Internet DRAFT - draft-vanderstok-core-coap-est
draft-vanderstok-core-coap-est
anima S. Kumar
Internet-Draft Philips Lighting Research
Intended status: Standards Track P. van der Stok
Expires: May 2, 2017 Consultant
October 29, 2016
EST based on DTLS secured CoAP (EST-coaps)
draft-vanderstok-core-coap-est-00
Abstract
Low-resource devices in a Low-power and Lossy Network (LLN) can
operate in a mesh network using the IPv6 over Low-power Personal Area
Networks (6LoWPAN) and IEEE 802.15.4 link-layer standards.
Provisioning these devices in a secure manner with keys (often called
security bootstrapping) used to encrypt and authenticate messages is
the subject of Bootstrapping of Remote Secure Key Infrastructures
(BRSKI) [I-D.ietf-anima-bootstrapping-keyinfra]. Enrollment over
Secure Transport (EST) [RFC7030], based on TLS and HTTP, is used for
BRSKI. This document defines how low-resource devices are expected
to use EST over DTLS and CoAP. 6LoWPAN fragmentation management and
minor extensions to CoAP are needed to enable EST over DTLS-secured
CoAP (EST-coaps).
Note
Many of the concepts in this document are taken over from [RFC7030].
Consequently, much text is directly traceable to [RFC7030]. The same
document structure is followed to point out the differences and
commonalities between EST and EST-coaps.
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 http://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 May 2, 2017.
Kumar & van der Stok Expires May 2, 2017 [Page 1]
Internet-Draft EST-coaps October 2016
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. Operational Scenarios Overview . . . . . . . . . . . . . . . 4
3. Protocol Design and Layering . . . . . . . . . . . . . . . . 5
3.1. CoAP response codes . . . . . . . . . . . . . . . . . . . 7
3.2. Message fragmentation using Block . . . . . . . . . . . . 7
3.3. CoAP message headers . . . . . . . . . . . . . . . . . . 8
4. Protocol Exchange Details . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12
8. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . 13
Appendix A. Operational Scenario Example Messages . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
IPv6 over Low-power Wireless Personal Area Networks (6LoWPANs)
[RFC4944] on IEEE 802.15.4 [ieee802.15.4] wireless networks is
becoming common in many professional application domains such as
lighting controls. However commissioning of such networks suffers
from a lack of standardized secure bootstrapping mechanisms for these
networks.
Although IEEE 802.15.4 defines how security can be enabled between
nodes within a single mesh network, it does not specify the
provisioning and management of the keys. Therefore securing a
6LoWPAN network with devices from multiple manufacturers with
Kumar & van der Stok Expires May 2, 2017 [Page 2]
Internet-Draft EST-coaps October 2016
different provisioning techniques is often tedious and time
consuming.
Bootstrapping of Remote Secure Infrastructures (BRSKI)
[I-D.ietf-anima-bootstrapping-keyinfra] addresses the issue of
bootstrapping networked devices in the context of Autonomic
Networking Integrated Model and Approach (ANIMA). However, BRSKI has
not been developed specifically for low-resource devices in
constrained networks. These networks use DTLS [RFC6347], CoAP
[RFC7252], and UDP instead of TLS [RFC5246], HTTP [RFC7230] and TCP.
BRSKI relies on Enrollment over Secure Transport (EST) [RFC7030] for
the provisioning of the operational domain certificates. Replacing
the EST invocations of TLS and HTTP by DTLS and CoAP invocations
enables applying BRSKI on CoAP-based low-resource devices.
The Figure 1 below shows the EST-coaps architecture.
+---------------------------------------------------------+
| |
| EST request/response messages |
| |
+---------------------------------------------------------+
| |
| CoAP for message transfer and signaling |
| |
+---------------------------------------------------------+
| |
| DTLS for transport security |
| |
+---------------------------------------------------------+
| |
| UDP for transport |
| |
+---------------------------------------------------------+
Figure 1: EST-coaps protocol layers
Although EST-coaps paves the way for the utilization of BRSKI for
constrained devices on constrained networks, some devices will not
have enough resources to handle the large payloads that come with
EST-coaps. It is up to the network designer to decide which devices
execute the BRSKI protocol and which not.
EST-coaps is designed for use in professional control networks such
as lighting. The autonomic bootstrapping is interesting because it
reduces the manual intervention during the commissioning of the
Kumar & van der Stok Expires May 2, 2017 [Page 3]
Internet-Draft EST-coaps October 2016
network. Typing in passwords is contrary to this wish. Therefore,
the password authentication of EST is not supported in EST-coaps.
In the constrained devices context it is very unlikely that full PKI
request messages will be used. For that reason, full PKI messages
are not supported in EST-coaps.
Because the relatively large messages involved in EST cannot be
readily transported over constrained (6LoWPAN, LLN) wireless
networks, this document defines the use of CoAP Block-Wise Transfer
("Block") [RFC7959] combined with DTLS to fragment EST messages at
the application layer.
1.1. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
All the terminology from EST [RFC7030] is included in this document
by reference.
2. Operational Scenarios Overview
Only the differences to EST with respect to operational scenarios are
described in this section. EST-coaps server authentication differs
from EST as follows:
o Replacement of TLS by DTLS and HTTP by CoAP, resulting in:
* DTLS-secured CoAP sessions between EST-coaps client and EST-
coaps server.
o Only certificate-based client authentication is supported, with as
result:
* The EST-coaps client does not support manual authentication (as
described in Section 4.4.1 of [RFC7030])
* The EST-coaps client does not support authentication at the
application layer.
o EST-coaps does not support full PKI request messages [RFC5272].
The following EST-coaps protocol parts are supported as described for
the equivalent EST parts:
Kumar & van der Stok Expires May 2, 2017 [Page 4]
Internet-Draft EST-coaps October 2016
1. Request of client certificates by submitting a enrollment request
to EST-coaps server.
2. Renewal of existing client certificates by submitting a re-
enrollment request to EST-coaps server.
3. Request of certificate with key pair generated by EST-coaps
server.
4. The EST-coaps client can request the attributes needed for
enrollment before the enrollment request is issued"
3. Protocol Design and Layering
The EST-coaps protocol design follows closely the EST design,
excluding some aspects that are not relevant for automatic
bootstrapping of constrained devices within a professional context.
The parts supported by EST-coaps are:
Message types:
* Simple PKI messages.
* CA certificate retrieval.
* CSR Attributes Request.
* Server-generated key request.
CoAP with Block-Wise Transfer:
* CoAP Block-Wise Transfer header Options for control of the
transfer of larger EST messages.
DTLS for transport security:
* Authentication of the EST-coaps server.
* Authentication of the EST-coaps client.
* Communication integrity and confidentiality.
* Channel-binding information for linking proof-of-identity with
message-based proof-of-possession (OPTIONAL).
Given that CoAP and DTLS can provide proof of identity for EST-coaps
clients and server, simple PKI messages can be used conformant to
section 3.1 of [RFC5272]. EST-coaps supports the certificate types
Kumar & van der Stok Expires May 2, 2017 [Page 5]
Internet-Draft EST-coaps October 2016
and Trust Anchors (TA) that are specified for EST in section 3 of
[RFC7030].
The EST-coaps server URI is identical to the EST URI (except for
replacing the scheme https by coaps):
coaps://www.example.com/.well-known/est
coaps://www.example.com/.well-known/est/arbitraryLabel1
See Figure 5 in section 3.2.2 of [RFC7030] for the path-suffixes
(operations) that are supported by EST.
EST-coaps uses CoAP to transfer EST messages, aided by Block-Wise
Transfer [RFC7959] to transport CoAP messages in blocks thus avoiding
(excessive) 6LoWPAN fragmentation of UDP datagrams. The use of
"Block" is specified in Section 3.2.
The content-format (media type equivalent) of the CoAP message
determines which EST message is transported in the CoAP payload. The
media types specified in the HTTP Content-Type header(see section
3.2.2 of [RFC7030]) are in EST-coaps specified by the Content-Format
Option (12) of CoAP. The combination of URI path-suffix and content-
format used MUST map to an allowed combination of path-suffix and
media type as defined for EST.
EST-coaps is designed for use between low-resource devices using CoAP
and hence does not need to send base64-encoded data. Simple binary
coding is more efficient (30% less payload compared to base64) and
well supported by CoAP. Therefore, the content formats specification
in Section 5 requires the use of binary encoding for all EST-coaps
CoAP payloads.
The functions of TLS specified for EST are in EST-coaps mapped to the
equivalent DTLS functions. However, DTLS sessions SHOULD remain open
for persistent EST-coaps connections to reduce storage load. For
example, a cacerts request followed by an enrollments request SHOULD
use the same DTLS session.
The mandatory cipher suite for DTLS is
TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 defined in [RFC7251] which is the
mandatory-to-implement cipher suite in CoAP. Additionally the curve
secp256r1 MUST be supported [RFC4492]; this curve is equivalent to
the NIST P-256 curve. The hash algorithm is SHA-256. DTLS
implementations MUST use the Supported Elliptic Curves and Supported
Point Formats Extensions [RFC4492]; the uncompressed point format
MUST be supported; [RFC6090] can be used as an implementation method.
Kumar & van der Stok Expires May 2, 2017 [Page 6]
Internet-Draft EST-coaps October 2016
3.1. CoAP response codes
Section 5.9 of [RFC7252] specifies the mapping of HTTP response codes
to CoAP response codes. Every time the HTTP response code 200 is
specified in [RFC7030] in response to a GET request, in EST-coaps the
equivalent CoAP response code 2.05 MUST be used. Response code HTTP
202 in EST is mapped as indicated below; while other HTTP 2xx
response codes are not used by EST. For the following HTTP 4xx error
codes that may occur: 400, 401, 403, 404, 405, 406, 412, 413, 415 ;
the equivalent CoAP response code for EST-coaps is 4.xx. For the
HTTP 5xx error codes: 500, 501, 502, 503, 504 the equivalent CoAP
response code is 5.xx.
HTTP response code 202 needs a different treatment from the one
described for [RFC7030]. A new CoAP response code 2.06 is needed.
When the EST over CoAP request cannot be treated immediately, a CoAP
response code 2.06 Delayed is returned with Content-Format:
application/link-format described in [RFC6690]. The payload of the
response contains a link to receive the delayed response.
ALTERNATIVE (to discuss) : a 2.06 Delayed response without payload
and the link to receive the delayed response indicated using the
Location-Path and Location-Query Options.
The waiting client may send GET requests to the returned link. When
the response is not available, the server returns response code 2.06
with again the link for the client to query. When the response is
available, the server returns the response code 2.05 Content with a
payload containing the requested response in the appropriate content
format.
3.2. Message fragmentation using Block
DTLS defines fragmentation only for the handshake part and not for
secure data exchange (DTLS records). [RFC6347] states "Each DTLS
record MUST fit within a single datagram". In order to avoid using
IP fragmentation, which is not supported by 6LoWPAN, invokers of the
DTLS record layer MUST size DTLS records so that they fit within any
Path MTU estimates obtained from the record layer. In addition,
invokers residing on a 6LoWPAN over IEEE 802.15.4 network SHOULD
attempt to size CoAP messages such that each DTLS record will fit
within one or two IEEE 802.15.4 frames only by choosing the
appropriate block sizes.
Certificates can vary greatly in size dependent on signature
algorithms and key sizes. For a 256-bit curve, common ECDSA sizes
fluctuate between 500 bytes and 1 KB. Some EST messages may be
several kilobytes in size. Given non-existence of IP fragmentation
in 6LoWPAN networks and its 1280 bytes MTU, EST-coaps needs to be
Kumar & van der Stok Expires May 2, 2017 [Page 7]
Internet-Draft EST-coaps October 2016
able to fragment EST messages into multiple DTLS datagrams with each
DTLS datagram containing a block of CoAP payload data. Further
considering the small payload size available to a CoAP message, which
can be as low as 68 bytes in case the message needs to fit into a
single IEEE 802.15.4 frame, fine-grained fragmentation of EST
messages is essential.
For CoAP, [RFC7959] specifies the "Block1" option for fragmentation
of the request payload and the "Block2" option for fragmentation of
the return payload. The CoAP client MAY specify the Block1 size and
MAY also specify the Block2 size. The CoAP server MAY specify the
Block2 size, but not the Block1 size.
Examples of fragmented messages are shown in Appendix A.
3.3. CoAP message headers
EST-coaps uses CoAP payload blocks that each fit in a single DTLS
record i.e. UDP datagram without causing IP fragmentation. The
returned CoAP response codes are specified in Section 3.1. The CoAP
Token value is not specified by EST-coaps and may be chosen by the
CoAP client according to [RFC7252].
An example HTTP request message cacerts in EST will look like:
REQ:
GET /.well-known/est/cacerts HTTP/1.1
Host: 192.0.2.1:8085
Accept: */*
RES:
HTTP/1.1 200 OK
Status: 200 OK
Content-Type: application/pkcs7-mime
Content-Transfer-Encoding : base64
Content-Length: 4246
payload
The corresponding EST-coaps request looks like:
REQ:
GET coaps://[192.0.2.1:8085]/.well-known/est/cacerts
RES:
2.05 Content (Content-Format: application/pkcs7-mime)
{payload}
Kumar & van der Stok Expires May 2, 2017 [Page 8]
Internet-Draft EST-coaps October 2016
4. Protocol Exchange Details
The EST-coaps client MUST be configured with an implicit TA database
or an explicit TA database. The authentication of the EST-coaps
server by the EST-coaps client is based on Certificate authentication
in the DTLS handshake.
The authentication of the EST-coaps client is based on client
certificate in the DTLS handshake. This can either be
o DTLS with a previously issued client certificate (e.g., an
existing certificate issued by the EST CA);
o DTLS with a previously installed certificate (e.g., manufacturer-
installed certificate or a certificate issued by some other
party);
The details on checking the validity of the certificates are
identical to EST.
The other protocol aspects such as simple enrollment (re-enrollment),
certificate attributes and CA certificate request are similar to EST
with the exception that these are performed on coaps (CoAP+DTLS) as
the transport. The required content-formats for these request and
response messages are defined in Section 5. The CoAP response codes
are defined in Section 3.1.
EST-coaps does not support full PKI Requests. Consequently, the
fullcmc request of section 4.3 of [RFC7030] and response MUST NOT be
supported by EST-coaps.
5. IANA Considerations
Additions to the sub-registry "CoAP Content-Formats", within the
"CoRE Parameters" registry are needed for the below media types.
These can be registered either in the Expert Review range (0-255) or
IETF Review range (256-9999).
1.
* application/pkcs7-mime
* Type name: application
* Subtype name: pkcs7-mime
* smime-type: certs-only
Kumar & van der Stok Expires May 2, 2017 [Page 9]
Internet-Draft EST-coaps October 2016
* ID: TBD1
* Required parameters: None
* Optional parameters: None
* Encoding considerations: Binary
* Security considerations: As defined in this specification
* Published specification: [RFC5751]
* Applications that use this media type: ANIMA Bootstrap (BRSKI)
and EST
2.
* application/pkcs8
* Type name: application
* Subtype name: pkcs8
* ID: TBD2
* Required parameters: None
* Optional parameters: None
* Encoding considerations: Binary
* Security considerations: As defined in this specification
* Published specification: [RFC5958]
* Applications that use this media type: ANIMA Bootstrap (BRSKI)
and EST
3.
* application/csrattrs
* Type name: application
* Subtype name: csrattrs
* ID: TBD3
Kumar & van der Stok Expires May 2, 2017 [Page 10]
Internet-Draft EST-coaps October 2016
* Required parameters: None
* Optional parameters: None
* Encoding considerations: Binary
* Security considerations: As defined in this specification
* Published specification: [RFC7030]
* Applications that use this media type: ANIMA Bootstrap (BRSKI)
and EST
4.
* application/pkcs10
* Type name: application
* Subtype name: pkcs10
* ID: TBD4
* Required parameters: None
* Optional parameters: None
* Encoding considerations: binary
* Security considerations: As defined in this specification
* Published specification: [RFC5967]
* Applications that use this media type: ANIMA bootstrap (BRSKI)
and EST
Additions to the sub-registry "CoAP Response Code", within the "CoRE
Parameters" registry are needed for the following response codes:
o Code: 2.06
o Description: Delayed
o Reference: this document
Kumar & van der Stok Expires May 2, 2017 [Page 11]
Internet-Draft EST-coaps October 2016
6. Security Considerations
The security considerations mentioned in EST applies also to EST-
coaps.
7. Acknowledgements
The authors are very grateful to Klaus Hartke for his detailed
explanations on the use of Block with DTLS. The authors would like
to thank Esko Dijk and Michael Verschoor for the valuable discussions
that helped in shaping the solution.
8. Change Log
9. References
9.1. Normative References
[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Behringer, M., and S.
Bjarnason, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
keyinfra-03 (work in progress), June 2016.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC4492] Blake-Wilson, S., Bolyard, N., Gupta, V., Hawk, C., and B.
Moeller, "Elliptic Curve Cryptography (ECC) Cipher Suites
for Transport Layer Security (TLS)", RFC 4492,
DOI 10.17487/RFC4492, May 2006,
<http://www.rfc-editor.org/info/rfc4492>.
[RFC5272] Schaad, J. and M. Myers, "Certificate Management over CMS
(CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
<http://www.rfc-editor.org/info/rfc5272>.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, DOI 10.17487/RFC5751, January
2010, <http://www.rfc-editor.org/info/rfc5751>.
[RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958,
DOI 10.17487/RFC5958, August 2010,
<http://www.rfc-editor.org/info/rfc5958>.
Kumar & van der Stok Expires May 2, 2017 [Page 12]
Internet-Draft EST-coaps October 2016
[RFC5967] Turner, S., "The application/pkcs10 Media Type", RFC 5967,
DOI 10.17487/RFC5967, August 2010,
<http://www.rfc-editor.org/info/rfc5967>.
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090,
DOI 10.17487/RFC6090, February 2011,
<http://www.rfc-editor.org/info/rfc6090>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <http://www.rfc-editor.org/info/rfc6347>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<http://www.rfc-editor.org/info/rfc6690>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<http://www.rfc-editor.org/info/rfc7030>.
[RFC7251] McGrew, D., Bailey, D., Campagna, M., and R. Dugal, "AES-
CCM Elliptic Curve Cryptography (ECC) Cipher Suites for
TLS", RFC 7251, DOI 10.17487/RFC7251, June 2014,
<http://www.rfc-editor.org/info/rfc7251>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.
[RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in
the Constrained Application Protocol (CoAP)", RFC 7959,
DOI 10.17487/RFC7959, August 2016,
<http://www.rfc-editor.org/info/rfc7959>.
9.2. Informative References
[ieee802.15.4]
Institute of Electrical and Electronics Engineers, , "IEEE
Standard 802.15.4-2006", 2006.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<http://www.rfc-editor.org/info/rfc4944>.
Kumar & van der Stok Expires May 2, 2017 [Page 13]
Internet-Draft EST-coaps October 2016
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC6838] Freed, N., Klensin, J., and T. Hansen, "Media Type
Specifications and Registration Procedures", BCP 13,
RFC 6838, DOI 10.17487/RFC6838, January 2013,
<http://www.rfc-editor.org/info/rfc6838>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
Appendix A. Operational Scenario Example Messages
This appendix provides detailed examples of the messages using DTLS
and BLOCK option Block2. The minimum PMTU is 1280 bytes, which is
the example value assumed for the DTLS datagram size. The example
block length is taken as 64 which gives an SZX value of 2.
The following is an example of a valid /cacerts exchange.
During the initial DTLS handshake, the client can ignore the optional
server-generated "certificate request" and can instead proceed with
the CoAP GET request. The content length of the cacerts response in
appendix A.1 of [RFC7030] is 4246 bytes using base64. This leads to
a length of 3185 bytes in binary. The CoAP message adds around 10
bytes, the DTLS record 29 bytes.
To avoid IP fragmentation, the CoAP block option is used and an MTU
of 127 is assumed to stay within one IEEE 802.15.4 packet. To stay
below the MTU of 127, the payload is split in 50 packets with a
payload of 64 bytes each. Fifty times the client sends an IPv6
packet containing the UDP datagram with the DTLS record that
encapsulates the CoAP Request. The server returns an IPv6 packet
containing the UDP datagram with the DTLS record that encapsulates
the CoAP response.
The CoAP request-response exchange with block option is shown below.
Block option is shown in a decomposed way indicating the kind of
Block option (2 in this case because used in the response) followed
by a colon, and then the block number (NUM), the more bit (M = 0
means last block), and block size exponent (2**(SZX+4)) separated by
slashes. The Length 64 is used with SZX= 2 to avoid IP
fragmentation.
Kumar & van der Stok Expires May 2, 2017 [Page 14]
Internet-Draft EST-coaps October 2016
The CoAP Request is sent with confirmable (CON) option and the
content format of the Response is /application/cacerts.
GET [192.0.2.1:8085]/.well-known/est/cacerts -->
<-- (2:0/1/64) 2.05 Content
GET URI (2:1/1/64) -->
<-- (2:1/1/64) 2.05 Content
|
|
|
GET URI (2:49/1/64) -->
<-- (2:49/0/64) 2.05 Content
Authors' Addresses
Sandeep S. Kumar
Philips Lighting Research
High Tech Campus 7
Eindhoven 5656 AE
NL
Email: ietf@sandeep.de
Peter van der Stok
Consultant
Email: consultancy@vanderstok.org
Kumar & van der Stok Expires May 2, 2017 [Page 15]
