draft-ietf-ace-coap-est-15.txt   draft-ietf-ace-coap-est-16.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: April 2, 2020 Cisco Systems Expires: April 24, 2020 Cisco Systems
M. Richardson M. Richardson
SSW SSW
S. Raza S. Raza
RISE SICS RISE SICS
September 30, 2019 October 22, 2019
EST over secure CoAP (EST-coaps) EST over secure CoAP (EST-coaps)
draft-ietf-ace-coap-est-15 draft-ietf-ace-coap-est-16
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.
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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 April 2, 2020. This Internet-Draft will expire on April 24, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 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
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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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 . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6
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 . . . . . . . . . . . . . . . . . . . 10 5.1. Discovery and URIs . . . . . . . . . . . . . . . . . . . 10
5.2. Mandatory/optional EST Functions . . . . . . . . . . . . 12 5.2. Mandatory/optional EST Functions . . . . . . . . . . . . 13
5.3. Payload formats . . . . . . . . . . . . . . . . . . . . . 13 5.3. Payload formats . . . . . . . . . . . . . . . . . . . . . 13
5.4. Message Bindings . . . . . . . . . . . . . . . . . . . . 14 5.4. Message Bindings . . . . . . . . . . . . . . . . . . . . 15
5.5. CoAP response codes . . . . . . . . . . . . . . . . . . . 15 5.5. CoAP response codes . . . . . . . . . . . . . . . . . . . 15
5.6. Message fragmentation . . . . . . . . . . . . . . . . . . 16 5.6. Message fragmentation . . . . . . . . . . . . . . . . . . 16
5.7. Delayed Responses . . . . . . . . . . . . . . . . . . . . 17 5.7. Delayed Responses . . . . . . . . . . . . . . . . . . . . 17
5.8. Server-side Key Generation . . . . . . . . . . . . . . . 19 5.8. Server-side Key Generation . . . . . . . . . . . . . . . 19
6. HTTPS-CoAPS Registrar . . . . . . . . . . . . . . . . . . . . 21 6. HTTPS-CoAPS Registrar . . . . . . . . . . . . . . . . . . . . 21
7. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 22 7. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 23
8. Deployment limitations . . . . . . . . . . . . . . . . . . . 23 8. Deployment limitations . . . . . . . . . . . . . . . . . . . 23
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24
9.1. Content-Format Registry . . . . . . . . . . . . . . . . . 24 9.1. Content-Format Registry . . . . . . . . . . . . . . . . . 24
9.2. Resource Type registry . . . . . . . . . . . . . . . . . 24 9.2. Resource Type registry . . . . . . . . . . . . . . . . . 24
10. Security Considerations . . . . . . . . . . . . . . . . . . . 25 10. Security Considerations . . . . . . . . . . . . . . . . . . . 25
10.1. EST server considerations . . . . . . . . . . . . . . . 25 10.1. EST server considerations . . . . . . . . . . . . . . . 25
10.2. HTTPS-CoAPS Registrar considerations . . . . . . . . . . 27 10.2. HTTPS-CoAPS Registrar considerations . . . . . . . . . . 27
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 28 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 27
12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
13.1. Normative References . . . . . . . . . . . . . . . . . . 28 13.1. Normative References . . . . . . . . . . . . . . . . . . 28
13.2. Informative References . . . . . . . . . . . . . . . . . 30 13.2. Informative References . . . . . . . . . . . . . . . . . 30
Appendix A. EST messages to EST-coaps . . . . . . . . . . . . . 32 Appendix A. EST messages to EST-coaps . . . . . . . . . . . . . 32
A.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 33 A.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 33
A.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 35 A.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 35
A.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 36 A.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 36
A.4. csrattrs . . . . . . . . . . . . . . . . . . . . . . . . 38 A.4. csrattrs . . . . . . . . . . . . . . . . . . . . . . . . 38
Appendix B. EST-coaps Block message examples . . . . . . . . . . 39 Appendix B. EST-coaps Block message examples . . . . . . . . . . 39
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C.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 44 C.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 44
C.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 45 C.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 45
C.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 47 C.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 47
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 49 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 49
1. Change Log 1. Change Log
EDNOTE: Remove this section before publication EDNOTE: Remove this section before publication
-16
Updates to address Yaron S.'s Secdir review.
Updates to address David S.'s Gen-ART review.
-15 -15
Updates to addressed Ben's AD follow up feedback. Updates to addressed Ben's AD follow up feedback.
-14 -14
Updates to complete Ben's AD review feedback and discussions. Updates to complete Ben's AD review feedback and discussions.
-13 -13
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+------------------------------------------------+ +------------------------------------------------+
| Secure Transport | | Secure Transport |
+------------------------------------------------+ +------------------------------------------------+
Figure 1: EST-coaps protocol layers Figure 1: EST-coaps protocol layers
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. Additionally, crypto agility is important, and the curve. After the standardization of [RFC7748], support for
recommendations in Section 4.4 of [RFC7925] and any updates to it Curve25519 will likely be required in the future by (D)TLS Profiles
concerning Curve25519 and other curves also apply. for the 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. DTLS 1.3 [I-D.ietf-tls-dtls13] format must also be supported. DTLS 1.3 [I-D.ietf-tls-dtls13]
implementations differ from DTLS 1.2 because they do not support implementations differ from DTLS 1.2 because they do not support
point format negotiation in favor of a single point format for each point format negotiation in favor of a single point format for each
curve. Thus, support for DTLS 1.3 does not mandate point format curve. Thus, support for DTLS 1.3 does not mandate point format
extensions and negotiation. In addition, in DTLS 1.3 the Supported extensions and negotiation. In addition, in DTLS 1.3 the Supported
Elliptic Curves extension has been renamed to Supported Groups. Elliptic Curves extension has been renamed to Supported Groups.
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clients and servers. When proof-of-possession is desired, a set of clients and servers. When proof-of-possession is desired, a set of
actions are required regarding the use of tls-unique, described in actions are required regarding the use of tls-unique, described in
Section 3.5 in [RFC7030]. The tls-unique information consists of the Section 3.5 in [RFC7030]. The tls-unique information consists of the
contents of the first "Finished" message in the (D)TLS handshake contents of the first "Finished" message in the (D)TLS handshake
between server and client [RFC5929]. The client adds the "Finished" between server and client [RFC5929]. The client adds the "Finished"
message as a ChallengePassword in the attributes section of the message as a ChallengePassword in the attributes section of the
PKCS#10 Request [RFC5967] to prove that the client is indeed in PKCS#10 Request [RFC5967] to prove that the client is indeed in
control of the private key at the time of the (D)TLS session control of the private key at the time of the (D)TLS session
establishment. establishment.
In the case of EST-coaps, the same operations can be performed during In the case of handshake message fragmentation, if proof-of-
the DTLS handshake. For DTLS 1.2, in the event of handshake message possession is desired, the Finished message added as the
fragmentation, the Hash of the handshake messages used in the MAC ChallengePassword in the CSR is calculated as specified by the DTLS
calculation of the Finished message must be computed as if each standards. We summarize it here for convenience. For DTLS 1.2, in
handshake message had been sent as a single fragment (Section 4.2.6 the event of handshake message fragmentation, the Hash of the
of [RFC6347]). The Finished message is calculated as shown in handshake messages used in the MAC calculation of the Finished
Section 7.4.9 of [RFC5246]. Similarly, for DTLS 1.3, the Finished
message must be computed as if each handshake message had been sent message must be computed as if each handshake message had been sent
as a single fragment (Section 5.8 of [I-D.ietf-tls-dtls13]) following as a single fragment (Section 4.2.6 of [RFC6347]). The Finished
the algorithm described in 4.4.4 of [RFC8446]. message is calculated as shown in Section 7.4.9 of [RFC5246].
Similarly, for DTLS 1.3, the Finished message must be computed as if
each handshake message had been sent as a single fragment
(Section 5.8 of [I-D.ietf-tls-dtls13]) following the algorithm
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.
Authenticating and negotiating DTLS keys requires resources on low- Authenticating and negotiating DTLS keys requires resources on low-
end endpoints and consumes valuable bandwidth. To alleviate this end endpoints and consumes valuable bandwidth. To alleviate this
situation, an EST-coaps DTLS connection MAY remain open for situation, an EST-coaps DTLS connection MAY remain open for
sequential EST transactions. For example, an EST csrattrs request sequential EST transactions. For example, an EST csrattrs request
that is followed by a simpleenroll request can use the same that is followed by a simpleenroll request can use the same
authenticated DTLS connection. However, when a cacerts request is authenticated DTLS connection. However, when a cacerts request is
included in the set of sequential EST transactions, some additional included in the set of sequential EST transactions, some additional
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Explicit TA database as explained in Section 10.1. 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 take place after 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. In some cases, like NAT
rebinding, keeping the state of a connection is not possible when rebinding, keeping the state of a connection is not possible when
devices sleep for extended periods of time. In such occasions, devices sleep for extended periods of time. In such occasions,
[I-D.ietf-tls-dtls-connection-id] negotiates a connection ID that can [I-D.ietf-tls-dtls-connection-id] negotiates a connection ID that can
eliminate the need for new handshake and its additional cost; or DTLS eliminate the need for new handshake and its additional cost; or DTLS
1.3 session resumption provides a less costly alternative than re- session resumption provides a less costly alternative than re-doing a
doing a full DTLS handshake. 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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| /serverkeygen | /skg (PKCS#7) | | /serverkeygen | /skg (PKCS#7) |
| /serverkeygen | /skc (application/pkix-cert) | | /serverkeygen | /skc (application/pkix-cert) |
| /csrattrs | /att | | /csrattrs | /att |
+------------------+------------------------------+ +------------------+------------------------------+
Table 1: Short EST-coaps URI path Table 1: Short EST-coaps URI path
The /skg message is the EST /serverkeygen equivalent where the client The /skg message is the EST /serverkeygen equivalent where the client
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, she 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]. The example below shows the discovery over "ace.est*" [RFC6690]. The example below shows the discovery over
CoAPS of the presence and location of EST-coaps resources. Linefeeds CoAPS of the presence and location of EST-coaps resources. Linefeeds
are included only for readability. are included only for readability.
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<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 he 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 she 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 latter ones are
deemed too expensive for low-resource devices in payload and deemed too expensive for low-resource devices in payload and
calculation times. calculation times.
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+----------+-----------------+-----------------+ +----------+-----------------+-----------------+
| Function | Response part 1 | Response part 2 | | Function | Response part 1 | Response part 2 |
+----------+-----------------+-----------------+ +----------+-----------------+-----------------+
| /skg | 284 | 281 | | /skg | 284 | 281 |
| /skc | 280 | TBD287 | | /skc | 280 | TBD287 |
+----------+-----------------+-----------------+ +----------+-----------------+-----------------+
Table 3: response content formats for skg and skc Table 3: response content formats for skg and skc
The key and certificate representations are ASN.1 encoded in binary The key and certificate representations are DER-encoded ASN.1, in its
format. An example is shown in Appendix A.3. native binary form. An example is shown in Appendix A.3.
5.4. Message Bindings 5.4. Message Bindings
The general EST-coaps message characteristics are: The general EST-coaps message characteristics are:
o EST-coaps servers sometimes need to provide delayed responses o EST-coaps servers sometimes need to provide delayed responses
which are preceded by an immediately returned empty ACK or an ACK which are preceded by an immediately returned empty ACK or an ACK
containing response code 5.03 as explained in Section 5.7. Thus, containing response code 5.03 as explained in Section 5.7. Thus,
it is RECOMMENDED for implementers to send EST-coaps requests in it is RECOMMENDED for implementers to send EST-coaps requests in
confirmable CON CoAP messages. confirmable CON CoAP messages.
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<-- (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 (i.e., minutes) in providing the response
(i.e., when a manual intervention is needed), he SHOULD respond with (i.e., when a manual intervention is needed), it SHOULD respond with
an ACK containing response code 5.03 (Service unavailable) and a Max- an ACK containing response code 5.03 (Service unavailable) and a Max-
Age Option to indicate the time the client SHOULD wait to request the Age Option to indicate the time the client SHOULD wait to request the
content later. After a delay of Max-Age, the client SHOULD resend content later. After a delay of Max-Age, the client SHOULD resend
the identical CSR to the server. As long as the server responds with the identical CSR to the server. As long as the server responds with
response code 5.03 (Service Unavailable) with a Max-Age Option, the response code 5.03 (Service Unavailable) with a Max-Age Option, the
client SHOULD keep resending the enrollment request until the server client SHOULD keep resending 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. 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 Option. The client waits for a period of Max-Age as many times as it
she receives the same 5.03 response and retransmits the enrollment receives the same 5.03 response and retransmits the enrollment
request until she 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)}-->
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the EST server when a Registrar is present. The EST server becomes the EST server when a Registrar is present. The EST server becomes
aware of the presence of a Registrar from its TLS client certificate aware of the presence of a Registrar from its TLS client certificate
that includes id-kp-cmcRA [RFC6402] extended key usage extension that includes id-kp-cmcRA [RFC6402] extended key usage extension
(EKU). As explained in Section 3.7 of [RFC7030], the "EST server (EKU). As explained in Section 3.7 of [RFC7030], the "EST server
SHOULD apply an authorization policy consistent with a Registrar SHOULD apply an authorization policy consistent with a Registrar
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".
For some use-cases, clients that leverage server-side key generation
might prefer for the enrolled keys to be generated by the Registrar
if the CA does not support server-side key generation. Such a
Registrar is responsible for generating a new CSR signed by a new key
which will be returned to the client along with the certificate from
the CA. In these cases, the Registrar MUST use random number
generation with proper entropy.
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 Media-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. to the client. This is a format conversion that does not require
decryption of the CMS EnvelopedData.
A deviation from the mappings in Table 1 could take place if clients
that leverage server-side key generation preferred for the enrolled
keys to be generated by the Registrar in the case the CA does not
support server-side key generation. Such a Registrar is responsible
for generating a new CSR signed by a new key which will be returned
to the client along with the certificate from the CA. In these
cases, the Registrar MUST use random number generation with proper
entropy.
Due to fragmentation of large messages into blocks, an EST-coaps-to- Due to fragmentation of large messages into blocks, an EST-coaps-to-
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
skipping to change at page 26, line 25 skipping to change at page 26, line 25
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 ensure
that the client is to be trusted. that the client is to 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 information about recommendations of TLS and DTLS are included in
[RFC7525]. [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
skipping to change at page 27, line 8 skipping to change at page 27, line 8
prf defined in [I-D.josefsson-sasl-tls-cb] by using a TLS exporter prf defined in [I-D.josefsson-sasl-tls-cb] by using a TLS exporter
[RFC5705] in TLS 1.2 or TLS 1.3's updated exporter (Section 7.5 of [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 [RFC8446]) value in place of the tls-unique value in the CSR. Such
mechanism has not been standardized yet. Adopting a channel binding mechanism has not been standardized yet. Adopting a channel binding
value generated from an exporter would break backwards compatibility value generated from an exporter would break backwards compatibility
for an RA that proxies through to a classic EST server. Thus, in for an RA that proxies through to a classic EST server. Thus, in
this specification we still depend on the tls-unique mechanism this specification we still depend on the tls-unique mechanism
defined in [RFC5929], especially since a 3SHAKE attack does not defined in [RFC5929], especially since a 3SHAKE attack does not
expose messages exchanged with EST-coaps. expose messages exchanged with EST-coaps.
Regarding the Certificate Signing Request (CSR), an EST-coaps server
is expected to be able to recover from improper CSR requests.
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
PoP linking is used the Registrar terminating the DTLS connection PoP linking is used the Registrar terminating the DTLS connection
skipping to change at page 27, line 33 skipping to change at page 27, line 30
transaction. The EST server could be configured to accept PoP transaction. The EST server could be configured to accept PoP
linking information that does not match the current TLS session linking information that does not match the current TLS session
because the authenticated EST Registrar is assumed to have verified because the authenticated EST Registrar is assumed to have verified
PoP linking downstream to the client. PoP linking downstream to the client.
The introduction of an EST-coaps-to-HTTP Registrar assumes the client The introduction of an EST-coaps-to-HTTP Registrar assumes the client
can authenticate the Registrar using its implicit or explicit TA can authenticate the Registrar using its implicit or explicit TA
database. It also assumes the Registrar has a trust relationship database. It also assumes the Registrar has a trust relationship
with the upstream EST server in order to act on behalf of the with the upstream EST server in order to act on behalf of the
clients. When a client uses the Implicit TA database for certificate clients. When a client uses the Implicit TA database for certificate
validation, she SHOULD confirm if the server is acting as an RA by validation, it SHOULD confirm if the server is acting as an RA by the
the presence of the id-kp-cmcRA EKU [RFC6402] in the server presence of the id-kp-cmcRA EKU [RFC6402] in the server certificate.
certificate.
In a server-side key generation case, if no end-to-end encryption is In a server-side key generation case, if no end-to-end encryption is
used, the Registrar may be able see the private key as it acts as a used, the Registrar may be able see the private key as it acts as a
man-in-the-middle. Thus, the client puts its trust on the Registrar man-in-the-middle. Thus, the client puts its trust on the Registrar
not exposing the private key. not exposing the private key.
Clients that leverage server-side key generation without end-to-end Clients that leverage server-side key generation without end-to-end
encryption of the private key (Section 5.8) have no knowledge if the encryption of the private key (Section 5.8) have no knowledge if the
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
skipping to change at page 28, line 48 skipping to change at page 28, line 42
[I-D.ietf-lamps-rfc5751-bis] [I-D.ietf-lamps-rfc5751-bis]
Schaad, J., Ramsdell, B., and S. Turner, "Secure/ Schaad, J., Ramsdell, B., and S. Turner, "Secure/
Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 Multipurpose Internet Mail Extensions (S/MIME) Version 4.0
Message Specification", draft-ietf-lamps-rfc5751-bis-12 Message Specification", draft-ietf-lamps-rfc5751-bis-12
(work in progress), September 2018. (work in progress), September 2018.
[I-D.ietf-tls-dtls13] [I-D.ietf-tls-dtls13]
Rescorla, E., Tschofenig, H., and N. Modadugu, "The Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version Datagram Transport Layer Security (DTLS) Protocol Version
1.3", draft-ietf-tls-dtls13-32 (work in progress), July 1.3", draft-ietf-tls-dtls13-33 (work in progress), October
2019. 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC2585] Housley, R. and P. Hoffman, "Internet X.509 Public Key [RFC2585] Housley, R. and P. Hoffman, "Internet X.509 Public Key
Infrastructure Operational Protocols: FTP and HTTP", Infrastructure Operational Protocols: FTP and HTTP",
RFC 2585, DOI 10.17487/RFC2585, May 1999, RFC 2585, DOI 10.17487/RFC2585, May 1999,
skipping to change at page 30, line 32 skipping to change at page 30, line 27
Security (TLS) Versions 1.2 and Earlier", RFC 8422, Security (TLS) Versions 1.2 and Earlier", RFC 8422,
DOI 10.17487/RFC8422, August 2018, DOI 10.17487/RFC8422, August 2018,
<https://www.rfc-editor.org/info/rfc8422>. <https://www.rfc-editor.org/info/rfc8422>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
13.2. Informative References 13.2. Informative References
[BCP195] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, May 2015,
<https://www.rfc-editor.org/info/bcp195>.
[COREparams] [COREparams]
"Constrained RESTful Environments (CoRE) Parameters", "Constrained RESTful Environments (CoRE) Parameters",
<https://www.iana.org/assignments/core-parameters/core- <https://www.iana.org/assignments/core-parameters/core-
parameters.xhtml>. parameters.xhtml>.
[I-D.ietf-tls-dtls-connection-id] [I-D.ietf-tls-dtls-connection-id]
Rescorla, E., Tschofenig, H., and T. Fossati, "Connection Rescorla, E., Tschofenig, H., and T. Fossati, "Connection
Identifiers for DTLS 1.2", draft-ietf-tls-dtls-connection- Identifiers for DTLS 1.2", draft-ietf-tls-dtls-connection-
id-06 (work in progress), July 2019. id-07 (work in progress), October 2019.
[I-D.josefsson-sasl-tls-cb] [I-D.josefsson-sasl-tls-cb]
Josefsson, S., "Channel Bindings for TLS based on the Josefsson, S., "Channel Bindings for TLS based on the
PRF", draft-josefsson-sasl-tls-cb-03 (work in progress), PRF", draft-josefsson-sasl-tls-cb-03 (work in progress),
March 2015. March 2015.
[I-D.moskowitz-ecdsa-pki] [I-D.moskowitz-ecdsa-pki]
Moskowitz, R., Birkholz, H., Xia, L., and M. Richardson, Moskowitz, R., Birkholz, H., Xia, L., and M. Richardson,
"Guide for building an ECC pki", draft-moskowitz-ecdsa- "Guide for building an ECC pki", draft-moskowitz-ecdsa-
pki-07 (work in progress), August 2019. pki-07 (work in progress), August 2019.
skipping to change at page 32, line 9 skipping to change at page 32, line 9
[RFC7251] McGrew, D., Bailey, D., Campagna, M., and R. Dugal, "AES- [RFC7251] McGrew, D., Bailey, D., Campagna, M., and R. Dugal, "AES-
CCM Elliptic Curve Cryptography (ECC) Cipher Suites for CCM Elliptic Curve Cryptography (ECC) Cipher Suites for
TLS", RFC 7251, DOI 10.17487/RFC7251, June 2014, TLS", RFC 7251, DOI 10.17487/RFC7251, June 2014,
<https://www.rfc-editor.org/info/rfc7251>. <https://www.rfc-editor.org/info/rfc7251>.
[RFC7299] Housley, R., "Object Identifier Registry for the PKIX [RFC7299] Housley, R., "Object Identifier Registry for the PKIX
Working Group", RFC 7299, DOI 10.17487/RFC7299, July 2014, Working Group", RFC 7299, DOI 10.17487/RFC7299, July 2014,
<https://www.rfc-editor.org/info/rfc7299>. <https://www.rfc-editor.org/info/rfc7299>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
[RFC7627] Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A., [RFC7627] Bhargavan, K., Ed., Delignat-Lavaud, A., Pironti, A.,
Langley, A., and M. Ray, "Transport Layer Security (TLS) Langley, A., and M. Ray, "Transport Layer Security (TLS)
Session Hash and Extended Master Secret Extension", Session Hash and Extended Master Secret Extension",
RFC 7627, DOI 10.17487/RFC7627, September 2015, RFC 7627, DOI 10.17487/RFC7627, September 2015,
<https://www.rfc-editor.org/info/rfc7627>. <https://www.rfc-editor.org/info/rfc7627>.
[RFC7748] Langley, A., Hamburg, M., and S. Turner, "Elliptic Curves
for Security", RFC 7748, DOI 10.17487/RFC7748, January
2016, <https://www.rfc-editor.org/info/rfc7748>.
[RSAfact] "Factoring RSA keys from certified smart cards: [RSAfact] "Factoring RSA keys from certified smart cards:
Coppersmith in the wild", Advances in Cryptology Coppersmith in the wild", Advances in Cryptology
- ASIACRYPT 2013, August 2013. - ASIACRYPT 2013, August 2013.
[tripleshake] [tripleshake]
"Triple Handshakes and Cookie Cutters: Breaking and Fixing "Triple Handshakes and Cookie Cutters: Breaking and Fixing
Authentication over TLS", IEEE Security and Privacy ISBN Authentication over TLS", IEEE Security and Privacy ISBN
978-1-4799-4686-0, May 2014. 978-1-4799-4686-0, May 2014.
Appendix A. EST messages to EST-coaps Appendix A. EST messages to EST-coaps
 End of changes. 30 change blocks. 
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