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Internet LAMPS Working Group Internet-Draft 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. 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. As a result of some of the implementation challenges, it came to light that the particular way of that RFC7030 (EST) says to use the CSR attributes was not universally agreed upon. This document therefore also provides a new straightforward approach: using a template for CSR contents that may be partially filled in by the server. This also allows an EST server to specify a subject Distinguished Name (DN).

Introduction 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. 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 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 id-ExtensionReq, which has the value 1.2.840.113549.1.9.14. Note that is the same as pkcs-9-at-extensionRequest defined in PKCS#9 . 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 particular extnID. With this understanding, the needs of and are satisfied with no change to the bits on the wire.

Use of CSR templates Alternatively to the unstructured inclusion of CSR attributes specified in with its limitations and ambiguities, describes an approach using a CSR template. An entire CSR object is returned with various fields filled out, and other fields waiting to be filled in. In that approach, a pKCS7PDU attribute includes a Full PKI Data content type and that in turn includes a CSR or CRMF formatted request (for details see Sections 5 or 9, respectively).
One 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. A similar method has been defined in CMP Updates and the Lightweight CMP profile , using a CSR template as defined for CRMF . Like the approach mentioned before, this method does not properly deal with absent RDNs (encoding them as empty strings), absent 'subjectPublicKey' fields (encoding them as empty BIT STRING), and absent X.509 extension values (encoding them as empty OCTET STRING), which may cause issues with strict ASN.1 parsing and decoding. We avoid these drawbacks as follows. This specification defines a new Certificate Request Information Template attribute for CsrAttrs (as given in ) that is essentially a partially filled in PKCS#10 CSR minus the signature wrapper: contains all detail. The CertificationRequestInfoTemplate closely resembles the CertificationRequestInfo from : with the following differences.

• The 'subject' field has been made OPTIONAL. It MUST be present if the server places any requirements on the RDNs of the subject name; otherwise it MUST be absent.
• RelativeDistinguishedNames (RDNs) in the 'subject' fields are allowed to have no value, which has been achieved by adding OPTIONAL to the 'value' field of SingleAttributeTemplate. If the client is expected to provide an RDN of a certain type such as commonName, the respective RDN MUST be present in the 'subject' field; otherwise it MUST be absent. If the RDN value is present, this means that the client is required to use the given value for the RDN, otherwise the client is expected to fill in the value.

• The 'subjectPKInfo' field has been made OPTIONAL. The field MUST be absent if the server places no requirements on the key. Otherwise it MUST be present, and the 'algorithm' field specifies the type of the key pair the client is expected to use.
• The 'subjectPublicKey' field contained in SubjectPublicKeyInfoTemplate has been made OPTIONAL because usually it is not needed. In case the server requires use of an RSA key and needs to specify its size, the field MUST be present and contain a dummy public key value of the desired RSA modulus length. Otherwise, the subjectPublicKey MUST be absent.

• A new OID id-aa-extensionReqTemplate and the related ExtensionTemplate structure is defined where the 'extnValue' field has been made OPTIONAL. This is only needed to enable specifying partial extensions with values to be filled in by the client; otherwise the id-ExtensionReq OID and the respective value of type ExtensionReq MUST be used.
  

For each extension of type Extension or ExtensionTemplate provided by the server, the client is expected to include an extension of the type given by the extnID. If the 'critical' field is present, the client is expected to use the given value. If the 'extnValue' is present (which is always the case when type Extension is used), the client is required to use the given extension value. Otherwise it is expected to fill in the extension value.
If the 'subjectAltName' extension contains the 'directoryName' choice containing the NULL-DN (i.e., an empty sequence of RDNs) or the 'iPAddress' choice with an empty OCTET STRING, this means that the client is expected to fill in the respective GeneralName value. The 'version' field of the CertificationRequestInfoTemplate MUST contain v1 (0). The 'attributes' field MUST NOT contain multiple id-aa-extensionReqTemplate attributes and MUST NOT contain both id-ExtensionReq and id-aa-extensionReqTemplate attributes. The 'values' field of an id-aa-extensionReqTemplate attribute MUST contain a set with exactly one element, and this element MUST be of type ExtensionTemplate. 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 names with given values "myDept" and "myGroup",
• the 'publicKey' field contains an Elliptic Curve Cryptography (ECC) key on curve secp256r1,
• the 'subjectAltName' extension with DNS name "www.myServer.com" and an empty IP address to be filled in,
• the 'keyUsage' extension marked critical with the value digitalSignature and keyAgreement, and
• the 'extKeyUsage' extension with value 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 unstructured list of 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 CertificationRequestInfoTemplate element.

Examples using the original RFC 7030 approach 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.

Require an RFC8994/ACP subjectAltName with specific otherName A single subjectAltName extension is specified in a single CsrAttrs 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. 0 104: SEQUENCE { <30 66> 2 102: SEQUENCE { <06 09> 4 9: OBJECT IDENTIFIER extensionRequest (1 2 840 113549 1 9 14) : (PKCS #9 via CRMF) <31 59> 15 89: SET { <30 57> 17 87: SEQUENCE { <30 55> 19 85: SEQUENCE { <06 03> 21 3: OBJECT IDENTIFIER subjectAltName (2 5 29 17) : (X.509 extension) <01 01> 26 1: BOOLEAN TRUE <04 4B> 29 75: OCTET STRING, encapsulates { <30 49> 31 73: SEQUENCE { 33 71: [0] { <06 08> 35 8: OBJECT IDENTIFIER '1 3 6 1 5 5 7 8 10' 45 59: [0] { <16 39> 47 57: IA5String : 'rfc8994+fd739fc23c3440112233445500000000+@acp.ex' : 'ample.com' : } : } : } : } : } : } : } : } : } ]]>

RFC7030 original example In this example, taken from , a few different attributes are included. The original encoding of the 'macAddress' part in the example is NOT CORRECT. It was not aligned with the definition of the Extension Request attribute as specified in . The revised encoding given here does not use an Extension Request attribute because the MAC Address is not an X.509 certificate extension by itself and because the server provides its OID without a value, which is not allowed syntactically within an Extension structure.

Base64 encoded example The Base64:

ASN.1 DUMP output The CsrAttrs structure contains:

1. The challengePassword attribute is included to indicate that the CSR should include this value.
2. An ecPublicKey OID is provided with the value secp384r1 to indicate what kind of public key should be submitted.
3. The macAddress OID 1.3.6.1.1.1.1.22 is included to indicate that the CSR is expected to include (in a subjectDirectoryAttributes extension) a MAC address value.
4. The ecdsaWithSHA384 OID is included to indicate what kind of hash is expected to be used for the self-signature in the PKCS#10 CSR.

0 50: 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) : } : } <06 07> 33 7: OBJECT IDENTIFIER '1 3 6 1 1 1 1 22' <06 08> 42 8: OBJECT IDENTIFIER ecdsaWithSHA384 (1 2 840 10045 4 3 3) : (ANSI X9.62 ECDSA algorithm with SHA384) : } ]]>

Require 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 The CsrAttrs structure contains:

1. The challengePassword attribute is included to indicate that the CSR should include this value.
2. An ecPublicKey OID is provided with the value secp521r1 to indicate what kind of public key should be submitted.
3. An extensionRequest container with a subjectAltName value containing the name potato@example.com
4. The ecdsaWithSHA512 OID is included to indicate the SHA-512 hash is expected to be used for the self-signature in the PKCS#10 CSR.

0 69: 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) : } : } <06 09> 33 9: OBJECT IDENTIFIER friendlyName (for PKCS #12) (1 2 840 113549 1 9 20) : (PKCS #9 via PKCS #12) <06 0A> 44 10: OBJECT IDENTIFIER '0 9 2342 19200300 100 1 5' <06 03> 56 3: OBJECT IDENTIFIER serialNumber (2 5 4 5) : (X.520 DN component) <06 08> 61 8: OBJECT IDENTIFIER ecdsaWithSHA512 (1 2 840 10045 4 3 4) : (ANSI X9.62 ECDSA algorithm with SHA512) : } ]]>

Require a public key of a specific size The CSR requires a public key of a specific size (Example harkins01)

Base64 encoded example The Base64:

ASN.1 DUMP output Provide a CSR with an RSA key that's 4096 bits and use SHA256 as the hash algorithm within the signature. 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. (Example harkins02)

Base64 encoded example The Base64:

ASN.1 DUMP output Provide a CSR with an ECC key from p384, include your serial number, and use SHA384 as the hash algorithm within the signature. 0 46: 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) : } : } <06 03> 33 3: OBJECT IDENTIFIER serialNumber (2 5 4 5) : (X.520 DN component) <06 08> 38 8: OBJECT IDENTIFIER ecdsaWithSHA384 (1 2 840 10045 4 3 3) : (ANSI X9.62 ECDSA algorithm with SHA384) : } ]]>

Require specific extensions and attributes The CSR is required to have an EC key, to include a serial number, a friendly name, favorite drink [OID 0.9.2342.19200300.100.1.5], and use SHA512 as the hash algorithm within the signature. (Example harkins03)

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 hash it with SHA512. 0 69: 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) : } : } <06 09> 33 9: OBJECT IDENTIFIER friendlyName (for PKCS #12) (1 2 840 113549 1 9 20) : (PKCS #9 via PKCS #12) <06 0A> 44 10: OBJECT IDENTIFIER '0 9 2342 19200300 100 1 5' <06 03> 56 3: OBJECT IDENTIFIER serialNumber (2 5 4 5) : (X.520 DN component) <06 08> 61 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
• 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 (id-aa-csrinfo) attribute; see
• One (TBD3) SMI Security for S/MIME Attributes (1.2.840.113549.1.9.16.2) registry for the extension request template (id-aa-extensionReqTemplate) attribute; see Appendix A

Acknowledgments 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. Russ Housley did many reviews of the ASN.1 and suggested many fixes. Deb Cooley did the usual Area Director Review.

References Normative References 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. 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 This memo represents a republication of PKCS #9 v2.0 from RSA Laboratories' Public-Key Cryptography Standards (PKCS) series, and change control is retained within the PKCS process. The body of this document, except for the security considerations section, is taken directly from that specification. This memo provides information for the Internet community. 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 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 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. 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. 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. 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. n.d. n.d. ITU-T

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 .