RFC 9908
Clarification and Enhancement of the CSR Attributes Definition in RFC 7030
RFC 9908: Clarification and Enhancement of the CSR Attributes Definition in RFC 7030 ✨
okay bestie, let's get into this one 💖 This is an Internet Standards Track document from the IETF, dated January 2026, and it's all about how EST servers tell clients what goes into their certificate signing requests 🎀
The authors are M. Richardson (Ed.) from Sandelman Software Works, O. Friel from Cisco, D. von Oheimb from Siemens, and D. Harkins from The Industrial Lounge 🫶
It updates RFC 7030 (the EST spec) and RFC 9148 (EST over CoAP) 🌸 It doesn't obsolete anything, and its ISSN is 2070-1721 💜
Okay, the big picture: RFC 7030 has a CSR Attributes Response that people kept reading differently 😭 Like, there was no universal understanding of what was being specified, so implementers were confused 💀 This doc fixes the encoding rules and adds a new, simpler approach where the server hands over a template for the CSR that's partially filled in. It also lets the server specify a subject Distinguished Name (DN) 🍓
Status of This Memo ✨
This is an Internet Standards Track document 🦋
It's a product of the Internet Engineering Task Force (IETF) and represents the consensus of the IETF community 👑 It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). More info on Internet Standards is in Section 2 of RFC 7841 💅
You can find the current status, errata, and feedback info at https://www.rfc-editor.org/info/rfc9908 🌈
Copyright Notice ✨
Copyright (c) 2026 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. Please read those carefully, because they spell out your rights and restrictions 🫶 Code Components pulled from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come without warranty as described in the Revised BSD License 🔥
Table of Contents 🧚
- Introduction
- Terminology
- CSR Attributes Handling
- Coexistence with Existing Implementations
- Examples Using the Original Approach in RFC 7030
- 5.1. Require an RFC 8994 / ACP subjectAltName with Specific otherName
- 5.1.1. Base64-Encoded Example
- 5.1.2. ASN.1 DUMP Output
- 5.2. Original Example in RFC 7030
- 5.2.1. Base64-Encoded Example
- 5.2.2. ASN.1 DUMP Output
- 5.3. Require a Specific subjectAltName Extension
- 5.3.1. Base64-Encoded Example
- 5.3.2. ASN.1 DUMP Output
- 5.4. Require a Public Key of a Specific Size
- 5.4.1. Base64-Encoded Example
- 5.4.2. ASN.1 DUMP Output
- 5.5. Require a Public Key of a Specific Curve
- 5.5.1. Base64-Encoded Example
- 5.5.2. ASN.1 DUMP Output
- 5.6. Require Specific Extensions and Attributes
- 5.6.1. Base64-Encoded Example
- 5.6.2. ASN.1 DUMP Output
- 5.1. Require an RFC 8994 / ACP subjectAltName with Specific otherName
- Security Considerations
- 6.1. Identity and Privacy Considerations
- IANA Considerations
- References
- 8.1. Normative References
- 8.2. Informative References Appendix A. ASN.1 Module Acknowledgments Authors' Addresses
1. Introduction 🎀
This doc updates RFC 7030 and clarifies how an EST server can use the CSR Attributes Response to specify both CSR attribute OIDs and CSR attribute values 💅 The big thing is that the server needs to be able to say "put this X.509 extension value in your CSR," because the client is supposed to include it in the next CSR 🫶
"Enrollment over Secure Transport" [RFC7030] is used in tons of applications 🌈 [RFC8994] and [RFC8995] show how to use it to build an Autonomic Control Plane (ACP) [RFC8368] 🦋
When bootstrapping the ACP, every node has to be given a very specific subjectAltName 😭 In [RFC8994], the ACP spec says the EST server uses the CSR Attributes ("/csrattrs") Request (specified in [RFC7030], Section 2.6) to send the real subjectAltName to the EST client, which then goes into its CSR and ends up in its End Entity (EE) certificate 🧚
Here's the tea ☕ Because of some implementation challenges, it came out that this way of using CSR Attributes wasn't universally agreed on, and people suggested it went against [RFC7030], Section 2.6 💀
[RFC7030], Section 2.6 says the CSR Attributes "can provide additional descriptive information that the EST server cannot access itself". This doc extends that so the EST server can also provide values it demands be used 🔥
After a lot of discussion, it was decided that Section 4.5 of [RFC7030] is hard to read and ambiguous to interpret, so it needs clarifying 🙈 Also, [RFC7030], Section 4.5.2 is extended to clarify the use of the existing ASN.1 syntax [X.680] [X.690] ✨
This covers all uses and is fully backward compatible with existing use, including the needs of [RFC8994] and [RFC8995] 💖
2. Terminology 💜
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here 🌸
3. CSR Attributes Handling 🦋
3.1. Extensions to RFC 7030, Section 2.6 ✨
This doc replaces the second paragraph in Section 2.6 of [RFC7030] with the following text 💅
These attributes can provide additional information that the EST server cannot access itself, such as the Media Access Control (MAC) address of an interface of the EST client. The EST server can also provide concrete values that it tells the client to include in the CSR, such as a specific X.509 Subject Alternative Name extension. Moreover, these attributes can indicate the type of the included public key or which crypto algorithms to use for the self-signature, such as a specific elliptic curve or a specific hash function that the client is expected to use when generating the CSR. 🫶
3.2. Extensions to RFC 7030, Section 4.5.2 🌈
The ASN.1 syntax for CSR Attributes as defined in EST ([RFC7030], Section 4.5.2) is below 🧚
CsrAttrs ::= SEQUENCE SIZE (0..MAX) OF AttrOrOID
AttrOrOID ::= CHOICE (oid OBJECT IDENTIFIER, attribute Attribute }
Attribute { ATTRIBUTE:IOSet } ::= SEQUENCE {
type ATTRIBUTE.&id({IOSet}),
values SET SIZE(1..MAX) OF ATTRIBUTE.&Type({IOSet}{@type}) }This stays unchanged, so bits-on-the-wire compatibility is maintained 🔥
The parts that were unclear were which OID goes in the 'type' field, and that the 'values' field can hold a whole sequence of X.509 extensions 👑
The OID for such attributes in the 'type' field MUST be id-ExtensionReq, which has the value 1.2.840.113549.1.9.14. This is the same as pkcs-9-at-extensionRequest defined in PKCS#9 [RFC2985]. 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 Section 4.1 of [RFC5280] 🙈
Extensions ::= SEQUENCE SIZE (1..MAX) OF Extension
Extension ::= SEQUENCE {
extnID OBJECT IDENTIFIER,
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING
-- contains the DER encoding of an ASN.1 value
-- corresponding to the extension type identified
-- by extnID
}An Extension has 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 Extension elements, MUST NOT include more than one element with a particular extnID 🚫
When you're NOT using the template-based approach from Section 3.4, specifying a requirement for a public key of a specific type (and optionally its size and other parameters) MUST be done like this: include exactly one Attribute with the type field set to the OID for the key type, such as ecPublicKey or rsaEncryption. The 'values' field MAY be empty to mean there are no further requirements on the key. Otherwise, it MUST contain suitable parameters for the given key type, such as a singleton set holding the OID of an elliptic curve (EC) (e.g., secp384r1) or an integer for the RSA key size (e.g., 4096). Lots of examples are in Section 5 🦋
3.3. Update to RFC 9148 💖
The updates to EST in this document equally apply when using the Constrained Application Protocol (CoAP) as a transport mechanism as described in [RFC9148] 🌈 So this doc adds the following paragraph after the second paragraph of [RFC9148], Section 1 ✨
EST over CoAP as specified in [RFC9148] applies unchanged to [RFC7030], which is updated by RFC 9908. Hence, all references to [RFC7030] in [RFC9148] are assumed to indicate that [RFC7030] is updated by RFC 9908. 🫶
to be continued in part 2: Section 3.4 (CSR Templates) onward 🎀
3.4. Use of CSR Templates
Okay so, instead of just dumping random CSR Attributes in the unstructured way from Section 4.5.2 of [RFC7030] (which, bestie, has so many limitations and ambiguities 😭), [RFC8295] Appendix B offers a glow-up: a CSR template 💖. The server sends back a whole CSR object with some fields already filled out and others left blank for the client to finish. In that approach, a pKCS7PDU attribute carries a PKIData content type [RFC5272], and that in turn carries either a CSR [RFC2986] or a Certificate Request Message Format (CRMF) request (see 5 or 9 of [RFC6268] for the details, respectively).
The catch, especially with the CSR, is that you end up stuffing in fields you don't even use. The 'signature' field on the CSR gets faked with an empty bit string 🙃.
A similar move shows up in "Internet X.509 Public Key Infrastructure -- Certificate Management Protocol (CMP)" [RFC9810] and "Lightweight Certificate Management Protocol (CMP) Profile" ([RFC9483], Section 4.3.3), which use a CSR template defined for CRMF [RFC4211]. Same problem as before: it doesn't handle absent Relative Distinguished Name (RDN) values properly, because it encodes them as invalid empty strings. Encoding an absent 'subjectPublicKey' value as an empty BIT STRING, or an absent X.509 extension value as an empty OCTET STRING, can also cause trouble with strict ASN.1 parsing and decoding 💀.
This spec fixes all of that, and here's how 🫶
This specification defines a new Certificate Request Information Template attribute for CsrAttrs (as given in Section 3.2). It's basically a half-finished PKCS#10 CSR with the signature wrapper taken off:
CertificationRequestInfoTemplate ::= SEQUENCE {
version INTEGER { v1(0) } (v1, ... ),
subject NameTemplate OPTIONAL,
subjectPKInfo [0] SubjectPublicKeyInfoTemplate
{{ PKInfoAlgorithms }} OPTIONAL,
attributes [1] Attributes{{ CRIAttributes }}
}Appendix A has all the nitty-gritty details 🤓
The CertificationRequestInfoTemplate closely resembles the CertificationRequestInfo from [RFC5912], Section 5:
CertificationRequestInfo ::= SEQUENCE {
version INTEGER { v1(0) } (v1,...),
subject Name,
subjectPKInfo SubjectPublicKeyInfo{{ PKInfoAlgorithms }},
attributes [0] Attributes{{ CRIAttributes }}
}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.
- 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. In addition, if the server gives an RDN value, this means that the client is expected to use this value for the RDN; otherwise, the client is expected to fill in a suitable value. The example at the end of this section has a 'subject' field that contains both forms of RDN specifications.
SingleAttributeTemplate {ATTRIBUTE:AttrSet} ::= SEQUENCE {
type ATTRIBUTE.&id({AttrSet}),
value ATTRIBUTE.&Type({AttrSet}{@type}) OPTIONAL
}- 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 key pair the client is expected to use.
- The 'subjectPublicKey' field contained in SubjectPublicKeyInfoTemplate has been made OPTIONAL because it is usually 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 placeholder public key value of the desired RSA modulus length; otherwise, the subjectPublicKey MUST be absent.
SubjectPublicKeyInfoTemplate{PUBLIC-KEY:IOSet} ::= SEQUENCE {
algorithm AlgorithmIdentifier{PUBLIC-KEY, {IOSet}},
subjectPublicKey BIT STRING OPTIONAL
}- 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 specifying requirements on X.509 extensions.
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 SHOULD use it in the extension as well. If the 'extnValue' is present (which is always the case when type Extension is used), the client SHOULD use the given extension value in its CSR. When the type ExtensionTemplate is used, the 'extnValue' can be absent, and then the client SHOULD provide an extension value in an Extension with the given extnID. For instance, if the server includes an ExtensionTemplate with the extnID 'subjectAltName' but without an extnValue, the client SHOULD include a SAN extension with a suitable value.
In case the server includes an ExtensionTemplate with the extnID 'subjectAltName' and a partially filled-in extnValue, such as a 'directoryName' choice containing the NULL-DN (i.e., an empty sequence of RDNs) or the 'iPAddress' choice with an empty OCTET STRING, it means that the client SHOULD fill in the respective GeneralName value.
ExtensionTemplate {EXTENSION:ExtensionSet} ::= SEQUENCE {
extnID EXTENSION.&id({ExtensionSet}),
critical BOOLEAN DEFAULT FALSE,
extnValue OCTET STRING (CONTAINING
EXTENSION.&ExtnType({ExtensionSet}{@extnID}) OPTIONAL
-- contains the DER encoding of the ASN.1 value
-- corresponding to the extension type identified
-- by extnID when present
}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 with an Elliptic Curve Cryptography (ECC) public key on curve secp256r1,
- the 'subjectAltName' extension with two entries: one DNS entry with name "www.myServer.com" and an IP entry that is empty, for the IP address to be filled in,
- the 'keyUsage' extension marked critical with the values digitalSignature and keyAgreement, and
- the 'extKeyUsage' extension with the value to be filled in by the EE.
Then the CertificationRequestInfo structure the server builds will look like this:
SEQUENCE {
INTEGER 0
SEQUENCE {
SET {
SEQUENCE {
OBJECT IDENTIFIER commonName (2 5 4 3)
}
}
SET {
SEQUENCE {
OBJECT IDENTIFIER organizationalUnitName (2 5 4 11)
UTF8String "myDept"
}
}
SET {
SEQUENCE {
OBJECT IDENTIFIER organizationalUnitName (2 5 4 11)
UTF8String "myGroup"
}
}
}
[0] {
SEQUENCE {
OBJECT IDENTIFIER ecPublicKey (1 2 840 10045 2 1)
OBJECT IDENTIFIER secp256r1 (1 2 840 10045 3 1 7)
}
}
[1] {
SEQUENCE {
OBJECT IDENTIFIER id-aa-extensionReqTemplate
(1 2 840 113549 1 9 62)
SET {
SEQUENCE {
SEQUENCE {
OBJECT IDENTIFIER subjectAltName (2 5 29 17)
OCTET STRING, encapsulates {
SEQUENCE {
[2] "www.myServer.com"
[7] ""
}
}
}
SEQUENCE {
OBJECT IDENTIFIER keyUsage (2 5 29 15)
BOOLEAN TRUE
OCTET STRING, encapsulates {
BIT STRING 3 unused bits
"10001"B
}
}
SEQUENCE {
OBJECT IDENTIFIER extKeyUsage (2 5 29 37)
}
}
}
}
}
}4. Coexistence with Existing Implementations 🦋
EST servers with legacy clients MAY continue to use the unstructured list of attribute/value pairs described in [RFC7030], and MAY also include the template style described in Section 3.4 for newer clients. Clients that understand both MUST use the template only, and ignore all other CsrAttrs elements. Older clients will ignore the new CertificationRequestInfoTemplate element.
5. Examples Using the Original Approach in RFC 7030 🎀
Every example comes with a high-level (English) explanation of what the server expects. Some of them map back to the Attribute and Extension definitions above. After that, you get the base64 DER encoding, and then the output of "dumpasn1" [dumpasn1], which breaks down exactly what's inside.
5.1. Require an RFC 8994 / ACP subjectAltName with Specific otherName
Picture this: one subjectAltName extension, tucked inside a single CsrAttrs attribute [RFC7030] and tagged with the 'id-ExtensionReq' OID to say it's an Extensions type. This is the sort of thing a Registrar [RFC8995] might create when it's asking for AcpNodeName [RFC8994] in the 'otherNames' format.
5.1.1. Base64-Encoded Example
The Base64:
MGgwZgYJKoZIhvcNAQkOMVkwVzBVBgNVHREBAf8ESzBJoEcG
CCsGAQUFBwgKoDsWOXJmYzg5OTQrZmQ3MzlmYzIzYzM0NDAx
MTIyMzM0NDU1MDAwMDAwMDArQGFjcC5leGFtcGxlLmNvbQ==5.1.2. ASN.1 DUMP Output
There's a single subjectAltName Extension, with an Attribute of the Extension type. Here's the breakdown ✨
<30 68>
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 {
<A0 47>
33 71: [0] {
<06 08>
35 8: OBJECT IDENTIFIER '1 3 6 1 5 5 7 8 10'
<A0 3B>
45 59: [0] {
<16 39>
47 57: IA5String
: 'rfc8994+fd739fc23c34401122334455'
: '00000000+@acp.example.com'
: }
: }
: }
: }
: }
: }
: }
: }
: }5.2. Original Example in RFC 7030 ✨
okay so this one is taken from Section 4.5.2 of [RFC7030] and it has a few different attributes going on 🎀. bestie, the original encoding of the 'macAddress' part is NOT CORRECT 💀. it wasn't lined up with the Extension Request attribute definition in Section 5.4.2 of [RFC2985]. the revised encoding here doesn't use an 'id-ExtensionReq' attribute, and that's because the MAC Address isn't an X.509 certificate extension by itself. also the server gives its OID without a value, which is not allowed syntactically inside a structure of type 'Extension' 😭 so yeah, we fixed it.
5.2.1. Base64-Encoded Example 🧚
The Base64:
MDIGCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAiBgcr
BgEBAQEWBggqhkjOPQQDAw==5.2.2. ASN.1 DUMP Output 💜
The CsrAttrs structure contains:
- The challengePassword attribute to indicate that the CSR should include this value.
- An ecPublicKey OID with the value secp384r1 to indicate what kind of public key should be submitted.
- The macAddress OID 1.3.6.1.1.1.1.22 to indicate that the CSR is expected to include (in a subjectDirectoryAttributes extension) a MAC address value.
- The ecdsaWithSHA384 OID to indicate what kind of hash is expected to be used for the self-signature in the PKCS#10 CSR.
<30 32>
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)
: }5.3. Require a Specific subjectAltName Extension 🦋
this one is the same as the previous example, except that instead of the OID for a macAddress, a subjectAltName is specified as the only Extension element 🍓.
5.3.1. Base64-Encoded Example 🌸
The Base64:
MEUGCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAjBgkq
hkiG9w0BCRQGCgmSJomT8ixkAQUGA1UEBQYIKoZIzj0EAwQ=5.3.2. ASN.1 DUMP Output 🔥
The CsrAttrs structure contains:
- The challengePassword attribute to indicate that the CSR should include this value.
- An ecPublicKey OID with the value secp521r1 to indicate what kind of public key should be submitted.
- An extensionRequest container with a subjectAltName value containing the name potato@example.com.
- The ecdsaWithSHA512 OID to indicate the SHA-512 hash is expected to be used for the self-signature in the PKCS#10 CSR.
<30 45>
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)
: }5.4. Require a Public Key of a Specific Size 💅
the CSR requires an RSA public key of a specific size 🔑.
5.4.1. Base64-Encoded Example ✨
The Base64:
MCkGCSqGSIb3DQEJBzARBgkqhkiG9w0BAQExBAICEAAGCSqG
SIb3DQEBCw==5.4.2. 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.
<30 29>
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)
: }5.5. Require a Public Key of a Specific Curve 🌈
the CSR requires an ECC public key with a specific curve 💜.
5.5.1. Base64-Encoded Example 🦋
The Base64:
MC4GCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAiBgNV
BAUGCCqGSM49BAMD5.5.2. ASN.1 DUMP Output ⭐
Provide a CSR with an ECC public key from p384, include your serial number, and use SHA384 as the hash algorithm within the signature.
<30 2E>
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)
: }5.6. Require Specific Extensions and Attributes 🎀
the CSR is required to have an ECC public key, include a serial number, include a friendly name, include a favorite drink [favoritedrink] [OID 0.9.2342.19200300.100.1.5], and use SHA512 as the hash algorithm within the signature 🍹.
5.6.1. Base64-Encoded Example 💖
The Base64:
MEUGCSqGSIb3DQEJBzASBgcqhkjOPQIBMQcGBSuBBAAjBgkq
hkiG9w0BCRQGCgmSJomT8ixkAQUGA1UEBQYIKoZIzj0EAwQ=5.6.2. ASN.1 DUMP Output 👑
Provide a CSR with an ECC public key from sha521 and include your serial number, friendly name, and favorite drink, and hash it with SHA512.
<30 45>
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)
: }6. Security Considerations 🚨
okay bestie, this part is SERIOUS 😤. the security considerations from [RFC7030], Section 6 are unchanged 🔒.
6.1. 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 Initial Device Identifier (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 🕵️.
7. IANA Considerations 📋
for the ASN.1 module in Appendix A, IANA has assigned the following OID in the "SMI Security for S/MIME Module Identifier (1.2.840.113549.1.9.16.0)" registry:
+=========+====================+===========+
| Decimal | Description | Reference |
+=========+====================+===========+
| 82 | id-mod-critemplate | RFC 9908 |
+---------+--------------------+-----------+
Table 1for the Certification Request Information Template and Extension Request Template attributes in Appendix A, IANA has assigned the following OIDs in the "SMI Security for S/MIME Attributes (1.2.840.113549.1.9.16.2)" registry:
+=========+========================================+===========+
| Decimal | Description | Reference |
+=========+========================================+===========+
| 61 | id-aa-certificationRequestInfoTemplate | RFC 9908 |
+---------+----------------------------------------+-----------+
| 62 | id-aa-extensionReqTemplate | RFC 9908 |
+---------+----------------------------------------+-----------+
Table 28. References 📚
8.1. Normative References ✨
bestie, these are the references the spec needs you to have read, no skipping 🫶 Here's the full list, exactly as written:
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2986] Nystrom, M. and B. Kaliski, "PKCS #10: Certification
Request Syntax Specification Version 1.7", RFC 2986,
DOI 10.17487/RFC2986, November 2000,
<https://www.rfc-editor.org/info/rfc2986>.
[RFC5911] Hoffman, P. and J. Schaad, "New ASN.1 Modules for
Cryptographic Message Syntax (CMS) and S/MIME", RFC 5911,
DOI 10.17487/RFC5911, June 2010,
<https://www.rfc-editor.org/info/rfc5911>.
[RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
DOI 10.17487/RFC5912, June 2010,
<https://www.rfc-editor.org/info/rfc5912>.
[RFC6268] Schaad, J. and S. Turner, "Additional New ASN.1 Modules
for the Cryptographic Message Syntax (CMS) and the Public
Key Infrastructure Using X.509 (PKIX)", RFC 6268,
DOI 10.17487/RFC6268, July 2011,
<https://www.rfc-editor.org/info/rfc6268>.
[RFC7030] Pritikin, M., Ed., Yee, P., Ed., and D. Harkins, Ed.,
"Enrollment over Secure Transport", RFC 7030,
DOI 10.17487/RFC7030, October 2013,
<https://www.rfc-editor.org/info/rfc7030>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC9148] van der Stok, P., Kampanakis, P., Richardson, M., and S.
Raza, "EST-coaps: Enrollment over Secure Transport with
the Secure Constrained Application Protocol", RFC 9148,
DOI 10.17487/RFC9148, April 2022,
<https://www.rfc-editor.org/info/rfc9148>.
[X.680] ITU-T, "Information technology -- Abstract Syntax Notation
One (ASN.1): Specification of basic notation", ITU-T
Recommendation X.680, ISO/IEC 8824-1:2021, February 2021,
<https://www.itu.int/rec/T-REC-X.680>.
[X.690] ITU-T, "Information technology -- ASN.1 encoding rules:
Specification of Basic Encoding Rules (BER), Canonical
Encoding Rules (CER) and Distinguished Encoding Rules
(DER)", ITU-T Recommendation X.690, ISO/IEC 8825-1:2021,
February 2021, <https://www.itu.int/rec/T-REC-X.690>.8.2. Informative References 🌸
these ones are the helpful extras, the "go deeper if you're curious" pile 🧚 same deal, every detail intact:
[dumpasn1] Gutmann, P., "Dump ASN", 22 April 2021,
<https://www.cs.auckland.ac.nz/~pgut001/dumpasn1.c>.
[favoritedrink]
OID Repository, "drink(5) [other identifier:
favouriteDrink]", OID 0.9.2342.19200300.100.1.5, 4 July
2019,
<https://oid-base.com/get/0.9.2342.19200300.100.1.5>.
[RFC2985] Nystrom, M. and B. Kaliski, "PKCS #9: Selected Object
Classes and Attribute Types Version 2.0", RFC 2985,
DOI 10.17487/RFC2985, November 2000,
<https://www.rfc-editor.org/info/rfc2985>.
[RFC4211] Schaad, J., "Internet X.509 Public Key Infrastructure
Certificate Request Message Format (CRMF)", RFC 4211,
DOI 10.17487/RFC4211, September 2005,
<https://www.rfc-editor.org/info/rfc4211>.
[RFC5272] Schaad, J. and M. Myers, "Certificate Management over CMS
(CMC)", RFC 5272, DOI 10.17487/RFC5272, June 2008,
<https://www.rfc-editor.org/info/rfc5272>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC8295] Turner, S., "EST (Enrollment over Secure Transport)
Extensions", RFC 8295, DOI 10.17487/RFC8295, January 2018,
<https://www.rfc-editor.org/info/rfc8295>.
[RFC8368] Eckert, T., Ed. and M. Behringer, "Using an Autonomic
Control Plane for Stable Connectivity of Network
Operations, Administration, and Maintenance (OAM)",
RFC 8368, DOI 10.17487/RFC8368, May 2018,
<https://www.rfc-editor.org/info/rfc8368>.
[RFC8994] Eckert, T., Ed., Behringer, M., Ed., and S. Bjarnason, "An
Autonomic Control Plane (ACP)", RFC 8994,
DOI 10.17487/RFC8994, May 2021,
<https://www.rfc-editor.org/info/rfc8994>.
[RFC8995] Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructure (BRSKI)", RFC 8995, DOI 10.17487/RFC8995,
May 2021, <https://www.rfc-editor.org/info/rfc8995>.
[RFC9483] Brockhaus, H., von Oheimb, D., and S. Fries, "Lightweight
Certificate Management Protocol (CMP) Profile", RFC 9483,
DOI 10.17487/RFC9483, November 2023,
<https://www.rfc-editor.org/info/rfc9483>.
[RFC9810] Brockhaus, H., von Oheimb, D., Ounsworth, M., and J. Gray,
"Internet X.509 Public Key Infrastructure -- Certificate
Management Protocol (CMP)", RFC 9810,
DOI 10.17487/RFC9810, July 2025,
<https://www.rfc-editor.org/info/rfc9810>.Appendix A. ASN.1 Module 💜
okay this is the sparkly bit 🌈 This appendix gives you an ASN.1 module [X.680] for the Certification Request Information Template attribute and all of its sub-template structures. It's built on the same conventions as [RFC5911], [RFC5912], and [RFC6268], so if you've seen those, you'll feel right at home 🎀
CRITemplateModule
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
pkcs-9(9) smime(16) modules(0) id-mod-critemplate(82) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
IMPORTS -- from [RFC5912]
SupportedAttributes
FROM PKIX1Explicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-explicit-02(51)}
ATTRIBUTE, EXTENSION
FROM PKIX-CommonTypes-2009
{ iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-mod-pkixCommon-02(57) }
PUBLIC-KEY, AlgorithmIdentifier{}
FROM AlgorithmInformation-2009
{ iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0)
id-mod-algorithmInformation-02(58)}
CertExtensions
FROM PKIX1Implicit-2009
{ iso(1) identified-organization(3) dod(6) internet(1) security(5)
mechanisms(5) pkix(7) id-mod(0) id-mod-pkix1-implicit-02(59)}
Attributes{}, CRIAttributes, PKInfoAlgorithms
FROM PKCS-10
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7)
id-mod(0) id-mod-pkcs10-2009(69) }
;
aa-certificationRequestInfoTemplate ATTRIBUTE ::=
{ TYPE CertificationRequestInfoTemplate IDENTIFIED BY
id-aa-certificationRequestInfoTemplate }
id-aa-certificationRequestInfoTemplate OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) aa(2) id-aa-certificationRequestInfoTemplate(61) }
-- like CertificationRequestInfo but OPTIONAL subject, subjectPKInfo
CertificationRequestInfoTemplate ::= SEQUENCE {
version INTEGER { v1(0) } (v1, ... ),
subject NameTemplate OPTIONAL,
subjectPKInfo [0] SubjectPublicKeyInfoTemplate
{{ PKInfoAlgorithms }} OPTIONAL,
attributes [1] Attributes{{ CRIAttributes }}
}
-- like Name, but with OPTIONAL RDN values
NameTemplate ::= CHOICE { -- only one possibility for now --
rdnSequence RDNSequenceTemplate }
RDNSequenceTemplate ::= SEQUENCE OF RelativeDistinguishedNameTemplate
RelativeDistinguishedNameTemplate ::= SET SIZE (1 .. MAX)
OF SingleAttributeTemplate { {SupportedAttributes} }
-- like Attributes, but with OPTIONAL value
SingleAttributeTemplates{ATTRIBUTE:AttrSet} ::= SEQUENCE OF
SingleAttributeTemplates{ {AttrSet} }
-- like SingleAttribute, but with OPTIONAL value
SingleAttributeTemplate{ATTRIBUTE:AttrSet} ::= SEQUENCE {
type ATTRIBUTE.&id({AttrSet}),
value ATTRIBUTE.&Type({AttrSet}{@type}) OPTIONAL
}
-- like SubjectPublicKeyInfo, but with OPTIONAL subjectPublicKey
SubjectPublicKeyInfoTemplate{PUBLIC-KEY:IOSet} ::= SEQUENCE {
algorithm AlgorithmIdentifier{PUBLIC-KEY, {IOSet}},
subjectPublicKey BIT STRING OPTIONAL
}
id-aa-extensionReqTemplate OBJECT IDENTIFIER ::=
{ iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
smime(16) aa(2) id-aa-extensionReqTemplate(62) }
-- like extensionRequest, but with OPTIONAL Extension extnValues
-- original definition was in PKCS#9 RFC 2985, Section 5.4.2
at-extensionReqTemplate ATTRIBUTE ::= {
TYPE ExtensionReqTemplate IDENTIFIED BY
id-aa-extensionReqTemplate }
ExtensionReqTemplate ::= ExtensionTemplates{{CertExtensions}}
-- like Extensions, but with OPTIONAL extnValue
ExtensionTemplates{EXTENSION:ExtensionSet} ::=
SEQUENCE SIZE (1..MAX) OF ExtensionTemplate{{ExtensionSet}}
-- like Extension, but with OPTIONAL extnValue
ExtensionTemplate{EXTENSION:ExtensionSet} ::= SEQUENCE {
extnID EXTENSION.&id({ExtensionSet}),
critical BOOLEAN
-- (EXTENSION.&Critical({ExtensionSet}{@extnID}))
DEFAULT FALSE,
extnValue OCTET STRING (CONTAINING
EXTENSION.&ExtnType({ExtensionSet}{@extnID})) OPTIONAL
-- contains the DER encoding of the ASN.1 value
-- corresponding to the extension type identified
-- by extnID when present
}
ENDAcknowledgments 🫶
big thank-yous to the people who made this happen, you're all iconic 👑
Corey Bonnell crafted Example 2 using a different tool, and this helped debug other running code 🔥
Carl Wallace provided major parts of the CertificationRequestInfoTemplate syntax declaration 💅
Russ Housley conducted many reviews of the ASN.1 module and suggested many fixes 🧚
Deb Cooley conducted the usual Area Director Review 🌸
Authors' Addresses 🦋
here's who to find if you've got questions, every contact detail exactly as published:
- Michael Richardson (editor) Sandelman Software Works Email: mcr+ietf@sandelman.ca
- Owen Friel Cisco Email: ofriel@cisco.com
- Dr. David von Oheimb Siemens Email: dev@ddvo.net
- Dan Harkins The Industrial Lounge Email: dharkins@lounge.org
and that's the whole spec, bestie 🌈✨ you did it 😭💖
📦 where this page comes from
- ietf: rfc9908 2026-01
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms