draft-ietf-ace-coap-est-17.txt   draft-ietf-ace-coap-est-18.txt 
ACE P. van der Stok ACE P. van der Stok
Internet-Draft Consultant Internet-Draft Consultant
Intended status: Standards Track P. Kampanakis Intended status: Standards Track P. Kampanakis
Expires: June 7, 2020 Cisco Systems Expires: July 9, 2020 Cisco Systems
M. Richardson M. Richardson
SSW SSW
S. Raza S. Raza
RISE SICS RISE SICS
December 5, 2019 January 6, 2020
EST over secure CoAP (EST-coaps) EST over secure CoAP (EST-coaps)
draft-ietf-ace-coap-est-17 draft-ietf-ace-coap-est-18
Abstract Abstract
Enrollment over Secure Transport (EST) is used as a certificate Enrollment over Secure Transport (EST) is used as a certificate
provisioning protocol over HTTPS. Low-resource devices often use the provisioning protocol over HTTPS. Low-resource devices often use the
lightweight Constrained Application Protocol (CoAP) for message lightweight Constrained Application Protocol (CoAP) for message
exchanges. This document defines how to transport EST payloads over exchanges. This document defines how to transport EST payloads over
secure CoAP (EST-coaps), which allows constrained devices to use secure CoAP (EST-coaps), which allows constrained devices to use
existing EST functionality for provisioning certificates. existing EST functionality for provisioning certificates.
skipping to change at page 1, line 40 skipping to change at page 1, line 40
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 7, 2020. This Internet-Draft will expire on July 9, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 7
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. DTLS and conformance to RFC7925 profiles . . . . . . . . . . 7 4. DTLS and conformance to RFC7925 profiles . . . . . . . . . . 7
5. Protocol Design . . . . . . . . . . . . . . . . . . . . . . . 10 5. Protocol Design . . . . . . . . . . . . . . . . . . . . . . . 10
5.1. Discovery and URIs . . . . . . . . . . . . . . . . . . . 11 5.1. Discovery and URIs . . . . . . . . . . . . . . . . . . . 10
5.2. Mandatory/optional EST Functions . . . . . . . . . . . . 13 5.2. Mandatory/optional EST Functions . . . . . . . . . . . . 13
5.3. Payload formats . . . . . . . . . . . . . . . . . . . . . 14 5.3. Payload formats . . . . . . . . . . . . . . . . . . . . . 13
5.4. Message Bindings . . . . . . . . . . . . . . . . . . . . 15 5.4. Message Bindings . . . . . . . . . . . . . . . . . . . . 15
5.5. CoAP response codes . . . . . . . . . . . . . . . . . . . 16 5.5. CoAP response codes . . . . . . . . . . . . . . . . . . . 15
5.6. Message fragmentation . . . . . . . . . . . . . . . . . . 17 5.6. Message fragmentation . . . . . . . . . . . . . . . . . . 16
5.7. Delayed Responses . . . . . . . . . . . . . . . . . . . . 18 5.7. Delayed Responses . . . . . . . . . . . . . . . . . . . . 17
5.8. Server-side Key Generation . . . . . . . . . . . . . . . 20 5.8. Server-side Key Generation . . . . . . . . . . . . . . . 19
6. HTTPS-CoAPS Registrar . . . . . . . . . . . . . . . . . . . . 22 6. HTTPS-CoAPS Registrar . . . . . . . . . . . . . . . . . . . . 21
7. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 24 7. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 23
8. Deployment limitations . . . . . . . . . . . . . . . . . . . 24 8. Deployment limitations . . . . . . . . . . . . . . . . . . . 23
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
9.1. Content-Format Registry . . . . . . . . . . . . . . . . . 25 9.1. Content-Format Registry . . . . . . . . . . . . . . . . . 24
9.2. Resource Type registry . . . . . . . . . . . . . . . . . 25 9.2. Resource Type registry . . . . . . . . . . . . . . . . . 24
10. Security Considerations . . . . . . . . . . . . . . . . . . . 26 9.3. Well-Known URIs Registry . . . . . . . . . . . . . . . . 25
10.1. EST server considerations . . . . . . . . . . . . . . . 26 10. Security Considerations . . . . . . . . . . . . . . . . . . . 25
10.2. HTTPS-CoAPS Registrar considerations . . . . . . . . . . 28 10.1. EST server considerations . . . . . . . . . . . . . . . 25
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 29 10.2. HTTPS-CoAPS Registrar considerations . . . . . . . . . . 27
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 28
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 29 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28
13.1. Normative References . . . . . . . . . . . . . . . . . . 29 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
13.2. Informative References . . . . . . . . . . . . . . . . . 31 13.1. Normative References . . . . . . . . . . . . . . . . . . 28
Appendix A. EST messages to EST-coaps . . . . . . . . . . . . . 33 13.2. Informative References . . . . . . . . . . . . . . . . . 30
A.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 34 Appendix A. EST messages to EST-coaps . . . . . . . . . . . . . 32
A.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 36 A.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 33
A.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 38 A.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 35
A.4. csrattrs . . . . . . . . . . . . . . . . . . . . . . . . 40 A.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 37
Appendix B. EST-coaps Block message examples . . . . . . . . . . 41 A.4. csrattrs . . . . . . . . . . . . . . . . . . . . . . . . 39
B.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 41 Appendix B. EST-coaps Block message examples . . . . . . . . . . 40
B.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 45 B.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 40
Appendix C. Message content breakdown . . . . . . . . . . . . . 46 B.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 44
C.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 46 Appendix C. Message content breakdown . . . . . . . . . . . . . 45
C.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 47 C.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 45
C.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 49 C.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 46
C.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 48
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50
1. Change Log 1. Change Log
EDNOTE: Remove this section before publication EDNOTE: Remove this section before publication
-18
IESG Reviews fixes.
Removed spurious lines introduced in v-17 due to xml2rfc v3.
-17 -17
v16 remnants by Ben K. v16 remnants by Ben K.
Typos. Typos.
-16 -16
Updates to address Yaron S.'s Secdir review. Updates to address Yaron S.'s Secdir review.
skipping to change at page 8, line 25 skipping to change at page 8, line 29
In accordance with sections 3.3 and 4.4 of [RFC7925], the mandatory In accordance with sections 3.3 and 4.4 of [RFC7925], the mandatory
cipher suite for DTLS in EST-coaps is cipher suite for DTLS in EST-coaps is
TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 [RFC7251]. Curve secp256r1 MUST TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 [RFC7251]. Curve secp256r1 MUST
be supported [RFC8422]; this curve is equivalent to the NIST P-256 be supported [RFC8422]; this curve is equivalent to the NIST P-256
curve. After the publication of [RFC7748], support for Curve25519 curve. After the publication of [RFC7748], support for Curve25519
will likely be required in the future by (D)TLS Profiles for the will likely be required in the future by (D)TLS Profiles for the
Internet of Things [RFC7925]. Internet of Things [RFC7925].
DTLS 1.2 implementations must use the Supported Elliptic Curves and DTLS 1.2 implementations must use the Supported Elliptic Curves and
Supported Point Formats Extensions in [RFC8422]. Uncompressed point Supported Point Formats Extensions in [RFC8422]. Uncompressed point
format must also be supported. format must also be supported. DTLS 1.3 [I-D.ietf-tls-dtls13]
implementations differ from DTLS 1.2 because they do not support
DTLS 1.3 [I-D.ietf-tls-dtls13] implementations differ from DTLS 1.2 point format negotiation in favor of a single point format for each
because they do not support point format negotiation in favor of a curve. Thus, support for DTLS 1.3 does not mandate point format
single point format for each curve. Thus, support for DTLS 1.3 does extensions and negotiation. In addition, in DTLS 1.3 the Supported
not mandate point format extensions and negotiation. In addition, in Elliptic Curves extension has been renamed to Supported Groups.
DTLS 1.3 the Supported Elliptic Curves extension has been renamed to
Supported Groups.
CoAP was designed to avoid IP fragmentation. DTLS is used to secure CoAP was designed to avoid IP fragmentation. DTLS is used to secure
CoAP messages. However, fragmentation is still possible at the DTLS CoAP messages. However, fragmentation is still possible at the DTLS
layer during the DTLS handshake when using ECC ciphersuites. If layer during the DTLS handshake when using ECC ciphersuites. If
fragmentation is necessary, "DTLS provides a mechanism for fragmentation is necessary, "DTLS provides a mechanism for
fragmenting a handshake message over several records, each of which fragmenting a handshake message over several records, each of which
can be transmitted separately, thus avoiding IP fragmentation" can be transmitted separately, thus avoiding IP fragmentation"
[RFC6347]. [RFC6347].
The authentication of the EST-coaps server by the EST-coaps client is The authentication of the EST-coaps server by the EST-coaps client is
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The authentication of the EST-coaps client MUST be with a client The authentication of the EST-coaps client MUST be with a client
certificate in the DTLS handshake. This can either be certificate in the DTLS handshake. This can either be
o a previously issued client certificate (e.g., an existing o a previously issued client certificate (e.g., an existing
certificate issued by the EST CA); this could be a common case for certificate issued by the EST CA); this could be a common case for
simple re-enrollment of clients. simple re-enrollment of clients.
o a previously installed certificate (e.g., manufacturer IDevID o a previously installed certificate (e.g., manufacturer IDevID
[ieee802.1ar] or a certificate issued by some other party). [ieee802.1ar] or a certificate issued by some other party).
IDevID's are expected to have a very long life, as long as the IDevID's are expected to have a very long life, as long as the
device, but under some conditions could expire. In that case, the device, but under some conditions could expire. In that case, the
server MAY want to authenticate a client certificate against its server MAY authenticate a client certificate against its trust
trust store although the certificate is expired (Section 10). store although the certificate is expired (Section 10).
EST-coaps supports the certificate types and Trust Anchors (TA) that EST-coaps supports the certificate types and Trust Anchors (TA) that
are specified for EST in Section 3 of [RFC7030]. are specified for EST in Section 3 of [RFC7030].
As described in Section 2.1 of [RFC5272] proof-of-identity refers to As described in Section 2.1 of [RFC5272] proof-of-identity refers to
a value that can be used to prove that the private key corresponding a value that can be used to prove that an end-entity or client is in
to the certified public key is in the possession of and can be used the possession of and can use the private key corresponding to the
by an end-entity or client. Additionally, channel-binding certified public key. Additionally, channel-binding information can
information can link proof-of-identity with an established link proof-of-identity with an established connection. Connection-
connection. Connection-based proof-of-possession is OPTIONAL for based proof-of-possession is OPTIONAL for EST-coaps clients and
EST-coaps clients and servers. When proof-of-possession is desired, servers. When proof-of-possession is desired, a set of actions are
a set of actions are required regarding the use of tls-unique, required regarding the use of tls-unique, described in Section 3.5 in
described in Section 3.5 in [RFC7030]. The tls-unique information [RFC7030]. The tls-unique information consists of the contents of
consists of the contents of the first "Finished" message in the the first "Finished" message in the (D)TLS handshake between server
(D)TLS handshake between server and client [RFC5929]. The client and client [RFC5929]. The client adds the "Finished" message as a
adds the "Finished" message as a ChallengePassword in the attributes ChallengePassword in the attributes section of the PKCS#10 Request
section of the PKCS#10 Request [RFC5967] to prove that the client is [RFC5967] to prove that the client is indeed in control of the
indeed in control of the private key at the time of the (D)TLS private key at the time of the (D)TLS session establishment.
session establishment.
In the case of handshake message fragmentation, if proof-of- In the case of handshake message fragmentation, if proof-of-
possession is desired, the Finished message added as the possession is desired, the Finished message added as the
ChallengePassword in the CSR is calculated as specified by the DTLS ChallengePassword in the CSR is calculated as specified by the DTLS
standards. We summarize it here for convenience. For DTLS 1.2, in standards. We summarize it here for convenience. For DTLS 1.2, in
the event of handshake message fragmentation, the Hash of the the event of handshake message fragmentation, the Hash of the
handshake messages used in the MAC calculation of the Finished handshake messages used in the MAC calculation of the Finished
message must be computed as if each handshake message had been sent message must be computed on each reassembled message, as if each
as a single fragment (Section 4.2.6 of [RFC6347]). The Finished message had not been fragmented (Section 4.2.6 of [RFC6347]). The
message is calculated as shown in Section 7.4.9 of [RFC5246]. Finished message is calculated as shown in Section 7.4.9 of
[RFC5246]. Similarly, for DTLS 1.3, the Finished message must be
Similarly, for DTLS 1.3, the Finished message must be computed as if computed as if each handshake message had been sent as a single
each handshake message had been sent as a single fragment fragment (Section 5.8 of [I-D.ietf-tls-dtls13]) following the
(Section 5.8 of [I-D.ietf-tls-dtls13]) following the algorithm algorithm described in 4.4.4 of [RFC8446].
described in 4.4.4 of [RFC8446].
In a constrained CoAP environment, endpoints can't always afford to In a constrained CoAP environment, endpoints can't always afford to
establish a DTLS connection for every EST transaction. establish a DTLS connection for every EST transaction. An EST-coaps
Authenticating and negotiating DTLS keys requires resources on low- DTLS connection MAY remain open for sequential EST transactions,
end endpoints and consumes valuable bandwidth. To alleviate this which was not the case with [RFC7030]. For example, if a /crts
situation, an EST-coaps DTLS connection MAY remain open for request is followed by a /sen request, both can use the same
sequential EST transactions which was not the case with [RFC7030]. authenticated DTLS connection. However, when a /crts request is
For example, an EST csrattrs request that is followed by a included in the set of sequential EST transactions, some additional
simpleenroll request can use the same authenticated DTLS connection. security considerations apply regarding the use of the Implicit and
However, when a cacerts request is included in the set of sequential Explicit TA database as explained in Section 10.1.
EST transactions, some additional security considerations apply
regarding the use of the Implicit and Explicit TA database as
explained in Section 10.1.
Given that after a successful enrollment, it is more likely that a Given that after a successful enrollment, it is more likely that a
new EST transaction will take place after a significant amount of new EST transaction will not take place for a significant amount of
time, the DTLS connections SHOULD only be kept alive for EST messages time, the DTLS connections SHOULD only be kept alive for EST messages
that are relatively close to each other. In some cases, like NAT that are relatively close to each other. These could include a /sen
rebinding, keeping the state of a connection is not possible when immediatelly following a /crts when a device is getting bootstrapped.
devices sleep for extended periods of time. In such occasions, In some cases, like NAT rebinding, keeping the state of a connection
[I-D.ietf-tls-dtls-connection-id] negotiates a connection ID that can is not possible when devices sleep for extended periods of time. In
eliminate the need for new handshake and its additional cost; or DTLS such occasions, [I-D.ietf-tls-dtls-connection-id] negotiates a
session resumption provides a less costly alternative than re-doing a connection ID that can eliminate the need for new handshake and its
full DTLS handshake. additional cost; or DTLS session resumption provides a less costly
alternative than re-doing a full DTLS handshake.
5. Protocol Design 5. Protocol Design
EST-coaps uses CoAP to transfer EST messages, aided by Block-Wise EST-coaps uses CoAP to transfer EST messages, aided by Block-Wise
Transfer [RFC7959] to avoid IP fragmentation. The use of Blocks for Transfer [RFC7959] to avoid IP fragmentation. The use of Blocks for
the transfer of larger EST messages is specified in Section 5.6. the transfer of larger EST messages is specified in Section 5.6.
Figure 1 shows the layered EST-coaps architecture. Figure 1 shows the layered EST-coaps architecture.
The EST-coaps protocol design follows closely the EST design. The The EST-coaps protocol design follows closely the EST design. The
supported message types in EST-coaps are: supported message types in EST-coaps are:
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o Server-side key generation messages to provide a client identity o Server-side key generation messages to provide a client identity
private key when the client chooses so. private key when the client chooses so.
While [RFC7030] permits a number of the EST functions to be used While [RFC7030] permits a number of the EST functions to be used
without authentication, this specification requires that the client without authentication, this specification requires that the client
MUST be authenticated for all functions. MUST be authenticated for all functions.
5.1. Discovery and URIs 5.1. Discovery and URIs
EST-coaps is targeted for low-resource networks with small packets. EST-coaps is targeted for low-resource networks with small packets.
Two types of installations are possible (1) rigid ones where the Two types of installations are possible: (1) rigid ones, where the
address and the supported functions of the EST server(s) are known, address and the supported functions of the EST server(s) are known,
and (2) flexible one where the EST server and it supported functions and (2) a flexible one, where the EST server and its supported
need to be discovered. functions need to be discovered.
For both types of installations, saving header space is important and For both types of installations, saving header space is important and
short EST-coaps URIs are specified in this document. These URIs are short EST-coaps URIs are specified in this document. These URIs are
shorter than the ones in [RFC7030]. Two example EST-coaps resource shorter than the ones in [RFC7030]. Two example EST-coaps resource
path names are: path names are:
coaps://example.com:<port>/.well-known/est/<short-est> coaps://example.com:<port>/.well-known/est/<short-est>
coaps://example.com:<port>/.well-known/est/ coaps://example.com:<port>/.well-known/est/ArbitraryLabel/<short-est>
ArbitraryLabel/<short-est>
The short-est strings are defined in Table 1.
Arbitrary Labels are usually defined and used by EST CAs in order to The short-est strings are defined in Table 1. Arbitrary Labels are
route client requests to the appropriate certificate profile. usually defined and used by EST CAs in order to route client requests
Implementers should consider using short labels to minimize to the appropriate certificate profile. Implementers should consider
transmission overhead. using short labels to minimize transmission overhead.
The EST-coaps server URIs, obtained through discovery of the EST- The EST-coaps server URIs, obtained through discovery of the EST-
coaps resource(s) as shown below, are of the form: coaps resource(s) as shown below, are of the form:
coaps://example.com:<port>/<root-resource>/<short-est> coaps://example.com:<port>/<root-resource>/<short-est>
coaps://example.com:<port>/<root-resource>/ coaps://example.com:<port>/<root-resource>/ArbitraryLabel/<short-est>
ArbitraryLabel/<short-est>
Figure 5 in Section 3.2.2 of [RFC7030] enumerates the operations and Figure 5 in Section 3.2.2 of [RFC7030] enumerates the operations and
corresponding paths which are supported by EST. Table 1 provides the corresponding paths which are supported by EST. Table 1 provides the
mapping from the EST URI path to the shorter EST-coaps URI path. mapping from the EST URI path to the shorter EST-coaps URI path.
+-------------------+-------------------------------+ +-------------------+-------------------------------+
| EST | EST-coaps | | EST | EST-coaps |
+-------------------+-------------------------------+ +-------------------+-------------------------------+
| /cacerts | /crts | | /cacerts | /crts |
| /simpleenroll | /sen | | /simpleenroll | /sen |
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requests a certificate in PKCS#7 format and a private key. If the requests a certificate in PKCS#7 format and a private key. If the
client prefers a single application/pkix-cert certificate instead of client prefers a single application/pkix-cert certificate instead of
PKCS#7, it will make an /skc request. In both cases (i.e., /skg, PKCS#7, it will make an /skc request. In both cases (i.e., /skg,
/skc) a private key MUST be returned. /skc) a private key MUST be returned.
Clients and servers MUST support the short resource EST-coaps URIs. Clients and servers MUST support the short resource EST-coaps URIs.
In the context of CoAP, the presence and location of (path to) the In the context of CoAP, the presence and location of (path to) the
EST resources are discovered by sending a GET request to "/.well- EST resources are discovered by sending a GET request to "/.well-
known/core" including a resource type (RT) parameter with the value known/core" including a resource type (RT) parameter with the value
"ace.est*" [RFC6690]. "ace.est*" [RFC6690]. The example below shows the discovery over
CoAPS of the presence and location of EST-coaps resources. Linefeeds
The example below shows the discovery over CoAPS of the presence and are included only for readability.
location of EST-coaps resources. Linefeeds are included only for
readability.
REQ: GET /.well-known/core?rt=ace.est* REQ: GET /.well-known/core?rt=ace.est*
RES: 2.05 Content RES: 2.05 Content
</est/crts>;rt="ace.est.crts";ct="281 TBD287", </est/crts>;rt="ace.est.crts";ct="281 TBD287",
</est/sen>;rt="ace.est.sen";ct="281 TBD287", </est/sen>;rt="ace.est.sen";ct="281 TBD287",
</est/sren>;rt="ace.est.sren";ct="281 TBD287", </est/sren>;rt="ace.est.sren";ct="281 TBD287",
</est/att>;rt="ace.est.att";ct=285, </est/att>;rt="ace.est.att";ct=285,
</est/skg>;rt="ace.est.skg";ct=62, </est/skg>;rt="ace.est.skg";ct=62,
</est/skc>;rt="ace.est.skc";ct=62 </est/skc>;rt="ace.est.skc";ct=62
skipping to change at page 13, line 21 skipping to change at page 12, line 50
ct="281 TBD287", ct="281 TBD287",
<coaps://[2001:db8:3::123]:61617/est/sren>;rt="ace.est.sren"; <coaps://[2001:db8:3::123]:61617/est/sren>;rt="ace.est.sren";
ct="281 TBD287", ct="281 TBD287",
<coaps://[2001:db8:3::123]:61617/est/att>;rt="ace.est.att"; <coaps://[2001:db8:3::123]:61617/est/att>;rt="ace.est.att";
ct=285, ct=285,
<coaps://[2001:db8:3::123]:61617/est/skg>;rt="ace.est.skg"; <coaps://[2001:db8:3::123]:61617/est/skg>;rt="ace.est.skg";
ct=62, ct=62,
<coaps://[2001:db8:3::123]:61617/est/skc>;rt="ace.est.skc"; <coaps://[2001:db8:3::123]:61617/est/skc>;rt="ace.est.skc";
ct=62 ct=62
The server MUST support the default /.well-known/est root resource The server MUST support the default /.well-known/est root resource.
The server SHOULD support resource discovery when it supports non-
. The server SHOULD support resource discovery when it supports non-
default URIs (like /est or /est/ArbitraryLabel) or ports. The client default URIs (like /est or /est/ArbitraryLabel) or ports. The client
SHOULD use resource discovery when it is unaware of the available SHOULD use resource discovery when it is unaware of the available
EST-coaps resources. EST-coaps resources.
Throughout this document the example root resource of /est is used. Throughout this document the example root resource of /est is used.
5.2. Mandatory/optional EST Functions 5.2. Mandatory/optional EST Functions
This specification contains a set of required-to-implement functions, This specification contains a set of required-to-implement functions,
optional functions, and not specified functions. The latter ones are optional functions, and not specified functions. The unspecified
deemed too expensive for low-resource devices in payload and functions are deemed too expensive for low-resource devices in
calculation times. payload and calculation times.
Table 2 specifies the mandatory-to-implement or optional Table 2 specifies the mandatory-to-implement or optional
implementation of the EST-coaps functions. Discovery of the implementation of the EST-coaps functions. Discovery of the
existence of optional functions is described in Section 5.1. existence of optional functions is described in Section 5.1.
+-------------------+--------------------------+ +-------------------+--------------------------+
| EST Functions | EST-coaps implementation | | EST Functions | EST-coaps implementation |
+-------------------+--------------------------+ +-------------------+--------------------------+
| /cacerts | MUST | | /cacerts | MUST |
| /simpleenroll | MUST | | /simpleenroll | MUST |
skipping to change at page 14, line 13 skipping to change at page 13, line 41
Table 2: List of EST-coaps functions Table 2: List of EST-coaps functions
5.3. Payload formats 5.3. Payload formats
EST-coaps is designed for low-resource devices and hence does not EST-coaps is designed for low-resource devices and hence does not
need to send Base64-encoded data. Simple binary is more efficient need to send Base64-encoded data. Simple binary is more efficient
(30% smaller payload for DER-encoded ASN.1) and well supported by (30% smaller payload for DER-encoded ASN.1) and well supported by
CoAP. Thus, the payload for a given Media-Type follows the ASN.1 CoAP. Thus, the payload for a given Media-Type follows the ASN.1
structure of the Media-Type and is transported in binary format. structure of the Media-Type and is transported in binary format.
The Content-Format (HTTP Media-Type equivalent) of the CoAP message The Content-Format (HTTP Content-Type equivalent) of the CoAP message
determines which EST message is transported in the CoAP payload. The determines which EST message is transported in the CoAP payload. The
Media-Types specified in the HTTP Content-Type header (Section 3.2.2 Media-Types specified in the HTTP Content-Type header field
of [RFC7030]) are specified by the Content-Format Option (12) of (Section 3.2.2 of [RFC7030]) are specified by the Content-Format
CoAP. The combination of URI-Path and Content-Format in EST-coaps Option (12) of CoAP. The combination of URI-Path and Content-Format
MUST map to an allowed combination of URI and Media-Type in EST. The in EST-coaps MUST map to an allowed combination of URI and Media-Type
required Content-Formats for these requests and response messages are in EST. The required Content-Formats for these requests and response
defined in Section 9.1. The CoAP response codes are defined in messages are defined in Section 9.1. The CoAP response codes are
Section 5.5. defined in Section 5.5.
Content-Format TBD287 can be used in place of 281 to carry a single Content-Format TBD287 can be used in place of 281 to carry a single
certificate instead of a PKCS#7 container in a /crts, /sen, /sren or certificate instead of a PKCS#7 container in a /crts, /sen, /sren or
/skg response. Content-Format 281 MUST be supported by EST-coaps /skg response. Content-Format 281 MUST be supported by EST-coaps
servers. Servers MAY also support Content-Format TBD287. It is up servers. Servers MAY also support Content-Format TBD287. It is up
to the client to support only Content-Format 281, TBD287 or both. to the client to support only Content-Format 281, TBD287 or both.
The client will use a COAP Accept Option in the request to express The client will use a COAP Accept Option in the request to express
the preferred response Content-Format. If an Accept Option is not the preferred response Content-Format. If an Accept Option is not
included in the request, the client is not expressing any preference included in the request, the client is not expressing any preference
and the server SHOULD choose format 281. and the server SHOULD choose format 281.
Content-Format 286 is used in /sen, /sren and /skg requests and 285 Content-Format 286 is used in /sen, /sren and /skg requests and 285
in /att responses. in /att responses.
A representation with Content-Format identifier 62 contains a A representation with Content-Format identifier 62 contains a
collection of representations along with their respective Content- collection of representations along with their respective Content-
skipping to change at page 14, line 40 skipping to change at page 14, line 21
the preferred response Content-Format. If an Accept Option is not the preferred response Content-Format. If an Accept Option is not
included in the request, the client is not expressing any preference included in the request, the client is not expressing any preference
and the server SHOULD choose format 281. and the server SHOULD choose format 281.
Content-Format 286 is used in /sen, /sren and /skg requests and 285 Content-Format 286 is used in /sen, /sren and /skg requests and 285
in /att responses. in /att responses.
A representation with Content-Format identifier 62 contains a A representation with Content-Format identifier 62 contains a
collection of representations along with their respective Content- collection of representations along with their respective Content-
Format. The Content-Format identifies the Media-Type application/ Format. The Content-Format identifies the Media-Type application/
multipart-core specified in [I-D.ietf-core-multipart-ct]. multipart-core specified in [I-D.ietf-core-multipart-ct]. For
example, a collection, containing two representations in response to
For example, a collection, containing two representations in response a EST-coaps server-side key generation /skg request, could include a
to a EST-coaps server-side key generation /skg request, could include private key in PKCS#8 [RFC5958] with Content-Format identifier 284
a private key in PKCS#8 [RFC5958] with Content-Format identifier 284
(0x011C) and a single certificate in a PKCS#7 container with Content- (0x011C) and a single certificate in a PKCS#7 container with Content-
Format identifier 281 (0x0119). Such a collection would look like Format identifier 281 (0x0119). Such a collection would look like
[284,h'0123456789abcdef', 281,h'fedcba9876543210'] in diagnostic CBOR [284,h'0123456789abcdef', 281,h'fedcba9876543210'] in diagnostic CBOR
notation. The serialization of such CBOR content would be notation. The serialization of such CBOR content would be
84 # array(4) 84 # array(4)
19 011C # unsigned(284) 19 011C # unsigned(284)
48 # bytes(8) 48 # bytes(8)
0123456789ABCDEF # "\x01#Eg\x89\xAB\xCD\xEF" 0123456789ABCDEF # "\x01#Eg\x89\xAB\xCD\xEF"
19 0119 # unsigned(281) 19 0119 # unsigned(281)
48 # bytes(8) 48 # bytes(8)
FEDCBA9876543210 # "\xFE\xDC\xBA\x98vT2\x10" FEDCBA9876543210 # "\xFE\xDC\xBA\x98vT2\x10"
Multipart /skg response serialization Multipart /skg response serialization
skipping to change at page 16, line 5 skipping to change at page 15, line 35
confirmable CON CoAP messages. confirmable CON CoAP messages.
o The CoAP Options used are Uri-Host, Uri-Path, Uri-Port, Content- o The CoAP Options used are Uri-Host, Uri-Path, Uri-Port, Content-
Format, Block1, Block2, and Accept. These CoAP Options are used Format, Block1, Block2, and Accept. These CoAP Options are used
to communicate the HTTP fields specified in the EST REST messages. to communicate the HTTP fields specified in the EST REST messages.
The Uri-host and Uri-Port Options can be omitted from the COAP The Uri-host and Uri-Port Options can be omitted from the COAP
message sent on the wire. When omitted, they are logically message sent on the wire. When omitted, they are logically
assumed to be the transport protocol destination address and port assumed to be the transport protocol destination address and port
respectively. Explicit Uri-Host and Uri-Port Options are respectively. Explicit Uri-Host and Uri-Port Options are
typically used when an endpoint hosts multiple virtual servers and typically used when an endpoint hosts multiple virtual servers and
uses the Options to route the requests accordingly. uses the Options to route the requests accordingly. Other COAP
Options should be handled in accordance with [RFC7252].
o Other COAP Options should be handled in accordance with [RFC7252].
o EST URLs are HTTPS based (https://), in CoAP these are assumed to o EST URLs are HTTPS based (https://), in CoAP these are assumed to
be translated to CoAPS (coaps://) be translated to CoAPS (coaps://)
Table 1 provides the mapping from the EST URI path to the EST-coaps Table 1 provides the mapping from the EST URI path to the EST-coaps
URI path. Appendix A includes some practical examples of EST URI path. Appendix A includes some practical examples of EST
messages translated to CoAP. messages translated to CoAP.
5.5. CoAP response codes 5.5. CoAP response codes
Section 5.9 of [RFC7252] and Section 7 of [RFC8075] specify the Section 5.9 of [RFC7252] and Section 7 of [RFC8075] specify the
mapping of HTTP response codes to CoAP response codes. The success mapping of HTTP response codes to CoAP response codes. The success
code in response to an EST-coaps GET request (/crts, /att), is 2.05. code in response to an EST-coaps GET request (/crts, /att), is 2.05.
Similarly, 2.04 Similarly, 2.04 is used in successful response to EST-coaps POST
requests (/sen, /sren, /skg, /skc).
is used in successfull response to EST-coaps POST requests (/sen,
/sren, /skg, /skc).
EST makes use of HTTP 204 or 404 responses when a resource is not EST makes use of HTTP 204 or 404 responses when a resource is not
available for the client. In EST-coaps 2.04 is used in response to a available for the client. In EST-coaps 2.04 is used in response to a
POST (/sen, /sren, /skg, /skc). 4.04 is used when the resource is not POST (/sen, /sren, /skg, /skc). 4.04 is used when the resource is not
available for the client. available for the client.
HTTP response code 202 with a Retry-After header in [RFC7030] has no HTTP response code 202 with a Retry-After header field in [RFC7030]
equivalent in CoAP. HTTP 202 with Retry-After is used in EST for has no equivalent in CoAP. HTTP 202 with Retry-After is used in EST
delayed server responses. Section 5.7 specifies how EST-coaps for delayed server responses. Section 5.7 specifies how EST-coaps
handles delayed messages with 5.03 responses with a Max-Age Option. handles delayed messages with 5.03 responses with a Max-Age Option.
Additionally, EST's HTTP 400, 401, 403, 404 and 503 status codes have Additionally, EST's HTTP 400, 401, 403, 404 and 503 status codes have
their equivalent CoAP 4.00, 4.01, 4.03, 4.04 and 5.03 response codes their equivalent CoAP 4.00, 4.01, 4.03, 4.04 and 5.03 response codes
in EST-coaps. in EST-coaps. Table 4 summarizes the EST-coaps response codes.
Table 4 summarizes the EST-coaps response codes.
+-----------------+-----------------+-------------------------------+ +-----------------+-----------------+-------------------------------+
| operation | EST-coaps | Description | | operation | EST-coaps | Description |
| | response code | | | | response code | |
+-----------------+-----------------+-------------------------------+ +-----------------+-----------------+-------------------------------+
| /crts, /att | 2.05 | Success. Certs included in | | /crts, /att | 2.05 | Success. Certs included in |
| | | the response payload. | | | | the response payload. |
| | 4.xx / 5.xx | Failure. | | | 4.xx / 5.xx | Failure. |
| /sen, /skg, | 2.04 | Success. Cert included in the | | /sen, /skg, | 2.04 | Success. Cert included in the |
| /sren, /skc | | response payload. | | /sren, /skc | | response payload. |
skipping to change at page 17, line 39 skipping to change at page 17, line 4
such that each DTLS record will fit within one or two IEEE 802.15.4 such that each DTLS record will fit within one or two IEEE 802.15.4
frames. frames.
That is not always possible in EST-coaps. Even though ECC That is not always possible in EST-coaps. Even though ECC
certificates are small in size, they can vary greatly based on certificates are small in size, they can vary greatly based on
signature algorithms, key sizes, and Object Identifier (OID) fields signature algorithms, key sizes, and Object Identifier (OID) fields
used. For 256-bit curves, common ECDSA cert sizes are 500-1000 bytes used. For 256-bit curves, common ECDSA cert sizes are 500-1000 bytes
which could fluctuate further based on the algorithms, OIDs, Subject which could fluctuate further based on the algorithms, OIDs, Subject
Alternative Names (SAN) and cert fields. For 384-bit curves, ECDSA Alternative Names (SAN) and cert fields. For 384-bit curves, ECDSA
certificates increase in size and can sometimes reach 1.5KB. certificates increase in size and can sometimes reach 1.5KB.
Additionally, there are times when the EST cacerts response from the Additionally, there are times when the EST cacerts response from the
server can include multiple certificates that amount to large server can include multiple certificates that amount to large
payloads. Section 4.6 of CoAP [RFC7252] describes the possible payloads. Section 4.6 of CoAP [RFC7252] describes the possible
payload sizes: "if nothing is known about the size of the headers, payload sizes: "if nothing is known about the size of the headers,
good upper bounds are 1152 bytes for the message size and 1024 bytes good upper bounds are 1152 bytes for the message size and 1024 bytes
for the payload size". Section 4.6 of [RFC7252] also suggests that for the payload size". Section 4.6 of [RFC7252] also suggests that
IPv4 implementations may want to limit themselves to more IPv4 implementations may want to limit themselves to more
conservative IPv4 datagram sizes such as 576 bytes. conservative IPv4 datagram sizes such as 576 bytes. Even with ECC,
EST-coaps messages can still exceed MTU sizes on the Internet or
Even with ECC, EST-coaps messages can still exceed MTU sizes on the 6LoWPAN [RFC4919] (Section 2 of [RFC7959]). EST-coaps needs to be
Internet or 6LoWPAN [RFC4919] (Section 2 of [RFC7959]). EST-coaps able to fragment messages into multiple DTLS datagrams.
needs to be able to fragment messages into multiple DTLS datagrams.
To perform fragmentation in CoAP, [RFC7959] specifies the Block1 To perform fragmentation in CoAP, [RFC7959] specifies the Block1
Option for fragmentation of the request payload and the Block2 Option Option for fragmentation of the request payload and the Block2 Option
for fragmentation of the return payload of a CoAP flow. As explained for fragmentation of the return payload of a CoAP flow. As explained
in Section 1 of [RFC7959], block-wise transfers should be used in in Section 1 of [RFC7959], block-wise transfers should be used in
Confirmable CoAP messages to avoid the exacerbation of lost blocks. Confirmable CoAP messages to avoid the exacerbation of lost blocks.
Both EST-coaps clients and servers MUST support Block2. EST-coaps EST-coaps servers MUST implement Block1 and Block2. EST-coaps
servers MUST also support Block1. The EST-coaps client MUST support clients MUST implement Block2. EST-coaps clients MUST implement
Block1 only if it sends EST-coaps requests with an IP packet size Block1 only if they are expecting to send EST-coaps requests with a
that exceeds the Path MTU. packet size that exceeds the Path MTU.
[RFC7959] also defines Size1 and Size2 Options to provide size [RFC7959] also defines Size1 and Size2 Options to provide size
information about the resource representation in a request and information about the resource representation in a request and
response. EST-client and server MAY support Size1 and Size2 Options. response. EST-client and server MAY support Size1 and Size2 Options.
Examples of fragmented EST-coaps messages are shown in Appendix B. Examples of fragmented EST-coaps messages are shown in Appendix B.
5.7. Delayed Responses 5.7. Delayed Responses
Server responses can sometimes be delayed. According to Server responses can sometimes be delayed. According to
skipping to change at page 18, line 37 skipping to change at page 17, line 49
request with an empty ACK with code 0.00, before sending the request with an empty ACK with code 0.00, before sending the
certificate to the client after a short delay. If the certificate certificate to the client after a short delay. If the certificate
response is large, the server will need more than one Block2 block to response is large, the server will need more than one Block2 block to
transfer it. transfer it.
This situation is shown in Figure 2. The client sends an enrollment This situation is shown in Figure 2. The client sends an enrollment
request that uses N1+1 Block1 blocks. The server uses an empty 0.00 request that uses N1+1 Block1 blocks. The server uses an empty 0.00
ACK to announce the delayed response which is provided later with ACK to announce the delayed response which is provided later with
2.04 messages containing N2+1 Block2 Options. The first 2.04 is a 2.04 messages containing N2+1 Block2 Options. The first 2.04 is a
confirmable message that is acknowledged by the client. Onwards, the confirmable message that is acknowledged by the client. Onwards, the
client acknowledges all subsequent Block2 blocks. client acknowledges all subsequent Block2 blocks. The notation of
Figure 2 is explained in Appendix B.1.
The notation of Figure 2 is explained in Appendix B.1.
POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR (frag# 1)} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR (frag# 1)} -->
<-- (ACK) (1:0/1/256) (2.31 Continue) <-- (ACK) (1:0/1/256) (2.31 Continue)
POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR (frag# 2)} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR (frag# 2)} -->
<-- (ACK) (1:1/1/256) (2.31 Continue) <-- (ACK) (1:1/1/256) (2.31 Continue)
. .
. .
. .
POST [2001:db8::2:1]:61616/est/sen(CON)(1:N1/0/256){CSR (frag# N1+1)}--> POST [2001:db8::2:1]:61616/est/sen(CON)(1:N1/0/256){CSR (frag# N1+1)}-->
<-- (0.00 empty ACK) <-- (0.00 empty ACK)
skipping to change at page 19, line 29 skipping to change at page 18, line 29
POST [2001:db8::2:1]:61616/est/sen (CON)(2:1/0/256) --> POST [2001:db8::2:1]:61616/est/sen (CON)(2:1/0/256) -->
<-- (ACK) (2:1/1/256) (2.04 Changed) {Cert resp (frag# 2)} <-- (ACK) (2:1/1/256) (2.04 Changed) {Cert resp (frag# 2)}
. .
. .
. .
POST [2001:db8::2:1]:61616/est/sen (CON)(2:N2/0/256) --> POST [2001:db8::2:1]:61616/est/sen (CON)(2:N2/0/256) -->
<-- (ACK) (2:N2/0/256) (2.04 Changed) {Cert resp (frag# N2+1)} <-- (ACK) (2:N2/0/256) (2.04 Changed) {Cert resp (frag# N2+1)}
Figure 2: EST-COAP enrollment with short wait Figure 2: EST-COAP enrollment with short wait
If the server is very slow (i.e., minutes) in providing the response If the server is very slow (for example, manual intervention is
(i.e., when a manual intervention is needed), it SHOULD respond with required which would take minutes), it SHOULD respond with an ACK
an ACK containing response code 5.03 (Service unavailable) and a Max- containing response code 5.03 (Service unavailable) and a Max-Age
Age Option to indicate the time the client SHOULD wait to request the Option to indicate the time the client SHOULD wait before sending
content later. After a delay of Max-Age, the client SHOULD resend another request to obtain the content. After a delay of Max-Age, the
the identical CSR to the server. As long as the server responds with client SHOULD resend the identical CSR to the server. As long as the
response code 5.03 (Service Unavailable) with a Max-Age Option, the server continues to respond with response code 5.03 (Service
client SHOULD keep resending the enrollment request until the server Unavailable) with a Max-Age Option, the client will continue to delay
for Max-Age and then resend the enrollment request until the server
responds with the certificate or the client abandons the request for responds with the certificate or the client abandons the request for
other reasons. policy or other reasons.
To demonstrate this scenario, Figure 3 shows a client sending an To demonstrate this scenario, Figure 3 shows a client sending an
enrollment request that uses N1+1 Block1 blocks to send the CSR to enrollment request that uses N1+1 Block1 blocks to send the CSR to
the server. The server needs N2+1 Block2 blocks to respond, but also the server. The server needs N2+1 Block2 blocks to respond, but also
needs to take a long delay (minutes) to provide the response. needs to take a long delay (minutes) to provide the response.
Consequently, the server uses a 5.03 ACK response with a Max-Age Consequently, the server uses a 5.03 ACK response with a Max-Age
Option. The client waits for a period of Max-Age as many times as it Option. The client waits for a period of Max-Age as many times as it
receives the same 5.03 response and retransmits the enrollment receives the same 5.03 response and retransmits the enrollment
request until it receives a certificate in a fragmented 2.04 request until it receives a certificate in a fragmented 2.04
response. response.
POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR (frag# 1)} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR (frag# 1)} -->
<-- (ACK) (1:0/1/256) (2.31 Continue) <-- (ACK) (1:0/1/256) (2.31 Continue)
POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR (frag# 2)} --> POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR (frag# 2)} -->
<-- (ACK) (1:1/1/256) (2.31 Continue) <-- (ACK) (1:1/1/256) (2.31 Continue)
. .
. .
. .
POST [2001:db8::2:1]:61616/est/sen(CON)(1:N1/0/256){CSR (frag# N1+1)}--> POST [2001:db8::2:1]:61616/est/sen(CON)(1:N1/0/256){CSR (frag# N1+1)}-->
skipping to change at page 20, line 43 skipping to change at page 19, line 43
. .
. .
. .
POST [2001:db8::2:1]:61616/est/sen (CON)(2:N2/0/256) --> POST [2001:db8::2:1]:61616/est/sen (CON)(2:N2/0/256) -->
<-- (ACK) (2:N2/0/256) (2.04 Changed) {Cert resp (frag# N2+1)} <-- (ACK) (2:N2/0/256) (2.04 Changed) {Cert resp (frag# N2+1)}
Figure 3: EST-COAP enrollment with long wait Figure 3: EST-COAP enrollment with long wait
5.8. Server-side Key Generation 5.8. Server-side Key Generation
In scenarios where it is desirable that the server generates the Private keys can be generated on the server to support scenarios
private key, server-side key generation is available. Such scenarios where serer-side key generation is needed. Such scenarios include
could be when it is considered more secure to generate at the server those where it is considered more secure to generate the long-lived,
the long-lived random private key that identifies the client, or when random private key that identifies the client at the server, or where
the resources spent to generate a random private key at the client the resources spent to generate a random private key at the client
are considered scarce, or when the security policy requires that the are considered scarce, or where the security policy requires that the
certificate public and corresponding private keys are centrally certificate public and corresponding private keys are centrally
generated and controlled. Of course, that does not eliminate the generated and controlled. As always, it is necessary to use proper
need for proper random numbers in various protocols like (D)TLS random numbers in various protocols such as (D)TLS (Section 10.1).
(Section 10.1).
When requesting server-side key generation, the client asks for the When requesting server-side key generation, the client asks for the
server or proxy to generate the private key and the certificate which server or proxy to generate the private key and the certificate,
are transferred back to the client in the server-side key generation which are transferred back to the client in the server-side key
response. In all respects, the server treats the CSR as it would generation response. In all respects, the server treats the CSR as
treat any enroll or re-enroll CSR; the only distinction here is that it would treat any enroll or re-enroll CSR; the only distinction here
the server MUST ignore the public key values and signature in the is that the server MUST ignore the public key values and signature in
CSR. These are included in the request only to allow re-use of the CSR. These are included in the request only to allow re-use of
existing codebases for generating and parsing such requests. existing codebases for generating and parsing such requests.
The client /skg request is for a certificate in a PKCS#7 container The client /skg request is for a certificate in a PKCS#7 container
and private key in two application/multipart-core elements. and private key in two application/multipart-core elements.
Respectively, an /skc request is for a single application/pkix-cert Respectively, an /skc request is for a single application/pkix-cert
certificate and a private key. The private key Content-Format certificate and a private key. The private key Content-Format
requested by the client is indicated in the PKCS#10 CSR request. If requested by the client is indicated in the PKCS#10 CSR request. If
the request contains SMIMECapabilities and DecryptKeyIdentifier or the request contains SMIMECapabilities and DecryptKeyIdentifier or
AsymmetricDecryptKeyIdentifier the client is expecting Content-Format AsymmetricDecryptKeyIdentifier the client is expecting Content-Format
280 for the private key. Then the private key is encrypted 280 for the private key. Then this private key is encrypted
symmetrically or asymmetrically as per [RFC7030]. The symmetric key symmetrically or asymmetrically as per [RFC7030]. The symmetric key
or the asymmetric keypair establishment method is out of scope of the or the asymmetric keypair establishment method is out of scope of
specification. A /skg or /skc request with a CSR without this specification. A /skg or /skc request with a CSR without
SMIMECapabilities expects an application/multipart-core with an SMIMECapabilities expects an application/multipart-core with an
unencrypted PKCS#8 private key with Content-Format 284. unencrypted PKCS#8 private key with Content-Format 284.
The EST-coaps server-side key generation response is returned with The EST-coaps server-side key generation response is returned with
Content-Format application/multipart-core Content-Format application/multipart-core
[I-D.ietf-core-multipart-ct] containing a CBOR array with four items [I-D.ietf-core-multipart-ct] containing a CBOR array with four items
(Section 5.3). The two representations (each consisting of two CBOR
(Section 5.3) array items) do not have to be in a particular order since each
representation is preceded by its Content-Format ID. Depending on
. The two representations (each consisting of two CBOR array items) the request, the private key can be in unprotected PKCS#8 [RFC5958]
do not have to be in a particular order since each representation is format (Content-Format 284) or protected inside of CMS SignedData
preceded by its Content-Format ID. Dependent on the request, the (Content-Format 280). The SignedData, placed in the outermost
private key can be in unprotected PKCS#8 [RFC5958] format (Content- container, is signed by the party that generated the private key,
Format 284) or protected inside of CMS SignedData (Content-Format which may be the EST server or the EST CA. SignedData placed within
280). The SignedData, placed in the outermost container, is signed the Enveloped Data does not need additional signing as explained in
by the party that generated the private key, which may be the EST Section 4.4.2 of [RFC7030]. In summary, the symmetrically encrypted
server or the EST CA. SignedData placed within the Enveloped Data key is included in the encryptedKey attribute in a KEKRecipientInfo
does not need additional signing as explained in Section 4.4.2 of structure. In the case where the asymmetric encryption key is
[RFC7030]. In summary, the symmetrically encrypted key is included suitable for transport key operations the generated private key is
in the encryptedKey attribute in a KEKRecipientInfo structure. In encrypted with a symmetric key. The symmetric key itself is
the case where the asymmetric encryption key is suitable for encrypted by the client-defined (in the CSR) asymmetric public key
transport key operations the generated private key is encrypted with and is carried in an encryptedKey attribute in a
a symmetric key which is encrypted by the client-defined (in the CSR) KeyTransRecipientInfo structure. Finally, if the asymmetric
asymmetric public key and is carried in an encryptedKey attribute in
a KeyTransRecipientInfo structure. Finally, if the asymmetric
encryption key is suitable for key agreement, the generated private encryption key is suitable for key agreement, the generated private
key is encrypted with a symmetric key which is encrypted by the key is encrypted with a symmetric key. The symmetric key itself is
client defined (in the CSR) asymmetric public key and is carried in encrypted by the client defined (in the CSR) asymmetric public key
an recipientEncryptedKeys attribute in a KeyAgreeRecipientInfo. and is carried in an recipientEncryptedKeys attribute in a
KeyAgreeRecipientInfo.
[RFC7030] recommends the use of additional encryption of the returned [RFC7030] recommends the use of additional encryption of the returned
private key. For the context of this specification, clients and private key. For the context of this specification, clients and
servers that choose to support server-side key generation MUST servers that choose to support server-side key generation MUST
support unprotected (PKCS#8) private keys (Content-Format 284). support unprotected (PKCS#8) private keys (Content-Format 284).
Symmetric or asymmetric encryption of the private key (CMS Symmetric or asymmetric encryption of the private key (CMS
EnvelopedData, Content-Format 280) SHOULD be supported for EnvelopedData, Content-Format 280) SHOULD be supported for
deployments where end-to-end encryption is needed between the client deployments where end-to-end encryption is needed between the client
and a server. Such cases could include architectures where an entity and a server. Such cases could include architectures where an entity
between the client and the CA terminates the DTLS connection between the client and the CA terminates the DTLS connection
skipping to change at page 23, line 28 skipping to change at page 22, line 25
client. For example, it could be configured to accept PoP linking client. For example, it could be configured to accept PoP linking
information that does not match the current TLS session because the information that does not match the current TLS session because the
authenticated EST client Registrar has verified this information when authenticated EST client Registrar has verified this information when
acting as an EST server". acting as an EST server".
Table 1 contains the URI mappings between EST-coaps and EST that the Table 1 contains the URI mappings between EST-coaps and EST that the
Registrar MUST adhere to. Section 5.5 of this specification and Registrar MUST adhere to. Section 5.5 of this specification and
Section 7 of [RFC8075] define the mappings between EST-coaps and HTTP Section 7 of [RFC8075] define the mappings between EST-coaps and HTTP
response codes, that determine how the Registrar MUST translate CoAP response codes, that determine how the Registrar MUST translate CoAP
response codes from/to HTTP status codes. The mapping from CoAP response codes from/to HTTP status codes. The mapping from CoAP
Content-Format to HTTP Media-Type is defined in Section 9.1. Content-Format to HTTP Content-Type is defined in Section 9.1.
Additionally, a conversion from CBOR major type 2 to Base64 encoding Additionally, a conversion from CBOR major type 2 to Base64 encoding
MUST take place at the Registrar. If CMS end-to-end encryption is MUST take place at the Registrar. If CMS end-to-end encryption is
employed for the private key, the encrypted CMS EnvelopedData blob employed for the private key, the encrypted CMS EnvelopedData blob
MUST be converted at the Registrar to binary CBOR type 2 downstream MUST be converted at the Registrar to binary CBOR type 2 downstream
to the client. This is a format conversion that does not require to the client. This is a format conversion that does not require
decryption of the CMS EnvelopedData. decryption of the CMS EnvelopedData.
A deviation from the mappings in Table 1 could take place if clients A deviation from the mappings in Table 1 could take place if clients
that leverage server-side key generation preferred for the enrolled that leverage server-side key generation preferred for the enrolled
keys to be generated by the Registrar in the case the CA does not keys to be generated by the Registrar in the case the CA does not
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HTTP Registrar MUST reassemble the BLOCKs before translating the HTTP Registrar MUST reassemble the BLOCKs before translating the
binary content to Base64, and consecutively relay the message binary content to Base64, and consecutively relay the message
upstream. upstream.
The EST-coaps-to-HTTP Registrar MUST support resource discovery The EST-coaps-to-HTTP Registrar MUST support resource discovery
according to the rules in Section 5.1. according to the rules in Section 5.1.
7. Parameters 7. Parameters
This section addresses transmission parameters described in sections This section addresses transmission parameters described in sections
4.7 and 4.8 of [RFC7252]. 4.7 and 4.8 of [RFC7252]. EST does not impose any unique values on
the CoAP parameters in [RFC7252], but the setting of the CoAP
EST does not impose any unique values on the CoAP parameters in parameter values may have consequence for the setting of the EST
[RFC7252], but the setting of the CoAP parameter values may have parameter values.
consequence for the setting of the EST parameter values.
It is recommended, based on experiments,
to follow the default CoAP configuration parameters ([RFC7252]). Implementations should follow the default CoAP configuration
However, depending on the implementation scenario, retransmissions parameters [RFC7252]. However, depending on the implementation
and timeouts can also occur on other networking layers, governed by scenario, retransmissions and timeouts can also occur on other
other configuration parameters. When a change in a server parameter networking layers, governed by other configuration parameters. When
has taken place, the parameter values in the communicating endpoints a change in a server parameter has taken place, the parameter values
MUST be adjusted as necessary. in the communicating endpoints MUST be adjusted as necessary.
Examples of how parameters could be adjusted include higher layer
congestion protocols, provisioning agents and configurations included
in firmware updates.
Some further comments about some specific parameters, mainly from Some further comments about some specific parameters, mainly from
Table 2 in [RFC7252]: Table 2 in [RFC7252]:
o NSTART: A parameter that controls the number of simultaneous o NSTART: A parameter that controls the number of simultaneous
outstanding interactions that a client maintains to a given outstanding interactions that a client maintains to a given
server. An EST-coaps client is expected to control at most one server. An EST-coaps client is expected to control at most one
interaction with a given server, which is the default NSTART value interaction with a given server, which is the default NSTART value
defined in [RFC7252]. defined in [RFC7252].
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9. IANA Considerations 9. IANA Considerations
9.1. Content-Format Registry 9.1. Content-Format Registry
Additions to the sub-registry "CoAP Content-Formats", within the Additions to the sub-registry "CoAP Content-Formats", within the
"CoRE Parameters" registry [COREparams] are specified in Table 5. "CoRE Parameters" registry [COREparams] are specified in Table 5.
These have been registered provisionally in the IETF Review or IESG These have been registered provisionally in the IETF Review or IESG
Approval range (256-9999). Approval range (256-9999).
+------------------------------+-------+----------------------------+ +------------------------------+-------+----------------------------+
| HTTP Media-Type | ID | Reference | | HTTP Content-Type | ID | Reference |
+------------------------------+-------+----------------------------+ +------------------------------+-------+----------------------------+
| application/pkcs7-mime; | 280 | [RFC7030] [I-D.ietf-lamps- | | application/pkcs7-mime; | 280 | [RFC7030] [I-D.ietf-lamps- |
| smime-type=server-generated- | | rfc5751-bis] [ThisRFC] | | smime-type=server-generated- | | rfc5751-bis] [ThisRFC] |
| key | | | | key | | |
| application/pkcs7-mime; | 281 | [I-D.ietf-lamps-rfc5751-bi | | application/pkcs7-mime; | 281 | [I-D.ietf-lamps-rfc5751-bi |
| smime-type=certs-only | | s] [ThisRFC] | | smime-type=certs-only | | s] [ThisRFC] |
| application/pkcs8 | 284 | [RFC5958] [I-D.ietf-lamps- | | application/pkcs8 | 284 | [RFC5958] [I-D.ietf-lamps- |
| | | rfc5751-bis] [ThisRFC] | | | | rfc5751-bis] [ThisRFC] |
| application/csrattrs | 285 | [RFC7030] | | application/csrattrs | 285 | [RFC7030] |
| application/pkcs10 | 286 | [RFC5967] [I-D.ietf-lamps- | | application/pkcs10 | 286 | [RFC5967] [I-D.ietf-lamps- |
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CSR attributes. CSR attributes.
o rt="ace.est.skg". This resource depicts the support of EST o rt="ace.est.skg". This resource depicts the support of EST
server-side key generation with the returned certificate in a server-side key generation with the returned certificate in a
PKCS#7 container. PKCS#7 container.
o rt="ace.est.skc". This resource depicts the support of EST o rt="ace.est.skc". This resource depicts the support of EST
server-side key generation with the returned certificate in server-side key generation with the returned certificate in
application/pkix-cert format. application/pkix-cert format.
9.3. Well-Known URIs Registry
A new additional reference is requested for the est URI in the Well-
Known URIs registry:
+------+--------+---------+---------+----------+---------+----------+
| URI | Change | Referen | Status | Related | Date Re | Date |
| Suff | Contro | ces | | Informat | gistere | Modified |
| ix | ller | | | ion | d | |
+------+--------+---------+---------+----------+---------+----------+
| est | IETF | [RFC703 | permane | | 2013-08 | [THIS |
| | | 0] | nt | | -16 | RFC's pu |
| | | [THIS | | | | blicatio |
| | | RFC] | | | | n date] |
+------+--------+---------+---------+----------+---------+----------+
10. Security Considerations 10. Security Considerations
10.1. EST server considerations 10.1. EST server considerations
The security considerations of Section 6 of [RFC7030] are only The security considerations of Section 6 of [RFC7030] are only
partially valid for the purposes of this document. As HTTP Basic partially valid for the purposes of this document. As HTTP Basic
Authentication is not supported, the considerations expressed for Authentication is not supported, the considerations expressed for
using passwords do not apply. The other portions of the security using passwords do not apply. The other portions of the security
considerations of [RFC7030] continue to apply. considerations of [RFC7030] continue to apply.
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private key (that corresponds to the public key enrolled in the CSR). private key (that corresponds to the public key enrolled in the CSR).
When server-side key generation is used, the constrained device When server-side key generation is used, the constrained device
depends on the server to generate the private key randomly, but it depends on the server to generate the private key randomly, but it
still needs locally generated random numbers for use in security still needs locally generated random numbers for use in security
protocols, as explained in Section 12 of [RFC7925]. Additionally, protocols, as explained in Section 12 of [RFC7925]. Additionally,
the transport of keys generated at the server is inherently risky. the transport of keys generated at the server is inherently risky.
For those deploying server-side key generation, analysis SHOULD be For those deploying server-side key generation, analysis SHOULD be
done to establish whether server-side key generation increases or done to establish whether server-side key generation increases or
decreases the probability of digital identity theft. decreases the probability of digital identity theft.
It is important to note that sources contributing to the randomness It is important to note that, as pointed out in [PsQs], sources
pool used to generate random numbers on laptops or desktop PCs are contributing to the randomness pool used to generate random numbers
not available on many constrained devices, such as mouse movement, on laptops or desktop PCs, such as mouse movement, timing of
timing of keystrokes, or air turbulence on the movement of hard drive keystrokes, or air turbulence on the movement of hard drive heads,
heads, as pointed out in [PsQs]. Other sources have to be used or are not available on many constrained devices. Other sources have to
dedicated hardware has to be added. Selecting hardware for an IoT be used or dedicated hardware has to be added. Selecting hardware
device that is capable of producing high-quality random numbers is for an IoT device that is capable of producing high-quality random
therefore important [RSAfact]. numbers is therefore important [RSAfact].
It is also RECOMMENDED that the Implicit Trust Anchor database used
for EST server authentication is carefully managed to reduce the
chance of a third-party CA with poor certification practices
jeopardizing authentication.
Disabling the Implicit Trust Anchor database after successfully As discussed in Section 6 of [RFC7030], it is "RECOMMENDED that the
receiving the Distribution of CA certificates response (Section 4.1.3 Implicit Trust Anchor database used for EST server authentication is
of [RFC7030]) limits any risk to the first DTLS exchange. carefully managed to reduce the chance of a third-party CA with poor
Alternatively, in a case where a /sen request immediately follows a certification practices jeopardizing authentication. Disabling the
/crts, a client MAY choose to keep the connection authenticated by Implicit Trust Anchor database after successfuly receiving the
the Implicit TA open for efficiency reasons (Section 4). A client Distribution of CA certificates response (Section 4.1.3) limits any
that interleaves EST-coaps /crts request with other requests in the risk to the first TLS exchange". Alternatively, in a case where a
same DTLS connection SHOULD revalidate the server certificate chain /sen request immediately follows a /crts, a client MAY choose to keep
against the updated Explicit TA from the /crts response before the connection authenticated by the Implicit TA open for efficiency
proceeding with the subsequent requests. If the server certificate reasons (Section 4). A client that interleaves EST-coaps /crts
chain does not authenticate against the database, the client SHOULD request with other requests in the same DTLS connection SHOULD
close the connection without completing the rest of the requests. revalidate the server certificate chain against the updated Explicit
The updated Explicit TA MUST continue to be used in new DTLS TA from the /crts response before proceeding with the subsequent
connections. requests. If the server certificate chain does not authenticate
against the database, the client SHOULD close the connection without
completing the rest of the requests. The updated Explicit TA MUST
continue to be used in new DTLS connections.
In cases where the IDevID used to authenticate the client is expired In cases where the IDevID used to authenticate the client is expired
the server MAY still authenticate the client because IDevIDs are the server MAY still authenticate the client because IDevIDs are
expected to live as long as the device itself (Section 4). In such expected to live as long as the device itself (Section 4). In such
occasions, checking the certificate revocation status or authorizing occasions, checking the certificate revocation status or authorizing
the client using another method is important for the server to ensure the client using another method is important for the server to raise
that the client is to be trusted. its confidence that the client can be trusted.
In accordance with [RFC7030], TLS cipher suites that include In accordance with [RFC7030], TLS cipher suites that include
"_EXPORT_" and "_DES_" in their names MUST NOT be used. More "_EXPORT_" and "_DES_" in their names MUST NOT be used. More
information about recommendations of TLS and DTLS are included in recommendations for secure use of TLS and DTLS are included in
[BCP195]. [BCP195].
As described in CMC, Section 6.7 of [RFC5272], "For keys that can be As described in CMC, Section 6.7 of [RFC5272], "For keys that can be
used as signature keys, signing the certification request with the used as signature keys, signing the certification request with the
private key serves as a PoP on that key pair". The inclusion of tls- private key serves as a PoP on that key pair". The inclusion of tls-
unique in the certificate request links the proof-of-possession to unique in the certificate request links the proof-of-possession to
the TLS proof-of-identity. This implies but does not prove that only the TLS proof-of-identity. This implies but does not prove that only
the authenticated client currently has access to the private key. the authenticated client currently has access to the private key.
What's more, CMC PoP linking uses tls-unique as it is defined in What's more, CMC PoP linking uses tls-unique as it is defined in
[RFC5929]. The 3SHAKE attack [tripleshake] poses a risk by allowing [RFC5929]. The 3SHAKE attack [tripleshake] poses a risk by allowing
a man-in-the-middle to leverage session resumption and renegotiation a man-in-the-middle to leverage session resumption and renegotiation
to inject himself between a client and server even when channel to inject himself between a client and server even when channel
binding is in use. binding is in use. Implementers should use the Extended Master
Secret Extension in DTLS [RFC7627] to prevent such attacks. In the
Implementers should use the Extended Master Secret Extension in DTLS context of this specification, an attacker could invalidate the
[RFC7627] to prevent such attacks. In the context of this purpose of the PoP linking ChallengePassword in the client request by
specification, an attacker could invalidate the purpose of the PoP resuming an EST-coaps connection. Even though the practical risk of
linking ChallengePassword in the client request by resuming an EST- such an attack to EST-coaps is not devastating, we would rather use a
coaps connection. Even though the practical risk of such an attack more secure channel binding mechanism. Such a mechanism could
to EST-coaps is not devastating, we would rather use a more secure include an updated tls-unique value generation like the tls-unique-
channel binding mechanism. Such a mechanism could include an updated prf defined in [I-D.josefsson-sasl-tls-cb] by using a TLS exporter
tls-unique value generation like the tls-unique-prf defined in [RFC5705] in TLS 1.2 or TLS 1.3's updated exporter (Section 7.5 of
[RFC8446]) value in place of the tls-unique value in the CSR. Such
[I-D.josefsson-sasl-tls-cb] by using a TLS exporter [RFC5705] in TLS mechanism has not been standardized yet. Adopting a channel binding
1.2 or TLS 1.3's updated exporter (Section 7.5 of [RFC8446]) value in value generated from an exporter would break backwards compatibility
place of the tls-unique value in the CSR. Such mechanism has not for an RA that proxies through to a classic EST server. Thus, in
been standardized yet. Adopting a channel binding value generated this specification we still depend on the tls-unique mechanism
from an exporter would break backwards compatibility for an RA that defined in [RFC5929], especially since a 3SHAKE attack does not
proxies through to a classic EST server. Thus, in this specification expose messages exchanged with EST-coaps.
we still depend on the tls-unique mechanism defined in [RFC5929],
especially since a 3SHAKE attack does not expose messages exchanged
with EST-coaps.
Interpreters of ASN.1 structures should be aware of the use of Interpreters of ASN.1 structures should be aware of the use of
invalid ASN.1 length fields and should take appropriate measures to invalid ASN.1 length fields and should take appropriate measures to
guard against buffer overflows, stack overruns in particular, and guard against buffer overflows, stack overruns in particular, and
malicious content in general. malicious content in general.
10.2. HTTPS-CoAPS Registrar considerations 10.2. HTTPS-CoAPS Registrar considerations
The Registrar proposed in Section 6 must be deployed with care, and The Registrar proposed in Section 6 must be deployed with care, and
only when direct client-server connections are not possible. When only when direct client-server connections are not possible. When
skipping to change at page 29, line 9 skipping to change at page 28, line 22
Registrar will be generating the private key and enrolling the Registrar will be generating the private key and enrolling the
certificates with the CA or if the CA will be responsible for certificates with the CA or if the CA will be responsible for
generating the key. In such cases, the existence of a Registrar generating the key. In such cases, the existence of a Registrar
requires the client to put its trust on the registrar when it is requires the client to put its trust on the registrar when it is
generating the private key. generating the private key.
11. Contributors 11. Contributors
Martin Furuhed contributed to the EST-coaps specification by Martin Furuhed contributed to the EST-coaps specification by
providing feedback based on the Nexus EST over CoAPS server providing feedback based on the Nexus EST over CoAPS server
implementation that started in 2015. implementation that started in 2015. Sandeep Kumar kick-started this
specification and was instrumental in drawing attention to the
Sandeep Kumar kick-started this specification and was instrumental in importance of the subject.
drawing attention to the importance of the subject.
12. Acknowledgements 12. Acknowledgements
The authors are very grateful to Klaus Hartke for his detailed The authors are very grateful to Klaus Hartke for his detailed
explanations on the use of Block with DTLS and his support for the explanations on the use of Block with DTLS and his support for the
Content-Format specification. The authors would like to thank Esko Content-Format specification. The authors would like to thank Esko
Dijk and Michael Verschoor for the valuable discussions that helped Dijk and Michael Verschoor for the valuable discussions that helped
in shaping the solution. They would also like to thank Peter in shaping the solution. They would also like to thank Peter
Panburana for his feedback on technical details of the solution. Panburana for his feedback on technical details of the solution.
Constructive comments were received from Benjamin Kaduk, Eliot Lear, Constructive comments were received from Benjamin Kaduk, Eliot Lear,
skipping to change at page 34, line 50 skipping to change at page 34, line 32
Option (Uri-Path) Option (Uri-Path)
Option Delta = 0x0 (option# 11+0=11) Option Delta = 0x0 (option# 11+0=11)
Option Length = 0x4 Option Length = 0x4
Option Value = "crts" Option Value = "crts"
Option (Accept) Option (Accept)
Option Delta = 0x6 (option# 11+6=17) Option Delta = 0x6 (option# 11+6=17)
Option Length = 0x2 Option Length = 0x2
Option Value = 281 Option Value = 281
Payload = [Empty] Payload = [Empty]
The Uri-Host and Uri-Port Options can be omitted if they coincide As specified in Section 5.10.1 of [RFC7252], the Uri-Host and Uri-
with the transport protocol destination address and port Port Options can be omitted if they coincide with the transport
respectively. Explicit Uri-Host and Uri-Port Options are typically protocol destination address and port respectively.
used when an endpoint hosts multiple virtual servers and uses the
Options to route the requests accordingly.
A 2.05 Content response with a cert in EST-coaps will then be A 2.05 Content response with a cert in EST-coaps will then be
2.05 Content (Content-Format: 281) 2.05 Content (Content-Format: 281)
{payload with certificate in binary format} {payload with certificate in binary format}
with CoAP fields with CoAP fields
Ver = 1 Ver = 1
T = 2 (ACK) T = 2 (ACK)
Code = 0x45 (2.05 Content) Code = 0x45 (2.05 Content)
 End of changes. 60 change blocks. 
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