrams are cryptographically authenticated).

7. On-path
adversaries can, in general, pose a harm to connectivity.

6. IANA Considerations

IANA is requested to allocate an entry to the existing TLS
"ContentType" registry, for the return_routability_check(TBD) defined
in this document.

7. Open Issues

- Should the return routability check use separate sequence numbers
and replay windows?

- Should the heartbeat message be re-used instead of the proposed
new message exchange?

9. References

9.1.

8. Normative References

[I-D.ietf-tls-dtls-connection-id]
Rescorla, E., Tschofenig, H., and T. Fossati, "Connection
Identifiers for DTLS 1.2", draft-ietf-tls-dtls-connection-
id-05
id-07 (work in progress), May October 2019.

[I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version
1.3", draft-ietf-tls-dtls13-31 draft-ietf-tls-dtls13-34 (work in progress), March
November 2019.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.

[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<https://www.rfc-editor.org/info/rfc5246>.

[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/info/rfc6347>.

[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.

9.2. URIs

[1] mailto:tls@ietf.org

[2] https://www1.ietf.org/mailman/listinfo/tls

[3] https://www.ietf.org/mail-archive/web/tls/current/index.html

Appendix A. History

RFC EDITOR: PLEASE REMOVE THE THIS SECTION

- 01: Removed text that overlapped with draft-ietf-tls-dtls-
connection-id

- 00: Initial version

Appendix B. Working Group Information

RFC EDITOR: PLEASE REMOVE THE THIS SECTION

The discussion list for the IETF TLS working group is located at the
e-mail address tls@ietf.org [1]. Information on the group and
information on how to subscribe to the list is at
https://www1.ietf.org/mailman/listinfo/tls [2]

Archives of the list can be found at: https://www.ietf.org/mail-
archive/web/tls/current/index.html [3]

Appendix C. Acknowledgements

We would like to thank Achim Kraus, Hanno Becker and Manuel Pegourie-
Gonnard for their input to this document.

Authors' Addresses

Thomas Fossati
Arm Limited

EMail: thomas.fossati@arm.com

Hannes Tschofenig (editor)
Arm Limited

EMail: hannes.tschofenig@arm.com