Internet-Draft Identifier Update for OSCORE March 2024
Höglund & Tiloca Expires 5 September 2024 [Page]
Workgroup:
CoRE Working Group
Internet-Draft:
draft-ietf-core-oscore-id-update-00
Published:
Intended Status:
Standards Track
Expires:
Authors:
R. Höglund
RISE AB
M. Tiloca
RISE AB

Identifier Update for OSCORE

Abstract

Two peers that communicate with the CoAP protocol can use the Object Security for Constrained RESTful Environments (OSCORE) protocol to protect their message exchanges end-to-end. To this end, the two peers share an OSCORE Security Context and a number of related identifiers. In particular, each of the two peers stores a Sender ID that identifies its own Sender Context within the Security Context, and a Recipient ID that identifies the Recipient Context associated with the other peer within the same Security Context. These identifiers are sent in plaintext within OSCORE-protected messages. Hence, they can be used to correlate messages exchanged between peers and track those peers, with consequent privacy implications. This document defines an OSCORE ID update procedure that two peers can use to update their OSCORE identifiers. This procedure can be run stand-alone or seamlessly integrated in an execution of the Key Update for OSCORE (KUDOS) procedure.

Discussion Venues

This note is to be removed before publishing as an RFC.

Discussion of this document takes place on the Constrained RESTful Environments Working Group mailing list (core@ietf.org), which is archived at https://mailarchive.ietf.org/arch/browse/core/.

Source for this draft and an issue tracker can be found at https://github.com/core-wg/oscore-id-update.

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 working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."

This Internet-Draft will expire on 5 September 2024.

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Table of Contents

1. Introduction

When using the CoAP protocol [RFC7252], two peers can use Object Security for Constrained RESTful Environments (OSCORE) protocol to protect their message exchanges end-to-end. To this end, the two peers share an OSCORE Security Context and a number of related identifiers.

As part of the shared Security Context, each peer stores one Sender Context identified by a Sender ID and used to protect its outgoing messages. Also, it stores a Recipient Context identified by a Recipient ID and used to unprotect the incoming messages from the other peer. That is, one's peer Sender ID (Recipient ID) is equal to the other peer's Recipient ID (Sender ID).

When receiving an OSCORE-protected message, the recipient peer uses its Recipient ID conveyed within the message or otherwise implied, in order to retrieve the correct Security Context and unprotect the message.

These identifiers are sent in plaintext within OSCORE-protected messages and are immutable throughout the lifetime of a Security Context, even in case the two peers migrate to a different network or simply change their addressing information. Therefore, the identifiers can be used to correlate messages that the two peers exchange at different points in time or through different paths, hence allowing for track them with consequent privacy implications.

In order to address this issue, this document defines an OSCORE ID update procedure that two peers can use to update their OSCORE Sender and Recipient IDs. For instance, two peers may want to use this procedure before switching to a different network, in order to make it more difficult to understand that their communication is continuing in the new network.

The OSCORE ID update procedure can be run stand-alone or seamlessly integrated in an execution of the Key Update for OSCORE (KUDOS) procedure [I-D.ietf-core-oscore-key-update].

1.1. 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.

Readers are expected to be familiar with the terms and concepts related to CoAP [RFC7252], Observe [RFC7641], CBOR [RFC8949], OSCORE [RFC8613], and KUDOS [I-D.ietf-core-oscore-key-update].

This document additionally uses the following terminology.

  • Initiator: the peer starting the OSCORE ID update procedure, by sending the first message.

  • Responder: the peer that receives the first message in an execution of the OSCORE ID update procedure.

  • Forward message flow: the execution workflow where the initiator acts as CoAP client (see Section 2.1.1).

  • Reverse message flow: the execution workflow where the initiator acts as CoAP server (see Section 2.1.2).

2. Update of OSCORE Sender/Recipient IDs

This section defines the procedure that two peers can perform, in order to update the OSCORE Sender/Recipient IDs that they use in their shared OSCORE Security Context.

When performing an update of OSCORE Sender/Recipient IDs, a peer provides its new intended OSCORE Recipient ID to the other peer, by means of the Recipient-ID Option defined in Section 2.1. Hereafter, this document refers to a message including the Recipient-ID Option as an "ID update (request/response) message".

This procedure can be initiated by either peer, i.e., the CoAP client or the CoAP server may start it by sending the first OSCORE IDs update message. The former case is denoted as the "forward message flow" and the latter as the "reverse message flow".

Furthermore, this procedure can be executed stand-alone, or instead seamlessly integrated in an execution of the KUDOS procedure for updating OSCORE keying material (see Section 4 of [I-D.ietf-core-oscore-key-update]) used in its FS mode or no-FS mode (see Section 4.5 of [I-D.ietf-core-oscore-key-update]).

An initiator terminates an ongoing OSCORE ID update procedure with another peer as failed, in case, after having sent the first ID update message for the procedure in question, a pre-defined amount of time has elapsed without receiving and successfully verifying the second ID update message from the other peer. It is RECOMMENDED that such an amount of time is equal to MAX_TRANSMIT_WAIT (see Section 4.8.2 of [RFC7252]).

A peer terminates an ongoing OSCORE ID update procedure with another peer as successful, in any of the following two cases.

A peer MUST NOT initiate an OSCORE ID update procedure with another peer, if it has another such procedure ongoing with that other peer.

Upon receiving a valid ID update message, a responder that supports the ID update update procedure MUST send the second ID update message, except in the following case.

2.1. The Recipient-ID Option

The Recipient ID-Option defined in this section has the properties summarized in Figure 1, which extends Table 4 of [RFC7252]. That is, the option is elective, safe to forward, part of the cache key, and non repeatable.

+-------+---+---+---+---+--------------+--------+--------+---------+
| No.   | C | U | N | R | Name         | Format | Length | Default |
+-------+---+---+---+---+--------------+--------+--------+---------+
|       |   |   |   |   |              |        |        |         |
| TBD24 |   |   |   |   | Recipient-ID | opaque | any    | (none)  |
|       |   |   |   |   |              |        |        |         |
+-------+---+---+---+---+--------------+--------+--------+---------+
          C=Critical, U=Unsafe, N=NoCacheKey, R=Repeatable
Figure 1: The Recipient-ID Option.

Note to RFC Editor: Following the registration of the CoAP Option Number 24, please replace "TBD24" with "24" in the figure above. Then, please delete this paragraph.

The option value can have an arbitrary length. Implementations can limit its length to that of the longest supported Recipient ID.

This document particularly defines how this option is used in messages protected with OSCORE. That is, when the option is included in an outgoing message, the option value specifies the new OSCORE Recipient ID that the sender endpoint intends to use with the other endpoint sharing the OSCORE Security Context.

Therefore, the maximum length of the option value is equal to the maximum length of OSCORE Sender/Recipient IDs. As defined in Section 3.3 of [RFC8613], this is determined by the size of the AEAD nonce of the used AEAD Algorithm in the OSCORE Security Context.

The Recipient-ID Option is of class E in terms of OSCORE processing (see Section 4.1 of [RFC8613]).

2.1.1. Forward Message Flow

Figure 2 shows an example of the OSCORE ID update procedure, run stand-alone and in the forward message flow, with the client acting as initiator. On each peer, SID and RID denote the OSCORE Sender ID and Recipient ID of that peer, respectively.

Appendix A.1 provides a different example of the OSCORE ID update procedure, as run integrated in an execution of KUDOS and in the forward message flow (see Section 4.3.1 of [I-D.ietf-core-oscore-key-update]).

Client Server (initiator) (responder) CTX_A { CTX_A { SID = 0x01 SID = 0x00 RID = 0x00 RID = 0x01 } } Request #1 Protect /temp with CTX_A OSCORE { ... kid: 0x01 Verify } with CTX_A Encrypted Payload { ... Recipient-ID: 0x42 ... Application Payload } Response #1 Protect OSCORE { with CTX_A ... Verify } with CTX_A Encrypted Payload { ... Recipient-ID: 0x78 ... Application Payload } CTX_B { CTX_B { SID = 0x78 SID = 0x42 RID = 0x42 RID = 0x78 } } Request #2 Protect /temp with CTX_B OSCORE { ... kid: 0x78 Verify } with CTX_B Encrypted Payload { ... Application Payload } Response #2 Protect OSCORE { with CTX_B ... Verify } with CTX_B Encrypted Payload { ... Application Payload } Discard CTX_A Request #3 Protect /temp with CTX_B OSCORE { ... kid: 0x78 Verify } with CTX_B Encrypted Payload { ... Application Payload } Discard CTX_A Response #3 Protect OSCORE { with CTX_B ... Verify } with CTX_B Encrypted Payload { ... Application Payload }
Figure 2: Example of the OSCORE ID update procedure with Forward Message Flow

Before the OSCORE ID update procedure starts, the client (the server) shares with the server (the client) an OSCORE Security Context CTX_A with Sender ID 0x01 (0x00) and Recipient ID 0x00 (0x01).

When starting the OSCORE ID update procedure, the client determines its new intended OSCORE Recipient ID 0x42. Then, the client prepares a CoAP request targeting an application resource at the server. The request includes the Recipient-ID Option, with value the client's new Recipient ID 0x42.

The client protects the request with CTX_A, i.e., by using the keying material derived from the client's current Sender ID 0x01. The protected request specifies the client's current Sender ID 0x01 in the 'kid' field of the OSCORE Option. After that, the client sends the request to the server as Request #1.

Upon receiving, decrypting, and successfully verifying the OSCORE message Request #1, the server retrieves the value 0x42 from the Recipient-ID Option, and determines its new intended OSCORE Recipient ID 0x78. Then, the server prepares a CoAP response including the Recipient-ID Option, with value the server's new Recipient ID 0x78.

The server protects the response with CTX_A, i.e., by using the keying material derived from the server's current Sender ID 0x00. After that, the server sends the response to the client.

Then, the server considers 0x42 and 0x78 as its new Sender ID and Recipient ID to use with the client, respectively. As shown in the example, the server practically installs a new OSCORE Security Context CTX_B where: i) its Sender ID and Recipient ID are 0x42 and 0x78, respectively; ii) the Sender Sequence Number and the Replay Window are re-initialized (see Section 3.2.2 of [RFC8613]); iii) anything else is like in the OSCORE Security Context used to encrypt the OSCORE message Response #1.

Upon receiving, decrypting, and successfully verifying the OSCORE message Response #1, the client considers 0x78 and 0x42 as the new Sender ID and Recipient ID to use with the server, respectively. As shown in the example, the client practically installs a new OSCORE Security Context CTX_B where: i) its Sender ID and Recipient ID are 0x78 and 0x42, respectively; ii) the Sender Sequence Number and the Replay Window are re-initialized (see Section 3.2.2 of [RFC8613]); iii) anything else is like in the OSCORE Security Context used to decrypt the OSCORE message Response #1.

From then on, the client and the server can exchange messages protected with the OSCORE Security Context CTX_B, i.e., according to the new OSCORE Sender/Recipient IDs and using new keying material derived from those.

That is, the client sends the OSCORE message Request #2, which is protected with CTX_B and specifies the new client's Sender ID 0x78 in the 'kid' field of the OSCORE Option.

Upon receiving the OSCORE message Request #2, the server retrieves the OSCORE Security Context CTX_B, according to its new Recipient ID 0x78 specified in the 'kid' field of the OSCORE Option. Then, the server decrypts and verifies the response by using CTX_B. Finally, the server prepares a CoAP response Response #2, protects it with CTX_B, and sends it to the client.

Upon receiving the OSCORE message Response #2, the client decrypts and verifies it with the OSCORE Security Context CTX_B. In case of successful verification, the client confirms that the server is aligned with the new OSCORE Sender/Recipient IDs, and thus discards the OSCORE Security Context CTX_A.

After that, one further exchange occurs, where both the CoAP request and the CoAP response are protected with the OSCORE Security Context CTX_B. In particular, upon receiving, decrypting, and successfully verifying the OSCORE message Request #3, the server confirms that the client is aligned with the new OSCORE Sender/Recipient IDs, and thus discards the OSCORE Security Context CTX_A.

2.1.2. Reverse Message Flow

Figure 3 shows an example of the OSCORE ID update procedure, run stand-alone and in the reverse message flow, with the server acting as initiator. On each peer, SID and RID denote the OSCORE Sender ID and Recipient ID of that peer, respectively.

Appendix A.2 provides a different example of the OSCORE ID update procedure, as run integrated in an execution of KUDOS and in the reverse message flow (see Section 4.3.2 of [I-D.ietf-core-oscore-key-update]).

Client Server (responder) (initiator) CTX_A { CTX_A { SID = 0x01 SID = 0x00 RID = 0x00 RID = 0x01 } } Request #1 Protect /temp with CTX_A OSCORE { ... kid: 0x01 Verify } with CTX_A Encrypted Payload { ... Application Payload } Response #1 Protect OSCORE { with CTX_A ... Verify } with CTX_A Encrypted Payload { ... Recipient-ID: 0x78 ... Application Payload } Request #2 Protect /temp with CTX_A OSCORE { ... kid: 0x01 Verify } with CTX_A Encrypted Payload { ... Recipient-ID: 0x42 ... Application Payload } CTX_B { SID = 0x42 RID = 0x78 } Response #2 Protect OSCORE { with CTX_A ... Verify } with CTX_A Encrypted Payload { ... Application Payload } CTX_B { SID = 0x78 RID = 0x42 } Request #3 Protect /temp with CTX_B OSCORE { ... kid: 0x78 Verify } with CTX_B Encrypted Payload { ... Application Payload } Response #3 Protect OSCORE { with CTX_B ... Verify } with CTX_B Encrypted Payload { ... Application Payload } Discard CTX_A Request #4 Protect /temp with CTX_B OSCORE { ... kid: 0x78 Verify } with CTX_B Encrypted Payload { ... Application Payload } Discard CTX_A Response #4 Protect OSCORE { with CTX_B ... Verify } with CTX_B Encrypted Payload { ... Application Payload }
Figure 3: Example of the OSCORE ID update procedure with Reverse Message Flow

Before the OSCORE ID update procedure starts, the client (the server) shares with the server (the client) an OSCORE Security Context CTX_A with Sender ID 0x01 (0x00) and Recipient ID 0x00 (0x01).

At first, the client prepares a CoAP Request #1 targeting an application resource at the server. The client protects the request with CTX_A, i.e., by using the keying material derived from the client's current Sender ID 0x01. The protected request specifies the client's current Sender ID 0x01 in the 'kid' field of the OSCORE Option. After that, the client sends the request to the server as Request #1.

Upon receiving, decrypting, and successfully verifying the OSCORE message Request #1, the server decides to start an OSCORE ID update procedure. To this end, the server determines its new intended OSCORE Recipient ID 0x78. Then, the server prepares a CoAP response as a reply to the just received request and including the Recipient-ID Option, with value the server's new Recipient ID 0x78.

The server protects the response with CTX_A, i.e., by using the keying material derived from the server's current Sender ID 0x00. After that, the server sends the response to the client as Response #1.

Upon receiving, decrypting, and successfully verifying the OSCORE message Response #1, the client retrieves the value 0x78 from the Recipient-ID Option, and determines its new intended OSCORE Recipient ID 0x42. Then, the client prepares a CoAP request targeting an application resource at the server. The request includes the Recipient-ID Option, with value the client's new Recipient ID 0x42.

The client protects the request with CTX_A, i.e., by using the keying material derived from the client's current Sender ID 0x01. The protected request specifies the client's current Sender ID 0x01 in the 'kid' field of the OSCORE Option. After that, the client sends the request to the server as Request #2.

Upon receiving, decrypting, and successfully verifying the OSCORE message Request #2, the server retrieves the value 0x42 from the Recipient-ID Option. Then the server considers 0x42 and 0x78 as the new Sender ID and Recipient ID to use with the client, respectively. As shown in the example, the server practically installs a new OSCORE Security Context CTX_B where: i) its Sender ID and Recipient ID are 0x42 and 0x78, respectively; ii) the Sender Sequence Number and the Replay Window are re-initialized (see Section 3.2.2 of [RFC8613]); iii) anything else is like in the OSCORE Security Context used to encrypt the OSCORE message Request #2.

Then, the server prepares a CoAP response, as a reply to the just received request, and protects it with CTX_A, i.e., by using the keying material derived from the server's current Sender ID 0x00. After that, the server sends the response to the client as Response #2.

Upon receiving, decrypting, and successfully verifying the OSCORE message Response #2, the client considers 0x78 and 0x42 as the new Sender ID and Recipient ID to use with the server, respectively. As shown in the example, the client practically installs a new OSCORE Security Context CTX_B where: i) its Sender ID and Recipient ID are 0x78 and 0x42, respectively; ii) the Sender Sequence Number and the Replay Window are re-initialized (see Section 3.2.2 of [RFC8613]); iii) anything else is like in the OSCORE Security Context used to decrypt the OSCORE response.

From then on, the client and the server can exchange messages protected with the OSCORE Security Context CTX_B, i.e., according to the new OSCORE Sender/Recipient IDs and using new keying material derived from those.

That is, the client sends the OSCORE message Request #3, which is protected with CTX_B and specifies the new client's Sender ID 0x78 in the 'kid' field of the OSCORE Option.

Upon receiving the OSCORE message Request #3, the server retrieves the OSCORE Security Context CTX_B, according to its new Recipient ID 0x78 specified in the 'kid' field of the OSCORE Option. Then, the server decrypts and verifies the response by using CTX_B. Finally, the server prepares a CoAP response, protects it with CTX_B, and sends it to the client as Response #3.

Upon receiving the OSCORE message Response #3, the client decrypts and verifies it with the OSCORE Security Context CTX_B. In case of successful verification, the client confirms that the server is aligned with the new OSCORE Sender/Recipient IDs, and thus discards the OSCORE Security Context CTX_A.

After that, one further exchange occurs, where both the CoAP request and the CoAP response are protected with the OSCORE Security Context CTX_B. In particular, upon receiving, decrypting, and successfully verifying the OSCORE message Request #4, the server confirms that the client is aligned with the new OSCORE Sender/Recipient IDs, and thus discards the OSCORE Security Context CTX_A.

2.1.3. Additional Actions for Execution

After having experienced a loss of state, a peer MUST NOT participate in a stand-alone OSCORE ID update procedure with another peer, until having performed a full-fledged establishment/renewal of an OSCORE Security Context with the other peer (e.g., by running KUDOS [I-D.ietf-core-oscore-key-update] or the authenticated key establishment protocol EDHOC [I-D.ietf-lake-edhoc]).

More precisely, a peer has experienced a loss of state if it cannot access the latest snapshot of the latest OSCORE Security Context CTX_OLD or the whole set of OSCORE Sender/Recipient IDs that have been used with the triplet (Master Secret, Master Salt, ID Context) of CTX_OLD. This can happen, for instance, after a device reboots.

Furthermore, when participating in a stand-alone OSCORE ID update procedure, a peer performs the following additional steps.

  • When a peer sends an ID update message, the value of the Recipient-ID Option that the peer specifies as its new intended OSCORE Recipient ID MUST fulfill both the following conditions: it is currently available as Recipient ID to use for the peer (see Section 3.3 of [RFC8613]); and the peer has never used it as Recipient ID with the current triplet (Master Secret, Master Salt, ID Context).

  • When receiving an ID update message, the peer MUST abort the procedure if it has already used the identifier specified in the Recipient-ID Option as its own Sender ID with the current triplet (Master Secret, Master Salt, ID Context).

In order to fulfill the conditions above, a peer has to keep track of the OSCORE Sender/Recipient IDs that it has used with the current triplet (Master Secret, Master Salt, ID Context) since the latest update of the OSCORE Master Secret (e.g., performed by running KUDOS).

2.2. Preserving Observations Across ID Updates

When running the OSCORE ID update procedure stand-alone or integrated in an execution of KUDOS, the following holds if Observe [RFC7641] is supported, in order to preserve ongoing observations beyond a change of OSCORE identifiers.

  • If a peer intends to keep active beyond an update of its Sender ID the observations where it is acting as CoAP client, then the peer:

    • MUST store the value of the 'kid' parameter from the original Observe requests, and retain it for the whole duration of the observations, throughout which the client MUST NOT update the stored value associated with the corresponding Observe registration request; and

    • MUST use the stored value of the 'kid' parameter from the original Observe registration request as value for the 'request_kid' parameter in the external_aad structure (see Section 5.4 of [RFC8613]), when verifying notifications for that observation as per Section 8.4.2 of [RFC8613].

  • If a peer is acting as CoAP server in an ongoing observation, then the peer:

    • MUST store the value of the 'kid' parameter from the original Observe registration request, and retain it for the whole duration of the observation, throughout which the peer MUST NOT update the stored value associated with the corresponding Observe registration request; and

    • MUST use the stored value of the 'kid' parameter from the original Observe registration request as value for the 'request_kid' parameter in the external_aad structure (see Section 5.4 of [RFC8613]), when protecting notifications for that observation as per Section 8.3.1 of [RFC8613].

3. Security Considerations

TODO Security

4. IANA Considerations

This document has the following actions for IANA.

Note to RFC Editor: Please replace all occurrences of "[RFC-XXXX]" with the RFC number of this specification and delete this paragraph.

4.1. CoAP Option Numbers Registry

IANA is asked to enter the following option number to the "CoAP Option Numbers" registry within the "Constrained RESTful Environments (CoRE) Parameters" registry group.

Table 1: New CoAP Option Number
Number Name Reference
TBD24 Recipient-ID [RFC-XXXX]

Note to RFC Editor: Following the registration of the CoAP Option Number 24, please replace "TBD24" with "24" in the table above. Then, please delete this paragraph.

5. References

5.1. Normative References

[I-D.ietf-core-oscore-key-update]
Höglund, R. and M. Tiloca, "Key Update for OSCORE (KUDOS)", Work in Progress, Internet-Draft, draft-ietf-core-oscore-key-update-07, , <https://datatracker.ietf.org/doc/html/draft-ietf-core-oscore-key-update-07>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC7252]
Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, , <https://www.rfc-editor.org/info/rfc7252>.
[RFC7641]
Hartke, K., "Observing Resources in the Constrained Application Protocol (CoAP)", RFC 7641, DOI 10.17487/RFC7641, , <https://www.rfc-editor.org/info/rfc7641>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
[RFC8613]
Selander, G., Mattsson, J., Palombini, F., and L. Seitz, "Object Security for Constrained RESTful Environments (OSCORE)", RFC 8613, DOI 10.17487/RFC8613, , <https://www.rfc-editor.org/info/rfc8613>.
[RFC8949]
Bormann, C. and P. Hoffman, "Concise Binary Object Representation (CBOR)", STD 94, RFC 8949, DOI 10.17487/RFC8949, , <https://www.rfc-editor.org/info/rfc8949>.

5.2. Informative References

[I-D.ietf-lake-edhoc]
Selander, G., Mattsson, J. P., and F. Palombini, "Ephemeral Diffie-Hellman Over COSE (EDHOC)", Work in Progress, Internet-Draft, draft-ietf-lake-edhoc-23, , <https://datatracker.ietf.org/doc/html/draft-ietf-lake-edhoc-23>.

Appendix A. Examples of OSCORE ID update procedure Integrated in KUDOS

The following section shows two examples where the OSCORE ID update procedure is performed together with the KUDOS procedure for updating OSCORE keying material.

A.1. Forward Message Flow

Figure 4 provides an example of the OSCORE ID update procedure, as run integrated in an execution of KUDOS and in the forward message flow (see Section 4.3.1 of [I-D.ietf-core-oscore-key-update]). On each peer, SID and RID denote the OSCORE Sender ID and Recipient ID of that peer, respectively.

Client Server (initiator) (responder) CTX_OLD { CTX_OLD { SID = 0x01 SID = 0x00 RID = 0x00 RID = 0x01 } } Generate N1 CTX_1 = updateCtx( X1, N1, CTX_OLD) Request #1 Protect with CTX_1 /.well-known/kudos OSCORE { ... d flag: 1 CTX_1 = updateCtx( x: X1 X1, nonce: N1 N1, ... CTX_OLD) kid: 0x01 } Verify with CTX_1 Encrypted Payload { ... Generate N2 Recipient-ID: 0x42 ... CTX_NEW = updateCtx( } Comb(X1,X2), Comb(N1 N2), CTX_OLD) Response #1 Protect with CTX_NEW OSCORE { ... CTX_NEW = updateCtx( Partial IV: 0 Comb(X1,X2), ... Comb(N1 N2), CTX_OLD) d flag: 1 x: X2 Verify with CTX_NEW nonce: N2 ... Discard CTX_OLD } Encrypted Payload { Update SID and ... Update SID and RID in CTX_NEW Recipient-ID: 0x78 RID in CTX_NEW ... CTX_NEW { } CTX_NEW { SID = 0x78 SID = 0x42 RID = 0x42 RID = 0x78 } } / The actual key update process ends here. / The two peers can use the new Security Context CTX_NEW. Request #2 Protect with CTX_NEW /temp OSCORE { ... kid: 0x78 Verify with CTX_NEW } Encrypted Payload { Discard CTX_OLD ... Application Payload } Response #2 Protect with CTX_NEW OSCORE { ... Verify with CTX_NEW } Encrypted Payload { ... Application Payload }
Figure 4: Example of the OSCORE ID update procedure with Forward Message Flow and Integrated in a KUDOS Execution.

A.2. Reverse Message Flow

Figure 5 provides an example of the OSCORE ID update procedure, as run integrated in an execution of KUDOS and in the reverse message flow (see Section 4.3.2 of [I-D.ietf-core-oscore-key-update]). On each peer, SID and RID denote the OSCORE Sender ID and Recipient ID of that peer, respectively.

Client Server (responder) (initiator) CTX_OLD { CTX_OLD { SID = 0x01 SID = 0x00 RID = 0x00 RID = 0x01 } } Request #1 Protect with CTX_OLD /temp OSCORE { ... kid: 0x01 } Verify with CTX_OLD Encrypted Payload { ... Generate N1 Application Payload } CTX_1 = updateCtx( X1, N1, CTX_OLD) Response #1 Protect with CTX_1 OSCORE { ... CTX_1 = updateCtx( Partial IV: 0 X1, ... N1, d flag: 1 CTX_OLD) x: X1 nonce: N1 Verify with CTX_1 ... } Generate N2 Encrypted Payload { ... CTX_NEW = updateCtx( Recipient-ID: 0x78 Comb(X1,X2), ... Comb(N1 N2), } CTX_OLD) Request #2 Protect with CTX_NEW /.well-known/kudos OSCORE { ... d flag: 1 CTX_NEW = updateCtx( x: X2 Comb(X1,X2), nonce: N2 Comb(N1 N2), y: w CTX_OLD) old_nonce: N1 kid: 0x01 ... } Verify with CTX_NEW Encrypted Payload { ... Discard CTX_OLD Recipient-ID: 0x42 ... Application Payload } Update SID and Update SID and RID in CTX_NEW RID in CTX_NEW CTX_NEW { CTX_NEW { SID = 0x78 SID = 0x42 RID = 0x42 RID = 0x78 } } / The actual key update process ends here. / The two peers can use the new Security Context CTX_NEW. Response #2 Protect with CTX_NEW OSCORE { ... Verify with CTX_NEW } Encrypted Payload { Discard CTX_OLD ... Application Payload } Request #3 Protect with CTX_NEW /temp OSCORE { ... kid: 0x78 Verify with CTX_NEW } Encrypted Payload { ... Application Payload } Response #3 Protect with CTX_NEW OSCORE { ... Verify with CTX_NEW } Encrypted Payload { ... Application Payload }
Figure 5: Example of the OSCORE ID update procedure with Reverse Message Flow and Integrated in a KUDOS Execution.

Appendix B. Document Updates

This section is to be removed before publishing as an RFC.

B.1. Version -00

  • Split out material from Key Update for OSCORE draft into this new document.

  • Extended terminology

  • Editorial improvements

Acknowledgments

The authors sincerely thank Christian Amsüss, Carsten Bormann, John Preuß Mattsson, and Göran Selander for their feedback and comments.

The work on this document has been partly supported by VINNOVA and the Celtic-Next project CRITISEC; and by the H2020 projects SIFIS-Home (Grant agreement 952652) and ARCADIAN-IoT (Grant agreement 101020259).

Authors' Addresses

Rikard Höglund
RISE AB
Isafjordsgatan 22
SE-16440 Stockholm Kista
Sweden
Marco Tiloca
RISE AB
Isafjordsgatan 22
SE-16440 Stockholm Kista
Sweden