< draft-tschofenig-tls-dtls-rrc-00.txt   draft-tschofenig-tls-dtls-rrc-01.txt >
TLS T. Fossati TLS T. Fossati
Internet-Draft H. Tschofenig, Ed. Internet-Draft H. Tschofenig, Ed.
Updates: 6347 (if approved) Arm Limited Updates: 6347 (if approved) Arm Limited
Intended status: Standards Track July 08, 2019 Intended status: Standards Track March 2, 2020
Expires: January 9, 2020 Expires: September 3, 2020
Return Routability Check for DTLS 1.2 and DTLS 1.3 Return Routability Check for DTLS 1.2 and DTLS 1.3
draft-tschofenig-tls-dtls-rrc-00 draft-tschofenig-tls-dtls-rrc-01
Abstract Abstract
This document specifies a return routability check for use in context This document specifies a return routability check for use in context
of the Connection ID (CID) construct for the Datagram Transport Layer of the Connection ID (CID) construct for the Datagram Transport Layer
Security (DTLS) protocol versions 1.2 and 1.3. Security (DTLS) protocol versions 1.2 and 1.3.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
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This Internet-Draft will expire on January 9, 2020. This Internet-Draft will expire on September 3, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
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than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3 2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
3. Application Layer Return Routability Check . . . . . . . . . 3 3. The Return Routability Check Message . . . . . . . . . . . . 3
4. The Return Routability Check Message . . . . . . . . . . . . 4 4. RRC Example . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. RRC Example . . . . . . . . . . . . . . . . . . . . . . . . . 5 5. Security and Privacy Considerations . . . . . . . . . . . . . 7
6. Security and Privacy Considerations . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 7 8. Normative References . . . . . . . . . . . . . . . . . . . . 7
9. Normative References . . . . . . . . . . . . . . . . . . . . 7 Appendix A. History . . . . . . . . . . . . . . . . . . . . . . 8
Appendix A. History . . . . . . . . . . . . . . . . . . . . . . 9 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 8
Appendix B. Working Group Information . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
In "classical" DTLS, selecting a security context of an incoming DTLS 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 record is accomplished with the help of the 5-tuple, i.e. source IP
address, source port, transport protocol, destination IP address, and address, source port, transport protocol, destination IP address, and
destination port. Changes to this 5 tuple can happen for a variety destination port. Changes to this 5 tuple can happen for a variety
reasons over the lifetime of the DTLS session. In the IoT content reasons over the lifetime of the DTLS session. In the IoT context,
NAT rebinding is a common reason with sleepy devices. Other examples NAT rebinding is common with sleepy devices. Other examples include
include end host mobility and multi-homing. Without CID, if the end host mobility and multi-homing. Without CID, if the source IP
source IP address and/or source port changes during the lifetime of address and/or source port changes during the lifetime of an ongoing
an ongoing DTLS session then the receiver will be unable to locate DTLS session then the receiver will be unable to locate the correct
the correct security context. As a result, the DTLS handshake has to security context. As a result, the DTLS handshake has to be re-run.
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 A CID is an identifier carried in the record layer header of a DTLS
datagram that gives the receiver additional information for selecting datagram that gives the receiver additional information for selecting
the appropriate security context. The CID mechanism has been the appropriate security context. The CID mechanism has been
specified in [I-D.ietf-tls-dtls-connection-id] for DTLS 1.2 and in specified in [I-D.ietf-tls-dtls-connection-id] for DTLS 1.2 and in
[I-D.ietf-tls-dtls13] for DTLS 1.3. [I-D.ietf-tls-dtls13] for DTLS 1.3.
An on-path adversary could intercept and modify the source IP address Section 6 of [I-D.ietf-tls-dtls-connection-id] describes how the use
(and the source port). Even if receiver checks the authenticity and of CID increases the attack surface by providing both on-path and
freshness of the packet, the recipient is fooled into changing the off-path attackers an opportunity for (D)DoS. It then goes on
CID-to-IP/port association. This attack is possible because the describing the steps a DTLS principal must take when a record with a
network and transport layer identifiers, such as source IP address CID is received that has a source address (and/or port) different
and source port numbers, are not integrity protected and from the one currently associated with the DTLS connection. However,
authenticated by the DTLS record layer. the actual mechanism for ensuring that the new peer address is
willing to receive and process DTLS records is left open. This
This attack makes strong assumptions on the attacker's abilities, and document standardizes a return routability check (RRC) as part of the
moreover it only misleads the peer until the next message gets DTLS protocol itself.
through un-intercepted.
A return routability check (RRC) is performed by the receiving peer The return routability check is performed by the receiving peer
before the CID-to-IP address/port binding is updated in that peer's 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 session state database. This is done in order to provide more
degree of confidence to the receiving peer that the sending peer is confidence to the receiving peer that the sending peer is reachable
reachable at the indicated address and port. 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 2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
This document assumes familiarity with the CID solutions defined for This document assumes familiarity with the CID format and protocol
DTLS 1.2 [I-D.ietf-tls-dtls-connection-id] and for DTLS 1.3 defined for DTLS 1.2 [I-D.ietf-tls-dtls-connection-id] and for DTLS
[I-D.ietf-tls-dtls13]. 1.3 [I-D.ietf-tls-dtls13].
3. Application Layer Return Routability Check 3. The Return Routability Check Message
When a record with CID is received that has the source address of the When a record with CID is received that has the source address of the
enclosing UDP datagram different from the one previously associated enclosing UDP datagram different from the one previously associated
with that CID, the receiver MUST NOT update its view of the peer's IP 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 address and port number with the source specified in the UDP datagram
before cryptographically validating the enclosed record(s). This is before cryptographically validating the enclosed record(s) but
to ensure that a man-on-the-middle attacker that sends a datagram instead perform a return routability check.
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 perform an
application layer 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
enum { enum {
invalid(0), invalid(0),
change_cipher_spec(20), change_cipher_spec(20),
alert(21), alert(21),
handshake(22), handshake(22),
application_data(23), application_data(23),
heartbeat(24), /* RFC 6520 */ heartbeat(24), /* RFC 6520 */
return_routability_check(TBD), /* NEW */ return_routability_check(TBD), /* NEW */
(255) (255)
} ContentType; } ContentType;
struct {
opaque cookie<1..2^16-1>;
} Cookie;
struct {
Cookie cookie;
} return_routability_check;
The newly introduced return_routability_check message contains a The newly introduced return_routability_check message contains a
cookie. The semantic of the cookie is similar to the cookie used in cookie. The semantic of the cookie is similar to the cookie used in
the HelloRetryRequest message defined in [RFC8446]. the HelloRetryRequest message defined in [RFC8446].
The return_routability_check message MUST be authenticated and The return_routability_check message MUST be authenticated and
encrypted using the currently active security context. encrypted using the currently active security context.
The endpoint that observes the peer's address update MUST stop The receiver that observes the peer's address and or port update MUST
sending any buffered application data (or limit the sending rate to a stop sending any buffered application data (or limit the sending rate
TBD threshold) and initiate the return routability check that to a TBD threshold) and initiate the return routability check that
proceeds as follows: 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 1. A cookie is placed in the return_routability_check message;
return_routability_check message echoes it back;
4. When the initiator receives and verifies the 2. The message is sent to the observed new address and a timeout T
return_routability_check message, it updates the peer address is started;
binding;
5. If T expires, or the address confirmation fails, the peer address 3. The peer endpoint, after successfully verifying the received
binding is not updated. return_routability_check message echoes it back;
After this point, any pending send operation is resumed to the bound 4. When the initiator receives and verifies the
peer address. return_routability_check message, it updates the peer address
binding;
struct { 5. If T expires, or the address confirmation fails, the peer address
opaque cookie<1..2^16-1>; binding is not updated.
} Cookie;
struct { After this point, any pending send operation is resumed to the bound
Cookie cookie; peer address.
} return_routability_check;
5. RRC Example 4. RRC Example
The example shown in Figure 1 illustrates a client and a server The example shown in Figure 1 illustrates a client and a server
exchanging application payloads protected by DTLS with an exchanging application payloads protected by DTLS with an
unilaterally used CIDs. At some point in the communication unilaterally used CIDs. At some point in the communication
interaction the IP address used by the client changes and, thanks to interaction the IP address used by the client changes and, thanks to
the CID usage, the security context to interpret the record is the CID usage, the security context to interpret the record is
successfully located by the server. However, the server wants to successfully located by the server. However, the server wants to
test the reachability of the client at his new IP address, to avoid 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 being abused (e.g., as an amplifier) by an attacker impersonating the
client. client.
skipping to change at page 7, line 5 skipping to change at page 7, line 5
<<< IP Address B <<< IP Address B
Verified >> Verified >>
<======== Application Data <======== Application Data
Src-IP=Z Src-IP=Z
Dst-IP=B Dst-IP=B
Figure 1: Return Routability Example Figure 1: Return Routability Example
6. Security and Privacy Considerations 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- Note that the return routability checks do not protect against
party flooding if the attacker is along the path, as the attacker can flooding of third-parties if the attacker is on-path, as the attacker
forward the return routability checks to the real peer (even if those can redirect the return routability checks to the real peer (even if
datagrams are cryptographically authenticated). those datagrams are cryptographically authenticated). On-path
adversaries can, in general, pose a harm to connectivity.
7. IANA Considerations 6. IANA Considerations
IANA is requested to allocate an entry to the existing TLS IANA is requested to allocate an entry to the existing TLS
"ContentType" registry, for the return_routability_check(TBD) defined "ContentType" registry, for the return_routability_check(TBD) defined
in this document. in this document.
8. Open Issues 7. Open Issues
- Should the return routability check use separate sequence numbers - Should the return routability check use separate sequence numbers
and replay windows? and replay windows?
- Should the heartbeat message be re-used instead of the proposed - Should the heartbeat message be re-used instead of the proposed
new message exchange? new message exchange?
9. References 8. Normative References
9.1. Normative References
[I-D.ietf-tls-dtls-connection-id] [I-D.ietf-tls-dtls-connection-id]
Rescorla, E., Tschofenig, H., and T. Fossati, "Connection Rescorla, E., Tschofenig, H., and T. Fossati, "Connection
Identifiers for DTLS 1.2", draft-ietf-tls-dtls-connection- Identifiers for DTLS 1.2", draft-ietf-tls-dtls-connection-
id-05 (work in progress), May 2019. id-07 (work in progress), October 2019.
[I-D.ietf-tls-dtls13] [I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version Datagram Transport Layer Security (DTLS) Protocol Version
1.3", draft-ietf-tls-dtls13-31 (work in progress), March 1.3", draft-ietf-tls-dtls13-34 (work in progress),
2019. November 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <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 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <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 Appendix A. History
RFC EDITOR: PLEASE REMOVE THE THIS SECTION RFC EDITOR: PLEASE REMOVE THE THIS SECTION
- Initial version - 01: Removed text that overlapped with draft-ietf-tls-dtls-
connection-id
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- - 00: Initial version
archive/web/tls/current/index.html [3]
Appendix C. Acknowledgements Appendix B. Acknowledgements
We would like to thank Achim Kraus, Hanno Becker and Manuel Pegourie- We would like to thank Achim Kraus, Hanno Becker and Manuel Pegourie-
Gonnard for their input to this document. Gonnard for their input to this document.
Authors' Addresses Authors' Addresses
Thomas Fossati Thomas Fossati
Arm Limited Arm Limited
EMail: thomas.fossati@arm.com EMail: thomas.fossati@arm.com
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