CoRE Working Group M. Tiloca
Internet-Draft RISE AB
Intended status: Standards Track E. Dijk
Expires: January 14, 2021 IoTconsultancy.nl
July 13, 2020
Proxy Operations for CoAP Group Communication
draft-tiloca-core-groupcomm-proxy-01
Abstract
This document specifies the operations performed by a forward-proxy,
when using the Constrained Application Protocol (CoAP) in group
communication scenarios. Proxy operations involve the processing of
individual responses from servers, as reply to a single request sent
by the client over unicast to the proxy, and then distributed by the
proxy over IP multicast to the servers. When receiving the different
responses via the proxy, the client is able to distinguish them and
their originator servers, by acquiring their addressing information.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. The Multicast-Signaling Option . . . . . . . . . . . . . . . 3
3. The Response-Forwarding Option . . . . . . . . . . . . . . . 4
4. Requirements and Objectives . . . . . . . . . . . . . . . . . 5
5. Protocol Description . . . . . . . . . . . . . . . . . . . . 6
5.1. Request Sending . . . . . . . . . . . . . . . . . . . . . 7
5.2. Request Processing at the Proxy . . . . . . . . . . . . . 8
5.3. Request and Response Processing at the Server . . . . . . 8
5.4. Response Processing at the Proxy . . . . . . . . . . . . 9
5.5. Response Processing at the Client . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6.1. Client Authentication . . . . . . . . . . . . . . . . . . 11
6.2. Multicast-Signaling Option . . . . . . . . . . . . . . . 11
6.3. Response-Forwarding Option . . . . . . . . . . . . . . . 12
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7.1. CoAP Option Numbers Registry . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
8.1. Normative References . . . . . . . . . . . . . . . . . . 13
8.2. Informative References . . . . . . . . . . . . . . . . . 14
Appendix A. Using OSCORE Between Client and Proxy . . . . . . . 14
A.1. Protecting the Request . . . . . . . . . . . . . . . . . 14
A.2. Verifying the Request . . . . . . . . . . . . . . . . . . 15
A.3. Protecting the Response . . . . . . . . . . . . . . . . . 15
A.4. Verifying the Response . . . . . . . . . . . . . . . . . 15
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
The Constrained Application Protocol (CoAP) [RFC7252] allows the
presence of forward-proxies, as intermediary entities supporting
clients to perform requests on their behalf.
CoAP supports also group communication over IP multicast
[I-D.ietf-core-groupcomm-bis], where a group request can be addressed
to multiple recipient servers, each of which may reply with an
individual unicast response. As discussed in Section 2.3.3 of
[I-D.ietf-core-groupcomm-bis], this group communication scenario
poses a number of issues and limitations to proxy operations.
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In particular, the client sends a single unicast request to the
proxy, which the proxy forwards to a group of servers over IP
multicast. Later on, the proxy delivers back to the client multiple
responses to the original unicast request. As defined by [RFC7252],
the multiple responses are delivered to the client inside separate
CoAP messages, all matching (by Token) to the client's original
unicast request. A possible alternative approach of performing
aggregation of responses into a single CoAP response would require a
specific aggregation content-format, which is not available yet.
Both these approaches have open issues.
This specification considers the former approach of how the proxy
forwards the individual responses to a CoAP group request back to the
client. The described method addresses all the related issues raised
in Section 2.3.3 of [I-D.ietf-core-groupcomm-bis].
To this end, a dedicated signaling protocol is defined, using two new
CoAP options. In particular, the client can explicitly confirm its
support for receiving multiple responses to a proxied unicast
request, i.e. one per originator server, and for how long it is
willing to wait for responses. Also, each server originating a
response indicates to the client its own addressing information.
This enables the client to distinguish the multiple, diffent
responses by origin and to possibly contact one or more of the
individual servers by a unicast request, optionally bypassing the
forward-proxy.
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 terms and concepts defined
in CoAP [RFC7252], Group Communication for CoAP
[I-D.ietf-core-groupcomm-bis], OSCORE [RFC8613] and Group OSCORE
[I-D.ietf-core-oscore-groupcomm].
2. The Multicast-Signaling Option
The Multicast-Signaling Option defined in this section has the
properties summarized in Figure 1, which extends Table 4 of
[RFC7252]. The option is intended only for CoAP requests.
Since the option is not Safe-to-Forward, the column "N" indicates a
dash for "not applicable". The value of the Multicast-Signaling
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Option specifies a timeout value in seconds, encoded as an unsigned
integer (see Section 3.2 of [RFC7252]).
+------+---+---+---+---+------------+--------+--------+---------+
| No. | C | U | N | R | Name | Format | Length | Default |
+------+---+---+---+---+------------+--------+--------+---------+
| | | | | | | | | |
| TBD1 | | x | - | | Multicast- | uint | 1-5 B | (none) |
| | | | | | Signaling | | | |
| | | | | | | | | |
+------+---+---+---+---+------------+--------+--------+---------+
C=Critical, U=Unsafe, N=NoCacheKey, R=Repeatable
(*) See below.
Figure 1: The Multicast-Signaling Option.
This document specifically defines how this option is used by a
client, to indicate to a forward-proxy its support for and interest
in receiving multiple responses to a proxied CoAP group request, i.e.
one per originator server, and for how long it is willing to wait for
receiving responses via that proxy (see Section 5.1 and Section 5.2).
The client, when sending a CoAP group request to a proxy via IP
unicast, to be forwarded by the proxy to a targeted group of servers,
includes the Multicast-Signaling Option into the request. The option
value indicates after what time period in seconds the client will
stop accepting responses matching its original unicast request, with
the exception of notifications if CoAP Observe is used [RFC7641].
This allows the intermediary proxy to stop forwarding responses back
to the client, if received from the servers later than a timeout
expiration.
The Multicast-Signaling Option is of class U for OSCORE
[RFC8613][I-D.ietf-core-oscore-groupcomm].
3. The Response-Forwarding Option
The Response-Forwarding Option defined in this section has the
properties summarized in Figure 2, which extends Table 4 of
[RFC7252]. The option is intended only for CoAP responses, and
builds on the Base-Uri option from Section 3 of
[I-D.bormann-coap-misc].
Since the option is intended only for responses, the column "N"
indicates a dash.
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+------+---+---+---+---+------------+--------+--------+---------+
| No. | C | U | N | R | Name | Format | Length | Default |
+------+---+---+---+---+------------+--------+--------+---------+
| | | | | | | | | |
| TBD2 | | | - | | Response- | string | 8-20 B | (none) |
| | | | | | Forwarding | | | |
| | | | | | | | | |
+------+---+---+---+---+------------+--------+--------+---------+
C=Critical, U=Unsafe, N=NoCacheKey, R=Repeatable
(*) See below.
Figure 2: The Response-Forwarding Option.
This document specifically defines how this option is used by a proxy
that forwards a request originated by a client over IP multicast.
Upon receiving a response to that request from a server, the proxy
includes the Response-Forwarding Option into the response sent to the
originator client (see Section 5). The proxy uses the option to
indicate to the client the addressing information of the server
generating the response.
The client can use the addressing information of the server specified
in the option to identify the response originator and possibly send
later unicast requests to directly, or via the proxy as CoAP unicast
requests.
The option value is an absolute-URI with no query component
([RFC3986], Section 4.3). If the port number is omitted in the
authority component, it is assumed that the port number where to send
unicast requests to the server is the same port number specified in
the group URI of the original unicast CoAP group request sent to the
proxy (see Section 5.1).
The Response-Forwarding Option is of class E for OSCORE
[RFC8613][I-D.ietf-core-oscore-groupcomm].
4. Requirements and Objectives
This specification assumes that the following requirements are
fulfilled.
o REQ1. The CoAP proxy is explicitly configured (white-list) to
allow proxied CoAP group requests from specific client(s).
o REQ2. The CoAP proxy MUST identify a client sending a CoAP group
request, in order to verify whether the client is white-listed to
do so. For example, this can rely on one of the following.
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* A DTLS channel [RFC6347][I-D.ietf-tls-dtls13] between the
client and the proxy, where the client has also been
authenticated during the secure channel establishment.
* A pairwise OSCORE Security Context between the client and the
proxy, as described in Appendix A.
o REQ3. If secure, end-to-end communication is required between the
client and the servers in the CoAP group, exchanged messages MUST
be protected by using Group OSCORE
[I-D.ietf-core-oscore-groupcomm], as discussed in Section 5.2 of
[I-D.ietf-core-groupcomm-bis]. This requires the client and the
servers to have previously joined the correct OSCORE group, for
instance by using the approach described in
[I-D.ietf-ace-key-groupcomm-oscore]. The correct OSCORE group to
join can be pre-configured or alternatively discovered, for
instance by using the approach described in
[I-D.tiloca-core-oscore-discovery].
This specification defines how to achieve the following objectives.
o OBJ1. The CoAP proxy gets an indication from the client that it
is in fact interested to and capable to receive multiple responses
to its unicast request containing a CoAP group URI.
o OBJ2. The CoAP proxy learns how long it should wait for responses
to a proxied request, before starting to ignore following
responses (except for notifications, if CoAP Observe is used
[RFC7641]).
o OBJ3. The CoAP proxy returns individual unicast responses to the
client, each of which matches the original unicast request to the
proxy.
o OBJ4. The CoAP client is able to distinguish the different
responses to the original unicast request, as well as their
corresponding originator servers.
o OBJ5. The CoAP client is enabled to optionally contact one or
more of the responding servers in the future, either directly or
via the CoAP proxy.
5. Protocol Description
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5.1. Request Sending
In order to send a request addressed to a group of servers via the
CoAP proxy, the client proceeds as follows.
1. The client prepares a request addressed to the CoAP proxy. The
request specifies the group URI as a string in the Proxi-URI
option, or by using the Proxy-Scheme option with the group URI
constructed from the URI-* options (see Section 2.3.3 of
[I-D.ietf-core-groupcomm-bis]).
2. The client MUST retain the Token value used for this original
unicast request beyond the reception of a first response matching
it. To this end, the client follows the same rules for Token
retention defined for multicast requests in Section 2.3.1 of
[I-D.ietf-core-groupcomm-bis]. In particular, it picks an amount
of time T to wait for before freeing up the Token value, such
that:
* T is smaller than the amount of time Tr it may pick to wait
for before potentially reusing the Token value.
* T includes the expected worst-case time taken by the request
and response processing on the forward-proxy plus the servers
in the addressed CoAP group.
* T includes the expected worst-case round-trip delay between
client and proxy, and between proxy and servers.
3. The client includes the Multicast-Signaling Option defined in
Section 2 into the unicast request to send to the proxy. The
option value specifies an amount of time T' < T. The difference
(T - T') should include the expected worst-case round-trip time
between the client and the forward-proxy.
4. The client processes the request as defined in
[I-D.ietf-core-groupcomm-bis], and also as in
[I-D.ietf-core-oscore-groupcomm] when secure group communication
is used between the client and the servers.
5. If OSCORE is used to protect the leg between the client and the
proxy (see REQ2 in Section 4), the client (further) protects the
unicast request as resulting at the end of step 4. In
particular, the client uses the pairwise OSCORE Security Context
it has with the proxy, as described in Appendix A.1.
6. The client sends the request to the proxy as a unicast CoAP
message.
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5.2. Request Processing at the Proxy
Upon receiving the request from the client, the proxy proceeds as
follows.
1. If OSCORE is used to protect the leg between the client and the
proxy (see REQ2 in Section 4), the proxy decrypts the request
using the pairwise OSCORE Security Context it has with the
client, as described in Appendix A.4.
2. The proxy identifies the client, and verifies that the client is
in fact white-listed to have its requests proxyied to CoAP group
URIs.
3. The proxy verifies the presence of the Multicast-Signaling
Option, as a confirmation that the client is fine to receive
multiple responses matching the same original request.
4. The proxy retrieves the value T' from the Multicast-Signaling
Option, and then removes the option from the client's request.
5. The proxy forwards the client's request to the group of servers.
In particular, the proxy sends it as a CoAP group request over IP
multicast, addressed to the group URI specified by the client.
6. The proxy sets a timeout with the value T' retrieved from the
Multicast-Signaling Option of the original unicast request. The
proxy will ignore responses to the forwarded group request coming
from servers, if received after the timeout expiration, with the
exception of Observe notifications (see Section 5.4).
5.3. Request and Response Processing at the Server
Upon receiving the group request from the proxy, a server proceeds as
follows.
1. The server processes the group request as defined in
[I-D.ietf-core-groupcomm-bis], and also as in
[I-D.ietf-core-oscore-groupcomm] when secure group communication
is used between the client and the server.
2. The server processes the response to be forwarded back to the
client as defined in [I-D.ietf-core-groupcomm-bis], and also as
in [I-D.ietf-core-oscore-groupcomm] when secure group
communication is used between the client and the server.
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5.4. Response Processing at the Proxy
Upon receiving a response matching the group request before the
amount of time T' has elapsed, the proxy proceeds as follows.
1. The proxy includes the Response-Forwarding Option defined in
Section 3 into the response. The proxy specifies as option value
the addressing information of the server generating the response,
encoded as an absolute-URI as defined in Section 3. In
particular:
* The authority component MUST specify the server IPv6 address
if the multicast request was destined for an IPv6 multicast
address, and MUST specify the server IPv4 address if the
multicast request was destined for an IPv4 address.
* The authority component MUST specify the port number of the
server as the source port number of the response, if this
differs from the port number specified in the group URI of the
original unicast CoAP group request (see Section 5.1).
Otherwise, the authority component MAY omit the port number.
When using Observe [RFC7641], the proxy includes the Response-
Forwarding Option also in every notification, including non-2.xx
notifications resulting in removing the proxy from the list of
observers.
2. If OSCORE is used to protect the leg between the client and the
proxy (see REQ2 in Section 4), the proxy (further) protects the
response using the pairwise OSCORE Security Context it has with
the client, as described in Appendix A.3.
3. The proxy forwards the response back to the client.
Upon timeout expiration, i.e. T' seconds after having sent the group
request over IP multicast, the proxy frees up its local Token value
associated to that request. Thus, following late responses to the
same group request will be discarded and not forwarded back to the
client.
When using CoAP Observe [RFC7641], the Token value is freed up only
if, after the timeout expiration, no 2.xx (Success) responses
matching the group request and also including an Observe option have
been received. Then, as long as observations are active with servers
in the group for the target resource of the group request,
notifications from those servers are forwarded back to the client.
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5.5. Response Processing at the Client
Upon receiving from the proxy a response matching the original
unicast request before the amount of time T has elapsed, the client
proceeds as follows.
1. The client processes the response as defined in
[I-D.ietf-core-groupcomm-bis].
2. If OSCORE is used to protect the leg between the client and the
proxy (see REQ2 in Section 4), the client decrypts the response
using the pairwise OSCORE Security Context it has with the proxy,
as described in Appendix A.4.
3. If secure group communication is used between the client and the
servers, the client processes the response, possibly as outcome
of step 2, as defined in [I-D.ietf-core-oscore-groupcomm].
4. The client identifies the originator server, whose addressing
information is specified as value of the Response-Forwarding
Option. If the port number is omitted in the value of the
Response-Forwarding Option, the client MUST assume that the port
number where to send unicast requests to the server is the same
port number specified in the group URI of the original unicast
CoAP group request sent to the proxy (see Section 5.1).
In particular, the client is able to distinguish different responses
as originated by different servers. Optionally, the client may
contact one or more of those servers individually, i.e. directly
(bypassing the proxy) or indirectly (via a proxied CoAP unicast
request).
Upon the timeout expiration, i.e. T seconds after having sent the
original unicast request to the proxy, the client frees up its local
Token value associated to that request. Note that, upon this timeout
expiration, the Token value is not eligible for possible reuse yet
(see Section 5.1). Thus, until the actual amount of time before
enabling Token reusage has elapsed, following late responses to the
same request forwarded by the proxy will be discarded, as not
matching (by Token) any active request from the client.
When using CoAP Observe [RFC7641], the Token value is freed up only
if, after the timeout expiration, no 2.xx (Success) responses
matching the original unicast request and also including an Observe
option have been received. If at least one such response has been
received, the client continues receiving those notifications as
forwarded by the proxy, as long as the observation for the target
resource of the original unicast request is active.
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6. Security Considerations
The security considerations from [RFC7252][I-D.ietf-core-groupcomm-bi
s][RFC8613][I-D.ietf-core-oscore-groupcomm] hold for this document.
Furthermore, the following additional considerations hold.
6.1. Client Authentication
As per the requirement REQ2 (see Section 4), the client has to
authenticate to the proxy when sending a group request to forward.
This leverages an established security association between the client
and the proxy, that the client uses to protect the group request,
before sending it to the proxy.
Note that, if the group request is (also) protected with Group
OSCORE, i.e. end-to-end between the client and the servers, the proxy
can authenticate the client by successfully verifying the
countersignature embedded in the group request. This requires that,
for each client to authenticate, the proxy stores the public key used
by that client in the OSCORE group.
Nevertheless, the client SHOULD still rely on a full-fledged,
pairwise secure association with the proxy. In addition to ensuring
the integrity of group requests sent to the proxy (see Section 6.2
and Section 6.3), this prevents the proxy from forwarding replayed
group requests with a valid countersignature, as injected by an
active, on-path adversary.
6.2. Multicast-Signaling Option
The Multicast-Signaling Option is of class U for OSCORE
[RFC8613][I-D.ietf-core-oscore-groupcomm]. This allows the proxy to
access the option value and retrieve the timeout value T', as well as
to remove the option altogether before forwarding the group request
to the servers.
The security association between the client and the proxy MUST
provide message integrity, so that further possible intermediaries as
well as on-path active adversaries are not able to remove the option
or alter its content, before the group request reaches the proxy.
Removing the option would otherwise result in the proxy not
forwarding the group request to the servers. Instead, altering the
option content would result in the proxy accepting and forwarding
back responses for an amount of time different than the one actually
indicated by the client.
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The security association between the client and the proxy SHOULD also
provide message confidentiality. Otherwise, further intermediares as
well as on-path passive adversaries would be able to simply access
the option content, and thus learn for how long the client is willing
to receive responses from the servers in the group via the proxy.
This may in turn be used to perform a more efficient, selective
suppression of responses from the servers.
When the client (further) protects the unicast request sent to the
proxy with OSCORE (see Appendix A) and/or with DTLS, both message
integrity and message confidentiality are achieved in the leg between
the client and the proxy.
6.3. Response-Forwarding Option
The Response-Forwarding Option is of class E for OSCORE
[RFC8613][I-D.ietf-core-oscore-groupcomm], and thus can be protected
end-to-end between the client and the proxy, which includes the
option into a server response before forwarding it back to the
client.
Since the security association between the client and the proxy
provides message integrity, any further intermediaries or on-path
active adversaries are not able to undetectably remove the Response-
Forwarding Option from a forwarded server response. This ensures
that the client can correctly distinguish the different responses and
identify their corresponding originator server.
7. IANA Considerations
This document has the following actions for IANA.
7.1. CoAP Option Numbers Registry
IANA is asked to enter the following option numbers to the "CoAP
Option Numbers" registry defined in [RFC7252] within the "CoRE
Parameters" registry.
+--------+---------------------+-------------------+
| Number | Name | Reference |
+--------+---------------------+-------------------+
| TBD1 | Multicast-Signaling | [[this document]] |
+--------+---------------------+-------------------+
| TBD2 | Response-Forwarding | [[this document]] |
+--------+---------------------+-------------------+
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8. References
8.1. Normative References
[I-D.ietf-core-groupcomm-bis]
Dijk, E., Wang, C., and M. Tiloca, "Group Communication
for the Constrained Application Protocol (CoAP)", draft-
ietf-core-groupcomm-bis-00 (work in progress), March 2020.
[I-D.ietf-core-oscore-groupcomm]
Tiloca, M., Selander, G., Palombini, F., and J. Park,
"Group OSCORE - Secure Group Communication for CoAP",
draft-ietf-core-oscore-groupcomm-09 (work in progress),
June 2020.
[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>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<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,
May 2017, <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, July 2019,
<https://www.rfc-editor.org/info/rfc8613>.
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8.2. Informative References
[I-D.bormann-coap-misc]
Bormann, C. and K. Hartke, "Miscellaneous additions to
CoAP", draft-bormann-coap-misc-27 (work in progress),
November 2014.
[I-D.ietf-ace-key-groupcomm-oscore]
Tiloca, M., Park, J., and F. Palombini, "Key Management
for OSCORE Groups in ACE", draft-ietf-ace-key-groupcomm-
oscore-07 (work in progress), June 2020.
[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-dtls13-38 (work in progress), May
2020.
[I-D.tiloca-core-oscore-discovery]
Tiloca, M., Amsuess, C., and P. Stok, "Discovery of OSCORE
Groups with the CoRE Resource Directory", draft-tiloca-
core-oscore-discovery-05 (work in progress), March 2020.
[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>.
Appendix A. Using OSCORE Between Client and Proxy
This section describes how OSCORE is used to protect messages
exchanged by a client and a proxy, using their pairwise OSCORE
Security Context.
This is especially convenient for the communication scenario
addressed in this document, when the client already supports and uses
Group OSCORE [I-D.ietf-core-oscore-groupcomm], to protect messages
end-to-end with the servers.
A.1. Protecting the Request
Before sending the CoAP request to the proxy, the client protects it
using the pairwise OSCORE Security Context it has with the proxy.
The client processes the CoAP request as defined in [RFC8613], with
the following differences.
o The Proxy-Uri option, if present, is not decomposed and recomposed
as defined in Section 4.1.3.3 of [RFC8613].
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o The following options, if present, are processed as Class E.
* Proxy-Uri, Proxy-Scheme, Uri-Host and Uri-Port.
* OSCORE, which is present if Group OSCORE is used between the
client and the servers, to achieve end-to-end secure group
communication.
Furthermore, the Multicast-Signaling Option is processed as Class E.
As in [RFC8613], the resulting message includes an outer OSCORE
Option, which reflects the usage of the pairwise OSCORE Security
Context between the client and the proxy.
A.2. Verifying the Request
The proxy verifies the CoAP request as defined in [RFC8613].
If secure group communication is also used between the client and the
servers, the resulting request to be forwarded to the servers is
protected with Group OSCORE [I-D.ietf-core-oscore-groupcomm], and it
includes a different OSCORE Option, which reflects the usage of the
group OSCORE Security Context between the client and the servers.
A.3. Protecting the Response
The proxy protects the CoAP response received from a server, using
the pairwise OSCORE Security Context it has with the client.
The proxy processes the CoAP response as defined in [RFC8613], with
the difference that the OSCORE Option, if present, is processed as
Class E. This is the case if Group OSCORE is used between the client
and the servers, to achieve end-to-end secure group communication.
As in [RFC8613], the resulting message to be forwarded back to the
client includes a different OSCORE Option, which reflects the usage
of the pairwise OSCORE Security Context between the client and the
proxy.
A.4. Verifying the Response
The client verifies the CoAP response received from the proxy as
defined in [RFC8613].
If secure group communication is also used between the client and the
servers, the resulting response is protected with Group OSCORE
[I-D.ietf-core-oscore-groupcomm]. In particular, it includes a
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different OSCORE Option, which reflects the usage of the group OSCORE
Security Context between the client and the servers.
Acknowledgments
The authors sincerely thank Christian Amsuess, Jim Schaad and Goeran
Selander for their comments and feedback.
The work on this document has been partly supported by VINNOVA and
the Celtic-Next project CRITISEC.
Authors' Addresses
Marco Tiloca
RISE AB
Isafjordsgatan 22
Kista SE-16440 Stockholm
Sweden
Email: marco.tiloca@ri.se
Esko Dijk
IoTconsultancy.nl
\________________\
Utrecht
The Netherlands
Email: esko.dijk@iotconsultancy.nl
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