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Internet LAMPS Working Group Internet-Draft The Enrollment over Secure Transport (EST, RFC7030) is ambiguous in its specification of the CSR Attributes Response. This has resulted in implementation challenges and implementor confusion. This document updates RFC7030 (EST) and clarifies how the CSR Attributes Response can be used by an EST server to specify both CSR attribute OIDs and also CSR attribute values, in particular X.509 extension values, that the server expects the client to include in subsequent CSR request. Moreover, it provides new convenient and straightforward approach: using a template for CSR contents that may be partially filled in by the server. This also allows specifying a subject Distinguished Name (DN).

Introduction Enrollment over Secure Transport (EST) has been used in a wide variety of applications. In particular, and describe a way to use it in order to build out an autonomic control plane (ACP) . The ACP requires that each node be given a very specific subjectAltName. In the ACP specification, the solution was for the EST server to use section 2.6 of to convey to the EST client the actual subjectAltName that will end up in its certificate. As a result of some implementation challenges, it came to light that this particular way of using the CSR attributes was not universally agreed upon, and it was suggested that it went contrary to section 2.6. Section 2.6 says that the CSR attributes "can provide additional descriptive information that the EST server cannot access itself". This is extended to describe how the EST server can provide values that it demands to use. After significant discussion, it has been determined that specification is sufficiently difficult to read and ambiguous to interpret that clarification is needed. This document motivates the different use cases, and provides additional worked out examples. Also, section 4.5.2 is extended to clarify the use of the existing ASN.1 syntax . This covers all uses and is fully backward compatible with existing use.

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 when, and only when, they appear in all capitals, as shown here.

CSR Attributes Handling

Extensions to RFC 7030 section 2.6. Replace the second paragraph with the following text:

Extensions to RFC 7030 section 4.5.2. The ASN.1 syntax for CSR Attributes as defined in EST section 4.5.2 is as follows: This remains unchanged, such that bits-on-the-wire compatibility is maintained. Key parts that were unclear were which OID to use in the 'type' field and that the 'values' field can contain an entire sequence of X.509 extensions. The OID to use for such attributes in the 'type' field MUST be extensionRequest, which has the numerical value 1.2.840.113549.1.9.14. There MUST be only one such Attribute. The 'values' field of this attribute MUST contain a set with exactly one element, and this element MUST be of type Extensions, as per : An Extension comprises the OID of the specific X.509 extension (extnID), optionally the 'critical' bit, and the extension value (extnValue). An Extensions structure, which is a sequence of elements of type Extension, MUST NOT include more than one element with a particiular extnID. With this understanding, the needs of and are satisfied with no change to the bits on the wire.

Use of CSR templates describes a mechanism that avoids the piecemeal inclusion of attributes that documented. Instead, an entire CSR object is returned with various fields filled out, and other fields waiting to be filled in, in a pKCS7PDU attribute. In that approach, the pKCS7PDU attribute includes a Full PKI Data content type and that in turn includes a CSR or CRMF formatted request; see Sections 5 and 9, respectively. The drawback to that approach, particularly for the CSR, is that some useless fields have to be included; specifically, the signature field on the CSR is faked with an empty bit string. We avoid this drawback as follows. This specification defines the Certificate Request Information Template attribute for CsrAttrs, see , that is essentially a partially filled in PKCS#10 CSR minus the signature wrapper as follows: contains all detail. Note that the CertificationRequestInfoTemplate closely resembles the CertificationRequestInfo from : with the following differences.

• The subject field is made OPTIONAL to cover the case the server does not provide any requrements on the subject name and its RDNs.
• RelativeDistinguishedNames (RDNs) in the subject fields are allowed to be empty, which is achieved by adding OPTIONAL to the value field of AttributeTypeAndValueTemplate. This means that the client is required to provide an RDN of the given type and fill in its value.

• The subjectPKInfo field is made OPTIONAL, such that the server can leave it out in case there are no requirements on the key.
  Otherwise the server specifies the algorithm of the key, i.e., the key type, in the algorithm field. The subjectPublicKey field contained in SubjectPublicKeyInfoTemplate is made OPTIONAL because usually it is left out, but in case the server needs to specify the size of an RSA key, the field is used to provide a dummy public key value of the desired RSA modulus length.

• A new OID pkcs-9-at-extensionRequestTemplate and the related ExtensionTemplate structure is defind where the extnValue field is optional. If the field is absent this means that the client is required to provide an X.509 extension with the given extnID and potentially the critical flag and fill in its value.

A similar method has been defined in CMP Updates and the Lightweight CMP profile , using a CSR template as defined for CRMF . That method does not properly deal with empty RDNs (encoding them as empty strings), absent subjectPublicKey fields (encoding them as empty BIT STRING), and empty X.509v3 extension values (encoding them as empty OCTET STRING), which may cause issues with strict ASN.1 parsing and decoding. The version code MUST be v1 (0). If the subjectPKInfo field is present, it indicates the type of the key pair the client is expected to use, where the subjectPublicKey MUST NOT be given except if the algorithm indicates RSA. The attributes field MUST NOT contain multiple extensionRequestTemplate attributes and MUST NOT contain both extensionRequest and extensionRequestTemplate attributes. Suppose the server requires that the CSR will contain:

• the subject field with a common name to be filled in by the EE and two organizational unit fields with given values "myDept" and "myGroup",
• the publicKey field contains an Elliptic Curve Cryptography (ECC) key on curve secp256r1,
• the subjectAltName X.509 extension with DNS name "www.myServer.com" and an IP address to be filled in,
• the keyUsage extension marked critical with the value digitalSignature and keyAgreement, and
• the extKeyUsage extension with values to be filled in by the EE.

Then the CertificationRequestInfo structure constructed by the server will be as follows:

Co-existence with existing implementations Legacy servers MAY continue to use the style piecemeal attribute/value pairs, and MAY also include the template style described in {#csrtemplate}. Clients which understand both MUST use the template only, and ignore all other CSRattrs elements. Older clients will ignore the new CertificateRequestInfoTemplate element.

Examples Each example has a high-level (English) explanation of what is expected. Some mapping back to the Attribute and Extension definitions above are included. The base64 DER encoding is then shown. The output of "dumpasn1" is then provided to detail what the contents are.

RFC8994/ACP subjectAltName with specific otherName A single subjectAltName extension is specified in a single Extension attribute. This is what might be created by an Registrar that is asking for AcpNodeName format otherNames.

Base64 encoded example The Base64:

ASN.1 DUMP output There is a single subjectAltName Extension with an Attribute with Extension type. 0 100: SEQUENCE { <30 62> 2 98: SEQUENCE { <06 09> 4 9: OBJECT IDENTIFIER extensionRequest (1 2 840 113549 1 9 14) : (PKCS #9 via CRMF) <31 55> 15 85: SET { <30 53> 17 83: SEQUENCE { <06 03> 19 3: OBJECT IDENTIFIER subjectAltName (2 5 29 17) : (X.509 extension) <01 01> 24 1: BOOLEAN TRUE <04 49> 27 73: OCTET STRING : A0 47 30 45 06 08 2B 06 .G0E..+. : 01 05 05 07 08 0A 0C 39 .......9 : 72 66 63 38 39 39 34 2B rfc8994+ : 66 64 37 33 39 66 63 32 fd739fc2 : 33 63 33 34 34 30 31 31 3c344011 : 32 32 33 33 34 34 35 35 22334455 : 30 30 30 30 30 30 30 30 00000000 : 2B 40 61 63 70 2E 65 78 +@acp.ex : 61 6D 70 6C 65 2E 63 6F ample.co : 6D m : } : } : } : } ]]>

RFC7030 original example In this example, taken from , a few different attributes are included.

Base64 encoded example The Base64:

ASN.1 DUMP output

1. The challengePassword attribute is included to indicate that the CSR should include this value.
2. An ecPublicKey attribute is provided with the value secp384r1 to indicate what kind of key should be submitted.
3. An extensionRequest container with an OID 1.3.6.1.1.1.1.22 (macAddress), but without a value, to indicate that the CSR should include an X.509v3 extension with this value.
4. The ecdsaWithSHA384 OID is included to indicate what kind of hash is expected to be used for the self-signature of the PCKS#10 CSR structure.

0 65: SEQUENCE { <06 09> 2 9: OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7) : (PKCS #9) <30 12> 13 18: SEQUENCE { <06 07> 15 7: OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1) : (ANSI X9.62 public key type) <31 07> 24 7: SET { <06 05> 26 5: OBJECT IDENTIFIER secp384r1 (1 3 132 0 34) : (SECG (Certicom) named elliptic curve) : } : } <30 16> 33 22: SEQUENCE { <06 09> 35 9: OBJECT IDENTIFIER extensionRequest (1 2 840 113549 1 9 14) : (PKCS #9 via CRMF) <31 09> 46 9: SET { <06 07> 48 7: OBJECT IDENTIFIER '1 3 6 1 1 1 1 22' : } : } <06 08> 57 8: OBJECT IDENTIFIER ecdsaWithSHA384 (1 2 840 10045 4 3 3) : (ANSI X9.62 ECDSA algorithm with SHA384) : } ]]>

EST server requires a specific subjectAltName extension This example is the same as the previous one except that instead of the OID for a macAddress, a subjectAltName is specified as the only Extension element.

Base64 encoded example The Base64:

ASN.1 DUMP output

1. The challengePassword attribute is included to indicate that the CSR should include this value.
2. An ecPublicKey attribute is provided with the value secp384r1 to indicate what kind of key should be submitted.
3. An extensionRequest container with a subjectAltName value containing the name potato@example.com
4. The ecdsaWithSHA384 OID is included to indicate what kind of hash is expected to be used for the self-signature of the PCKS#10 CSR structure.

0 102: SEQUENCE { <06 09> 2 9: OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7) : (PKCS #9) <30 12> 13 18: SEQUENCE { <06 07> 15 7: OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1) : (ANSI X9.62 public key type) <31 07> 24 7: SET { <06 05> 26 5: OBJECT IDENTIFIER secp384r1 (1 3 132 0 34) : (SECG (Certicom) named elliptic curve) : } : } <30 3B> 33 59: SEQUENCE { <06 09> 35 9: OBJECT IDENTIFIER extensionRequest (1 2 840 113549 1 9 14) : (PKCS #9 via CRMF) <31 2E> 46 46: SET { <30 2C> 48 44: SEQUENCE { <06 03> 50 3: OBJECT IDENTIFIER subjectAltName (2 5 29 17) : (X.509 extension) <01 01> 55 1: BOOLEAN TRUE <04 22> 58 34: OCTET STRING : A0 20 30 1E 06 08 2B 06 . 0...+. : 01 05 05 07 08 0A 0C 12 ........ : 70 6F 74 61 74 6F 40 65 potato@e : 78 61 6D 70 6C 65 2E 63 xample.c : 6F 6D om : } : } : } <06 08> 94 8: OBJECT IDENTIFIER ecdsaWithSHA384 (1 2 840 10045 4 3 3) : (ANSI X9.62 ECDSA algorithm with SHA384) : } ]]>

Require a public key of a specific size The CSR requires a public key of a specific size

Base64 encoded example The Base64:

ASN.1 DUMP output

1. Provide a CSR with an RSA key that's 4096 bits and sign it with sha256

0 41: SEQUENCE { <06 09> 2 9: OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7) : (PKCS #9) <30 11> 13 17: SEQUENCE { <06 09> 15 9: OBJECT IDENTIFIER rsaEncryption (1 2 840 113549 1 1 1) : (PKCS #1) <31 04> 26 4: SET { <02 02> 28 2: INTEGER 4096 : } : } <06 09> 32 9: OBJECT IDENTIFIER sha256WithRSAEncryption (1 2 840 113549 1 1 11) : (PKCS #1) : } ]]>

Require a public key of a specific curve The CSR requires a public key with a specific curve

Base64 encoded example The Base64:

ASN.1 DUMP output Provide a CSR with an ECC key from p384, include your serial number, and sign it with sha384. 0 61: SEQUENCE { <06 09> 2 9: OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7) : (PKCS #9) <30 12> 13 18: SEQUENCE { <06 07> 15 7: OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1) : (ANSI X9.62 public key type) <31 07> 24 7: SET { <06 05> 26 5: OBJECT IDENTIFIER secp384r1 (1 3 132 0 34) : (SECG (Certicom) named elliptic curve) : } : } <30 12> 33 18: SEQUENCE { <06 09> 35 9: OBJECT IDENTIFIER extensionRequest (1 2 840 113549 1 9 14) : (PKCS #9 via CRMF) <31 05> 46 5: SET { <06 03> 48 3: OBJECT IDENTIFIER serialNumber (2 5 4 5) : (X.520 DN component) : } : } <06 08> 53 8: OBJECT IDENTIFIER ecdsaWithSHA384 (1 2 840 10045 4 3 3) : (ANSI X9.62 ECDSA algorithm with SHA384) : } ]]>

Require a specific extension The CSR is required to have an EC key, to include a serial number, a friendly name, favorite drink, and be signed with SHA512.

Base64 encoded example The Base64:

ASN.1 DUMP output Provide a CSR with an EC key from sha521, include your serial number, friendly name, and favorite drink, and sign it with sha512 0 84: SEQUENCE { <06 09> 2 9: OBJECT IDENTIFIER challengePassword (1 2 840 113549 1 9 7) : (PKCS #9) <30 12> 13 18: SEQUENCE { <06 07> 15 7: OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1) : (ANSI X9.62 public key type) <31 07> 24 7: SET { <06 05> 26 5: OBJECT IDENTIFIER secp521r1 (1 3 132 0 35) : (SECG (Certicom) named elliptic curve) : } : } <30 29> 33 41: SEQUENCE { <06 09> 35 9: OBJECT IDENTIFIER extensionRequest (1 2 840 113549 1 9 14) : (PKCS #9 via CRMF) <31 1C> 46 28: SET { <06 03> 48 3: OBJECT IDENTIFIER serialNumber (2 5 4 5) : (X.520 DN component) <06 09> 53 9: OBJECT IDENTIFIER : friendlyName (for PKCS #12) (1 2 840 113549 1 9 20) : (PKCS #9 via PKCS #12) <06 0A> 64 10: OBJECT IDENTIFIER '0 9 2342 19200300 100 1 5' : } : } <06 08> 76 8: OBJECT IDENTIFIER ecdsaWithSHA512 (1 2 840 10045 4 3 4) : (ANSI X9.62 ECDSA algorithm with SHA512) : } ]]>

Security Considerations The security considerations from EST section 6 are unchanged.

Identity and Privacy Considerations An EST server may use this mechanism to instruct the EST client about the identities it should include in the CSR it sends as part of enrollment. The client may only be aware of its IDevID Subject, which includes a manufacturer serial number. The EST server can use this mechanism to tell the client to include a specific fully qualified domain name in the CSR in order to complete domain ownership proofs required by the CA. Additionally, the EST server may deem the manufacturer serial number in an IDevID as personally identifiable information, and may want to specify a new random opaque identifier that the pledge should use in its CSR. This may be desirable if the CA and EST server have different operators.

IANA Considerations IANA is asked to allocate two new Object Identifiers:

• One (TBD1) from the SMI Security for S/MIME Module Identifier (1.2.840.113549.1.9.16.0) registry for the ASN.1 module: id-mod-critemplate; see , and
• One (TBD2) from the SMI Security for S/MIME Attributes (1.2.840.113549.1.9.16.2) registry for the Certification Request Information Template (csrinfo) attribute; see and .
• One (TBD3) from the PKCS#9 (1 2 840 113549 1 9) registry - TODO COMPLETE THIS ITEM

Acknowledgements Corey Bonnell crafted example02 using a different tool, and this helped debug other running code. Carl Wallace provided major parts of the CertificationRequestInfoTemplate syntax declaration.

Changelog

References Normative References This document defines the base syntax for CMC, a Certificate Management protocol using the Cryptographic Message Syntax (CMS). This protocol addresses two immediate needs within the Internet Public Key Infrastructure (PKI) community: 1. The need for an interface to public key certification products and services based on CMS and PKCS #10 (Public Key Cryptography Standard), and 2. The need for a PKI enrollment protocol for encryption only keys due to algorithm or hardware design. CMC also requires the use of the transport document and the requirements usage document along with this document for a full definition. [STANDARDS-TRACK] This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK] The Cryptographic Message Syntax (CMS) format, and many associated formats, are expressed using ASN.1. The current ASN.1 modules conform to the 1988 version of ASN.1. This document updates those ASN.1 modules to conform to the 2002 version of ASN.1. There are no bits-on-the-wire changes to any of the formats; this is simply a change to the syntax. This document is not an Internet Standards Track specification; it is published for informational purposes. The Public Key Infrastructure using X.509 (PKIX) certificate format, and many associated formats, are expressed using ASN.1. The current ASN.1 modules conform to the 1988 version of ASN.1. This document updates those ASN.1 modules to conform to the 2002 version of ASN.1. There are no bits-on-the-wire changes to any of the formats; this is simply a change to the syntax. This document is not an Internet Standards Track specification; it is published for informational purposes. The Cryptographic Message Syntax (CMS) format, and many associated formats, are expressed using ASN.1. The current ASN.1 modules conform to the 1988 version of ASN.1. This document updates some auxiliary ASN.1 modules to conform to the 2008 version of ASN.1; the 1988 ASN.1 modules remain the normative version. There are no bits- on-the-wire changes to any of the formats; this is simply a change to the syntax. This document is not an Internet Standards Track specification; it is published for informational purposes. This document profiles certificate enrollment for clients using Certificate Management over CMS (CMC) messages over a secure transport. This profile, called Enrollment over Secure Transport (EST), describes a simple, yet functional, certificate management protocol targeting Public Key Infrastructure (PKI) clients that need to acquire client certificates and associated Certification Authority (CA) certificates. It also supports client-generated public/private key pairs as well as key pairs generated by the CA. Autonomic functions need a control plane to communicate, which depends on some addressing and routing. This Autonomic Control Plane should ideally be self-managing and be as independent as possible of configuration. This document defines such a plane and calls it the "Autonomic Control Plane", with the primary use as a control plane for autonomic functions. It also serves as a "virtual out-of-band channel" for Operations, Administration, and Management (OAM) communications over a network that provides automatically configured, hop-by-hop authenticated and encrypted communications via automatically configured IPv6 even when the network is not configured or is misconfigured. This document specifies automated bootstrapping of an Autonomic Control Plane. To do this, a Secure Key Infrastructure is bootstrapped. This is done using manufacturer-installed X.509 certificates, in combination with a manufacturer's authorizing service, both online and offline. We call this process the Bootstrapping Remote Secure Key Infrastructure (BRSKI) protocol. Bootstrapping a new device can occur when using a routable address and a cloud service, only link-local connectivity, or limited/disconnected networks. Support for deployment models with less stringent security requirements is included. Bootstrapping is complete when the cryptographic identity of the new key infrastructure is successfully deployed to the device. The established secure connection can be used to deploy a locally issued certificate to the device as well. ITU-T ITU-T In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References Operations, Administration, and Maintenance (OAM), as per BCP 161, for data networks is often subject to the problem of circular dependencies when relying on connectivity provided by the network to be managed for the OAM purposes. Provisioning while bringing up devices and networks tends to be more difficult to automate than service provisioning later on. Changes in core network functions impacting reachability cannot be automated because of ongoing connectivity requirements for the OAM equipment itself, and widely used OAM protocols are not secure enough to be carried across the network without security concerns. This document describes how to integrate OAM processes with an autonomic control plane in order to provide stable and secure connectivity for those OAM processes. This connectivity is not subject to the aforementioned circular dependencies. This document describes the Certificate Request Message Format (CRMF) syntax and semantics. This syntax is used to convey a request for a certificate to a Certification Authority (CA), possibly via a Registration Authority (RA), for the purposes of X.509 certificate production. The request will typically include a public key and the associated registration information. This document does not define a certificate request protocol. [STANDARDS-TRACK] This document contains a set of updates to the syntax of Certificate Management Protocol (CMP) version 2 and its HTTP transfer mechanism. This document updates RFCs 4210, 5912, and 6712. The aspects of CMP updated in this document are using EnvelopedData instead of EncryptedValue, clarifying the handling of p10cr messages, improving the crypto agility, as well as adding new general message types, extended key usages to identify certificates for use with CMP, and well-known URI path segments. CMP version 3 is introduced to enable signaling support of EnvelopedData instead of EncryptedValue and signal the use of an explicit hash AlgorithmIdentifier in certConf messages, as far as needed. This document aims at simple, interoperable, and automated PKI management operations covering typical use cases of industrial and Internet of Things (IoT) scenarios. This is achieved by profiling the Certificate Management Protocol (CMP), the related Certificate Request Message Format (CRMF), and transfer based on HTTP or Constrained Application Protocol (CoAP) in a succinct but sufficiently detailed and self-contained way. To make secure certificate management for simple scenarios and constrained devices as lightweight as possible, only the most crucial types of operations and options are specified as mandatory. More specialized or complex use cases are supported with optional features. The EST (Enrollment over Secure Transport) protocol defines the Well-Known URI (Uniform Resource Identifier) -- /.well-known/est -- along with a number of other path components that clients use for PKI (Public Key Infrastructure) services, namely certificate enrollment (e.g., /simpleenroll). This document defines a number of other PKI services as additional path components -- specifically, firmware and trust anchors as well as symmetric, asymmetric, and encrypted keys. This document also specifies the PAL (Package Availability List), which is an XML (Extensible Markup Language) file or JSON (JavaScript Object Notation) object that clients use to retrieve packages available and authorized for them. This document extends the EST server path components to provide these additional services.

ASN.1 Module This appendix provides an ASN.1 module for the Certification Request Information Template attribute, and it follows the conventions established in , , and .