Requesting a Freshness Nonce for Attestation Evidence in Certificate Signing Requests

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Table of Contents

1. Introduction

[I-D.ietf-lamps-csr-attestation] specifies how Evidence, as defined in the RATS Architecture [RFC9334], can be conveyed in a Certificate Signing Request (CSR) using PKCS#10 [RFC2986] or the Certificate Request Message Format (CRMF) [RFC4211]. The RATS Architecture calls for establishing the freshness of Evidence, see Section 10 of [RFC9334]. A common method for establishing freshness is the use of nonces. Such nonces must be provided by the Relying Party or Verifier and included in the Evidence by the Attester.¶

When the CSR is conveyed using a certificate lifecycle management protocol, such as CMP [RFC9810], EST [RFC7030], or CMC [RFC10002], the end entity can request the required nonce from a Registration Authority or Certification Authority (RA/CA) in a prior message exchange and pass it to the Attester to produce fresh Evidence.¶

This document describes how an end entity can request a nonce from an RA/CA using CMP, EST, and CMC.¶

The following topics are out of scope for this document and either covered in other specifications or are implementation or deployment details:¶

• whether a CSR requires one or more nonces,¶

• how the end entity forwards the nonce to the Attester,¶

• whether the RA/CA or the Verifier generates the nonce and how those entities communicate with each other, and¶

• other methods for establishing freshness.¶

In this context, the end entity is a device that contains one or more Attesters, and the RA/CA acts as a Relying Party that communicates with one or more Verifiers.¶

2. Terminology and Requirements Language

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.¶

This document uses RATS and PKIX terminology as described in Section 3 of [I-D.ietf-lamps-csr-attestation]. It also uses terminology from the applicable certificate lifecycle management protocols: CMP, EST, and CMC.¶

3. Architecture and Message Formats

According to [I-D.ietf-lamps-csr-attestation], a CSR can contain multiple AttestationStatements and multiple certificates for validating those AttestationStatements. This document describes how an end entity can use CMP, EST, or CMC to request a nonce from the RA/CA for a specific type of Evidence to be included in the CSR.¶

The end entity sends a nonce request message with the following fields:¶

• len: In this OPTIONAL field, the end entity can specify the desired length of the requested nonce in bytes as a value between 8 and 64.¶

• reqTypeInfo: This OPTIONAL structure groups the type-specific information for the nonce request. It contains:¶

  • type: This field specifies the type of the reqInfo structure.¶

  • reqInfo: This OPTIONAL field contains the type-specific content that the RA/CA requires to generate respInfo.¶

The RA/CA can return the requested nonce in a nonce response message together with information specific to the generation of the Evidence.¶

The nonce response message has the following fields:¶

• nonce: This field MUST contain the nonce if the RA/CA is able and willing to provide it. If a specific length was requested, the RA/CA SHOULD provide a nonce of that size. If the RA/CA doesn't need a proof of freshness, the nonce MUST be zero-length.¶

• expiry: In this OPTIONAL field, the RA/CA can indicate in seconds, as a non-negative integer value, how long it expects the nonce to remain acceptable; the response therefore needs to be conveyed promptly. The field is only a hint to the end entity about how long the RA/CA (and possibly the Verifier) anticipate storing state. If this field is absent, no indication about the expected lifetime of the nonce is provided. An end entity MAY send Evidence containing this nonce even after the indicated period has elapsed. It is then up to the RA/CA to decide whether to accept the Evidence.¶

• respTypeInfo: This OPTIONAL structure groups the type-specific information for the nonce response. It contains:¶

  • type: This field specifies the type of the respInfo structure. The type in the nonce response message is defined by the type in the nonce request message.¶

  • respInfo: This OPTIONAL field contains the type-specific content requested by the end entity for generating the Evidence.¶

This document does not further specify the content of the reqInfo and respInfo structures; those structures must be defined elsewhere. Each definition must assign an object identifier and specify the exact content of the corresponding field. The definition of the reqInfo structure must also specify the type of the expected respInfo structure. The message structure and the reqInfo or respInfo structures can use different encodings. For example, an ASN.1 message can contain reqInfo or respInfo encoded as JSON, if necessary. The reqInfo structure may be used to provide the required information to the RA/CA to route the nonce request to the appropriate Verifier when multiple Verifiers are supported. The respInfo structure may be used to convey Generic Information Elements (Section 6 of [I-D.ietf-rats-reference-interaction-models]) such as Attesting Environment IDs and Claim Selection. Appendix A provides an informative example using a TPM PCR selection.¶

The generic message flow between the end entity and the RA/CA is shown in Figure 1.¶

The nonce request and response messages MUST be transferred within the same PKI management operation context provided by the certificate lifecycle management protocol being used, just as the certification request and response messages are, so that the RA/CA can unambiguously associate the provided nonce with the Evidence in the CSR. This association is required because the RA/CA treats the Evidence carried in the CSR as opaque and therefore cannot rely on inspecting the Evidence to determine which previously issued nonce applies to that CSR.¶

The nonce request and nonce response messages allow the end entity to request only one nonce and one respInfo structure from the RA/CA. If the end entity wants to include multiple attestation statements in a CSR, it can use the Composite Attester model described in Section 3.3 of [RFC9334] and [I-D.richardson-rats-composite-attesters], i.e., together with a conceptual message wrapper (CMW) [I-D.ietf-rats-msg-wrap] structure, as described in Section 4.3 of [I-D.ietf-lamps-csr-attestation]. The Lead Attester should then pass the nonce, or a value derived from it if the selected attestation statement type defines a deterministic nonce transformation (see Section 8), to the sub-Attesters. Based on Figure 2 of [I-D.richardson-rats-composite-attesters], Figure 2 shows an example of how a nonce can be distributed among several Attesters in an end entity. If multiple respInfo structures are required, the reqInfo and respInfo structures can also use a CMW.¶

The interaction between the end entity and the RA/CA is illustrated in Figure 3.¶

The following sections define the generic data structures for nonce request and nonce response message content. CMP and CMC use ASN.1, while EST uses JSON and CBOR, both defined using CDDL.¶

ATTESTATION-NONCE-REQUEST ::= TYPE-IDENTIFIER
AttestationNonceRequestSet ATTESTATION-NONCE-REQUEST ::= {
   ... -- None defined in this document --
}

ATTESTATION-NONCE-RESPONSE ::= TYPE-IDENTIFIER
AttestationNonceResponseSet ATTESTATION-NONCE-RESPONSE ::= {
   ... -- None defined in this document --
}

NonceRequestTypeInfo ::= SEQUENCE {
    type ATTESTATION-NONCE-REQUEST.&id(
                 {AttestationNonceRequestSet}),
    -- identifies the nonce-request syntax for the selected
    --   attestation statement type
    reqInfo  ATTESTATION-NONCE-REQUEST.&Type(
                 {AttestationNonceRequestSet}{@type}) OPTIONAL
    -- contains type-specific nonce-request information
}

NonceResponseTypeInfo ::= SEQUENCE {
    type ATTESTATION-NONCE-RESPONSE.&id(
                 {AttestationNonceResponseSet}),
    -- identifies the nonce-response syntax for the selected
    --   attestation statement type
    respInfo ATTESTATION-NONCE-RESPONSE.&Type(
                 {AttestationNonceResponseSet}{@type}) OPTIONAL
    -- contains type-specific nonce-response information
}

 NonceRequest ::= SEQUENCE {
    len      INTEGER (8..64) OPTIONAL,
    -- indicates the desired length of the requested nonce
    reqTypeInfo NonceRequestTypeInfo OPTIONAL
 }

 NonceResponse ::= SEQUENCE {
    nonce    OCTET STRING (SIZE(0 | 8..64)),
    -- contains the nonce, preferably of length len
    -- a zero-length OCTET STRING indicates that no proof of
    --   freshness is required
    expiry   INTEGER (0..MAX) OPTIONAL,
    -- hint indicating how long in seconds the nonce issuer
    --   expects the nonce to remain acceptable
    respTypeInfo NonceResponseTypeInfo OPTIONAL
 }

nonce-request = {
  ? "len": nonce-length,
  ? "reqTypeInfo": nonce-request-type-info
}

nonce-request-type-info = {
  "type": dotted-decimal-oid,
  ? "reqInfo": any
}

nonce-response-json = {
    "nonce": json-nonce,
  ? "expiry": uint,
  ? "respTypeInfo": nonce-response-type-info-json
}

nonce-response-type-info-json = {
  "type": dotted-decimal-oid,
  ? "respInfo": any
}

nonce-response-cbor = {
    "nonce": cbor-nonce,
  ? "expiry": uint,
  ? "respTypeInfo": nonce-response-type-info-cbor
}

nonce-response-type-info-cbor = {
  "type": dotted-decimal-oid,
  ? "respInfo": any
}

nonce-length = 8..64
cbor-nonce = h'' / bstr .size (8..64)
json-nonce = "" / base64url-nonce
base64url-nonce = tstr .regexp "[A-Za-z0-9_-]{11,86}"
dotted-decimal-oid = tstr

4. Use with CMP

The nonce request and nonce response message content is conveyed as ASN.1 content, see Section 3.1, in a general message (genm) Section 5.3.19 of [RFC9810] and general response (genp) Section 5.3.20 of [RFC9810], respectively.¶

GenMsg:    {id-it TBD1}, NonceRequest
GenRep:    {id-it TBD2}, NonceResponse

id-it-nonceRequest OBJECT IDENTIFIER ::= { id-it TBD1 }
NonceRequestValue ::= NonceRequest

id-it-nonceResponse OBJECT IDENTIFIER ::= { id-it TBD2 }
NonceResponseValue ::= NonceResponse

When CMP is transferred over HTTP, the OPTIONAL <operation> path segment defined in Section 3.4 of [RFC9811] MAY be used for the nonce request message.¶

When CMP is transferred over CoAP, the OPTIONAL <operation> path segment defined in Section 2.1 of [RFC9482] MAY be used for the nonce request message.¶

To ensure that the nonce request and response messages are associated with the subsequent request and response messages used to transmit the CSR, the transaction identifier specified in Section 5.1.1 of [RFC9810] MUST be used.¶

In the event of a possible error or if the RA/CA is unable or unwilling to provide the requested nonce, CMP offers several ways to indicate this. Which variant fits depends on the circumstances.¶

• Respond with an error message containing the PKIFailureInfo bit as defined in [RFC9810], see also [RFC9483].¶

• If HTTP or CoAP is used for transferring the general message, return a status code on transfer level as described in [RFC9811] or [RFC9482].¶

5. Use with EST

The nonce request and nonce response message content is conveyed as JSON [RFC8259] or CBOR [RFC8949] according to the CDDL definition, see Section 3.2, between end entity (EST client) and RA/CA (EST server). A compliant EST server MUST provide an EST endpoint with the path segment getnonce when EST is transferred over HTTPS and with the path segment nonce when EST is transferred over secure CoAP.¶

Depending on whether additional parameters are to be transferred, the end entity uses either the GET or POST method:¶

• The GET method MUST be used if no optional content is to be transferred.¶

• The POST method MUST be used if nonce request message content encoded in JSON or CBOR is to be transferred.¶

GET /.well-known/est/getnonce HTTP/1.1

HTTP/1.1 200 OK
Cache-Control: no-store
Content-Type: application/est-attestation-freshness+json

{
  "nonce": "MTIzNDU2Nzg5MDEyMzQ1Njc4OTAxMjM0NTY3ODkwMTI",
  "expiry": 600
}

POST /.well-known/est/getnonce HTTP/1.1
Content-Type: application/est-attestation-freshness+json

{
  "len": 32
}

HTTP/1.1 200 OK
Cache-Control: no-store
Content-Type: application/est-attestation-freshness+json

{
  "nonce": "MTIzNDU2Nzg5MDEyMzQ1Njc4OTAxMjM0NTY3ODkwMTI",
  "expiry": 600
}

6. Use with CMC

The nonce request and nonce response message content is conveyed as ASN.1, see Section 3.1, as CMC Controls in a Full PKI Request, see Section 6 of [RFC10002]. The received nonce can be used for a CSR to be transferred in a Full PKI Request. A Simple PKI Request cannot be used because it cannot carry the required transaction identifier.¶

To transfer the controls, the content type id-data SHOULD be used.¶

cmc-nonceReq CMC-CONTROL ::=
    { NonceRequest IDENTIFIED BY id-cmc-nonceReq }
id-cmc-nonceReq OBJECT IDENTIFIER ::= { id-cmc TBD4 }

cmc-nonceResp CMC-CONTROL ::=
    { NonceResponse IDENTIFIED BY id-cmc-nonceResp }
id-cmc-nonceResp OBJECT IDENTIFIER ::= { id-cmc TBD5 }

The following example shows the nonce request and nonce response message content:¶

ContentInfo.contentType = id-data
ContentInfo.content
   controlSequence
      {101, id-cmc-transactionId, 10132985123483401}
      {102, id-cmc-senderNonce, 10001}
      {103, id-cmc-nonceReq, <NonceRequest>}

ContentInfo.contentType = id-data
ContentInfo.content
   controlSequence
      {101, id-cmc-transactionId, 10132985123483401}
      {102, id-cmc-senderNonce, 10005}
      {103, id-cmc-recipientNonce, 10001}
      {104, id-cmc-nonceResp, <NonceResponse>}

To ensure that the nonce request and response messages are associated with the subsequent request and response messages used to transmit the CSR, the transaction identifier specified in Section 6.6 of [RFC10002] MUST be used. The same transaction identifier MUST be used for the nonce request and response messages and for the subsequent request and response messages used to transmit the CSR. The senderNonce and recipientNonce controls specified in Section 6.6 of [RFC10002] can be used to pair each CMC request with its corresponding response, but they do not replace the transaction identifier used to associate the nonce exchange with the subsequent CSR exchange.¶

In the event of an error, or if the CMC server is unable or unwilling to provide the requested nonce, the CMC server MAY return status information about the request using either an Extended CMC Status Info Control or a CMC Status Info Control, as defined in Section 6.1 of [RFC10002].¶

7. IANA Considerations

8. Operational Considerations

When the RA/CA is requested to provide a nonce to an end entity, it can generate the nonce locally or obtain it through an interaction with the Verifier. According to the IETF RATS architecture [RFC9334], the Verifier is responsible for validating Evidence about an Attester and generating Attestation Results for use by a Relying Party.¶

A non-empty nonce MUST contain a random byte sequence with at least 64 bits of entropy. The RA/CA MUST ensure that a nonce it generates is unique and MUST NOT reuse it. If the RA/CA obtains a nonce from the Verifier, it MUST ensure that the Verifier uses the same policy for uniqueness and non-reuse properties.¶

The length of the nonce depends on the attestation technology in use, as specific nonce lengths may be required by the end entity. This specification assumes that the RA/CA possesses knowledge, either out-of-band or through the len field in the nonce request message, regarding the required nonce length for the attestation technology. Nonces of incorrect length may cause the attestation to fail.¶

For instance, the PSA attestation token [RFC9783] supports nonce lengths of 32, 48, and 64 bytes. Other attestation technologies employ nonces of similar lengths.¶

The end entity MUST use the received nonce if the attestation technology supports its length. If the selected attestation statement type defines a deterministic nonce transformation for use by a specific Attester or sub-Attester, the end entity MUST apply only that transformation and only for the purpose defined by that specification.¶

If type-specific response information is returned with the nonce, the end entity MUST process that information according to the selected type when invoking the attestation technology. Such information MAY include parameters or metadata needed to apply, identify, or validate a deterministic nonce transformation defined by the attestation statement type.¶

While this specification does not address the semantics of the attestation API or the underlying software/hardware architecture, the API returns Evidence from the Attester in a format specific to the attestation technology used and identified by the AttestationStatement type. The returned Evidence is encapsulated in the AttestationStatement within the AttestationBundle carried in the CSR, as defined in [I-D.ietf-lamps-csr-attestation]. The software generating the CSR treats the attestation statement payload as an opaque blob and does not interpret its format. It is crucial to note that the nonce is included in the Evidence, either implicitly or explicitly, and MUST NOT be conveyed in CSR structures outside of the attestation statement payload.¶

The freshness established by the nonce applies to the Evidence as bound to the nonce used by the attestation technology. This specification does not assign independent freshness semantics to other claims contained in the Evidence. The interpretation of any other claim, including whether it represents current state, historical state, configuration state, or measurement results, is defined by the attestation technology, the appraisal policy, and the Verifier or Relying Party processing rules.¶

Using nonces causes the RA/CA to create state for outstanding freshness challenges. This state increases the attack surface for denial-of-service attacks, for example by causing the RA/CA to allocate memory for many nonce requests that never result in corresponding Evidence. The RA/CA SHOULD reduce this exposure by limiting nonce lifetimes, bounding the number of outstanding nonces, applying rate limits, associating nonce state with an authenticated or otherwise constrained requester where possible, and promptly discarding expired state. The use of a stateless cookie mechanism to reduce this state-management burden is also possible but not further detailed in this specification.¶

9. Security Considerations

This specification details the process of obtaining a nonce via CMP, EST, and CMC. Therefore, the security considerations of these protocols apply. Regarding the use of attestation statements in a CSR, the security considerations outlined in [I-D.ietf-lamps-csr-attestation] are pertinent to this specification.¶

The security properties of remote attestation do not generally depend on the confidentiality of the nonce. However, optional type-specific request or response information conveyed together with the nonce can reveal privacy-sensitive or deployment-sensitive information, such as platform topology, certificate identifiers, or measurement selections.¶

[RFC9334] defines the IETF remote attestation architecture and extensively discusses nonce-based freshness. Specific attestation technology specifications such as [RFC9711] and [RFC9783] offer guidance on replay protection using nonces. This document defers specific recommendations to those specifications.¶

If an attestation technology or Composite Attester profile transforms a received nonce before embedding it in Evidence, that transformation MUST be deterministic and MUST preserve at least the minimum entropy required by the attestation technology. The defining specification MUST ensure that the Verifier has enough information to reconstruct or validate the transformed value. Specifications defining such transformations SHOULD use well-analyzed cryptographic mechanisms for nonce expansion or size adjustment to ensure that the resulting entropy and security properties remain acceptable.¶

If type-specific information is used, the corresponding specification MUST define the syntax and semantics of that information, including any confidentiality requirements. Implementations SHOULD minimize the amount of such information returned by the RA/CA. When confidentiality is required by deployment policy or by the attestation technology specification, implementations MUST protect this information using the message or transport security mechanisms of the enrollment protocol.¶

10. References

Appendix A. Example: TPM 2.0 PCR Selection for reqInfo and respInfo

This appendix provides an informative example showing how reqInfo and respInfo can be used with a TPM 2.0-based attestation procedure such as the challenge-response exchange described in Section 2.1.1.3.2 of [RFC9684].¶

In this example, the end entity wants to obtain a nonce for use with a TPM 2.0 attestation statement. The end entity first requests a nonce from the RA/CA. The reqInfo field can carry optional information from the Attester side that helps the Verifier prepare the TPM 2.0 challenge, such as which Attestation Key certificates are available.¶

The resulting NonceResponse corresponds to the TPM 2.0 challenge parameters from [RFC9684], with one exception: the nonce-value from the RFC 9684 challenge is conveyed in this document's top-level nonce field rather than inside respInfo. The remaining challenge parameters, such as the selected PCR bank, PCR indices, and the selected Attestation Key certificate, are conveyed in respInfo.¶

The exact syntax of reqInfo and respInfo is defined by the specification of the OID in the respective type field. The JSON-like notation below shows examples only and is used to explain the role of these fields:¶

NonceRequest = {
  "len": 32,
  "reqTypeInfo": {
    "type": "1.2.3.4.5",
    "reqInfo": {
      "certificate-name": ["aik-1", "aik-2"],
      "supported-hash-algo": ["TPM_ALG_SHA256"]
    }
  }
}

NonceResponse = {
  "nonce": "MTIzNDU2Nzg5MDEyMzQ1Njc4OTAxMjM0NTY3ODkwMTI",
  "expiry": 600,
  "respTypeInfo": {
    "type": "1.2.3.4.6",
    "respInfo": {
      "tpm20-pcr-selection": [
        {
          "tpm20-hash-algo": "TPM_ALG_SHA256",
          "pcr-index": [0, 1, 2, 3]
        }
      ],
      "certificate-name": "aik-1"
    }
  }
}

In this example:¶

• reqInfo.certificate-name lets the Attester indicate more than one available Attestation Key certificate when multiple TPM attestation keys are present.¶

• respInfo.tpm20-pcr-selection identifies the PCR bank and PCR indices that the Attester is expected to include in the TPM quote or equivalent Evidence.¶

• respInfo.certificate-name identifies which Attestation Key certificate the Attester is to use when generating the fresh Evidence associated with the returned nonce.¶

This example is intended only to explain the purpose of reqInfo and respInfo. It does not define a new reqInfo or respInfo type, a new OID, or a TPM attestation profile. The TPM quote itself, its signature, and any optional unsigned PCR values are conveyed later as Evidence and are not part of respInfo.¶

Appendix B. ASN.1 Module

The following module adheres to ASN.1 specifications [X.680] and [X.690].¶

<CODE BEGINS>

Att-Fresh-Req
  { iso(1) identified-organization(3) dod(6) internet(1)
  security(5) mechanisms(5) pkix(7) id-mod(0)
  id-mod-att-fresh-req (TBDMOD) }

DEFINITIONS IMPLICIT TAGS ::=
BEGIN
EXPORTS ALL;
IMPORTS

id-it
  FROM PKIXCMP-2023
    { iso(1) identified-organization(3) dod(6) internet(1)
      security(5) mechanisms(5) pkix(7) id-mod(0)
      id-mod-cmp2023-02(116) }

id-cmc, CMC-CONTROL
FROM EnrollmentMessageSyntax-2025
   { iso(1) identified-organization(3) dod(6) internet(1)
     security(5) mechanisms(5) pkix(7) id-mod(0)
     id-mod-enrollMsgSyntax-2025(124) }

;

-- NonceRequest and NonceResponse types

ATTESTATION-NONCE-REQUEST ::= TYPE-IDENTIFIER

AttestationNonceRequestSet ATTESTATION-NONCE-REQUEST ::= {
   ... -- None defined in this document --
}

ATTESTATION-NONCE-RESPONSE ::= TYPE-IDENTIFIER

AttestationNonceResponseSet ATTESTATION-NONCE-RESPONSE ::= {
   ... -- None defined in this document --
}

NonceRequestTypeInfo ::= SEQUENCE {
    type ATTESTATION-NONCE-REQUEST.&id(
                 {AttestationNonceRequestSet}),
    -- identifies the nonce-request syntax for the selected
    --   attestation statement type
    reqInfo  ATTESTATION-NONCE-REQUEST.&Type(
                 {AttestationNonceRequestSet}{@type}) OPTIONAL
    -- contains type-specific nonce-request information
}

NonceResponseTypeInfo ::= SEQUENCE {
    type ATTESTATION-NONCE-RESPONSE.&id(
                 {AttestationNonceResponseSet}),
    -- identifies the nonce-response syntax for the selected
    --   attestation statement type
    respInfo ATTESTATION-NONCE-RESPONSE.&Type(
                 {AttestationNonceResponseSet}{@type}) OPTIONAL
    -- contains type-specific nonce-response information
}

 NonceRequest ::= SEQUENCE {
    len      INTEGER (8..64) OPTIONAL,
    -- indicates the desired length of the requested nonce
    reqTypeInfo NonceRequestTypeInfo OPTIONAL
 }

 NonceResponse ::= SEQUENCE {
    nonce    OCTET STRING (SIZE(0 | 8..64)),
    -- contains the nonce, preferably of length len
    -- a zero-length OCTET STRING indicates that no proof of
    --   freshness is required
    expiry   INTEGER (0..MAX) OPTIONAL,
    -- hint indicating how long in seconds the nonce issuer
    --   expects the nonce to remain acceptable
    respTypeInfo NonceResponseTypeInfo OPTIONAL
 }
 id-it-nonceRequest OBJECT IDENTIFIER ::= { id-it TBD1 }
    NonceRequestValue ::= NonceRequest

 id-it-nonceResponse OBJECT IDENTIFIER ::= { id-it TBD2 }
    NonceResponseValue ::= NonceResponse

 cmc-nonceReq CMC-CONTROL ::=
     { NonceRequest IDENTIFIED BY id-cmc-nonceReq }
 id-cmc-nonceReq OBJECT IDENTIFIER ::= { id-cmc TBD4 }

 cmc-nonceResp CMC-CONTROL ::=
     { NonceResponse IDENTIFIED BY id-cmc-nonceResp }
 id-cmc-nonceResp OBJECT IDENTIFIER ::= { id-cmc TBD5 }

END
<CODE ENDS>

Acknowledgments

We would like to thank Russ Housley, Thomas Fossati, Watson Ladd, Ionut Mihalcea, Carl Wallace, and Michael StJohns for their review comments.¶

Authors' Addresses