Return Routability Check for DTLS 1.2 and DTLS 1.3
draft-ietf-tls-dtls-rrc-03
The information below is for an old version of the document.
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| Authors | Hannes Tschofenig , Thomas Fossati | ||
| Last updated | 2021-12-21 (Latest revision 2021-11-26) | ||
| Replaces | draft-tschofenig-tls-dtls-rrc | ||
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draft-ietf-tls-dtls-rrc-03
TLS H. Tschofenig, Ed.
Internet-Draft T. Fossati, Ed.
Updates: 6347 (if approved) Arm Limited
Intended status: Standards Track December 21, 2021
Expires: June 24, 2022
Return Routability Check for DTLS 1.2 and DTLS 1.3
draft-ietf-tls-dtls-rrc-03
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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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 24, 2022.
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This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
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material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
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than English.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3
3. RRC Extension . . . . . . . . . . . . . . . . . . . . . . . . 4
4. The Return Routability Check Message . . . . . . . . . . . . 4
5. Path Validation Procedure . . . . . . . . . . . . . . . . . . 5
5.1. Path Challenge Requirements . . . . . . . . . . . . . . . 5
5.2. Path Response Requirements . . . . . . . . . . . . . . . 6
5.3. Timer Choice . . . . . . . . . . . . . . . . . . . . . . 6
6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
7. Security and Privacy Considerations . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 10
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. History . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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.
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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 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.
Note however that, irrespective of CID, if RRC has been successfully
negotiated by the peers, path validation can be used at any time by
either endpoint. For instance, an endpoint might use RRC to check
that a peer is still in possession of its address after a period of
quiescence.
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]. The presentation language used in this
document is described in Section 4 of [RFC8446].
This document reuses the definition of "anti-amplification limit"
from [RFC9000] to mean three times the amount of data received from
an unvalidated address. This includes all DTLS records originating
from that source address, excluding discarded ones.
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3. RRC Extension
The use of RRC is negotiated via the "rrc" DTLS-only extension. On
connecting, the client includes the "rrc" extension in its
ClientHello if it wishes to use RRC. If the server is capable of
meeting this requirement, it responds with a "rrc" extension in its
ServerHello. The "extension_type" value for this extension is TBD1
and the "extension_data" field of this extension is empty. The
client and server MUST NOT use RRC unless both sides have
successfully exchanged "rrc" extensions.
Note that the RRC extension applies to both DTLS 1.2 and DTLS 1.3.
4. 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(TBD2), /* NEW */
(255)
} ContentType;
uint64 Cookie;
enum {
path_challenge(0),
path_response(1),
reserved(2..255)
} rrc_msg_type;
struct {
rrc_msg_type msg_type;
select (return_routability_check.msg_type) {
case path_challenge: Cookie;
case path_response: Cookie;
};
} return_routability_check;
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The newly introduced "return_routability_check" message contains a
cookie. The cookie is a 8-byte field containing arbitrary data.
The "return_routability_check" message MUST be authenticated and
encrypted using the currently active security context.
5. Path Validation Procedure
The receiver that observes the peer's address or port update MUST
stop sending any buffered application data (or limit the data sent to
the unvalidated address to the anti-amplification limit) and initiate
the return routability check that proceeds as follows:
1. An unpredictable cookie is placed in a "return_routability_check"
message of type path_challenge;
2. The message is sent to the observed new address and a timer T
(see Section 5.3) is started;
3. The peer endpoint, after successfully verifying the received
"return_routability_check" message responds by echoing the cookie
value in a "return_routability_check" message of type
path_response;
4. When the initiator receives and verifies the
"return_routability_check" message contains the sent cookie, 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.
Section 5.1 and Section 5.2 contain the requirements for the
initiator and responder roles, broken down per protocol phase.
5.1. Path Challenge Requirements
- The initiator MAY send multiple "return_routability_check"
messages of type path_challenge to cater for packet loss on the
probed path.
o Each path_challenge SHOULD go into different transport packets.
(Note that the DTLS implementation may not have control over
the packetization done by the transport layer.)
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o The transmission of subsequent path_challenge messages SHOULD
be paced to decrease the chance of loss.
o Each path_challenge message MUST contain random data.
- The initiator MAY use padding using the record padding mechanism
available in DTLS 1.3 (and in DTLS 1.2, when CID is enabled on the
sending direction) up to the anti-amplification limit to probe if
the path MTU (PMTU) for the new path is still acceptable.
5.2. Path Response Requirements
- The responder MUST NOT delay sending an elicited path_response
message.
- The responder MUST send exactly one path_response messages for
each received path_request.
- The responder MUST send the path_response on the network path
where the corresponding path_challenge has been received, so that
validation succeeds only if the path is functional in both
directions.
o The initiator MUST NOT enforce this behaviour
- The initiator MUST silently discard any invalid path_response it
receives.
Note that RRC does not cater for PMTU discovery on the reverse path.
If the responder wants to do PMTU discovery using RRC, it should
initiate a new path validation procedure.
5.3. Timer Choice
When setting T, implementations are cautioned that the new path could
have a longer round-trip time (RTT) than the original.
In settings where there is external information about the RTT of the
active path, implementations SHOULD use T = 3xRTT.
If an implementation has no way to obtain information regarding the
RTT of the active path, a value of 1s SHOULD be used.
Profiles for specific deployment environments - for example,
constrained networks [I-D.ietf-uta-tls13-iot-profile] - MAY specify a
different, more suitable value.
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6. Example
The example TLS 1.3 handshake shown in Figure 1 shows a client and a
server negotiating the support for CID and for the RRC extension.
Client Server
Key ^ ClientHello
Exch | + key_share
| + signature_algorithms
| + rrc
v + connection_id=empty
-------->
ServerHello ^ Key
+ key_share | Exch
+ connection_id=100 |
+ rrc v
{EncryptedExtensions} ^ Server
{CertificateRequest} v Params
{Certificate} ^
{CertificateVerify} | Auth
<-------- {Finished} v
^ {Certificate}
Auth | {CertificateVerify}
v {Finished} -------->
[Application Data] <-------> [Application Data]
+ Indicates noteworthy extensions sent in the
previously noted message.
* Indicates optional or situation-dependent
messages/extensions that are not always sent.
{} Indicates messages protected using keys
derived from a [sender]_handshake_traffic_secret.
[] Indicates messages protected using keys
derived from [sender]_application_traffic_secret_N.
Figure 1: Message Flow for Full TLS Handshake
Once a connection has been established the client and the server
exchange application payloads protected by DTLS with an unilaterally
used CIDs. In our case, the client is requested to use CID 100 for
records sent to the server.
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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.
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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
path_challenge(cookie)
Src-IP=Z
Dst-IP=B
Return Routability Check -------->
path_response(cookie)
Src-IP=B
Dst-IP=Z
<<< IP Address B
Verified >>
<======== Application Data
Src-IP=Z
Dst-IP=B
Figure 2: Return Routability Example
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7. 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.
8. IANA Considerations
IANA is requested to allocate an entry to the TLS "ContentType"
registry, for the "return_routability_check(TBD2)" defined in this
document. The "return_routability_check" content type is only
applicable to DTLS 1.2 and 1.3.
IANA is requested to allocate the extension code point (TBD1) for the
"rrc" extension to the "TLS ExtensionType Values" registry as
described in Table 1.
+-------+-------------+-------+-----------+-------------+-----------+
| Value | Extension | TLS | DTLS-Only | Recommended | Reference |
| | Name | 1.3 | | | |
+-------+-------------+-------+-----------+-------------+-----------+
| TBD1 | rrc | CH, | Y | N | RFC-THIS |
| | | SH | | | |
+-------+-------------+-------+-----------+-------------+-----------+
Table 1: rrc entry in the TLS ExtensionType Values registry
9. Open Issues
Issues against this document are tracked at https://github.com/tlswg/
dtls-rrc/issues
10. Acknowledgments
We would like to thank Achim Kraus, Hanno Becker, Hanno Boeck, Manuel
Pegourie-Gonnard, Mohit Sahni and Rich Salz for their input to this
document.
11. References
11.1. Normative References
[I-D.ietf-tls-dtls-connection-id]
RTFM, Inc., Arm Limited, Arm Limited, and Bosch.IO GmbH,
"Connection Identifiers for DTLS 1.2", draft-ietf-tls-
dtls-connection-id-13 (work in progress), June 2021.
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[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-dtls13-43 (work in progress), April
2021.
[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>.
11.2. Informative References
[I-D.ietf-uta-tls13-iot-profile]
Arm Limited and Arm Limited, "TLS/DTLS 1.3 Profiles for
the Internet of Things", draft-ietf-uta-tls13-iot-
profile-03 (work in progress), October 2021.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
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Appendix A. History
[[CREF1: RFC EDITOR: PLEASE REMOVE THIS SECTION]]
draft-ietf-tls-dtls-rrc-02
- Undo the TLS flags extension for negotiating RRC, use a new
extension type
draft-ietf-tls-dtls-rrc-01
- Use the TLS flags extension for negotiating RRC
- Enhanced IANA consideration section
- Expanded example section
- Revamp message layout:
o Use 8-byte fixed size cookies
o Explicitly separate path challenge from response
draft-ietf-tls-dtls-rrc-00
- Draft name changed after WG adoption
draft-tschofenig-tls-dtls-rrc-01
- Removed text that overlapped with draft-ietf-tls-dtls-connection-
id
draft-tschofenig-tls-dtls-rrc-00
- Initial version
Authors' Addresses
Hannes Tschofenig (editor)
Arm Limited
EMail: hannes.tschofenig@arm.com
Thomas Fossati (editor)
Arm Limited
EMail: thomas.fossati@arm.com
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