--- 1/draft-ietf-ace-coap-est-08.txt 2019-02-27 07:13:48.570658626 -0800 +++ 2/draft-ietf-ace-coap-est-09.txt 2019-02-27 07:13:48.670661080 -0800 @@ -1,23 +1,23 @@ ACE P. van der Stok Internet-Draft Consultant Intended status: Standards Track P. Kampanakis -Expires: August 10, 2019 Cisco Systems +Expires: August 31, 2019 Cisco Systems M. Richardson SSW S. Raza RISE SICS - February 6, 2019 + February 27, 2019 EST over secure CoAP (EST-coaps) - draft-ietf-ace-coap-est-08 + draft-ietf-ace-coap-est-09 Abstract Enrollment over Secure Transport (EST) is used as a certificate provisioning protocol over HTTPS. Low-resource devices often use the lightweight Constrained Application Protocol (CoAP) for message exchanges. This document defines how to transport EST payloads over secure CoAP (EST-coaps), which allows constrained devices to use existing EST functionality for provisioning certificates. @@ -29,98 +29,117 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - This Internet-Draft will expire on August 10, 2019. + This Internet-Draft will expire on August 31, 2019. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 3 - 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 5 + 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 6 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 - 4. Conformance to RFC7925 profiles . . . . . . . . . . . . . . . 6 - 5. Protocol Design . . . . . . . . . . . . . . . . . . . . . . . 7 - 5.1. Discovery and URIs . . . . . . . . . . . . . . . . . . . 8 - 5.2. Mandatory/optional EST Functions . . . . . . . . . . . . 10 - 5.3. Payload formats . . . . . . . . . . . . . . . . . . . . . 10 - 5.4. Message Bindings . . . . . . . . . . . . . . . . . . . . 12 - 5.5. CoAP response codes . . . . . . . . . . . . . . . . . . . 13 - 5.6. Message fragmentation . . . . . . . . . . . . . . . . . . 13 - 5.7. Delayed Responses . . . . . . . . . . . . . . . . . . . . 14 - 5.8. Server-side Key Generation . . . . . . . . . . . . . . . 16 - 6. DTLS Transport Protocol . . . . . . . . . . . . . . . . . . . 18 - 7. HTTPS-CoAPS Registrar . . . . . . . . . . . . . . . . . . . . 19 - 8. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 21 - 9. Deployment limitations . . . . . . . . . . . . . . . . . . . 21 - 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22 - 10.1. Content-Format Registry . . . . . . . . . . . . . . . . 22 - 10.2. Resource Type registry . . . . . . . . . . . . . . . . . 22 - 11. Security Considerations . . . . . . . . . . . . . . . . . . . 23 - 11.1. EST server considerations . . . . . . . . . . . . . . . 23 - 11.2. HTTPS-CoAPS Registrar considerations . . . . . . . . . . 25 - 12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25 - 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 26 - 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 26 - 14.1. Normative References . . . . . . . . . . . . . . . . . . 26 - 14.2. Informative References . . . . . . . . . . . . . . . . . 28 + 4. DTLS and conformance to RFC7925 profiles . . . . . . . . . . 6 + 5. Protocol Design . . . . . . . . . . . . . . . . . . . . . . . 9 + 5.1. Discovery and URIs . . . . . . . . . . . . . . . . . . . 9 + 5.2. Mandatory/optional EST Functions . . . . . . . . . . . . 11 + 5.3. Payload formats . . . . . . . . . . . . . . . . . . . . . 12 + 5.4. Message Bindings . . . . . . . . . . . . . . . . . . . . 13 + 5.5. CoAP response codes . . . . . . . . . . . . . . . . . . . 14 + 5.6. Message fragmentation . . . . . . . . . . . . . . . . . . 14 + 5.7. Delayed Responses . . . . . . . . . . . . . . . . . . . . 15 + 5.8. Server-side Key Generation . . . . . . . . . . . . . . . 17 + 6. HTTPS-CoAPS Registrar . . . . . . . . . . . . . . . . . . . . 19 + 7. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 20 + 8. Deployment limitations . . . . . . . . . . . . . . . . . . . 21 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 + 9.1. Content-Format Registry . . . . . . . . . . . . . . . . . 21 + 9.2. Resource Type registry . . . . . . . . . . . . . . . . . 22 + 10. Security Considerations . . . . . . . . . . . . . . . . . . . 23 + 10.1. EST server considerations . . . . . . . . . . . . . . . 23 + 10.2. HTTPS-CoAPS Registrar considerations . . . . . . . . . . 24 + 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25 + 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25 + 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 26 + 13.1. Normative References . . . . . . . . . . . . . . . . . . 26 + 13.2. Informative References . . . . . . . . . . . . . . . . . 27 Appendix A. EST messages to EST-coaps . . . . . . . . . . . . . 30 - A.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 31 - A.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 33 - A.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 35 - A.4. csrattrs . . . . . . . . . . . . . . . . . . . . . . . . 37 - Appendix B. EST-coaps Block message examples . . . . . . . . . . 38 - B.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 38 - B.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 42 - Appendix C. Message content breakdown . . . . . . . . . . . . . 43 - C.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 43 - C.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 45 - C.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 46 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 48 + A.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 30 + A.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 32 + A.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 34 + A.4. csrattrs . . . . . . . . . . . . . . . . . . . . . . . . 36 + Appendix B. EST-coaps Block message examples . . . . . . . . . . 37 + B.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 37 + B.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 41 + Appendix C. Message content breakdown . . . . . . . . . . . . . 42 + C.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 42 + C.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 44 + C.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 45 + + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 47 1. Change Log EDNOTE: Remove this section before publication + -09 + + WGLC comments taken into account + + consensus about discovery of content-format + + added additional path for content-format selection + + merged DTLS sections + -08 added application/pkix-cert Content-Format TBD287. + discovery text clarified + + Removed text on ct negotiation in connection to multipart-core + + removed text that duplicates or contradicts RFC7252 (thanks Klaus) + Stated that well-known/est is compulsory Use of response codes clarified. removed bugs: Max-Age and Content-Format Options in Request Accept Option explained for est/skg and added in enroll example - Persistenc of DTLS connection clarified. + Added second URI /skc for server-side key gen and a simple cert + (not PKCS#7) + + Persistence of DTLS connection clarified. Minor text fixes. -07: redone examples from scratch with openssl Updated authors. Added CoAP RST as a MAY for an equivalent to an HTTP 204 message. @@ -186,21 +205,21 @@ Added parameter discussion in section 8 Concluded Content-Format specification using multipart-ct draft examples updated -01: Editorials done. - Redefinition of proxy to Registrar in Section 7. Explained better + Redefinition of proxy to Registrar in Section 6. Explained better the role of https-coaps Registrar, instead of "proxy" Provide "observe" Option examples extended block message example. inserted new server key generation text in Section 5.8 and motivated server key generation. Broke down details for DTLS 1.3 @@ -219,77 +238,99 @@ 2. Introduction "Classical" Enrollment over Secure Transport (EST) [RFC7030] is used for authenticated/authorized endpoint certificate enrollment (and optionally key provisioning) through a Certificate Authority (CA) or Registration Authority (RA). EST transports messages over HTTPS. This document defines a new transport for EST based on the Constrained Application Protocol (CoAP) since some Internet of Things (IoT) devices use CoAP instead of HTTP. Therefore, this - specification utilizes DTLS [RFC6347], CoAP [RFC7252] and UDP instead - of TLS [RFC8446], HTTP [RFC7230] and TCP. + specification utilizes DTLS [RFC6347] and CoAP [RFC7252] instead of + TLS [RFC8446] and HTTP [RFC7230]. EST responses can be relatively large and for this reason this specification also uses CoAP Block-Wise Transfer [RFC7959] to offer a fragmentation mechanism of EST messages at the CoAP layer. This document also profiles the use of EST to only support certificate-based client authentication. HTTP Basic or Digest - authentication (as described in Section 3.2.3 of [RFC7030] are not + authentication (as described in Section 3.2.3 of [RFC7030]) are not supported. 3. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. Many of the concepts in this document are taken from [RFC7030]. Consequently, much text is directly traceable to [RFC7030]. -4. Conformance to RFC7925 profiles +4. DTLS and conformance to RFC7925 profiles This section describes how EST-coaps fits into the profiles of low- resource devices described in [RFC7925]. EST-coaps can transport certificates and private keys. Certificates are responses to (re-)enrollment requests or requests for a trusted certificate list. Private keys can be transported as responses to a server-side key - generation request as described in section 4.4 of [RFC7030] and + generation request as described in Section 4.4 of [RFC7030] and discussed in Section 5.8 of this document. - As per Sections 3.3 and 4.4 of [RFC7925], the mandatory cipher suite + EST-coaps depends on a secure transport mechanism that secures the + exchanged CoAP messages. DTLS is one such secure protocol. No other + changes are necessary regarding the secure transport of EST messages. + + +------------------------------------------------+ + | EST request/response messages | + +------------------------------------------------+ + | CoAP for message transfer and signaling | + +------------------------------------------------+ + | Secure Transport | + +------------------------------------------------+ + + Figure 1: EST-coaps protocol layers + + As per sections 3.3 and 4.4 of [RFC7925], the mandatory cipher suite for DTLS in EST-coaps is TLS_ECDHE_ECDSA_WITH_AES_128_CCM_8 [RFC7251]. Curve secp256r1 MUST be supported [RFC8422]; this curve - is equivalent to the NIST P-256 curve. Crypto agility is important, - and the recommendations in [RFC7925] section 4.4 and any updates to - RFC7925 concerning Curve25519 and other CFRG curves also apply. + is equivalent to the NIST P-256 curve. Additionally, crypto agility + is important, and the recommendations in Section 4.4 of [RFC7925] and + any updates to it concerning Curve25519 and other curves also apply. - DTLS1.2 implementations MUST use the Supported Elliptic Curves and - Supported Point Formats Extensions [RFC8422]. Uncompressed point - format MUST also be supported. [RFC6090] is a summary of the ECC - algorithms. DTLS 1.3 [I-D.ietf-tls-dtls13] implementations differ - from DTLS 1.2 because they do not support point format negotiation in - favor of a single point format for each curve. Thus, support for - DTLS 1.3 does not mandate point formation extensions and negotiation. + DTLS 1.2 implementations must use the Supported Elliptic Curves and + Supported Point Formats Extensions in [RFC8422]. Uncompressed point + format must also be supported. DTLS 1.3 [I-D.ietf-tls-dtls13] + implementations differ from DTLS 1.2 because they do not support + point format negotiation in favor of a single point format for each + curve. Thus, support for DTLS 1.3 does not mandate point format + extensions and negotiation. + + CoAP was designed to avoid IP fragmentation. DTLS is used to secure + CoAP messages. However, fragmentation is still possible at the DTLS + layer during the DTLS handshake when using ECC ciphersuites. If + fragmentation is necessary, "DTLS provides a mechanism for + fragmenting a handshake message over several records, each of which + can be transmitted separately, thus avoiding IP fragmentation" + [RFC6347]. The authentication of the EST-coaps server by the EST-coaps client is based on certificate authentication in the DTLS handshake. The EST- coaps client MUST be configured with at least an Implicit TA database - from its manufacturer which will enable the authentication of the - server the first time before updating its trust anchor (Explicit TA) - [RFC7030]. + which will enable the authentication of the server the first time + before updating its trust anchor (Explicit TA) [RFC7030]. The authentication of the EST-coaps client MUST be with a client certificate in the DTLS handshake. This can either be + o a previously issued client certificate (e.g., an existing certificate issued by the EST CA); this could be a common case for simple re-enrollment of clients. o a previously installed certificate (e.g., manufacturer IDevID [ieee802.1ar] or a certificate issued by some other party); the server is expected to trust that certificate. 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 server MAY want to authenticate a client certificate against its trust store @@ -286,239 +327,264 @@ o a previously issued client certificate (e.g., an existing certificate issued by the EST CA); this could be a common case for simple re-enrollment of clients. o a previously installed certificate (e.g., manufacturer IDevID [ieee802.1ar] or a certificate issued by some other party); the server is expected to trust that certificate. 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 server MAY want to authenticate a client certificate against its trust store - although the certificate is expired (Section 11). + although the certificate is expired (Section 10). -5. Protocol Design + EST-coaps supports the certificate types and Trust Anchors (TA) that + are specified for EST in Section 3 of [RFC7030]. - EST-coaps uses CoAP to transfer EST messages, aided by Block-Wise - Transfer [RFC7959] to avoid (excessive) fragmentation of UDP - datagrams. The use of Blocks for the transfer of larger EST messages - is specified in Section 5.6. Figure 1 below shows the layered EST- - coaps architecture. + CoAP and DTLS can provide proof-of-identity for EST-coaps clients and + servers with simple PKI messages as described in Section 3.1 of + [RFC5272]. Moreover, channel-binding information for linking proof- + of-identity with connection-based proof-of-possession is OPTIONAL for + EST-coaps. When proof-of-possession is desired, a set of actions are + required regarding the use of tls-unique, described in Section 3.5 in + [RFC7030]. The tls-unique information consists of the contents of + the first "Finished" message in the (D)TLS handshake between server + and client [RFC5929]. The client adds the "Finished" message as a + ChallengePassword in the attributes section of the 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 establishment. - +------------------------------------------------+ - | EST request/response messages | - +------------------------------------------------+ - | CoAP for message transfer and signaling | - +------------------------------------------------+ - | DTLS for transport security | - +------------------------------------------------+ - | UDP for transport | - +------------------------------------------------+ + In the case of EST-coaps, the same operations can be performed during + the DTLS handshake. For DTLS 1.2, in the event of handshake message + fragmentation, the Hash of the handshake messages used in the MAC + calculation of the Finished message must be computed as if each + handshake message had been sent as a single fragment (Section 4.2.6 + of [RFC6347]). The Finished 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]. - Figure 1: EST-coaps protocol layers + In a constrained CoAP environment, endpoints can't always afford to + establish a DTLS connection for every EST transaction. + Authenticating and negotiating DTLS keys requires resources on low- + end endpoints and consumes valuable bandwidth. To alleviate this + situation, an EST-coaps DTLS connection MAY remain open for + sequential EST transactions. For example, an EST csrattrs request + that is followed by a simpleenroll request can use the same + authenticated DTLS connection. However, when a cacerts request is + included in the set of sequential 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 + new EST transaction will take place after a significant amount of + time, the DTLS connections SHOULD only be kept alive for EST messages + that are relatively close to each other. In some cases, like NAT + rebinding, keeping the state of a connection is not possible when + devices sleep for extended periods of time. In such occasions, + [I-D.ietf-tls-dtls-connection-id] negotiates a connection ID that can + eliminate the need for new handshake and its additional cost. + +5. Protocol Design + + EST-coaps uses CoAP to transfer EST messages, aided by Block-Wise + Transfer [RFC7959] to avoid IP fragmentation. The use of Blocks for + the transfer of larger EST messages is specified in Section 5.6. + Figure 1 shows the layered EST-coaps architecture. The EST-coaps protocol design follows closely the EST design. The supported message types in EST-coaps are: - o CA certificate retrieval, needed to receive the complete set of CA + o CA certificate retrieval needed to receive the complete set of CA certificates. - o Simple enroll and reenroll, for a CA to sign public client- + o Simple enroll and re-enroll for a CA to sign public client identity key. - o Certificate Signing Request (CSR) Attributes messages that informs - the client of the fields to include in generated CSR. + o Certificate Signing Request (CSR) attribute messages that inform + the client of the fields to include in a CSR. - o Server-side key generation messages to provide a private client- + o Server-side key generation messages to provide a private client identity key when the client choses so. 5.1. Discovery and URIs EST-coaps is targeted for low-resource networks with small packets. Saving header space is important and short EST-coaps URIs are specified in this document. These URIs are shorter than the ones in [RFC7030]. Two example EST-coaps resource path names are: - coaps://est-coaps.example.ietf.org:/.well-known/est/ - coaps://est-coaps.example.ietf.org:/.well-known/est/ + coaps://est-coaps.example.org:/.well-known/est/ + coaps://est-coaps.example.org:/.well-known/est/ ArbitraryLabel/ The short-est strings are defined in Table 1. The ArbitraryLabel path-segment, if used, SHOULD be of the shortest length possible (Sections 3.1 and 3.2.2 of [RFC7030]. Arbitrary Labels are usually defined and used by EST CAs in order to route client requests to the appropriate certificate profile. The EST-coaps server URIs, obtained through discovery of the EST- coaps root resource(s) as shown below, are of the form: - coaps://est-coaps.example.ietf.org:// - coaps://est-coaps.example.ietf.org:// + coaps://est-coaps.example.org:// + coaps://est-coaps.example.org:// ArbitraryLabel/ - 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 mapping from the EST URI path to the shorter EST-coaps URI path. - +------------------+-----------+ + +------------------+-------------------------------+ | EST | EST-coaps | - +------------------+-----------+ + +------------------+-------------------------------+ | /cacerts | /crts | | /simpleenroll | /sen | | /simplereenroll | /sren | | /csrattrs | /att | - | /serverkeygen | /skg | - +------------------+-----------+ + | /serverkeygen | /skg (PKCS#7) | + | /serverkeygen | /skc (application/pkix-cert) | + +------------------+-------------------------------+ - Table 1: Table 1: Short EST-coaps URI path + Table 1: Short EST-coaps URI path - Clients and servers MUST support the short resource URIs. The - corresponding longer URIs from [RFC7030] MAY be supported. + The /skg message is the EST /serverkeygen equivalent where the client + requests for a certificate in PKCS#7 format and a private key. If + the client prefers a single application/pkix-cert certificate instead + of PKCS#7, he will make an /skc request. + + Clients and servers MUST support the short resource URIs. In the context of CoAP, the presence and location of (path to) the management data are discovered by sending a GET request to "/.well- known/core" including a resource type (RT) parameter with the value - "ace.est" [RFC6690]. Upon success, the return payload will contain + "ace.est*" [RFC6690]. Upon success, the return payload will contain the root resource of the EST resources. The example below shows the discovery of the presence and location of EST-coaps resources. Linefeeds are included only for readability. REQ: GET /.well-known/core?rt=ace.est* RES: 2.05 Content - ; rt="ace.est", ;rt="ace.est.crts";ct="281 TBD287", ;rt="ace.est.sen";ct="281 TBD287", ;rt="ace.est.sren";ct="281 TBD287", ;rt="ace.est.att";ct=285, - ;rt="ace.est.skg";ct="62 280 284 281 TBD287" + ;rt="ace.est.skg";ct=62, + ;rt="ace.est.skc";ct=62 - The first line of the discovery response above MUST be included. The - five consecutive lines after the first MAY be included. The return - of the content types allows the client to choose the most appropriate - one. + The first three lines of the discovery response above MUST be + returned if the server supports resource discovery. The last three + lines are only included if the corresponding EST functions are + implemented. The Content-Formats in the response allow the client to + request one that is supported by the server. - Port numbers, not returned in the example, are assumed to be the - default numbers 5683 and 5684 for CoAP and CoAPS respectively - (Sections 12.6 and 12.7 of [RFC7252]). Discoverable port numbers MAY - be returned in the of the payload - [I-D.ietf-core-resource-directory]. An example response payload for - non-default CoAPS server port 61617 follows below. Linefeeds were - included only for readability. + Discoverable port numbers can be returned in the response payload. + An example response payload for non-default CoAPS server port 61617 + follows below. Linefeeds were included only for readability. REQ: GET /.well-known/core?rt=ace.est* RES: 2.05 Content - ;rt="ace.est"; - anchor="coap://[2001:db8:3::123]:61617", - ;rt="ace.est.crts"; - ct="281 TBD287";anchor="coap://[2001:db8:3::123]:61617", - ;rt="ace.est.sen"; - ct="281 TBD287";anchor="coap://[2001:db8:3::123]:61617", - ;rt="ace.est.sren"; - ct="281 TBD287";anchor="coap://[2001:db8:3::123]:61617", - ;rt="ace.est.att"; - ct="285";anchor="coap://[2001:db8:3::123]:61617", - ;rt="ace.est.skg"; - ct="62 280 284 281 TBD287";anchor="coap://[2001:db8:3::123]:61617" + ;rt="ace.est.crts"; + ct="281 TBD287", + ;rt="ace.est.sen"; + ct="281 TBD287", + ;rt="ace.est.sren"; + ct="281 TBD287", + ;rt="ace.est.att"; + ct=285, + ;rt="ace.est.skg"; + ct=62, + ;rt="ace.est.skc"; + ct=62 - The server MUST support the default /.well-known/est server root - resource and port 5684. Resource discovery is necessary when the IP - address of the server is unknown to the client. Resource discovery - SHOULD be employed when non-default URIs (like /est or /est/ - ArbitraryLabel) or ports are supported by the server, when the client - is unaware of what EST-coaps resources are available or if the client - considers sending two Uri-Path Options to convey the resource is - wasteful. + The server MUST support the default /.well-known/est root resource. + The server SHOULD support resource discovery when he supports non- + default URIs (like /est or /est/ArbitraryLabel) or ports. The client + SHOULD use resource discovery when /.well-known/est fails or when the + client is unaware of the available EST-coaps resources. It is up to the implementation to choose its root resource; throughout this document the example root resource /est is used. 5.2. Mandatory/optional EST Functions This specification contains a set of required-to-implement functions, optional functions, and not specified functions. The latter ones are deemed too expensive for low-resource devices in payload and calculation times. Table 2 specifies the mandatory-to-implement or optional - implementation of the est-coaps functions. + implementation of the EST-coaps functions. Discovery of the + existence of optional functions is described in Section 5.1. +------------------+--------------------------+ | EST Functions | EST-coaps implementation | +------------------+--------------------------+ | /cacerts | MUST | | /simpleenroll | MUST | | /simplereenroll | MUST | - | /fullcmc | Not specified | - | /serverkeygen | OPTIONAL | | /csrattrs | OPTIONAL | + | /serverkeygen | OPTIONAL | + | /fullcmc | Not specified | +------------------+--------------------------+ - Table 2: Table 2: List of EST-coaps functions + Table 2: List of EST-coaps functions While [RFC7030] permits a number of these functions to be used without authentication, this specification requires that the client MUST be authenticated for all functions. 5.3. Payload formats + EST-coaps is designed for low-resource devices and hence does not + need to send Base64-encoded data. Simple binary is more efficient + (30% smaller payload) and well supported by CoAP. Thus, the payload + for a given Media-Type follows the ASN.1 structure of the Media-Type + and is transported in binary format. + The Content-Format (HTTP Media-Type equivalent) of the CoAP message determines which EST message is transported in the CoAP payload. The - Media-Types specified in the HTTP Content-Type header (section 3.2.2 - of [RFC7030]) are in EST-coaps specified by the Content-Format Option - (12) of CoAP. The combination of URI-Path and Content-Format in EST- - coaps MUST map to an allowed combination of URI and Media-Type in - EST. The required Content-Formats for these requests and response - messages are defined in Section 10.1. The CoAP response codes are - defined in Section 5.5. + Media-Types specified in the HTTP Content-Type header (Section 3.2.2 + of [RFC7030]) are specified by the Content-Format Option (12) of + CoAP. The combination of URI-Path and Content-Format in EST-coaps + MUST map to an allowed combination of URI and Media-Type in EST. The + required Content-Formats for these requests and response messages are + defined in Section 9.1. The CoAP response codes are defined in + Section 5.5. 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 /skg response. Content-Format 281 MUST be supported by EST-coaps servers. Servers MAY also support Content-Format TBD287. It is up to the client to support only Content-Format 281, TBD287 or both. - The client is expected to use an COAP Accept Option in the request to - express the preferred response Content-Format. If an Accept Option - is not included in the request, the client is not expressing any - preference and the server SHOULD choose format 281. If the preferred - Content-Format cannot be returned, the server MUST send a 4.06 (Not - Acceptable) response, unless another error code takes precedence for - the response [RFC7252]. + The client will use a COAP Accept Option in the request to express + the preferred response Content-Format. If an Accept Option is not + included in the request, the client is not expressing any preference + and the server SHOULD choose format 281. Content-Format 286 is used in /sen, /sren and /skg requests and 285 in /att responses. - EST-coaps is designed for low-resource devices and hence does not - need to send Base64-encoded data. Simple binary is more efficient - (30% smaller payload) and well supported by CoAP. Thus, the payload - for a given Media-Type follows the ASN.1 structure of the Media-Type - and is transported in binary format. - - *application/multipart-core* - A representation with Content-Format identifier 62 contains a collection of representations along with their respective Content- Format. The Content-Format identifies the Media-Type application/ - multipart-core specified in [I-D.ietf-core-multipart-ct]. - - The collection is encoded as a CBOR array [RFC7049] with an even - number of elements. The second, fourth, sixth, etc. element is a - binary string containing a representation. The first, third, fifth, - etc. element is an unsigned integer specifying the Content-Format - identifier of the consecutive representation. For example, a - collection containing two representations in response to a EST-coaps - server-side key generation request, could include a private key in - PKCS#8 [RFC5958] with Content-Format identifier 284 (0x011C) and a - single certificate in a PKCS#7 container with Content-Format - identifier 281 (0x0119). Such a collection would look like + multipart-core specified in [I-D.ietf-core-multipart-ct]. For + example, a collection, containing two representations in response to + a EST-coaps server-side key generation /skg request, could include a + private key in PKCS#8 [RFC5958] with Content-Format identifier 284 + (0x011C) and a single certificate in a PKCS#7 container with Content- + Format identifier 281 (0x0119). Such a collection would look like [284,h'0123456789abcdef', 281,h'fedcba9876543210'] in diagnostic CBOR notation. The serialization of such CBOR content would be + 84 # array(4) 19 011C # unsigned(284) 48 # bytes(8) 0123456789ABCDEF # "\x01#Eg\x89\xAB\xCD\xEF" 19 0119 # unsigned(281) 48 # bytes(8) FEDCBA9876543210 # "\xFE\xDC\xBA\x98vT2\x10" Multipart /skg response serialization @@ -515,92 +581,86 @@ 84 # array(4) 19 011C # unsigned(284) 48 # bytes(8) 0123456789ABCDEF # "\x01#Eg\x89\xAB\xCD\xEF" 19 0119 # unsigned(281) 48 # bytes(8) FEDCBA9876543210 # "\xFE\xDC\xBA\x98vT2\x10" Multipart /skg response serialization - When the returned certificate is a single X.509 certificate (not a - PKCS#7 container) the Content-Format identifier is TBD287 (0x011F) - instead of 281. In cases where the private key is encrypted with CMS - (as explained in Section 5.8) the Content-Format identifier is 280 + When the client makes an /skc request the certificate returned with + the private key is a single X.509 certificate (not a PKCS#7 + container) with Content-Format identifier TBD287 (0x011F) instead of + 281. In cases where the private key is encrypted with CMS (as + explained in Section 5.8) the Content-Format identifier is 280 (0x0118) instead of 284. The key and certificate representations are ASN.1 encoded in binary format. An example is shown in Appendix A.3. 5.4. Message Bindings The general EST-coaps message characteristics are: - o All EST-coaps messages expect a response from the server, thus the - client MUST send the requests over confirmable CON CoAP messages. - - o The Ver, TKL, Token, and Message ID values of the CoAP header are - not affected by EST. + o All EST-coaps request messages expect an acknowledgement (with a + response payload); EST-coaps requests are confirmable CON CoAP + messages. o The CoAP Options used are Uri-Host, Uri-Path, Uri-Port, Content- - Format, Accept and Location-Path. These CoAP Options are used to - communicate the HTTP fields specified in the EST REST messages. - The Uri-Host and Uri-Port Options are optional. They are usually - omitted as the DTLS destination and port are sufficient. Explicit - Uri-Host and Uri-Port Options are typically used when an endpoint - hosts multiple virtual servers and uses the Options to route the - requests accordingly. Alternatively, if a UDP port to a server is - blocked, someone could send the DTLS packets to a known open port - on the server and use the Uri-Port to convey the intended port he - is attempting to reach. + Format, Block, Accept and Location-Path. These CoAP Options are + used to communicate the HTTP fields specified in the EST REST + messages. The URI-host and Uri-Port Options can be omitted from + the COAP message sent on the wire. When omitted, they are + logically assumed to be the transport protocol destination address + and port respectively. Explicit Uri-Host and Uri-Port Options are + typically used when an endpoint hosts multiple virtual servers and + uses the Options to route the requests accordingly. Other COAP + Options should be handled in accordance with [RFC7252]. o EST URLs are HTTPS based (https://), in CoAP these are assumed to be translated to CoAPS (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 messages translated to CoAP. 5.5. CoAP response codes Section 5.9 of [RFC7252] and Section 7 of [RFC8075] specify the mapping of HTTP response codes to CoAP response codes. Every time the HTTP response code 200 is specified in [RFC7030] in response to a - GET request (/cacerts, /csrattrs), in EST-coaps the equivalent CoAP - response code 2.05 or 2.03 MUST be used. Similarly, 2.01, 2.02 or + GET request (/cacerts, /csrattrs), the equivalent CoAP response code + 2.05 or 2.03 MUST be used in EST-coaps. Similarly, 2.01, 2.02 or 2.04 MUST be used in response to EST POST requests (/simpleenroll, /simplereenroll, /serverkeygen). - Response code HTTP 202 Retry-After that existed in EST has no + HTTP response code 202 with a Retry-After header in [RFC7030] has no equivalent in CoAP. Retry-After is used in EST for delayed server responses. Section 5.7 specifies how EST-coaps handles delayed messages. EST makes use of HTTP 204 and 404 responses when a resource is not available for the client. The equivalent CoAP codes to use in an EST-coaps responses are 2.04 and 4.04. Additionally, EST's HTTP 401 error translates to 4.01 in EST-coaps. Other EST HTTP error messages are 400, 423 and 503. Their equivalent CoAP errors are 4.00, 4.03 and 5.03 respectively. In case a CoAP Option is unrecognized and critical, the server is expected to return a 4.02 (Bad Option). - Moreover, if the Content-Format requested in the client Accept - Option, is not supported the server MUST return a 4.06 (Not - Acceptable), unless another error code takes precedence for the - response. 5.6. Message fragmentation DTLS defines fragmentation only for the handshake and not for secure data exchange (DTLS records). [RFC6347] states that to avoid using IP fragmentation, which involves error-prone datagram reconstitution, - invokers of the DTLS record layer SHOULD size DTLS records so that + invokers of the DTLS record layer should size DTLS records so that they fit within any Path MTU estimates obtained from the record layer. In addition, invokers residing on a 6LoWPAN over IEEE - 802.15.4 [ieee802.15.4] network SHOULD attempt to size CoAP messages + 802.15.4 [ieee802.15.4] network should attempt to size CoAP messages such that each DTLS record will fit within one or two IEEE 802.15.4 frames. That is not always possible in EST-coaps. Even though ECC certificates are small in size, they can vary greatly based on signature algorithms, key sizes, and Object Identifier (OID) fields used. For 256-bit curves, common ECDSA cert sizes are 500-1000 bytes which could fluctuate further based on the algorithms, OIDs, Subject Alternative Names (SAN) and cert fields. For 384-bit curves, ECDSA certificates increase in size and can sometimes reach 1.5KB. @@ -625,36 +685,38 @@ supported for EST-coaps enrollment requests that exceed the Path MTU. [RFC7959] also defines Size1 and Size2 Options to provide size information about the resource representation in a request and response. EST-client and server MAY support Size1 and Size2 Options. Examples of fragmented EST-coaps messages are shown in Appendix B. 5.7. Delayed Responses - Server responses can sometimes be delayed. According to section - 5.2.2 of [RFC7252], a slow server can acknowledge the request and - respond later with the requested resource representation. In + Server responses can sometimes be delayed. According to + Section 5.2.2 of [RFC7252], a slow server can acknowledge the request + and respond later with the requested resource representation. In particular, a slow server can respond to an EST-coaps enrollment request with an empty ACK with code 0.00, before sending the - certificate to the server 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 blocks - to transfer it. 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 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 confirmable message that is acknowledged by the - client with an ACK. Onwards, having received the first 256 bytes in - the first Block2 block, the client asks for a block reduction to 128 - bytes in a confirmable enrollment request Uri-Path and acknowledges - the Block2 blocks sent up to that point. + to transfer it. + + 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 + 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 + confirmable message that is acknowledged by the client. Onwards, + having received the first 256 bytes in the first Block2 block, the + client asks for a block reduction to 128 bytes in a confirmable + enrollment request and acknowledges the Block2 blocks sent up to that + point. POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR req} --> <-- (ACK) (1:0/1/256) (2.31 Continue) POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR req} --> <-- (ACK) (1:1/1/256) (2.31 Continue) . . . POST [2001:db8::2:1]:61616/est/sen (CON)(1:N1/0/256){CSR req} --> <-- (0.00 empty ACK) @@ -667,29 +729,29 @@ <-- (ACK) (2:1/1/128) (2.04 Changed) {Cert resp} . . . POST [2001:db8::2:1]:61616/est/sen (CON)(2:N2/0/128) --> <-- (ACK) (2:N2/0/128) (2.04 Changed) {Cert resp} Figure 2: EST-COAP enrollment with short wait If the server is very slow (i.e. minutes) in providing the response - (i.e. when a manual intervention is needed), the server SHOULD - respond with 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 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 response code 5.03 (Service Unavailable) - with a Max-Age Option, the client SHOULD keep resending the - enrollment request until the server responds with the certificate or - the client abandons for other reasons. + (i.e. when a manual intervention is needed), he SHOULD respond with + 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 + 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 + response code 5.03 (Service Unavailable) with a Max-Age Option, the + client SHOULD keep resending the enrollment request until the server + responds with the certificate or the client abandons for other + reasons. To demonstrate this scenario, Figure 3 shows a client sending an 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 needs to take a long delay (minutes) to provide the response. 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 he receives the same 5.03 response and retransmits the enrollment request until he receives a certificate in a fragmented 2.01 response. Note that the server asks for a decrease in the block size @@ -737,135 +799,70 @@ In these scenarios, server-side key generation can be used. The client asks for the server or proxy to generate the private key and the certificate which are transferred back to the client in the server-side key generation response. In all respects, the server SHOULD treat the CSR as it would treat any enroll or re-enroll CSR; the only distinction here is that the server MUST ignore the public key values and signature in the CSR. These are included in the request only to allow re-use of existing codebases for generating and parsing such requests. - The client /skg request needs to communicate to the server the - Content-Format of the application/multipart-core elements. The key - Content-Format requested by the client is depicted in the PKCS#10 - request. If the request contains SMIMECapabilities the client is - expecting Content-Format 280. Otherwise he expects a PKCS#8 key in - Content-Format 284. The client expresses the preferred certificate - Content-Format in his /skg request by using an Accept Option. The - Accept Option is 281 when preferring a certificate in a PKCS#7 - container or TBD287 when preferring a single X.509 certificate. - - [RFC7030] provides two methods, symmetric and asymmetric, to - optionally encrypt the generated key. The methods are signaled by - the client by using the relevant attributes (SMIMECapabilities and - DecryptKeyIdentifier or AsymmetricDecryptKeyIdentifier) in the CSR - request. The symmetric key or the asymmetric keypair establishment - method is out of scope of the specification. + The client /skg request is for a certificate in a PKCS#7 container + and private key in two application/multipart-core elements. + Respectively, an /skc request is for a single application/pkix-cert + certificate and a private key. The private key Content-Format + requested by the client is depicted in the PKCS#10 CSR request. If + the request contains SMIMECapabilities and DecryptKeyIdentifier or + AsymmetricDecryptKeyIdentifier the client is expecting Content-Format + 280 for the private key. Then the private key is encrypted + symmetrically or asymmetrically as per [RFC7030]. The symmetric key + or the asymmetric keypair establishment method is out of scope of the + specification. A /skg or /skc request with a CSR without + SMIMECapabilities expects an application/multipart-core with an + unencrypted PKCS#8 private key with Content-Format 284. The EST-coaps server-side key generation response is returned with Content-Format application/multipart-core [I-D.ietf-core-multipart-ct] containing a CBOR array with four items - Section 5.3. The certificate part exactly matches the response from - an enrollment response. The private key can be in unprotected PKCS#8 - [RFC5958] format (Content-Format 284) or protected inside of CMS - SignedData (Content-Format 280). The SignedData is signed by the - party that generated the private key, which may be the EST server or - the EST CA. The SignedData is further protected by placing it inside - of a CMS EnvelopedData as explained in Section 4.4.2 of [RFC7030]. - In summary, the symmetrically encrypted key is included in the - encryptedKey attribute in a KEKRecipientInfo structure. In the case - where the asymmetric encryption key is suitable for transport key - operations the generated private key is encrypted with a symmetric + (Section 5.3) . The two representations (each consisting of two CBOR + array items) do not have to be in a particular order since each + representation is preceded by its Content-Format ID. The private key + can be in unprotected PKCS#8 [RFC5958] format (Content-Format 284) or + protected inside of CMS SignedData (Content-Format 280). The + SignedData is signed by the party that generated the private key, + which may be the EST server or the EST CA. The SignedData is further + protected by placing it inside of a CMS EnvelopedData as explained in + Section 4.4.2 of [RFC7030]. In summary, the symmetrically encrypted + key is included in the encryptedKey attribute in a KEKRecipientInfo + structure. In the case where the asymmetric encryption key is + suitable for transport key operations the generated private key is + encrypted with a symmetric key which is encrypted by the client + defined (in the CSR) 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 key is encrypted with a symmetric key which is encrypted by the client defined (in the CSR) 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 - key is encrypted with a symmetric key which is encrypted by the - client defined (in the CSR) asymmetric public key and is carried in - an recipientEncryptedKeys attribute in a KeyAgreeRecipientInfo. + public key and is carried in an recipientEncryptedKeys attribute in a + KeyAgreeRecipientInfo. [RFC7030] recommends the use of additional encryption of the returned private key. For the context of this specification, clients and servers that choose to support server-side key generation MUST support unprotected (PKCS#8) private keys (Content-Format 284). Symmetric or asymmetric encryption of the private key (CMS EnvelopedData, Content-Format 280) SHOULD be supported for deployments where end-to-end encryption needs to be provided between the client and a server. Such cases could include architectures where an entity between the client and the CA terminates the DTLS connection (Registrar in Figure 4). -6. DTLS Transport Protocol - - EST-coaps depends on a secure transport mechanism over UDP that - secures the exchanged CoAP messages. DTLS is one such secure - protocol. EST depended in TLS. No other changes are necessary - regarding the secure transport of EST messages. - - CoAP was designed to avoid fragmentation. DTLS is used to secure - CoAP messages. However, fragmentation is still possible at the DTLS - layer during the DTLS handshake when using ECC ciphersuites. If - fragmentation is necessary, "DTLS provides a mechanism for - fragmenting a handshake message over several records, each of which - can be transmitted separately, thus avoiding IP fragmentation" - [RFC6347]. - - The DTLS handshake is authenticated by using certificates. EST-coaps - supports the certificate types and Trust Anchors (TA) that are - specified for EST in Section 3 of [RFC7030]. - - CoAP and DTLS can provide proof-of-identity for EST-coaps clients and - servers with simple PKI messages as described in Section 3.1 of - [RFC5272]. Moreover, channel-binding information for linking proof- - of-identity with connection-based proof-of-possession is OPTIONAL for - EST-coaps. When proof-of-possession is desired, a set of actions are - required regarding the use of tls-unique, described in section 3.5 in - [RFC7030]. The tls-unique information consists of the contents of - the first "Finished" message in the (D)TLS handshake between server - and client [RFC5929]. The client adds the "Finished" message as a - ChallengePassword in the attributes section of the 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 establishment. - - In the case of EST-coaps, the same operations can be performed during - the DTLS handshake. For DTLS 1.2, in the event of handshake message - fragmentation, the Hash of the handshake messages used in the MAC - calculation of the Finished message MUST be computed as if each - handshake message had been sent as a single fragment (Section 4.2.6 - of [RFC6347]). The Finished 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 - establish a DTLS connection for every EST transaction. - Authenticating and negotiating DTLS keys requires resources on low- - end endpoints and consumes valuable bandwidth. To alleviate this - situation, an EST-coaps DTLS connection MAY remain open for - sequential EST transactions. For example, an EST csrattrs request - that is followed by a simpleenroll request can use the same - authenticated DTLS connection. However, when a cacerts request is - included in the set of sequential EST transactions, some additional - security considerations apply regarding the use of the Implicit and - Explicit TA database as explained in Section 11.1. - - Given that after a successful enrollment, it is more likely that a - new EST transaction will take place after a significant amount of - time, the DTLS connections SHOULD only be kept alive for EST messages - that are relatively close to each other. In some cases, like NAT - rebinding, keeping the state of a connection is not possible when - devices sleep for extended periods of time. In such occasions, - [I-D.ietf-tls-dtls-connection-id] negotiates a connection ID that can - eliminate the need for new handshake and its additional cost. - -7. HTTPS-CoAPS Registrar +6. HTTPS-CoAPS Registrar In real-world deployments, the EST server will not always reside within the CoAP boundary. The EST server can exist outside the constrained network in which case it will support TLS/HTTP instead of CoAPS. In such environments EST-coaps is used by the client within the CoAP boundary and TLS is used to transport the EST messages outside the CoAP boundary. A Registrar at the edge is required to operate between the CoAP environment and the external HTTP network as shown in Figure 4. @@ -887,173 +884,168 @@ The EST-coaps-to-HTTPS Registrar MUST terminate EST-coaps downstream and initiate EST connections over TLS upstream. The Registrar MUST authenticate and OPTIONALLY authorize the clients and it MUST be authenticated by the EST server or CA. The trust relationship between the Registrar and the EST server SHOULD be pre-established for the Registrar to proxy these connections on behalf of various clients. When enforcing Proof-of-Possession (POP) linking, the DTLS tls-unique value of the (D)TLS session is used to prove that the private key - corresponding to the public key is in the possession of and was used - to establish the connection by the client as explained in Section 6). + corresponding to the public key is in the possession of the client + and was used to establish the connection as explained in Section 4. The POP linking information is lost between the EST-coaps client and the EST server when a Registrar is present. The EST server becomes aware of the presence of a Registrar from its TLS client certificate that includes id-kp-cmcRA [RFC6402] extended key usage extension (EKU). As explained in Section 3.7 of [RFC7030], the EST server SHOULD apply an authorization policy consistent with a Registrar client. For example, it could be configured to accept POP linking information that does not match the current TLS session because the authenticated EST client Registrar has verified this information when 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. In these - cases, the Registrar MUST support random number generation using - proper entropy. Such 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. + if the CA does not support server-side key generation. Such + 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 support random number + generation using proper entropy. Table 1 contains the URI mappings between EST-coaps and EST that the Registrar MUST adhere to. Section 5.5 of this specification and Section 7 of [RFC8075] define the mappings between EST-coaps and HTTP response codes, that determine how the Registrar MUST translate CoAP response codes from/to HTTP status codes. The mapping from CoAP - Content-Format to HTTP Media-Type is defined in Section 10.1. + Content-Format to HTTP Media-Type is defined in Section 9.1. Additionally, a conversion from CBOR major type 2 to Base64 encoding MUST take place at the Registrar when server-side key generation is supported. If CMS end-to-end encryption is employed for the private key, the encrypted CMS EnvelopedData blob MUST be converted to binary in CBOR type 2 downstream to the client. Due to fragmentation of large messages into blocks, an EST-coaps-to- HTTP Registrar MUST reassemble the BLOCKs before translating the binary content to Base64, and consecutively relay the message upstream. - For the discovery of the EST server by the EST client in the CoAP - environment, the EST-coaps-to-HTTP Registrar MUST announce itself - according to the rules in Section 5.1. The available actions of the - Registrars MUST be announced with as many resource paths necessary. + If necessary, the EST-coaps-to-HTTP Registrar will support resouce + discovery according to the rules in Section 5.1. -8. Parameters +7. Parameters This section addresses transmission parameters described in sections 4.7 and 4.8 of [RFC7252]. EST does not impose any unique values on the CoAP parameters in [RFC7252], but the EST parameter values need to be tuned to the CoAP parameter values. It is RECOMMENDED, based on experiments, to follow the default CoAP configuration parameters ([RFC7252]). However, depending on the implementation scenario, retransmissions and timeouts can also occur on other networking layers, governed by other configuration parameters. A change in a server parameter MUST ensure the adjusted value is also available to all the endpoints with which these adjusted values are to be used to communicate. Some further comments about some specific parameters, mainly from Table 2 in [RFC7252]: - o NSTART: Limit the number of simultaneous outstanding interactions - that a client maintains to a given server. EST-coaps clients - SHOULD use 1, which is the default. A EST-coaps client is not - expected to interact with more than one servers at the same time. + o NSTART: A parameter that controls the number of simultaneous + outstanding interactions that a client maintains to a given + server. An EST-coaps client is not expected to interact with more + than one servers at the same time, which is the default NSTART + value defined in [RFC7252]. o DEFAULT_LEISURE: This setting is only relevant in multicast scenarios, outside the scope of EST-coaps. o PROBING_RATE: A parameter which specifies the rate of re-sending non-confirmable messages. The EST messages are defined to be sent as CoAP confirmable messages, hence this setting is not applicable. Finally, the Table 3 parameters in [RFC7252] are mainly derived from Table 2. Directly changing parameters on one table would affect parameters on the other. -9. Deployment limitations +8. Deployment limitations Although EST-coaps paves the way for the utilization of EST by constrained devices in constrained networks, some classes of devices - [RFC7228] will not have enough resources to handle the large payloads - that come with EST-coaps. The specification of EST-coaps is intended - to ensure that EST works for networks of constrained devices that - choose to limit their communications stack to UDP/DTLS/CoAP. It is - up to the network designer to decide which devices execute the EST - protocol and which do not. + [RFC7228] will not have enough resources to handle the payloads that + come with EST-coaps. The specification of EST-coaps is intended to + ensure that EST works for networks of constrained devices that choose + to limit their communications stack to DTLS/CoAP. It is up to the + network designer to decide which devices execute the EST protocol and + which do not. -10. IANA Considerations +9. IANA Considerations -10.1. Content-Format Registry +9.1. Content-Format Registry Additions to the sub-registry "CoAP Content-Formats", within the "CoRE Parameters" registry [COREparams] are specified in Table 3. These have been registered provisionally in the Expert Review range (0-255). +------------------------------+-------+----------------------------+ | HTTP Media-Type | ID | Reference | +------------------------------+-------+----------------------------+ | application/pkcs7-mime; | 280 | [RFC7030] [I-D.ietf-lamps- | | smime-type=server-generated- | | rfc5751-bis] | | key | | | | application/pkcs7-mime; | 281 | [I-D.ietf-lamps-rfc5751-bi | | smime-type=certs-only | | s] | - | application/pkcs7-mime; | 282 | [RFC5273] [I-D.ietf-lamps- | - | smime-type=CMC-request | | rfc5751-bis] | - | application/pkcs7-mime; | 283 | [RFC5273] [I-D.ietf-lamps- | - | smime-type=CMC-response | | rfc5751-bis] | | application/pkcs8 | 284 | [RFC5958] [I-D.ietf-lamps- | | | | rfc5751-bis] | | application/csrattrs | 285 | [RFC7030] [RFC7231] | | application/pkcs10 | 286 | [RFC5967] [I-D.ietf-lamps- | | | | rfc5751-bis] | | application/pkix-cert | TBD28 | [RFC2585] | | | 7 | | +------------------------------+-------+----------------------------+ - Table 3: Table 3: New CoAP Content-Formats + Table 3: New CoAP Content-Formats - The Content-Formats 281 to 286 have been the subject of an earlier - temporary allocation. It is suggested that 287 is allocated to - TBD287. + It is suggested that 287 is allocated to TBD287. -10.2. Resource Type registry +9.2. Resource Type registry - This memo registers a new Resource Type (rt=) Link Target Attributes - in the "Resource Type (rt=) Link Target Attribute Values" subregistry + This memo registers new Resource Type (rt=) Link Target Attributes in + the "Resource Type (rt=) Link Target Attribute Values" subregistry under the "Constrained RESTful Environments (CoRE) Parameters" registry. - o rt="ace.est". This EST resource is used to query and return the - supported EST resources of a CoAP server. - o rt="ace.est.crts". This resource depicts the support of EST get cacerts. o rt="ace.est.sen". This resource depicts the support of EST simple enroll. o rt="ace.est.sren". This resource depicts the support of EST simple reenroll. o rt="ace.est.att". This resource depicts the support of EST CSR attributes. o rt="ace.est.skg". This resource depicts the support of EST - server-side key generation. + server-side key generation with the returned certificate in a + PKCS#7 container. -11. Security Considerations + o rt="ace.est.skc". This resource depicts the support of EST + server-side key generation with the returned certificate in + application/pkix-cert format. -11.1. EST server considerations +10. Security Considerations + +10.1. EST server considerations The security considerations of Section 6 of [RFC7030] are only partially valid for the purposes of this document. As HTTP Basic Authentication is not supported, the considerations expressed for using passwords do not apply. Given that the client has only limited resources and may not be able to generate sufficiently random keys to encrypt its identity, it is possible that the client uses server generated private/public keys. The transport of these keys is inherently risky. Analysis SHOULD be @@ -1062,21 +1054,21 @@ 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 receiving the Distribution of CA certificates response (Section 4.1.3 of [RFC7030]) limits any risk to the first DTLS exchange. Alternatively, in a case where a /sen request immediately follows a /crt, a client MAY choose to keep the connection authenticated by the Implicit TA open for efficiency - reasons (Section 6). A client that pipelines EST-coaps /crt request + reasons (Section 4). A client that pipelines EST-coaps /crt request with other requests in the same DTLS connection SHOULD revalidate the server certificate chain against the updated Explicit TA from the /crt response before proceeding with the subsequent 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 the server MAY still authenticate the client because IDevIDs are @@ -1104,38 +1096,38 @@ binding is in use. The attack was possible because of certain (D)TLS implementation imperfections. In the context of this specification, an attacker could invalidate the purpose of the POP linking ChallengePassword in the client request by resuming an EST-coaps connection. Even though the practical risk of such an attack to EST- coaps is not devastating, we would rather use a more secure channel binding mechanism. Such a mechanism could include an updated tls- unique value generation like the tls-unique-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 [RFC8446]). Such - mechanism has not been standardized yet. Adopting in this document a - channel binding value generated from an exporter would break - backwards compatibility. Thus, in this specification we still depend - in the tls-unique mechanism defined in [RFC5929], especially since - the practicality of such an attack would not expose any messages - exchanged with EST-coaps. + mechanism has not been standardized yet. Adopting a channel binding + value generated from an exporter would break backwards compatibility. + Thus, in this specification we still depend in the tls-unique + mechanism defined in [RFC5929], especially since the practicality of + such an attack would not expose any messages exchanged with EST- + coaps. Regarding the Certificate Signing Request (CSR), a CA is expected to be able to enforce policies to recover from improper CSR requests. Interpreters of ASN.1 structures should be aware of the use of invalid ASN.1 length fields and should take appropriate measures to guard against buffer overflows, stack overruns in particular, and malicious content in general. -11.2. HTTPS-CoAPS Registrar considerations +10.2. HTTPS-CoAPS Registrar considerations - The Registrar proposed in Section 7 must be deployed with care, and + The Registrar proposed in Section 6 must be deployed with care, and only when the recommended connections are impossible. When POP linking is used the Registrar terminating the TLS connection establishes a new one with the upstream CA. Thus, it is impossible for POP linking to be enforced end-to-end for the EST transaction. The EST server could be configured to accept POP linking information that does not match the current TLS session because the authenticated EST Registrar client has verified this information when acting as an EST server. The introduction of an EST-coaps-to-HTTP Registrar assumes the client @@ -1133,70 +1125,68 @@ linking is used the Registrar terminating the TLS connection establishes a new one with the upstream CA. Thus, it is impossible for POP linking to be enforced end-to-end for the EST transaction. The EST server could be configured to accept POP linking information that does not match the current TLS session because the authenticated EST Registrar client has verified this information when acting as an EST server. The introduction of an EST-coaps-to-HTTP Registrar assumes the client can trust the registrar using its implicit or explicit TA database. + It also assumes the Registrar has a trust relationship with the upstream EST server in order to act on behalf of the clients. When a client uses the Implicit TA database for certificate validation, he SHOULD confirm if the server is acting as an RA by the presence of - the id-kp-cmcRA [RFC6402] EKU in the server certificate. If the - server certificate does not include the EKU, it is RECOMMENDED that - the client includes "Linking Identity and POP Information" - (Section 6) in requests. + the id-kp-cmcRA EKU [RFC6402] in the server certificate. 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 man-in-the-middle. Thus, the client puts its trust on the Registrar not exposing the private key. Clients that leverage server-side key generation without end-to-end encryption of the private key (Section 5.8) have no knowledge if the Registrar will be generating the private key and enrolling the certificates with the CA or if the CA will be responsible for generating the key. In such cases, the existence of a Registrar requires the client to put its trust on the registrar doing the right thing if it is generating the private key. -12. Contributors +11. Contributors Martin Furuhed contributed to the EST-coaps specification by providing feedback based on the Nexus EST over CoAPS server implementation that started in 2015. Sandeep Kumar kick-started this specification and was instrumental in drawing attention to the importance of the subject. -13. Acknowledgements +12. Acknowledgements The authors are very grateful to Klaus Hartke for his detailed explanations on the use of Block with DTLS and his support for the Content-Format specification. The authors would like to thank Esko Dijk and Michael Verschoor for the valuable discussions that helped in shaping the solution. They would also like to thank Peter Panburana for his feedback on technical details of the solution. Constructive comments were received from Benjamin Kaduk, Eliot Lear, Jim Schaad, Hannes Tschofenig, Julien Vermillard, John Manuel, Oliver - Pfaff and Pete Beal. + Pfaff, Pete Beal and Carsten Bormann. Interop tests were done by Oliver Pfaff, Thomas Werner, Oskar Camezind, Bjorn Elmers and Joel Hoglund. Robert Moskowitz provided code to create the examples. -14. References +13. References -14.1. Normative References +13.1. Normative References [I-D.ietf-core-multipart-ct] Fossati, T., Hartke, K., and C. Bormann, "Multipart Content-Format for CoAP", draft-ietf-core-multipart-ct-02 (work in progress), August 2018. [I-D.ietf-tls-dtls13] Rescorla, E., Tschofenig, H., and N. Modadugu, "The Datagram Transport Layer Security (DTLS) Protocol Version 1.3", draft-ietf-tls-dtls13-30 (work in progress), @@ -1227,24 +1217,20 @@ [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, . [RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed., "Enrollment over Secure Transport", RFC 7030, DOI 10.17487/RFC7030, October 2013, . - [RFC7049] Bormann, C. and P. Hoffman, "Concise Binary Object - Representation (CBOR)", RFC 7049, DOI 10.17487/RFC7049, - October 2013, . - [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . [RFC7959] Bormann, C. and Z. Shelby, Ed., "Block-Wise Transfers in the Constrained Application Protocol (CoAP)", RFC 7959, DOI 10.17487/RFC7959, August 2016, . @@ -1255,32 +1241,27 @@ . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . -14.2. Informative References +13.2. Informative References [COREparams] IANA, "Constrained RESTful Environments (CoRE) Parameters", . - [I-D.ietf-core-resource-directory] - Shelby, Z., Koster, M., Bormann, C., Stok, P., and C. - Amsuess, "CoRE Resource Directory", draft-ietf-core- - resource-directory-19 (work in progress), January 2019. - [I-D.ietf-lamps-rfc5751-bis] Schaad, J., Ramsdell, B., and S. Turner, "Secure/ Multipurpose Internet Mail Extensions (S/MIME) Version 4.0 Message Specification", draft-ietf-lamps-rfc5751-bis-12 (work in progress), September 2018. [I-D.ietf-tls-dtls-connection-id] Rescorla, E., Tschofenig, H., Fossati, T., and T. Gondrom, "Connection Identifiers for DTLS 1.2", draft-ietf-tls- dtls-connection-id-02 (work in progress), October 2018. @@ -1311,42 +1292,32 @@ [RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and Goals", RFC 4919, DOI 10.17487/RFC4919, August 2007, . [RFC5272] Schaad, J. and M. Myers, "Certificate Management over CMS (CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008, . - [RFC5273] Schaad, J. and M. Myers, "Certificate Management over CMS - (CMC): Transport Protocols", RFC 5273, - DOI 10.17487/RFC5273, June 2008, - . - [RFC5705] Rescorla, E., "Keying Material Exporters for Transport Layer Security (TLS)", RFC 5705, DOI 10.17487/RFC5705, March 2010, . [RFC5929] Altman, J., Williams, N., and L. Zhu, "Channel Bindings for TLS", RFC 5929, DOI 10.17487/RFC5929, July 2010, . [RFC5958] Turner, S., "Asymmetric Key Packages", RFC 5958, DOI 10.17487/RFC5958, August 2010, . - [RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic - Curve Cryptography Algorithms", RFC 6090, - DOI 10.17487/RFC6090, February 2011, - . - [RFC6402] Schaad, J., "Certificate Management over CMS (CMC) Updates", RFC 6402, DOI 10.17487/RFC6402, November 2011, . [RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for Constrained-Node Networks", RFC 7228, DOI 10.17487/RFC7228, May 2014, . [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer @@ -1393,86 +1364,81 @@ Fournet, Alfredo Pironti, Pierre-Yves Strub, "Triple Handshakes and Cookie Cutters: Breaking and Fixing Authentication over TLS", IEEE Security and Privacy ISBN 978-1-4799-4686-0, May 2014. Appendix A. EST messages to EST-coaps This section shows similar examples to the ones presented in Appendix A of [RFC7030]. The payloads in the examples are the hex encoded binary, generated with 'xxd -p', of the PKI certificates - created following [I-D.moskowitz-ecdsa-pki]. The payloads are shown - unencrypted. In practice the message content would be binary - formatted and transferred over an encrypted DTLS tunnel. The - hexadecimal representations in the examples below would NOT be - transported in hex, but in binary. Hex is used for visualization - purposes because a binary representation cannot be rendered well in - text. + created following [I-D.moskowitz-ecdsa-pki]. Hex is used for + visualization purposes because a binary representation cannot be + rendered well in text. The hexadecimal representations would not be + transported in hex, but in binary. The payloads are shown + unencrypted. In practice the message content would be transferred + over an encrypted DTLS tunnel. The certificate responses included in the examples contain Content- Format 281 (application/pkcs7). If the client had requested Content- - Format TBD287 (application/pkix-cert) with an Accept Option, the - server would respond a single DER binary certificate. + Format TBD287 (application/pkix-cert) by querying /est/skc, the + server would respond with a single DER binary certificate. - These examples assume that the resource discovery, returned a short - base path of "/est". + These examples assume a short root resource path of "/est". The corresponding CoAP headers are only shown in Appendix A.1. Creating CoAP headers is assumed to be generally understood. The message content breakdown is presented in Appendix C. A.1. cacerts In EST-coaps, a cacerts message can be: - GET coaps://est-coaps.example.ietf.org:9085/est/crts + GET coaps://est-coaps.example.org:9085/est/crts (Accept: 281) The corresponding CoAP header fields are shown below. The use of block and DTLS are worked out in Appendix B. Ver = 1 T = 0 (CON) Code = 0x01 (0.01 is GET) Token = 0x9a (client generated) Options - Option (Uri-Host) [optional] + Option (Uri-Host) Option Delta = 0x3 (option# 3) Option Length = 0x9 - Option Value = est-coaps.example.ietf.org - Option (Uri-Port) [optional] + Option Value = est-coaps.example.org + Option (Uri-Port) Option Delta = 0x4 (option# 3+4=7) Option Length = 0x4 Option Value = 9085 Option (Uri-Path) Option Delta = 0x4 (option# 7+4=11) Option Length = 0x5 Option Value = "est" Option (Uri-Path) Option Delta = 0x0 (option# 11+0=11) Option Length = 0x6 Option Value = "crts" Option (Accept) Option Delta = 0x6 (option# 11+6=17) Option Length = 0x2 Option Value = 281 Payload = [Empty] - The Uri-Host and Uri-Port Options are optional. They are usually - omitted as the DTLS destination and port are sufficient. Explicit - Uri-Host and Uri-Port Options are typically used when an endpoint - hosts multiple virtual servers and uses the Options to route the - requests accordingly. Alternatively, if a UDP port to a server is - blocked, someone could send the DTLS packets to a known open port on - the server and use the Uri-Port to convey the intended port he is - attempting to reach. + The Uri-Host and Uri-Port Options can be omitted if they coincide + with the transport protocol destination address and port + respectively. Explicit Uri-Host and Uri-Port Options are typically + 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 2.05 Content (Content-Format: 281) {payload with certificate in binary format} with CoAP fields Ver = 1 T = 2 (ACK) Code = 0x45 (2.05 Content) @@ -1513,21 +1479,21 @@ The breakdown of the payload is shown in Appendix C.1. A.2. enroll / reenroll During the (re-)enroll exchange the EST-coaps client uses a CSR (Content-Format 286) request in the POST request payload. The Accept option tells the server that the client is expecting Content-Format 281 (PKCS#7) in the response. As shown in Appendix C.2, the CSR contains a ChallengePassword which is used for POP linking - (Section 6). + (Section 4). POST [2001:db8::2:1]:61616/est/sen (Token: 0x45) (Accept: 281) (Content-Format: 286) [ The hexadecimal representation below would NOT be transported in hex, but in binary. Hex is used because a binary representation cannot be rendered well in text. ] @@ -1574,31 +1540,26 @@ 041496600d8716bf7fd0e752d0ac760777ad665d02a0301f0603551d2304 183016801468d16551f951bfc82a431d0d9f08bc2d205b1160300e060355 1d0f0101ff0404030205a0302a0603551d1104233021a01f06082b060105 05070804a013301106092b06010401b43b0a01040401020304300a06082a 8648ce3d0403020349003046022100c0d81996d2507d693f3c48eaa5ee94 91bda6db214099d98117c63b361374cd86022100a774989f4c321a5cf25d 832a4d336a08ad67df20f1506421188a0ade6d349236a1003100 The breakdown of the request and response is shown in Appendix C.2. - As described in Section 5.7, if the server is not able to provide a - response immediately, it sends an empty ACK with response code 5.03 - (Service Unavailable) and the Max-Age Option. See Figure 3 for an - example exchange. - A.3. serverkeygen In a serverkeygen exchange the CoAP POST request looks like POST coaps://192.0.2.1:8085/est/skg (Token: 0xa5) - (Accept: 281) + (Accept: 62) (Content-Format: 286) [ The hexadecimal representation below would NOT be transported in hex, but in binary. Hex is used because a binary representation cannot be rendered well in text. ] 3081cf3078020100301631143012060355040a0c0b736b67206578616d70 6c653059301306072a8648ce3d020106082a8648ce3d030107034200041b b8c1117896f98e4506c03d70efbe820d8e38ea97e9d65d52c8460c5852c5 1dd89a61370a2843760fc859799d78cd33f3c1846e304f1717f8123f1a28 @@ -1662,39 +1623,39 @@ in hex, but in binary. Hex is used because a binary representation cannot be rendered well in text. ] 307c06072b06010101011630220603883701311b131950617273652053455 420617320322e3939392e31206461746106092a864886f70d010907302c06 0388370231250603883703060388370413195061727365205345542061732 0322e3939392e32206461746106092b240303020801010b06096086480165 03040202 A 2.05 Content response should contain attributes which are relevant - for the authenticated client. This example is copied from section - A.2 in [RFC7030], where the base64 representation is replaced with a - hexadecimal representation of the equivalent binary format. The EST- - coaps server returns attributes that the client can ignore if they - are unknown to him. + for the authenticated client. This example is copied from + Section A.2 in [RFC7030], where the base64 representation is replaced + with a hexadecimal representation of the equivalent binary format. + The EST-coaps server returns attributes that the client can ignore if + they are unknown to him. Appendix B. EST-coaps Block message examples Two examples are presented in this section: 1. a cacerts exchange shows the use of Block2 and the block headers 2. an enroll exchange shows the Block1 and Block2 size negotiation for request and response payloads. The payloads are shown unencrypted. In practice the message contents would be binary formatted and transferred over an encrypted DTLS tunnel. The corresponding CoAP headers are only shown in - Appendix B.1. Creating CoAP headers are assumed to be generally + Appendix B.1. Creating CoAP headers is assumed to be generally known. B.1. cacerts This section provides a detailed example of the messages using DTLS and BLOCK option Block2. The minimum PMTU is 1280 bytes, which is the example value assumed for the DTLS datagram size. The example block length is taken as 64 which gives an SZX value of 2. The following is an example of a cacerts exchange over DTLS. The @@ -1713,66 +1674,63 @@ option:NUM/M/size) indicating the kind of Block Option (2 in this case) followed by a colon, and then the block number (NUM), the more bit (M = 0 in Block2 response means it is last block), and block size with exponent (2**(SZX+4)) separated by slashes. The Length 64 is used with SZX=2 to avoid IP fragmentation. The CoAP Request is sent confirmable (CON) and the Content-Format of the response, even though not shown, is 281 (application/pkcs7-mime; smime-type=certs-only). The transfer of the 10 blocks with partially filled block NUM=9 is shown below - GET coaps://est-coaps.example.ietf.org:9085/est/crts (2:0/0/64) --> + GET coaps://est-coaps.example.org:9085/est/crts (2:0/0/64) --> <-- (2:0/1/64) 2.05 Content - GET coaps://est-coaps.example.ietf.org:9085/est/crts (2:1/0/64) --> + GET coaps://est-coaps.example.org:9085/est/crts (2:1/0/64) --> <-- (2:1/1/64) 2.05 Content | | | - GET coaps://est-coaps.example.ietf.org:9085/est/crts (2:9/0/64) --> + GET coaps://est-coaps.example.org:9085/est/crts (2:9/0/64) --> <-- (2:9/0/64) 2.05 Content The header of the GET request looks like Ver = 1 T = 0 (CON) Code = 0x01 (0.1 GET) Token = 0x9a (client generated) Options - Option (Uri-Host) [optional] + Option (Uri-Host) Option Delta = 0x3 (option# 3) Option Length = 0x9 - Option Value = est-coaps.example.ietf.org - Option (Uri-Port) [optional] + Option Value = est-coaps.example.org + Option (Uri-Port) Option Delta = 0x4 (option# 3+4=7) Option Length = 0x4 Option Value = 9085 Option (Uri-Path) Option Delta = 0x4 (option# 7+4=11) Option Length = 0x5 Option Value = "est" Option (Uri-Path)Uri-Path) Option Delta = 0x0 (option# 11+0=11) Option Length = 0x6 Option Value = "crts" Option (Accept) Option Delta = 0x6 (option# 11+6=17) Option Length = 0x2 Option Value = 281 Payload = [Empty] - The Uri-Host and Uri-Port Options are optional. They are usually - omitted as the DTLS destination and port are sufficient. Explicit - Uri-Host and Uri-Port Options are typically used when an endpoint - hosts multiple virtual servers and uses the Options to route the - requests accordingly. Alternatively, if a UDP port to a server is - blocked, someone could send the DTLS packets to a known open port on - the server and use the Uri-Port to convey the intended port he is - attempting to reach. + The Uri-Host and Uri-Port Options can be omitted if they coincide + with the transport protocol destination address and port + respectively. Explicit Uri-Host and Uri-Port Options are typically + used when an endpoint hosts multiple virtual servers and uses the + Options to route the requests accordingly. For further detailing the CoAP headers, the first two and the last blocks are written out below. The header of the first Block2 response looks like Ver = 1 T = 2 (ACK) Code = 0x45 (2.05 Content) Token = 0x9a (copied from request by server) Options Option @@ -1837,26 +1795,25 @@ in hex, but in binary. Hex is used because a binary representation cannot be rendered well in text. ] Payload = 2ec0b4af52d46f3b7ecc9687ddf267bcec368f7b7f1353272f022047a28a e5c7306163b3c3834bab3c103f743070594c089aaa0ac870cd13b902caa1 003100 B.2. enroll / reenroll - In this example the requested Block2 size of 256 bytes, required by + In this example, the requested Block2 size of 256 bytes, required by the client, is transferred to the server in the very first request message. The block size 256=(2**(SZX+4)) which gives SZX=4. The - notation for block numbering is the same as in Appendix B.1. It is - assumed that CSR takes N1+1 blocks and the cert response takes N2+1 - blocks. The header fields and the payload are omitted for brevity. + notation for block numbering is the same as in Appendix B.1. The + header fields and the payload are omitted for brevity. POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR req} --> <-- (ACK) (1:0/1/256) (2.31 Continue) POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR req} --> <-- (ACK) (1:1/1/256) (2.31 Continue) . . . POST [2001:db8::2:1]:61616/est/sen (CON)(1:N1/0/256){CSR req} --> <-- (ACK) (1:N1/0/256)(2:0/1/256)(2.04 Changed){Cert resp} @@ -1873,22 +1830,22 @@ N1+1 blocks have been transferred from client to the server and N2+1 blocks have been transferred from server to client. Appendix C. Message content breakdown This appendix presents the breakdown of the hexadecimal dumps of the binary payloads shown in Appendix A. C.1. cacerts - Breakdown of cacerts response containing one root CA certificate. - + The breakdown of cacerts response containing one root CA certificate + is Certificate: Data: Version: 3 (0x2) Serial Number: 91:89:bc:df:9c:99:24:4b Signature Algorithm: ecdsa-with-SHA256 Issuer: C=US, ST=CA, L=LA, O=Example Inc, OU=certification, CN=Root CA Validity Not Before: Jan 7 10:40:41 2019 GMT @@ -1920,21 +1877,21 @@ X509v3 Subject Alternative Name: email:certify@example.com Signature Algorithm: ecdsa-with-SHA256 30:45:02:21:00:da:e3:7c:96:f1:54:c3:2e:c0:b4:af:52:d4: 6f:3b:7e:cc:96:87:dd:f2:67:bc:ec:36:8f:7b:7f:13:53:27: 2f:02:20:47:a2:8a:e5:c7:30:61:63:b3:c3:83:4b:ab:3c:10: 3f:74:30:70:59:4c:08:9a:aa:0a:c8:70:cd:13:b9:02:ca C.2. enroll / reenroll - The breakdown of the request is + The breakdown of the enrollment request is Certificate Request: Data: Version: 0 (0x0) Subject: C=US, ST=CA, L=LA, O=example Inc, OU=IoT/serialNumber=Wt1234 Subject Public Key Info: Public Key Algorithm: id-ecPublicKey Public-Key: (256 bit) pub: @@ -1950,23 +1907,23 @@ Requested Extensions: X509v3 Subject Alternative Name: othername: Signature Algorithm: ecdsa-with-SHA256 30:45:02:21:00:92:56:3a:54:64:63:bd:9e:cf:f1:70:d0:fd: 1f:2e:f0:d3:d0:12:16:0e:5e:e9:0c:ff:ed:ab:ec:9b:9a:38: 92:02:20:17:9f:10:a3:43:61:09:05:1a:ba:d1:75:90:a0:9b: c8:7c:4d:ce:54:53:a6:fc:11:35:a1:e8:4e:ed:75:43:77 The CSR contained a ChallengePassword which is used for POP linking - (Section 6). + (Section 4). - The breakdown of the issued certificate response is + The breakdown of the issued certificate is Certificate: Data: Version: 3 (0x2) Serial Number: 9112578475118446130 (0x7e7661d7b54e4632) Signature Algorithm: ecdsa-with-SHA256 Issuer: C=US, ST=CA, O=Example Inc, OU=certification, CN=802.1AR CA Validity Not Before: Jan 31 11:29:16 2019 GMT Not After : Dec 31 23:59:59 9999 GMT @@ -1998,21 +1955,22 @@ X509v3 Subject Alternative Name: othername: Signature Algorithm: ecdsa-with-SHA256 30:46:02:21:00:c0:d8:19:96:d2:50:7d:69:3f:3c:48:ea:a5: ee:94:91:bd:a6:db:21:40:99:d9:81:17:c6:3b:36:13:74:cd: 86:02:21:00:a7:74:98:9f:4c:32:1a:5c:f2:5d:83:2a:4d:33: 6a:08:ad:67:df:20:f1:50:64:21:18:8a:0a:de:6d:34:92:36 C.3. serverkeygen - The following is the breakdown of the request example used. + The following is the breakdown of the server-side key generation + request. Certificate Request: Data: Version: 0 (0x0) Subject: O=skg example Subject Public Key Info: Public Key Algorithm: id-ecPublicKey Public-Key: (256 bit) pub: 04:1b:b8:c1:11:78:96:f9:8e:45:06:c0:3d:70:ef: @@ -2023,39 +1981,39 @@ ASN1 OID: prime256v1 NIST CURVE: P-256 Attributes: a0:00 Signature Algorithm: ecdsa-with-SHA256 30:44:02:20:38:7c:d4:e9:cf:62:8d:4a:f7:7f:92:eb:ed:48: 90:d9:d1:41:dc:a8:6c:d2:75:7d:d1:4c:bd:59:cd:f6:96:18: 02:20:2f:24:5e:82:8c:77:75:43:78:b6:66:60:a4:97:7f:11: 3c:ac:da:a0:cc:7b:ad:7d:14:74:a7:fd:15:5d:09:0d - The following is the breakdown of the private key content of the - server-side key generation response payload. + Following is the breakdown of the private key content of the server- + side key generation response. Private-Key: (256 bit) priv: 0b:9a:67:78:5b:65:e0:73:60:b6:d2:8c:fc:1d:3f: 39:25:c0:75:57:99:de:ec:a7:45:37:2b:01:69:7b: d8:a6 pub: 04:1b:b8:c1:11:78:96:f9:8e:45:06:c0:3d:70:ef: be:82:0d:8e:38:ea:97:e9:d6:5d:52:c8:46:0c:58: 52:c5:1d:d8:9a:61:37:0a:28:43:76:0f:c8:59:79: 9d:78:cd:33:f3:c1:84:6e:30:4f:17:17:f8:12:3f: 1a:28:4c:c9:9f ASN1 OID: prime256v1 NIST CURVE: P-256 - The following is the breakdown of the certificate of the second part - of the server-side key generation response payload. + The following is the breakdown of the certificate in the server-side + key generation response payload. Certificate: Data: Version: 3 (0x2) Serial Number: 1327972925857878603 (0x126de8571518524b) Signature Algorithm: ecdsa-with-SHA256 Issuer: O=skg example Validity Not Before: Jan 9 08:57:08 2019 GMT Not After : Jan 4 08:57:08 2039 GMT