Network Working Group Michael Peck, NSA
Internet-Draft Sean Turner, IECA
Intended Status: Informational December 2, 2009
Expires: June 2, 2010
Suite B Profile of Certificate Management over CMS
draft-turner-suiteb-cmc-00.txt
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Abstract
The United States Government has published guidelines for "NSA Suite
B Cryptography", which defines cryptographic algorithm policy for
national security applications. This document specifies a profile of
the Certificate Management over CMS (CMC) protocol for managing Suite
B X.509 public key certificates. This profile is a refinement of
RFC5272, RFC5273, and RFC5274.
1. Introduction
This document specifies a profile for using the Certificate
Management over CMS (CMC) protocol, defined in [RFC5272], [RFC5273],
and [RFC5274], to manage X.509 public key certificates compliant with
the United States National Security Agency's Suite B Cryptography as
defined in the Suite B Certificate and Certificate Revocation List
(CRL) Profile [SBCERT]. This document specifically focuses on
defining CMC interactions for both initial enrollment and rekey of
Suite B public key certificates between a client and a Certification
Authority (CA). One or more Registration Authorities (RAs) may act
as intermediaries between the client and the CA. This profile may be
further tailored by specific communities to meet their needs.
Specific communities will also define Certificate Policies that
implementations must comply with.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The terminology in [RFC5272] Section 2.1 applies to this profile.
3. Requirements and Assumptions
All key pairs are on either the curve P-256 or the curve P-384. FIPS
186-3 [FIPS1863] or NIST Special Publication 800-56A [SP80056A]
provides useful guidance for elliptic curve key pair generation.
This document assumes that the required trust anchors have been
securely provisioned to the client and, when applicable, any RAs.
All requirements in [RFC5272], [RFC5273], and [RFC5274] apply, except
where overridden by this profile.
This profile was developed with the scenarios described in Appendix A
in mind. However, use of this profile is not limited to just those
scenarios.
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The term "client" in this profile typically refers to an End-Entity
(EE). However, it may instead refer to a third party acting on the
End-Entity's behalf. The client may or may not be the entity that
actually generates the key pair, but it does perform the CMC protocol
interactions with the RA and/or CA. For example, the client may be a
token management system that communicates with a cryptographic token
through an out-of-band secure protocol.
This profile may be used to manage RA or CA certificates. In that
case, the RA or CA whose certificate is being managed is considered
to be the End-Entity.
4. Client Requirements: Generating PKI Requests
This section specifies the conventions employed when a client
requests a certificate from a Public Key Infrastructure (PKI).
The Full PKI Request MUST be used and it MUST be encapsulated in a
SignedData, as per [RFC5008]. The PKIData content type complies with
[RFC5272] with the following additional guidance:
o controlSequence MUST be present. It MUST include the following
CMC controls: Transaction ID and Sender Nonce. Other CMC
controls MAY be included.
o If the request is being authenticated using a shared secret,
then the following guidance in this paragraph applies:
Identity Proof Version 2 control MUST be included. hashAlgId
MUST be id-sha256 for P-256 certificate requests, and MUST be
id-sha384 for P-384 certificate requests, as per [SHA2].
macAlgId MUST be HMAC-SHA256 for P-256 certificate requests,
and MUST be HMAC-SHA384 for P-384 certificate requests, as per
[RFC4231]. If the subject included in the certificate request
is NULL or otherwise does not uniquely identify the End-
Entity, then the POP Link Random control MUST be included to
prevent substitution attacks, and the POP Link Witness Version
2 control MUST be included in the inner PKCS #10 or CRMF
request as described in Sections 4.1 and 4.2.
o reqSequence MUST be present. It MUST include at least one tcr
(see Section 4.1) or crm (see Section 4.2) TaggedRequest.
Support for the orm choice is OPTIONAL.
If the Full PKI Request contains a P-256 public key, then the
SignedData encapsulating the Full PKI Request MUST be generated using
either SHA-256 and ECDSA with P-256, or using SHA-384 and ECDSA with
P-384, as per [RFC5008]. If the Full PKI Request contains a P-384
public key, then the SignedData MUST be generated using SHA-384 and
ECDSA with P-384, as per [RFC5008].
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The Full PKI Request SHOULD be signed using the private key that
corresponds to the subject public key of an existing signature
certificate. However, during initial enrollment, an appropriate
signature certificate may not yet exist. If the Full PKI Request
includes one or more signature certificate requests, then for initial
enrollment authenticated using a shared secret when no appropriate
certificate yet exists, the Full PKI Request MAY instead be signed
using the private key corresponding to the subject public key of one
of the requested signature certificates. The Full PKI Request MUST
NOT ever be signed using a key pair intended for use in a key
establishment certificate.
4.1. Tagged Certificate Request
The reqSequence tcr choice conveys PKCS #10 [RFC2986] syntax. The
CertificateRequest MUST comply with [RFC5272] Section 3.2.1.2.1 with
the following additional guidance:
o subjectPublicKeyInfo MUST be set as defined in 4.4 of [SBCERT];
o attributes MUST include one ExtensionReq attribute. The Key
Usage extension MUST be included and it MUST be set as per
[SBCERT]. For rekey, if the subject is NULL, then the
SubjectAltName extension MUST be included and set equal to the
SubjectAltName of the certificate being rekeyed. Other
extension requests MAY be included as desired.
o For non-rekey requests, if the Full PKI Request encapsulating
this Tagged Certificate Request is being signed by a key for
which a certificate currently exists, and the Subject in the
certificate request is NULL or otherwise does not uniquely
identify the End-Entity, then the SigningCertificateV2
attribute, as defined in [RFC5035], SHOULD also be included in
the attributes field. Support for the policies field is
optional. The ESSCertIDV2 hashAlgorithm field MUST be set to
id-sha256 for P-256 certificate requests and id-sha384 for P-
384 certificate requests. Presence of this attribute protects
against substitution attacks.
o If the request is being authenticated using a shared secret,
and the Subject in the certificate request is NULL or
otherwise does not uniquely identify the End-Entity, then the
POP Link Witness Version 2 control MUST be included in the
attributes field. keyGenAlgorithm MUST be id-sha256 for P-256
certificate requests and MUST be id-sha384 for P-384
certificate requests. macAlgorithm MUST be HMAC-SHA256 for P-
256 certificate requests, and MUST be HMAC-SHA384 for P-384
certificate requests. Presence of this attribute protects
against substitution attacks.
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o signatureAlgorithm MUST be ecdsa-with-sha256 for P-256
certificate requests, and MUST be ecdsa-with-sha384 for P-384
certificate requests;
o signature MUST be generated using the private key corresponding
to the public key in the CertificationRequestInfo, for both
signature and key establishment certificate requests. The
signature provides proof of possession of the private key to the
Certification Authority.
4.2. Certificate Request Message
The reqSequence crm choice conveys Certificate Request Message Format
(CRMF) [RFC4211] syntax. The CertReqMsg MUST comply with [RFC5272]
Section 3.2.1.2.2 with the following additional guidance:
o popo MUST be included using the signature (POPOSigningKey) Proof
of Possession choice and set as defined in [RFC4211] section 4.1
for both signature and key establishment certification requests.
The POPOSigningKey poposkInput field MUST be omitted. The
POPOSigningKey algorithmIdentifier MUST be ecdsa-with-sha256 for
P-256 certificate requests, and MUST be ecdsa-with-sha384 for P-
384 certificate requests. The signature MUST be generated using
the private key corresponding to the public key in the
CertTemplate.
The CertTemplate MUST comply with [RFC5272] Section 3.2.1.2.2 with
the following additional guidance:
o version MAY be included and, if included, it MUST be set to 2 as
per paragraph 4.3 of [SBCERT];
o publicKey MUST be set as defined in 4.4 of [SBCERT];
o extensions MUST include at least the Key Usage extension and it
MUST be set as per [SBCERT]. For rekey, if the subject is NULL,
then the SubjectAltName extension MUST be included and set equal
to the SubjectAltName of the certificate being rekeyed. Other
extension requests MAY be included as desired.
For non-rekey requests, if the Full PKI Request encapsulating this
Certificate Request Message is being signed by a key for which a
certificate currently exists, and the Subject in the certificate
request is NULL or otherwise does not uniquely identify the End-
Entity, then the SigningCertificateV2 attribute, as defined in
[RFC5035], SHOULD be included in the controls field. Support for the
policies field is optional. The ESSCertIDV2 hashAlgorithm field MUST
be set to id-sha256 for P-256 certificate requests and id-sha384 for
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P-384 certificate requests. Presence of this attribute protects
against substitution attacks.
If the request is being authenticated using a shared secret, and the
Subject in the certificate request is NULL or otherwise does not
uniquely identify the End-Entity, then the POP Link Witness Version 2
control MUST be included in the controls field. keyGenAlgorithm MUST
be id-sha256 for P-256 certificate requests and MUST be id-sha384 for
P-384 certificate requests. macAlgorithm MUST be HMAC-SHA256 for P-
256 certificate requests and MUST be HMAC-SHA384 for P-384
certificate requests. Presence of this attribute protects against
substitution attacks.
5. RA Requirements: Processing PKI Requests (Client to CA)
This section addresses the optional case where one or more RAs act as
intermediaries between the client and CA as described in Section 7 of
[RFC5272]. In this section, the term "client" refers to the entity
from which the RA received the PKI Request. This section is only
applicable to RAs.
5.1. RA Generated PKI Requests
If the RA encapsulates the client-generated PKI Request in a new RA-
signed PKI Request, it will create a Full PKI Request encapsulated in
a SignedData. If the request contains a certification request for a
P-256 public key, then the SignedData MUST be generated using either
SHA-256 and ECDSA with P-256 or SHA-384 and ECDSA with P-384, as per
[RFC5008]. If the request contains a certification request for a P-
384 public key, then the SignedData MUST be generated using SHA-384
and ECDSA with P-384, as per [RFC5008]. The PKIData content type
complies with [RFC5272] with the following additional guidance:
o controlSequence MUST be present. It MUST include the following
CMC controls: Transaction ID and Sender Nonce. Other
appropriate CMC controls MAY be included.
o cmsSequence MUST be present. It contains the original,
unmodified request received from the client.
6. CA Requirements
This section specifies the requirements for CAs that receive PKI
Requests and that generate PKI Responses.
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6.1. CA Processing of PKI Requests
CAs MUST ensure that only the permitted signature, hash, and MAC
algorithms described throughout this profile are used, and otherwise
reject the request.
For requests involving an RA, the CA MUST verify the RA's
authorization. Only RAs can include the Modify Certification Request
control. The following certificate fields MUST NOT be modifiable
using the Modify Certification Request control: version, publicKey,
and the key usage extension. The request MUST be rejected if an
attempt to modify those certificate request fields is present.
If the client generated PKI Request includes a SigningCertificateV2
attribute either in the CertRequest controls field for a CRMF request
or in the tcr attributes field for a PKCS#10 request, then the CA
SHOULD ensure that the certificate referenced in the attribute
corresponds to the private key used to sign the PKI Request. If the
CA performs this check, and the referenced certificate doesn't
correspond to the private key used to sign the PKI Request, then the
CA MUST reject the PKI Request.
6.2. CA Generated PKI Responses
The Full PKI Response MUST be used and it MUST be encapsulated in a
SignedData, as per [RFC5008]. The PKIResponse content type complies
with [RFC5272] with the following additional guidance:
o controlSequence MUST be included. It MUST include the following
CMC controls: Extended CMC Status Info, Transaction ID, Sender
Nonce, and Recipient Nonce. Other appropriate CMC controls MAY
be included.
o If the SigningCertificateV2 check is performed and does not
pass, then the Extended CMC Status Info CMCStatus value MUST
be set to failed.
If the PKI Response is in response to an RA encapsulated PKI Request,
then the above PKI Response is encapsulated in another CA generated
PKI Response. That PKI Response MUST be encapsulated in a
SignedData, as per [RFC5008]. The above PKI Response is placed in
the encapsulating PKI Response cmsSequence field. The other fields
are as above. The following illustrates a successful CA response to
an RA encapsulated PKI Request:
SignedData (applied by the CA)
PKIData
controlSequence (Extended CMC Status Info, Transaction ID,
Sender Nonce, Recipient Nonce)
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cmsSequence
SignedData (applied by CA and includes returned
certificates)
PKIData
controlSequence (Extended CMC Status Info, Transaction
ID, Sender Nonce, Recipient Nonce)
The same private key used to sign certificates MUST NOT be used to
sign Full PKI Response messages. Instead, a separate certificate
authorized to sign CMC responses MUST be used. Certificates
authorized to sign Full PKI Responses SHOULD include the id-kp-cmcCA
following Extended Key Usage (EKU):
id-kp-cmcCA OBJECT IDENTIFIER ::= { id-TBSL }
The certificate authorized to sign Full PKI Responses MAY also
include the Cryptographic Message Syntax (CMS) Content Constraints
(CCC) certificate extension [CCC]. CCC SHOULD be included if
constraints are to be placed on the content types generated.
The signature on the SignedData MUST be generated using either ECDSA
P-256 with SHA-256 or ECDSA P-384 with SHA-384. If the Full PKI
Response is a successful response to a P-256 public key certificate
request, then the SignedData MUST be generated using either SHA-256
and ECDSA with P-256 or SHA-384 and ECDSA with P-384, as per
[RFC5008]. If the Full PKI Response is a successful response to a P-
384 public key certificate request, then the SignedData MUST be
generated using SHA-384 and ECDSA with P-384, as per [RFC5008]. If
the Full PKI Response is an unsuccessful response to a PKI Request,
then the SignedData MUST be signed by either SHA-256 and ECDSA with
P-256 or SHA-384 and ECDSA with P-384. If the Full PKI Response is a
successful response to a PKI Request that only contained a Get
Certificate or Get CRL control, then the SignedData MUST be signed by
either SHA-256 and ECDSA with P-256 or SHA-384 and ECDSA with P-384.
7. Client Requirements: Processing PKI Responses
Clients MUST authenticate all PKI Responses. This includes verifying
that the PKI Response is signed by a CA whose certificate validates
back to a trust anchor and that the CA's certificate either includes
the id-kp-cmcCA EKU, includes an appropriate CMS Content Constraints
extension, or is determined to be authorized to sign responses
through an implementation specific mechanism. The PKI Response MAY
be signed by an RA if it is an error message, or if the PKI Response
contains an inner PKI Response signed by a CA. In that case, each
layer of PKI Response must still contain a valid signature signed by
an entity with a valid certificate that verifies back to an
acceptable trust anchor.
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When a newly issued certificate is included in the PKI Response, the
client MUST verify that the newly issued certificate's public key
matches the public key that the client requested. The client MUST
also ensure that the certificate's signature is valid and that the
signature validates back to an acceptable trust anchor.
PKI Responses that do not pass these tests MUST be rejected.
8. CMC Controls
When the Identity Proof V2 control is used, the shared-secret MUST be
randomly generated and securely distributed. The shared-secret MUST
provide at least 128 bits of strength for P-256 certificate requests
and at least 192 bits of strength for P-384 certificate requests.
9. Security Considerations
The security considerations in [RFC5272], [RFC5273], and [RFC5274]
apply.
Compliant with NIST Special Publication 800-57 [SP80057], this
profile defines proof-of-possession of a key establishment private
key by performing a digital signature. Except for one-time proof-of-
possession, a single key pair MUST NOT be used for both signature and
key establishment.
This specification requires implementations to generate key pairs and
other random values. The use of inadequate pseudo-random number
generators (PRNGs) can result in little or no security. The
generation of quality random numbers is difficult. NIST Special
Publication 800-90 [SP80090] or FIPS 186 [FIPS1863] may offer
guidance.
When RAs are used, the list of authorized RAs must be securely
distributed out-of-band to CAs.
10. IANA Considerations
None: All identifiers are already registered. Please remove this
section prior to publication as an RFC.
11. References
11.1. Normative References
[CCC] Housley, R., Wallace, C., and S. Ashmore, "Cryptographic
Message Syntax (CMS) Content Constraints X.509
Certificate Extension", draft-housley-cms-content-
constraints-extn-02, work-in-progress.
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[FIPS1863] National Institute of Standards and Technology (NIST),
FIPS 186-3 DRAFT: Digital Signature Standard (DSS),
November 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, March 1997.
[RFC2986] Kaliski, B., "PKCS #10: Certification Request Syntax
v1.5", RFC 2986, November 2000.
[RFC4086] Eastlake, D., 3rd, Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC
4086, June 2005.
[RFC4211] J. Schaad, "Internet X.509 Public Key Infrastructure
Certificate Request Message Format (CRMF)", RFC 4211,
September 2005.
[RFC4231] M. Nystrom, "Identifiers and Test Vectors for HMAC-SHA-
224, HMAC-SHA-256, HMAC-SHA-384, and HMAC-SHA-512", RFC
4231, December 2005.
[RFC5008] Solinas, J. and R. Housley, "Suite B in
Secure/Multipurpose Internet Mail Extensions (S/MIME)",
RFC 5008, September 2007.
[RFC5035] J. Schaad, "Extended Security Services (ESS) Update:
Adding Algorithm Agility", RFC 5035, August 2007.
[RFC5272] Schaad, J. and M. Myers, "Certificate Management over CMS
(CMC)", RFC 5272, June 2008.
[RFC5273] Schaad, J. and M. Myers, "Certificate Management over CMS
(CMC): Transport Protocols", RFC 5273, June 2008.
[RFC5274] Schaad, J. and M. Myers, "Certificate Management Messages
over CMS (CMC): Compliance Requirements", RFC 5274, June
2008.
[SBCERT] Solinas, J., and L. Zieglar, "Suite B Certificate and
Certificate Revocation List (CRL) Profile", draft-
solinas-suiteb-cert-profile-04.txt, work-in-progress.
/** RFC EDITOR: Please replace "SBCERT" with RFC#### when draft-
solinas-suiteb-cert-profile is published.
[SHA2] S. Turner, "Using SHA2 Algorithms with CMS", draft-ietf-
smime-sha2-11.txt, work-in-progress.
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/** RFC EDITOR: Please replace "SHA2" with RFC#### when draft-ietf-
smime-sha2 is published.
[SP80056A] National Institute of Standards and Technology (NIST),
Special Publication 800-56 A: Recommendation for Pair-
Wise Key Establishment Schemes Using Discrete Logarithm
Cryptography, March 2007.
11.2. Informative References
[SP80057] National Institute of Standards and Technology (NIST),
Special Publication 800-57 Part 1: Recommendation for Key
Management, March 2007.
[SP80090] National Institute of Standards and Technology (NIST),
Special Publication 800-90: Recommendation for Random
Number Generation Using Deterministic Random Number Bits
Generators (Revised), March 2007.
Authors' Addresses
Michael Peck
National Security Agency
9800 Savage Road Ste 6704
Ft. Meade, MD 20755-6704
USA
Email: mpeck@restarea.ncsc.mil
Sean Turner
IECA, Inc.
3057 Nutley Street, Suite 106
Fairfax, VA 22031
USA
Email: turners@ieca.com
Appendix A. Scenarios
This section illustrates several potential certificate initial
enrollment and rekey scenarios supported by this profile. This
section does not intend to place any limits or restrictions on the
use of CMC.
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A.1. Initial Enrollment of Signature or CA Certificates
This section describes three scenarios for authenticating initial
signature or CA certificate enrollment requests:
1. Previously installed signature certificate (e.g., Manufacturer
Installed Certificate);
2. Shared secret distributed securely out-of-band;
3. RA authentication.
A.1.1. Previously Installed Signature Certificate
In this scenario, the EE has had a signature certificate installed by
the cryptographic module manufacturer. As the EE already has a
signature certificate, it can be used to authenticate a request for a
new certificate. The EE signs the Full PKI Request with the private
key that corresponds to the subject public key of a previously
installed signature certificate. The CA will recognize the
authorization of the previously installed certificate and issue an
appropriate certificate to the EE. The Subject in the previously
installed certificate and in the newly issued certificate are not
required to match.
A.1.2. Shared Secret Distributed Securely Out-of-Band
In this scenario, the CA distributes a shared secret out-of-band to
the EE that the EE uses to authenticate its certificate request. The
EE signs the Full PKI Request with the private key for which the
certification is being requested. The EE includes the Identity Proof
Version 2 control to authenticate the request using the shared
secret. The CA uses either the Identification control or the Subject
in the EE's enclosed PKCS #10 or CRMF certification request message
to identify the request. The EE performs either the POP Link Witness
Version 2 mechanism as described in [RFC5272] section 6.3.1.1 or the
Shared-Subject/Subject DN Linking mechanism as described in [RFC5272]
section 6.3.2. The Subject in the enclosed PKCS #10 or CRMF
certificate request does not necessarily match the issued
certificate, as it may just be used to help identify the request (and
corresponding shared secret) to the CA.
A.1.3. RA Authentication
In this scenario, the EE does not automatically authenticate its
enrollment request to the CA, either because the EE has nothing to
authenticate the request with, or because organizational policy
requires RA involvement. The EE creates a Full PKI Request and sends
it to an RA. The RA verifies the authenticity of the request, then,
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if approved, encapsulates and signs the request as described in
Section 5.2, forwarding the new request on to the CA. The Subject in
the PKCS #10 or CRMF certification request is not required to match
the issued certificate, it may just be used to help identify the
request to the RA and/or CA.
A.2. Initial Enrollment of Key Establishment Certificates
This scenario addresses the initial enrollment of End-Entity Key
Establishment Certificates. This scenario requires that the End-
Entity holds a private key corresponding to either a previously
installed signature certificate (see Section A.1.1) or End-Entity
signature certificate. The private key corresponding to the existing
certificate is used to sign the Full PKI Request for the Key
Establishment Certificate.
A.3. Rekey
There are two scenarios to support the rekey of certificates that are
already enrolled. One addresses the rekey of signature certificates
and the other addresses the rekey of key establishment certificates.
Typically, organizational policy will require certificates to be
currently valid to be rekeyed, and may require initial enrollment to
be repeated when rekey is not possible.
A.3.1. Rekey of Signature Certificates
When a signature certificate is rekeyed, the PKCS #10 or CRMF
certification request message enclosed in the Full PKI Request will
include the same Subject as the current signature certificate. The
Full PKI Request will be signed by the current private key
corresponding to the current signature certificate.
A.3.2. Rekey of Key Establishment Certificates
Rekey of a key establishment certificate is handled equivalently to
its initial enrollment as described in Section A.2.
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