Internet DRAFT - draft-tschofenig-tls-dtls-rrc
draft-tschofenig-tls-dtls-rrc
TLS T. Fossati
Internet-Draft H. Tschofenig, Ed.
Updates: 6347 (if approved) Arm Limited
Intended status: Standards Track March 2, 2020
Expires: September 3, 2020
Return Routability Check for DTLS 1.2 and DTLS 1.3
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
3. The Return Routability Check Message . . . . . . . . . . . . 3
4. RRC Example . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Security and Privacy Considerations . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Normative References . . . . . . . . . . . . . . . . . . . . 7
Appendix A. History . . . . . . . . . . . . . . . . . . . . . . 8
Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 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 context,
NAT rebinding is common 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.
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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 and
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 address (and/or port) different
from the one currently associated with the DTLS connection. However,
the actual mechanism for ensuring that the new peer address is
willing to receive and process DTLS records is left open. This
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 more
confidence to the receiving peer that the sending peer is reachable
at the indicated address and port.
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 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. 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) but
instead perform a return routability 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;
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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 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.
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
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being abused (e.g., as an amplifier) by an attacker impersonating the
client.
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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
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5. Security and Privacy Considerations
Note that the return routability checks do not protect against
flooding of third-parties if the attacker is on-path, as the attacker
can redirect the return routability checks to the real peer (even if
those datagrams are cryptographically authenticated). 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?
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-07 (work in progress), 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-dtls13-34 (work in progress),
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>.
[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>.
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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. 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
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