[Search] [txt|pdf|bibtex] [Tracker] [WG] [Email] [Nits]

Versions: 00 02                                                         
Internet Draft                           C. Adams (Entrust Technologies)
PKIX Working Group                       M. Myers (VeriSign)
Expires in 6 months                                       February 1998

                  Internet X.509 Public Key Infrastructure
                   Certificate Management Message Formats

1. Status of this Memo

This document is an Internet-Draft.  Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, and
its working groups.  Note that other groups may also distribute working
documents as Internet-Drafts.

Internet-Drafts are draft documents valid for a maximum of 6 months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference material
or to cite them other than as "work in progress."

To learn the current status of any Internet-Draft, please check the
"1id-abstracts.txt" listing contained in the Internet-Drafts Shadow
Directories on ftp.is.co.za(Africa), nic.nordu.net (Europe),
munnari.oz.au (Pacific Rim), ds.internic.net (US East Coast), or
ftp.isi.edu (US West Coast).

2. Abstract

This is a draft of the Internet X.509 Public Key Infrastructure (PKI)
Certificate Management Messages Formats (CMMF).  It establishes
harmonized message formats to be used in conjunction with security
protocol implementations that require interaction with a Public Key
Infrastructure (PKI).

This draft is being discussed on the ''ietf-pkix'' mailing list. To
subscribe, send a message to ietf-pkix-request@tandem.com with the
single word “subscribe” in the body of the message.

3. Introduction

This document defines message formats to be used between a PKI client
and a PKI server or service(where a PKI is defined to encompass the
roles of Registration Authority and Certification Authority).  Using
these message formats, a PKI client may:
- Request public key certification
     - Responses may include CA-generated key pairs
- Request revocation of a certificate
- Receive announcements directly from a PKI on:
     - CA Key Update
     - Renewed Certificates
     - Subscriber Revocation notices
     - CRL refresh

Myers, Adams                                                    [Page 1]

INTERNET DRAFT                                             February 1998

- Request data of a PKI, including:
     - One’s own or others’ certificate
     - CRL download

The specification of a transaction protocol using these message formats
is beyond the scope of this document. It is expected that such protocols
will be defined with a view towards localized interoperability needs.
Where requirements exist to exchange information which is substantially
aligned with the message content in this document, such protocols should
reference these message formats.

"RECOMMENDED", "MAY", and "OPTIONAL" in this document (in uppercase,
as shown) are to be interpreted as described in [RFC2119].
4. Common Data Structures

Several structures are common to more than one message format.  These

- Status information
- Failure information
- Certificate identification
- Encrypted values

4.1 Status Information

Responses may include status information pertaining to a prior request.
The following values are defined:

  PKIStatus ::= INTEGER {
      granted                (0),
      -- you got exactly what you asked for
      grantedWithMods        (1),
      -- you got something like what you asked for; the
      -- requester is responsible for ascertaining the differences
      rejection              (2),
      -- you don't get it, more information elsewhere in the message
      waiting                (3),
      -- the request body part has not yet been processed,
      -- expect to hear more later
      revocationWarning      (4),
      -- this message contains a warning that a revocation is
      -- imminent
      revocationNotification (5),
      -- notification that a revocation has occurred
      keyUpdateWarning       (6)
      -- update already done for the oldCertId specified in
      -- FullCertTemplate

Myers, Adams                                                    [Page 2]

INTERNET DRAFT                                             February 1998

4.2 Failure Information

The following values may be used to provide more information about
failure cases.

  PKIFailureInfo ::= BIT STRING {
  -- since we can fail in more than one way!
  -- More codes may be added in the future if/when required.
      badAlg           (0),
      -- unrecognized or unsupported Algorithm Identifier
      badMessageCheck  (1),
      -- integrity check failed (e.g., signature did not verify)
      badRequest       (2),
      -- transaction not permitted or supported
      badTime          (3),
      -- messageTime was not sufficiently close to the system time,
      -- as defined by local policy
      badCertId        (4),
      -- no certificate could be found matching the provided criteria
      badDataFormat    (5),
      -- the data submitted has the wrong format
      wrongAuthority   (6),
      -- the authority indicated in the request is different from the
      -- one creating the response token
      incorrectData    (7),
      -- the requester's data is incorrect (used for notary services)
      missingTimeStamp (8)
      -- when the timestamp is missing but should be there (by policy)

  PKIStatusInfo ::= SEQUENCE {
      status        PKIStatus,
      statusString  PKIFreeText     OPTIONAL,
      failInfo      PKIFailureInfo  OPTIONAL }

4.3 Certificate Identification

In order to identify particular certificates the following data
structure is used.

CertId ::= SEQUENCE {
      issuer           GeneralName,
      serialNumber     INTEGER }

4.4 Encrypted Values

Certain values in responses may require encryption beyond that that
which may be performed in a PKI protocol.  For example, a CA may
generate key pairs for subscribers but deliver them via an RA. As a
general rule RAs should be prohibited from unnecessary or inadvertent
contact with a subscriber’s private keys.

Myers, Adams                                                    [Page 3]

INTERNET DRAFT                                             February 1998

EncryptedData ::= CHOICE {
      encryptedValue      [0] EncryptedValue,
      cMSEnveloped        [1] EnvelopedData,
      pKCS8               [2] EncryptedPrivateKeyInfo,
      pKCS12              [3] KeysAndCertificates }

The syntax of encryptedValue is defined below.  The EnvelopedData syntax
of cMSEnveloped is defined by [CMS].  The EncryptedPrivateKeyInfo syntax
of pKCS8 is defined by [PKCS8].  The KeysAndCertificates syntax is
defined by [pKCS12].

EncryptedValue ::= SEQUENCE {
      encValue          BIT STRING,
      -- the encrypted value itself
      intendedAlg   [0] AlgorithmIdentifier  OPTIONAL,
      -- the intended algorithm for which the value will be used
      symmAlg       [1] AlgorithmIdentifier  OPTIONAL,
      -- the symmetric algorithm used to encrypt the value
      encSymmKey    [2] BIT STRING           OPTIONAL,
      -- the (encrypted) symmetric key used to encrypt the value
      keyAlg        [3] AlgorithmIdentifier  OPTIONAL
      -- algorithm used to encrypt the symmetric key

Use of this data structure requires that the creator and intended
recipient respectively be able to encrypt and decrypt. Typically, this
will mean that the sender and recipient have, or are able to generate, a
shared secret key.

For Diffie-Hellman keys, the encSymmKey field of EncryptedValue is not
included. For RSA, encSymmKey is a symmetric key encrypted under the
subscriber’s public RSA key.

If the recipient of the PKIMessage already possesses a private key
usable for decryption, then the encSymmKey field MAY contain a session
key encrypted using the recipient’s public key.

5. Message Formats

5.1 Certification Request

[CRMF] defines the preferred structure for production of certification
requests.  It is a flexible mechanism designed to enable mandatory and
optional cryptographic algorithms, centralized key generation, a variety
of proof-of-possession options and several other control features useful
to a robust PKI client enrollment capability.

Current industry practice can be supported for clients through use of
the following structure.
    endEntityInfo    EndEntityInfo,
    regInfo          OCTET STRING OPTIONAL

Myers, Adams                                                    [Page 4]

INTERNET DRAFT                                             February 1998

The endEntityInfo field is used to carry a public key, to prove
possession of the public key and to provide additional ASN.1 attributes
useful to production of the resulting certificate.

The regInfo field contains supplementary information related to the
context of the certification request when such information is required
to fulfill a certification request.  This information could include
subscriber contact information, billing information or other
ancillary information useful to fulfillment of the certification

Current industry practice has established two structures for producing a
signed public key. The use of explicit tagging below allows
disambiguation among these options while maintaining bits on the wire
compatibility with prior implementations:

endEntityInfo :: CHOICE {
pKCS10         CertificationRequest,
signedKey  [0] SignedPublicKeyAndChallenge

SignedPublicKeyAndChallenge :: SEQUENCE {
publicKeyAndChallenge PublicKeyAndChallenge,
signatureAlgorithm AlgorithmIdentifier,
signature BIT STRING

PublicKeyAndChallenge :: SEQUENCE {
spki SubjectPublicKeyInfo,
challenge IA5String

CertificationRequest ::=         SEQUENCE {
  certificationRequestInfo         SEQUENCE {
    version                          INTEGER,
    subject                          Name,
    subjectPublicKeyInfo             SEQUENCE {
      algorithm                        AlgorithmIdentifier,
      subjectPublicKey                 BIT STRING }
    attributes                     [0] IMPLICIT SET OF Attribute }
  signatureAlgorithm               AlgorithmIdentifier,
  signature                        BIT STRING }

The client MAY incorporate one or more standard X.509 v3 extensions in
the request as an ExtensionReq attribute:

ExtensionReq ::= SEQUENCE OF Extension

where Extension is imported from PKIX Part 1 and ExtensionReq is
identified by the OID value {pkcs-9 14}.

Myers, Adams                                                    [Page 5]

INTERNET DRAFT                                             February 1998

5.2 Certification Response

Two options are established for the response to a certification request:
a simple form that enables basic interoperability and a form that
enables generation of subscriber private keys by the CA.

5.2.1 Use of SignedData

[CMS] supports a degenerate case of the SignedData content type where
there are no signers on the content. This degenerate case is used to
convey certificate and CRL information. Certification Authorities MAY
use this format for returning certificate information resulting from the
successful fulfillment of a certification request. The certificate
response MUST include the actual subject certificate corresponding to
the information in the certification request. The response SHOULD
include other certificates which link the issuer to higher level
certification authorities and corresponding CRLs.

CertRep  ::= SEQUENCE {
    response    SignedData, OPTIONAL
    rspInfo     OCTET STRING

Successful requests would include the resulting certificate(s) in the
response field along with any additional {name, value} information
useful to client-side processing of a successful request.  In the event
of an unsuccessful request, the rspInfo field contains information
regarding the failure which may be useful to the requesting entity.

RspInfo content MAY include state information the PKI client needs such
as the contents of the regInfo in the CRMF ( see [CRMF]). Other
additional data could include detailed error information that uniquely
identifies an information field supplied in the original regInfo; e.g.
the Zip Code was incorrect for the specified address or locale or
billing failed because credit card information was in error.

5.2.2 CertRepContent

A CertRepContent data structure contains a CA public key, a status value
and optionally failure information, a subject certificate, and an
encrypted private key.

  CertRepContent ::= SEQUENCE {
      caPubs    [1] SEQUENCE SIZE (1..MAX) OF Certificate OPTIONAL,
      response  SEQUENCE of CertResponse }

  CertResponse ::= SEQUENCE {
      certReqId           INTEGER,
      -- to match this response with corresponding request (a value
      -- of -1 is to be used if certReqId is not specified in the
      -- corresponding request)
      status              PKIStatusInfo,
      certifiedKeyPair    CertifiedKeyPair,   OPTIONAL }

Myers, Adams                                                    [Page 6]

INTERNET DRAFT                                             February 1998

  CertifiedKeyPair ::= SEQUENCE {
      certOrEncCert       CertOrEncCert,
      privateKey      [0] EncryptedValue      OPTIONAL,
      publicationInfo [1] PKIPublicationInfo  OPTIONAL }

  CertOrEncCert ::= CHOICE {
      certificate     [0] Certificate,
      encryptedCert   [1] EncryptedValue }

Given an EncryptedCert and the relevant decryption key the certificate
may be obtained. The purpose of this is to allow a CA to return the
value of a certificate, but with the constraint that only the intended
recipient can obtain the actual certificate. The benefit of this
approach is that a CA may reply with a certificate even in the absence
of a proof that the requester is the end entity which can use the
relevant private key (note that the proof is not obtained until
confirmation of receipt is received by the CA). Thus the CA will not
have to revoke that certificate in the event that something goes wrong
with the proof of possession.

5.3 GetCertInitial

The GetCertInitial message is used to poll for the certificate
associated with prior request if the response to that prior request was
a CertRep message with a status of PENDING.

Certificates are normally referenced using the CA DN and the certificate
serial number.  In this case however a certificate has not yet been
issued.  Thus the CA and Subject DNs are present in the message as a
means to identify the requested certification.

IssuerAndSubject ::= SEQUENCE {
   issuer Name,
   subject Name }

5.4 GetCRL

This operation is used to retrieve CRLs from a certificate server or
service’s repository. This message is useful in circumstances where a
fully-deployed Directory is either infeasible or undesired.

The GetCRL message body consists of the following syntax:

    issuerName  Name,
    cRLName       GeneralName, OPTIONAL
    time          GeneralizedTime, OPTIONAL
    reasons       ReasonFlags OPTIONAL }

The Name component is the value of the Issuer DN in the subject certifi-
cate. The cRLName component may be the value of CRLDistributionPoints in
the subject certificate or equivalent value in the event the certificate
does not contain such a value.  The time component is used by the client

Myers, Adams                                                    [Page 7]

INTERNET DRAFT                                             February 1998

to specify from among potentially several issues of CRL that one whose
thisUpdate value is less than but nearest to the specified time.  In the
absence of a time component, the CA always returns with the most recent
CRL.  The reasons field can be used to specify from among CRLs
partitioned by reason codes.

5.5 Revocation Request

Two options are established to enable programmatic submission of a
revocation request.

5.5.1 RevRequest

RevRequest ::= SEQUENCE {
    issuerName  Name,
    serialNumber  INTEGER,
    reason        ReasonFlags,
    passphrase    OCTET STRING OPTIONAL,
    comment       PrintableString OPTIONAL }

For a revocation request to become a reliable object in the event of a
dispute, a strong proof of originator authenticity is required. A
Registration Authority’s digital signature on the request can provide
this proof for certificates within the scope of the RA’s revocation
authority. However, in the instance when an end-entity has lost use of
their signature private key, it is impossible to produce a reliable
digital signature. [CRMF] provides for the use specification of a
passphrase during enrollment which may be used as an alternative
authenticator in the instance of loss of use. The acceptability of this
practice is a matter of local security policy.

5.5.2 RevReqContent

When requesting revocation of a certificate (or several certificates)
the following data structure is used.

RevReqContent ::= SEQUENCE OF RevDetails

  RevDetails ::= SEQUENCE {
      certDetails         CertTemplate,
      -- allows requester to specify as much as they can about
      -- the cert. for which revocation is requested
      -- (e.g., for cases in which serialNumber is not available)
      revocationReason    ReasonFlags,
      -- from the Draft Amendment (DAM), so CA knows what to use in
      -- Distribution point
      badSinceDate        GeneralizedTime  OPTIONAL,
      -- indicates best knowledge of sender
      crlEntryDetails     Extensions
      -- requested crlEntryExtensions

Myers, Adams                                                    [Page 8]

INTERNET DRAFT                                             February 1998

5.6 Revocation Response

The response to the above message. If produced, this is sent to the
requester of the revocation. (A separate revocation announcement message
MAY be sent to the subject of the certificate for which revocation was

  RevRepContent ::= SEQUENCE {
      status        SEQUENCE SIZE (1..MAX) OF PKIStatusInfo,
      -- in same order as was sent in RevReqContent
      revCerts  [0] SEQUENCE SIZE (1..MAX) OF CertId OPTIONAL,
      -- IDs for which revocation was requested (same order as status)
      crls      [1] SEQUENCE SIZE (1..MAX) OF CertificateList  OPTIONAL
      -- the resulting CRLs (there may be more than one)

5.7 Challenge-Response Proof Of Possession

[CRMF] establishes the basis for a challenge-response proof of
possession technique.  The challenge-response messages for proof of
possession of a private decryption key are specified as follows (see
[MvOV97, p.404], for  details).

  POPODecKeyChallContent ::= SEQUENCE OF Challenge
  -- One Challenge per encryption key certification request (in the
  -- same order as these requests appear in FullCertTemplates).

  Challenge ::= SEQUENCE {
      owf                 AlgorithmIdentifier  OPTIONAL,
      -- MUST be present in the first Challenge; MAY be omitted in any
      -- subsequent Challenge in POPODecKeyChallContent (if omitted,
      -- then the owf used in the immediately preceding Challenge is
      -- to be used).
      witness             OCTET STRING,
      -- the result of applying the one-way function (owf) to a
      -- randomly-generated INTEGER, A.  [Note that a different
      -- INTEGER MUST be used for each Challenge.]
      challenge           OCTET STRING
      -- the encryption (under the public key for which the cert.
      -- request is being made) of Rand, where Rand is specified as
      --   Rand ::= SEQUENCE {
      --      int      INTEGER,
      --       - the randomly-generated INTEGER A (above)
      --      sender   GeneralName
      --       - the sender's name (as included in PKIHeader)
      --   }

  -- One INTEGER per encryption key certification request (in the
  -- same order as these requests appear in FullCertTemplates).  The
  -- retrieved INTEGER A (above) is returned to the sender of the
  -- corresponding Challenge.

Myers, Adams                                                    [Page 9]

INTERNET DRAFT                                             February 1998

5.8 PKI Confirmation content

This data structure is used in three-way protocols as the final
PKIMessage. Its content is the same in all cases - actually there is no
content since the PKIHeader carries all the required information.

  PKIConfirmContent ::= NULL

5.9 Announcements

>From time to time a PKI may need to distribute information to its
clients or subscribers.  These messages are generally unsolicited and
consequently reverse the flow of request-response behavior.
Implementers of protocols that use these message formats should take
this effect into account.

5.9.1 CA Key Update Announcement content

When a CA updates its own key pair the following data structure MAY be
used to announce this event.

  CAKeyUpdAnnContent ::= SEQUENCE {
      oldWithNew          Certificate, -- old pub signed with new priv
      newWithOld          Certificate, -- new pub signed with old priv
      newWithNew          Certificate  -- new pub signed with new priv

To change the key of the CA, the CA does the following:

  1.Generate a new key pair;

  2.Create a certificate containing the old CA public key signed with
    the new private key (the "old with new" certificate);

  3.Create a certificate containing the new CA public key signed with
    the old private key (the "new with old" certificate);

  4.Create a certificate containing the new CA public key signed with
    the new private key (the "new with new" certificate);

  5.Publish these new certificates via the directory and/or other means

  6.Export the new CA public key so that end entities may acquire it
    using the "out-of-band" mechanism (if required).

The old CA private key is then no longer required. The old CA public key
will however remain in use for some time. The time when the old CA
public key is no longer required (other than for non-repudiation) will
be when all end entities of this CA have securely acquired the new CA
public key.

The "old with new" certificate must have a validity period starting at
the generation time of the old key pair and ending at the expiry date of
the old public key.
Myers, Adams                                                   [Page 10]

INTERNET DRAFT                                             February 1998

The "new with old" certificate must have a validity period starting at
the generation time of the new key pair and ending at the time by which
all end entities of this CA will securely possess the new CA public key
(at the latest, the expiry date of the old public key).

The "new with new" certificate must have a validity period starting at
the generation time of the new key pair and ending at the time by which
the CA will next update its key pair.

5.9.2 Certificate Announcement

This structure MAY be used to announce the existence of certificates.

Note that this message is intended to be used for those cases (if any)
where there is no pre-existing method for publication of certificates;
it is not intended to be used where, for example, X.500 is the
method for publication of certificates.

  CertAnnContent ::= Certificate

5.9.3 CRL Announcement

When a CA issues a new CRL (or set of CRLs) the following data structure
MAY be used to announce this event.

  CRLAnnContent ::= SEQUENCE OF CertificateList

5.9.4 Revocation Announcement

When a CA has revoked, or is about to revoke, a particular certificate
it MAY issue an announcement of this (possibly upcoming) event.

  RevAnnContent ::= SEQUENCE {
      status              PKIStatus,
      certId              CertId,
      willBeRevokedAt     GeneralizedTime,
      badSinceDate        GeneralizedTime,
      crlDetails          Extensions  OPTIONAL
      -- extra CRL details(e.g., crl number, reason, location, etc.)

A CA MAY use such an announcement to warn (or notify) a subject that its
certificate is about to be (or has been) revoked. This would typically
be used where the request for revocation did not come from the subject

The willBeRevokedAt field contains the time at which a new entry will be
added to the relevant CRLs.

5.10 Key recovery Response

For key recovery responses the following syntax is used.  For some
status values (e.g., waiting) none of the optional fields will be
Myers, Adams                                                   [Page 11]

INTERNET DRAFT                                             February 1998

  KeyRecRepContent ::= SEQUENCE {
      status          PKIStatusInfo,
      newSigCert  [0] Certificate                   OPTIONAL,
      caCerts     [1] SEQUENCE SIZE (1..MAX) OF
                                   Certificate      OPTIONAL,
      keyPairHist [2] SEQUENCE SIZE (1..MAX) OF
                                   CertifiedKeyPair OPTIONAL

5.11 PKI General Message content

>From time to time a PKI MAY announce other information not explicitly
called out in this specification.  In such cases the following structure
MAY be used to unambiguously identify this information when transmitted
as a PKI message.

InfoTypeAndValue ::= SEQUENCE {
      infoType               OBJECT IDENTIFIER,
      infoValue              ANY DEFINED BY infoType  OPTIONAL
  -- Example InfoTypeAndValue contents include, but are not limited to:
  --  { CAProtEncCert    = {id-it 1}, Certificate                     }
  --  { SignKeyPairTypes = {id-it 2}, SEQUENCE OF AlgorithmIdentifier }
  --  { EncKeyPairTypes  = {id-it 3}, SEQUENCE OF AlgorithmIdentifier }
  --  { PreferredSymmAlg = {id-it 4}, AlgorithmIdentifier             }
  --  { CAKeyUpdateInfo  = {id-it 5}, CAKeyUpdAnnContent              }
  --  { CurrentCRL       = {id-it 6}, CertificateList                 }
  -- where {id-it} = {id-pkix 4} = {1 3 6 1 5 5 7 4}
  -- This construct MAY also be used to define new PKIX Certificate
  -- Management Protocol request and response messages, or general-
  -- purpose (e.g., announcement) messages for future needs or for
  -- specific environments.

  GenMsgContent ::= SEQUENCE OF InfoTypeAndValue
  -- May be sent by EE, RA, or CA (depending on message content).
  -- The OPTIONAL infoValue parameter of InfoTypeAndValue will typically
  -- be omitted for some of the examples given above.  The receiver is
  -- free to ignore any contained OBJ. IDs that it does not recognize.
  -- If sent from EE to CA, the empty set indicates that the CA may send
  -- any/all information that it wishes.

5.12 PKI General Response content

GenRepContent ::= SEQUENCE OF InfoTypeAndValue
  -- The receiver is free to ignore any contained OBJ. IDs that it does
  -- not recognize.

5.13 Error Message

  ErrorMsgContent ::= SEQUENCE {
      pKIStatusInfo          PKIStatusInfo,
      errorCode              INTEGER           OPTIONAL,

Myers, Adams                                                   [Page 12]

INTERNET DRAFT                                             February 1998

      -- implementation-specific error codes
      errorDetails           PKIFreeText       OPTIONAL
      -- implementation-specific error details


This entire memo is about security mechanisms.

One cryptographic consideration is worth explicitly spelling out. In
the protocols specified above, when an end entity is required to
prove possession of a decryption key, it is effectively challenged
to decrypt something (its own certificate). This scheme (and many
others!) could be vulnerable to an attack if the possessor of the
decryption key in question could be fooled into decrypting an
arbitrary challenge and returning the cleartext to an attacker.
Although in this specification a number of other failures in
security are required in order for this attack to succeed, it is
conceivable that some future services (e.g., notary, trusted time)
could potentially be vulnerable to such attacks. For this reason we
re-iterate the general rule that implementations should be very
careful about decrypting arbitrary "ciphertext" and revealing
recovered "plaintext" since such a practice can lead to serious
security vulnerabilities.

7. References

   [COR95]   ISO/IEC JTC 1/SC 21, Technical Corrigendum 2 to ISO/IEC
             9594-8: 1990 & 1993 (1995:E), July 1995.

   [MvOV97]  A. Menezes, P. van Oorschot, S. Vanstone, "Handbook of
             Applied Cryptography", CRC Press, 1997.

   [PKCS7]   RSA Laboratories, "The Public-Key Cryptography Standards
             (PKCS)", RSA Data Security Inc., Redwood City, California,
             November 1993 Release.

   [PKCS10]  RSA Laboratories, "The Public-Key Cryptography Standards
             (PKCS)", RSA Data Security Inc., Redwood City, California,
             November 1993 Release.

   [PKCS11]  RSA Laboratories, "The Public-Key Cryptography Standards -
             PKCS #11:  Cryptographic token interface standard", RSA
             Data Security Inc., Redwood City, California, April 28,

   [RFC2104] H. Krawczyk, M. Bellare, R. Canetti, "HMAC:  Keyed Hashing
             for Message Authentication", Internet Request for Comments
             2104, February, 1997.

Myers, Adams                                                   [Page 13]

INTERNET DRAFT                                             February 1998

   [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
             Requirement Levels", Internet Request for Comments 2119
             (Best Current Practice: BCP 14), March, 1997.

   [X509-AM] ISO/IEC JTC1/SC 21, Draft Amendments DAM 4 to ISO/IEC
             9594-2, DAM 2 to ISO/IEC 9594-6, DAM 1 to ISO/IEC 9594-7,
             and DAM 1 to ISO/IEC 9594-8 on Certificate Extensions,
             1 December, 1996.

   [CRMF]    M. Myers, C. Adams, D. Solo, D. Kemp,
             Certificate Request Message Format,
             February, 1998

   [CMS]     R. Housley, Cryptographic Message Syntax
             December, 1997

   [PKCS8]   Private Key Information Syntax Standard, v1.2
             RSA Laboratories Technical Note
             November 1, 1993

Authors' Addresses
   Michael Myers
   VeriSign, Inc.
   1390 Shorebird Way,
   Mountain View, CA  94043

   Carlisle Adams
   Entrust Technologies
   750 Heron Road, Suite E08,
   Ottawa, Ontario
   Canada K1V 1A7