--- 1/draft-ietf-ace-coap-est-17.txt 2020-01-06 10:13:15.392369309 -0800 +++ 2/draft-ietf-ace-coap-est-18.txt 2020-01-06 10:13:15.492371862 -0800 @@ -1,23 +1,23 @@ ACE P. van der Stok Internet-Draft Consultant Intended status: Standards Track P. Kampanakis -Expires: June 7, 2020 Cisco Systems +Expires: July 9, 2020 Cisco Systems M. Richardson SSW S. Raza RISE SICS - December 5, 2019 + January 6, 2020 EST over secure CoAP (EST-coaps) - draft-ietf-ace-coap-est-17 + draft-ietf-ace-coap-est-18 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. @@ -29,85 +29,91 @@ 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 June 7, 2020. + This Internet-Draft will expire on July 9, 2020. Copyright Notice - Copyright (c) 2019 IETF Trust and the persons identified as the + Copyright (c) 2020 IETF Trust and the persons identified as the document authors. All rights reserved. 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 . . . . . . . . . . . . . . . . . . . . . . . . 7 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 7 4. DTLS and conformance to RFC7925 profiles . . . . . . . . . . 7 5. Protocol Design . . . . . . . . . . . . . . . . . . . . . . . 10 - 5.1. Discovery and URIs . . . . . . . . . . . . . . . . . . . 11 + 5.1. Discovery and URIs . . . . . . . . . . . . . . . . . . . 10 5.2. Mandatory/optional EST Functions . . . . . . . . . . . . 13 - 5.3. Payload formats . . . . . . . . . . . . . . . . . . . . . 14 + 5.3. Payload formats . . . . . . . . . . . . . . . . . . . . . 13 5.4. Message Bindings . . . . . . . . . . . . . . . . . . . . 15 - 5.5. CoAP response codes . . . . . . . . . . . . . . . . . . . 16 - 5.6. Message fragmentation . . . . . . . . . . . . . . . . . . 17 - 5.7. Delayed Responses . . . . . . . . . . . . . . . . . . . . 18 - 5.8. Server-side Key Generation . . . . . . . . . . . . . . . 20 - 6. HTTPS-CoAPS Registrar . . . . . . . . . . . . . . . . . . . . 22 - 7. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 24 - 8. Deployment limitations . . . . . . . . . . . . . . . . . . . 24 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25 - 9.1. Content-Format Registry . . . . . . . . . . . . . . . . . 25 - 9.2. Resource Type registry . . . . . . . . . . . . . . . . . 25 - 10. Security Considerations . . . . . . . . . . . . . . . . . . . 26 - 10.1. EST server considerations . . . . . . . . . . . . . . . 26 - 10.2. HTTPS-CoAPS Registrar considerations . . . . . . . . . . 28 - 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 29 - 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 29 - 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 29 - 13.1. Normative References . . . . . . . . . . . . . . . . . . 29 - 13.2. Informative References . . . . . . . . . . . . . . . . . 31 - Appendix A. EST messages to EST-coaps . . . . . . . . . . . . . 33 - A.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 34 - A.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 36 - A.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 38 - A.4. csrattrs . . . . . . . . . . . . . . . . . . . . . . . . 40 - Appendix B. EST-coaps Block message examples . . . . . . . . . . 41 - B.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 41 - B.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 45 - Appendix C. Message content breakdown . . . . . . . . . . . . . 46 - C.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 46 - C.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 47 - C.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 49 - - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 51 + 5.5. CoAP response codes . . . . . . . . . . . . . . . . . . . 15 + 5.6. Message fragmentation . . . . . . . . . . . . . . . . . . 16 + 5.7. Delayed Responses . . . . . . . . . . . . . . . . . . . . 17 + 5.8. Server-side Key Generation . . . . . . . . . . . . . . . 19 + 6. HTTPS-CoAPS Registrar . . . . . . . . . . . . . . . . . . . . 21 + 7. Parameters . . . . . . . . . . . . . . . . . . . . . . . . . 23 + 8. Deployment limitations . . . . . . . . . . . . . . . . . . . 23 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 24 + 9.1. Content-Format Registry . . . . . . . . . . . . . . . . . 24 + 9.2. Resource Type registry . . . . . . . . . . . . . . . . . 24 + 9.3. Well-Known URIs Registry . . . . . . . . . . . . . . . . 25 + 10. Security Considerations . . . . . . . . . . . . . . . . . . . 25 + 10.1. EST server considerations . . . . . . . . . . . . . . . 25 + 10.2. HTTPS-CoAPS Registrar considerations . . . . . . . . . . 27 + 11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 28 + 12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 + 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 28 + 13.1. Normative References . . . . . . . . . . . . . . . . . . 28 + 13.2. Informative References . . . . . . . . . . . . . . . . . 30 + Appendix A. EST messages to EST-coaps . . . . . . . . . . . . . 32 + A.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 33 + A.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 35 + A.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 37 + A.4. csrattrs . . . . . . . . . . . . . . . . . . . . . . . . 39 + Appendix B. EST-coaps Block message examples . . . . . . . . . . 40 + B.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 40 + B.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 44 + Appendix C. Message content breakdown . . . . . . . . . . . . . 45 + C.1. cacerts . . . . . . . . . . . . . . . . . . . . . . . . . 45 + C.2. enroll / reenroll . . . . . . . . . . . . . . . . . . . . 46 + C.3. serverkeygen . . . . . . . . . . . . . . . . . . . . . . 48 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50 1. Change Log EDNOTE: Remove this section before publication + -18 + + IESG Reviews fixes. + + Removed spurious lines introduced in v-17 due to xml2rfc v3. + -17 v16 remnants by Ben K. Typos. -16 Updates to address Yaron S.'s Secdir review. @@ -346,28 +351,26 @@ In accordance with 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. After the publication of [RFC7748], support for Curve25519 will likely be required in the future by (D)TLS Profiles for the Internet of Things [RFC7925]. 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. In addition, in - DTLS 1.3 the Supported Elliptic Curves extension has been renamed to - Supported Groups. + 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. In addition, in DTLS 1.3 the Supported + Elliptic Curves extension has been renamed to Supported Groups. CoAP was designed to avoid IP fragmentation. DTLS is used to secure CoAP 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 @@ -379,80 +382,76 @@ 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). 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 10). + server MAY authenticate a client certificate against its trust + store although the certificate is expired (Section 10). EST-coaps supports the certificate types and Trust Anchors (TA) that are specified for EST in Section 3 of [RFC7030]. As described in Section 2.1 of [RFC5272] proof-of-identity refers to - a value that can be used to prove that the private key corresponding - to the certified public key is in the possession of and can be used - by an end-entity or client. Additionally, channel-binding - information can link proof-of-identity with an established - connection. Connection-based proof-of-possession is OPTIONAL for - EST-coaps clients and servers. 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. + a value that can be used to prove that an end-entity or client is in + the possession of and can use the private key corresponding to the + certified public key. Additionally, channel-binding information can + link proof-of-identity with an established connection. Connection- + based proof-of-possession is OPTIONAL for EST-coaps clients and + servers. 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 handshake message fragmentation, if proof-of- possession is desired, the Finished message added as the ChallengePassword in the CSR is calculated as specified by the DTLS standards. We summarize it here for convenience. 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]. + message must be computed on each reassembled message, as if each + message had not been fragmented (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 which was not the case with [RFC7030]. - 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. + establish a DTLS connection for every EST transaction. An EST-coaps + DTLS connection MAY remain open for sequential EST transactions, + which was not the case with [RFC7030]. For example, if a /crts + request is followed by a /sen request, both can use the same + authenticated DTLS connection. However, when a /crts 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 + new EST transaction will not take place for 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; or DTLS - session resumption provides a less costly alternative than re-doing a - full DTLS handshake. + that are relatively close to each other. These could include a /sen + immediatelly following a /crts when a device is getting bootstrapped. + 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; or DTLS session resumption provides a less costly + alternative than re-doing a full DTLS handshake. 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: @@ -469,47 +468,43 @@ o Server-side key generation messages to provide a client identity private key when the client chooses so. While [RFC7030] permits a number of the EST functions to be used without authentication, this specification requires that the client MUST be authenticated for all functions. 5.1. Discovery and URIs EST-coaps is targeted for low-resource networks with small packets. - Two types of installations are possible (1) rigid ones where the + Two types of installations are possible: (1) rigid ones, where the address and the supported functions of the EST server(s) are known, - and (2) flexible one where the EST server and it supported functions - need to be discovered. + and (2) a flexible one, where the EST server and its supported + functions need to be discovered. For both types of installations, 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://example.com:/.well-known/est/ - coaps://example.com:/.well-known/est/ - ArbitraryLabel/ - - The short-est strings are defined in Table 1. + coaps://example.com:/.well-known/est/ArbitraryLabel/ - Arbitrary Labels are usually defined and used by EST CAs in order to - route client requests to the appropriate certificate profile. - Implementers should consider using short labels to minimize - transmission overhead. + The short-est strings are defined in Table 1. Arbitrary Labels are + usually defined and used by EST CAs in order to route client requests + to the appropriate certificate profile. Implementers should consider + using short labels to minimize transmission overhead. The EST-coaps server URIs, obtained through discovery of the EST- coaps resource(s) as shown below, are of the form: coaps://example.com:// - coaps://example.com:// - ArbitraryLabel/ + coaps://example.com://ArbitraryLabel/ 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 | @@ -525,25 +520,23 @@ requests a certificate in PKCS#7 format and a private key. If the client prefers a single application/pkix-cert certificate instead of PKCS#7, it will make an /skc request. In both cases (i.e., /skg, /skc) a private key MUST be returned. Clients and servers MUST support the short resource EST-coaps URIs. In the context of CoAP, the presence and location of (path to) the EST resources are discovered by sending a GET request to "/.well- known/core" including a resource type (RT) parameter with the value - "ace.est*" [RFC6690]. - - The example below shows the discovery over CoAPS of the presence and - location of EST-coaps resources. Linefeeds are included only for - readability. + "ace.est*" [RFC6690]. The example below shows the discovery over + CoAPS 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.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 @@ -569,35 +562,34 @@ 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 root resource - - . The server SHOULD support resource discovery when it supports non- + The server MUST support the default /.well-known/est root resource. + The server SHOULD support resource discovery when it supports non- default URIs (like /est or /est/ArbitraryLabel) or ports. The client SHOULD use resource discovery when it is unaware of the available EST-coaps resources. Throughout this document the example root resource of /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. + optional functions, and not specified functions. The unspecified + functions 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. Discovery of the existence of optional functions is described in Section 5.1. +-------------------+--------------------------+ | EST Functions | EST-coaps implementation | +-------------------+--------------------------+ | /cacerts | MUST | | /simpleenroll | MUST | @@ -610,36 +602,35 @@ Table 2: List of EST-coaps 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 for DER-encoded ASN.1) 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 + The Content-Format (HTTP Content-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 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. + Media-Types specified in the HTTP Content-Type header field + (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 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. A representation with Content-Format identifier 62 contains a collection of representations along with their respective Content- @@ -637,29 +628,29 @@ 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. 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]. - - 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 + 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 @@ -694,56 +685,51 @@ confirmable CON CoAP messages. o The CoAP Options used are Uri-Host, Uri-Path, Uri-Port, Content- Format, Block1, Block2, and Accept. 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. - - o Other COAP Options should be handled in accordance with [RFC7252]. + 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. The success code in response to an EST-coaps GET request (/crts, /att), is 2.05. - Similarly, 2.04 - - is used in successfull response to EST-coaps POST requests (/sen, - /sren, /skg, /skc). + Similarly, 2.04 is used in successful response to EST-coaps POST + requests (/sen, /sren, /skg, /skc). EST makes use of HTTP 204 or 404 responses when a resource is not available for the client. In EST-coaps 2.04 is used in response to a POST (/sen, /sren, /skg, /skc). 4.04 is used when the resource is not available for the client. - HTTP response code 202 with a Retry-After header in [RFC7030] has no - equivalent in CoAP. HTTP 202 with Retry-After is used in EST for - delayed server responses. Section 5.7 specifies how EST-coaps + HTTP response code 202 with a Retry-After header field in [RFC7030] + has no equivalent in CoAP. HTTP 202 with Retry-After is used in EST + for delayed server responses. Section 5.7 specifies how EST-coaps handles delayed messages with 5.03 responses with a Max-Age Option. Additionally, EST's HTTP 400, 401, 403, 404 and 503 status codes have their equivalent CoAP 4.00, 4.01, 4.03, 4.04 and 5.03 response codes - in EST-coaps. - - Table 4 summarizes the EST-coaps response codes. + in EST-coaps. Table 4 summarizes the EST-coaps response codes. +-----------------+-----------------+-------------------------------+ | operation | EST-coaps | Description | | | response code | | +-----------------+-----------------+-------------------------------+ | /crts, /att | 2.05 | Success. Certs included in | | | | the response payload. | | | 4.xx / 5.xx | Failure. | | /sen, /skg, | 2.04 | Success. Cert included in the | | /sren, /skc | | response payload. | @@ -765,42 +751,42 @@ 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. + Additionally, there are times when the EST cacerts response from the server can include multiple certificates that amount to large payloads. Section 4.6 of CoAP [RFC7252] describes the possible payload sizes: "if nothing is known about the size of the headers, good upper bounds are 1152 bytes for the message size and 1024 bytes for the payload size". Section 4.6 of [RFC7252] also suggests that IPv4 implementations may want to limit themselves to more - conservative IPv4 datagram sizes such as 576 bytes. - - Even with ECC, EST-coaps messages can still exceed MTU sizes on the - Internet or 6LoWPAN [RFC4919] (Section 2 of [RFC7959]). EST-coaps - needs to be able to fragment messages into multiple DTLS datagrams. + conservative IPv4 datagram sizes such as 576 bytes. Even with ECC, + EST-coaps messages can still exceed MTU sizes on the Internet or + 6LoWPAN [RFC4919] (Section 2 of [RFC7959]). EST-coaps needs to be + able to fragment messages into multiple DTLS datagrams. To perform fragmentation in CoAP, [RFC7959] specifies the Block1 Option for fragmentation of the request payload and the Block2 Option for fragmentation of the return payload of a CoAP flow. As explained in Section 1 of [RFC7959], block-wise transfers should be used in Confirmable CoAP messages to avoid the exacerbation of lost blocks. - Both EST-coaps clients and servers MUST support Block2. EST-coaps - servers MUST also support Block1. The EST-coaps client MUST support - Block1 only if it sends EST-coaps requests with an IP packet size - that exceeds the Path MTU. + EST-coaps servers MUST implement Block1 and Block2. EST-coaps + clients MUST implement Block2. EST-coaps clients MUST implement + Block1 only if they are expecting to send EST-coaps requests with a + packet size that exceeds 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 @@ -810,23 +796,22 @@ request with an empty ACK with code 0.00, before sending the certificate to the client after a short delay. If the certificate response is large, the server will need more than one Block2 block 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, the - client acknowledges all subsequent Block2 blocks. - - The notation of Figure 2 is explained in Appendix B.1. + client acknowledges all subsequent Block2 blocks. The notation of + Figure 2 is explained in Appendix B.1. POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR (frag# 1)} --> <-- (ACK) (1:0/1/256) (2.31 Continue) POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR (frag# 2)} --> <-- (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)}--> <-- (0.00 empty ACK) @@ -838,40 +823,40 @@ POST [2001:db8::2:1]:61616/est/sen (CON)(2:1/0/256) --> <-- (ACK) (2:1/1/256) (2.04 Changed) {Cert resp (frag# 2)} . . . 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)} 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), it 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 + If the server is very slow (for example, manual intervention is + required which would take minutes), it 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 before sending + another request to obtain the content. After a delay of Max-Age, the + client SHOULD resend the identical CSR to the server. As long as the + server continues to respond with response code 5.03 (Service + Unavailable) with a Max-Age Option, the client will continue to delay + for Max-Age and then resend the enrollment request until the server responds with the certificate or the client abandons the request for - other reasons. + policy or 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 it receives the same 5.03 response and retransmits the enrollment request until it receives a certificate in a fragmented 2.04 - response. POST [2001:db8::2:1]:61616/est/sen (CON)(1:0/1/256) {CSR (frag# 1)} --> <-- (ACK) (1:0/1/256) (2.31 Continue) POST [2001:db8::2:1]:61616/est/sen (CON)(1:1/1/256) {CSR (frag# 2)} --> <-- (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)}--> @@ -898,80 +883,78 @@ . . . 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)} Figure 3: EST-COAP enrollment with long wait 5.8. Server-side Key Generation - In scenarios where it is desirable that the server generates the - private key, server-side key generation is available. Such scenarios - could be when it is considered more secure to generate at the server - the long-lived random private key that identifies the client, or when + Private keys can be generated on the server to support scenarios + where serer-side key generation is needed. Such scenarios include + those where it is considered more secure to generate the long-lived, + random private key that identifies the client at the server, or where the resources spent to generate a random private key at the client - are considered scarce, or when the security policy requires that the + are considered scarce, or where the security policy requires that the certificate public and corresponding private keys are centrally - generated and controlled. Of course, that does not eliminate the - need for proper random numbers in various protocols like (D)TLS - (Section 10.1). + generated and controlled. As always, it is necessary to use proper + random numbers in various protocols such as (D)TLS (Section 10.1). When requesting server-side key generation, 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 treats 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 + 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 treats 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 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 indicated 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 + 280 for the private key. Then this 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 + or the asymmetric keypair establishment method is out of scope of + this 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 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. Dependent on the request, 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, placed in the outermost container, is signed - by the party that generated the private key, which may be the EST - server or the EST CA. SignedData placed within the Enveloped Data - does not need additional signing 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 + (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. Depending on + the request, 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, placed in the outermost + container, is signed by the party that generated the private key, + which may be the EST server or the EST CA. SignedData placed within + the Enveloped Data does not need additional signing 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. The symmetric key itself 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. + key is encrypted with a symmetric key. The symmetric key itself is + encrypted by the client defined (in the CSR) asymmetric 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 is needed between the client and a server. Such cases could include architectures where an entity between the client and the CA terminates the DTLS connection @@ -1028,21 +1010,21 @@ 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". 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 9.1. + Content-Format to HTTP Content-Type is defined in Section 9.1. Additionally, a conversion from CBOR major type 2 to Base64 encoding MUST take place at the Registrar. If CMS end-to-end encryption is employed for the private key, the encrypted CMS EnvelopedData blob MUST be converted at the Registrar to binary CBOR type 2 downstream 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 @@ -1056,34 +1038,34 @@ HTTP Registrar MUST reassemble the BLOCKs before translating the binary content to Base64, and consecutively relay the message upstream. The EST-coaps-to-HTTP Registrar MUST support resource discovery according to the rules in Section 5.1. 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 setting of the CoAP parameter values may have - consequence for the setting of the EST parameter values. - - It is recommended, based on experiments, + 4.7 and 4.8 of [RFC7252]. EST does not impose any unique values on + the CoAP parameters in [RFC7252], but the setting of the CoAP + parameter values may have consequence for the setting of the EST + parameter values. - 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. When a change in a server parameter - has taken place, the parameter values in the communicating endpoints - MUST be adjusted as necessary. + Implementations should 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. When + a change in a server parameter has taken place, the parameter values + in the communicating endpoints MUST be adjusted as necessary. + Examples of how parameters could be adjusted include higher layer + congestion protocols, provisioning agents and configurations included + in firmware updates. Some further comments about some specific parameters, mainly from Table 2 in [RFC7252]: 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 expected to control at most one interaction with a given server, which is the default NSTART value defined in [RFC7252]. @@ -1113,21 +1095,21 @@ 9. IANA Considerations 9.1. Content-Format Registry Additions to the sub-registry "CoAP Content-Formats", within the "CoRE Parameters" registry [COREparams] are specified in Table 5. These have been registered provisionally in the IETF Review or IESG Approval range (256-9999). +------------------------------+-------+----------------------------+ - | HTTP Media-Type | ID | Reference | + | HTTP Content-Type | ID | Reference | +------------------------------+-------+----------------------------+ | application/pkcs7-mime; | 280 | [RFC7030] [I-D.ietf-lamps- | | smime-type=server-generated- | | rfc5751-bis] [ThisRFC] | | key | | | | application/pkcs7-mime; | 281 | [I-D.ietf-lamps-rfc5751-bi | | smime-type=certs-only | | s] [ThisRFC] | | application/pkcs8 | 284 | [RFC5958] [I-D.ietf-lamps- | | | | rfc5751-bis] [ThisRFC] | | application/csrattrs | 285 | [RFC7030] | | application/pkcs10 | 286 | [RFC5967] [I-D.ietf-lamps- | @@ -1160,20 +1142,36 @@ CSR attributes. o rt="ace.est.skg". This resource depicts the support of EST server-side key generation with the returned certificate in a PKCS#7 container. 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. +9.3. Well-Known URIs Registry + + A new additional reference is requested for the est URI in the Well- + Known URIs registry: + + +------+--------+---------+---------+----------+---------+----------+ + | URI | Change | Referen | Status | Related | Date Re | Date | + | Suff | Contro | ces | | Informat | gistere | Modified | + | ix | ller | | | ion | d | | + +------+--------+---------+---------+----------+---------+----------+ + | est | IETF | [RFC703 | permane | | 2013-08 | [THIS | + | | | 0] | nt | | -16 | RFC's pu | + | | | [THIS | | | | blicatio | + | | | RFC] | | | | n date] | + +------+--------+---------+---------+----------+---------+----------+ + 10. Security Considerations 10.1. 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. The other portions of the security considerations of [RFC7030] continue to apply. @@ -1184,92 +1182,87 @@ private key (that corresponds to the public key enrolled in the CSR). When server-side key generation is used, the constrained device depends on the server to generate the private key randomly, but it still needs locally generated random numbers for use in security protocols, as explained in Section 12 of [RFC7925]. Additionally, the transport of keys generated at the server is inherently risky. For those deploying server-side key generation, analysis SHOULD be done to establish whether server-side key generation increases or decreases the probability of digital identity theft. - It is important to note that sources contributing to the randomness - pool used to generate random numbers on laptops or desktop PCs are - not available on many constrained devices, such as mouse movement, - timing of keystrokes, or air turbulence on the movement of hard drive - heads, as pointed out in [PsQs]. Other sources have to be used or - dedicated hardware has to be added. Selecting hardware for an IoT - device that is capable of producing high-quality random numbers is - therefore important [RSAfact]. - - It is also RECOMMENDED that the Implicit Trust Anchor database used - for EST server authentication is carefully managed to reduce the - chance of a third-party CA with poor certification practices - jeopardizing authentication. + It is important to note that, as pointed out in [PsQs], sources + contributing to the randomness pool used to generate random numbers + on laptops or desktop PCs, such as mouse movement, timing of + keystrokes, or air turbulence on the movement of hard drive heads, + are not available on many constrained devices. Other sources have to + be used or dedicated hardware has to be added. Selecting hardware + for an IoT device that is capable of producing high-quality random + numbers is therefore important [RSAfact]. - 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 - /crts, a client MAY choose to keep the connection authenticated by - the Implicit TA open for efficiency reasons (Section 4). A client - that interleaves EST-coaps /crts request with other requests in the - same DTLS connection SHOULD revalidate the server certificate chain - against the updated Explicit TA from the /crts 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. + As discussed in Section 6 of [RFC7030], it is "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 successfuly receiving the + Distribution of CA certificates response (Section 4.1.3) limits any + risk to the first TLS exchange". Alternatively, in a case where a + /sen request immediately follows a /crts, a client MAY choose to keep + the connection authenticated by the Implicit TA open for efficiency + reasons (Section 4). A client that interleaves EST-coaps /crts + request with other requests in the same DTLS connection SHOULD + revalidate the server certificate chain against the updated Explicit + TA from the /crts 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 expected to live as long as the device itself (Section 4). In such occasions, checking the certificate revocation status or authorizing - the client using another method is important for the server to ensure - that the client is to be trusted. + the client using another method is important for the server to raise + its confidence that the client can be trusted. In accordance with [RFC7030], TLS cipher suites that include "_EXPORT_" and "_DES_" in their names MUST NOT be used. More - information about recommendations of TLS and DTLS are included in + recommendations for secure use of TLS and DTLS are included in [BCP195]. As described in CMC, Section 6.7 of [RFC5272], "For keys that can be used as signature keys, signing the certification request with the 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 the TLS proof-of-identity. This implies but does not prove that only the authenticated client currently has access to the private key. What's more, CMC PoP linking uses tls-unique as it is defined in [RFC5929]. The 3SHAKE attack [tripleshake] poses a risk by allowing a man-in-the-middle to leverage session resumption and renegotiation to inject himself between a client and server even when channel - binding is in use. - - Implementers should use the Extended Master Secret Extension in DTLS - [RFC7627] to prevent such attacks. 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]) value in - place of the tls-unique value in the CSR. Such mechanism has not - been standardized yet. Adopting a channel binding value generated - from an exporter would break backwards compatibility for an RA that - proxies through to a classic EST server. Thus, in this specification - we still depend on the tls-unique mechanism defined in [RFC5929], - especially since a 3SHAKE attack does not expose messages exchanged - with EST-coaps. + binding is in use. Implementers should use the Extended Master + Secret Extension in DTLS [RFC7627] to prevent such attacks. 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]) value in place of the tls-unique value in the CSR. Such + mechanism has not been standardized yet. Adopting a channel binding + value generated from an exporter would break backwards compatibility + for an RA that proxies through to a classic EST server. Thus, in + this specification we still depend on the tls-unique mechanism + defined in [RFC5929], especially since a 3SHAKE attack does not + expose messages exchanged with EST-coaps. Interpreters of ASN.1 structures should be aware of the use of invalid ASN.1 length fields and should take appropriate measures to guard against buffer overflows, stack overruns in particular, and malicious content in general. 10.2. HTTPS-CoAPS Registrar considerations The Registrar proposed in Section 6 must be deployed with care, and only when direct client-server connections are not possible. When @@ -1299,24 +1292,23 @@ 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 when it is generating the private key. 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. + implementation that started in 2015. Sandeep Kumar kick-started this + specification and was instrumental in drawing attention to the + importance of the subject. 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, @@ -1578,25 +1570,23 @@ Option (Uri-Path) Option Delta = 0x0 (option# 11+0=11) Option Length = 0x4 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 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. + As specified in Section 5.10.1 of [RFC7252], the Uri-Host and Uri- + Port Options can be omitted if they coincide with the transport + protocol destination address and port respectively. 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)