wdiff draft-ietf-cat-kerberos-pk-init-23.txt draft-ietf-cat-kerberos-pk-init-24.txt

NETWORK WORKING GROUP B. Tung
Internet-Draft USC Information Sciences Institute
Expires: August 4, 13, 2005 L. Zhu
Microsoft Corporation
January 31,
February 9, 2005

Public Key Cryptography for Initial Authentication in Kerberos
draft-ietf-cat-kerberos-pk-init-23
draft-ietf-cat-kerberos-pk-init-24

Status of this Memo

This document is an Internet-Draft and is subject to all provisions
of Section 3 of RFC 3667. By submitting this Internet-Draft, each
author represents that any applicable patent or other IPR claims of
which he or she is aware have been or will be disclosed, and any of
which he or she become aware will be disclosed, in accordance with
RFC 3668.

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This Internet-Draft will expire on August 4, 13, 2005.

Abstract

This document describes protocol extensions (hereafter called PKINIT)
to the Kerberos protocol specification. These extensions provide a
method for integrating public key cryptography into the initial
authentication exchange, by passing digital certificates and
associated authenticators using asymmetric-key signature and/or
encryption algorithms in pre-authentication data fields.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1 Definitions, Requirements, and Constants . . . . . . . . . 4
3.1.1 Required Algorithms . . . . . . . . . . . . . . . . . 4
3.1.2 Defined Message and Encryption Types . . . . . . . . . 5
3.1.3 Algorithm Identifiers . . . . . . . . . . . . . . . . 6
3.2 PKINIT Pre-authentication Syntax and Use . . . . . . . . . 6
3.2.1 Generation of Client Request . . . . . . . . . . . . . 7 6
3.2.2 Receipt of Client Request . . . . . . . . . . . . . . 9 10
3.2.3 Generation of KDC Reply . . . . . . . . . . . . . . . 12 13
3.2.4 Receipt of KDC Reply . . . . . . . . . . . . . . . . . 17 19
3.3 Interoperability Requirements . . . . . . . . . . . . . . 20
3.4 KDC Indication of PKINIT Support . . . . . . . . . . . . . 18 20
4. Security Considerations . . . . . . . . . . . . . . . . . . . 18 21
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19 22
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 22
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20 23
7.1 Normative References . . . . . . . . . . . . . . . . . . . 20 23
7.2 Informative References . . . . . . . . . . . . . . . . . . 21 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 21 24
A. PKINIT ASN.1 Module . . . . . . . . . . . . . . . . . . . . . 21 25
Intellectual Property and Copyright Statements . . . . . . . . 27 30

1. Introduction

A client typically authenticates itself to a service in Kerberos
using three distinct though related exchanges. First, the client
requests a ticket-granting ticket (TGT) from the Kerberos
authentication server (AS). Then, it uses the TGT to request a
service ticket from the Kerberos ticket-granting server (TGS).
Usually, the AS and TGS are integrated in a single device known as a
Kerberos Key Distribution Center, or KDC. (In this document, we will
refer to both
the AS and the TGS are referred to as the KDC.) Finally, the client
uses the service ticket to authenticate itself to the service.

The advantage afforded by the TGT is that the client exposes his
long-term secrets only once. The TGT and its associated session key
can then be used for any subsequent service ticket requests. One
result of this is that all further authentication is independent of
the method by which the initial authentication was performed.
Consequently, initial authentication provides a convenient place to
integrate public-key cryptography into Kerberos authentication.

As defined in [CLAR], Kerberos authentication exchanges use
symmetric-key cryptography, in part for performance. One
disadvantage of using symmetric-key cryptography is that the keys
must be shared, so that before a client can authenticate itself, he
must already be registered with the KDC.

Conversely, public-key cryptography (in conjunction with an
established Public Key Infrastructure) permits authentication without
prior registration with a KDC. Adding it to Kerberos allows the
widespread use of Kerberized applications by clients without
requiring them to register first with a KDC--a requirement that has
no inherent security benefit.

As noted above, a convenient and efficient place to introduce
public-key cryptography into Kerberos is in the initial
authentication exchange. This document describes the methods and
data formats for integrating public-key cryptography into Kerberos
initial authentication.

2. Conventions Used in This Document

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].

In this document, the encryption key used to encrypt the enc-part
field of the KDC-REP in the AS-REP [CLAR] is referred to as the KDC
AS reply key.

3. Extensions

This section describes extensions to [CLAR] for supporting the use of
public-key cryptography in the initial request for a ticket.

Briefly, this document defines the following extensions to [CLAR]:

1. The client indicates the use of public-key authentication by
including a special preauthenticator in the initial request. This
preauthenticator contains the client's public-key data and a
signature.

2. The KDC tests the client's request against its authentication
policy and trusted Certification Authorities (CAs).

3. If the request passes the verification tests, the KDC replies as
usual, but the reply is encrypted using either:

a. a key generated through a Diffie-Hellman (DH) key exchange
[RFC2631]
[RFC2631][IEEE1363] with the client, signed using the KDC's
signature key; or

b. a symmetric encryption key, signed using the KDC's signature
key and encrypted using the client's public key.

Any keying material required by the client to obtain the
encryption key for decrypting the KDC reply is returned in a
pre-authentication field accompanying the usual reply.

4. The client validates the KDC's signature, obtains the encryption
key, decrypts the reply, and then proceeds as usual.

Section 3.1 of this document enumerates the required algorithms and
necessary extension message types. Section 3.2 describes the
extension messages in greater detail.

3.1 Definitions, Requirements, and Constants

3.1.1 Required Algorithms

All PKINIT implementations MUST support the following algorithms:

o KDC AS reply key: key enctype: AES256-CTS-HMAC-SHA1-96 etype [KCRYPTO].

o Signature algorithm: sha-1WithRSAEncryption [RFC3279].

o KDC AS reply key delivery method: ephemeral-ephemeral Diffie-Hellman key exchange (Diffie-Hellman keys are not cached).
[RFC2631].

3.1.2 Defined Message and Encryption Types

PKINIT makes use of the following new pre-authentication types:

PA-PK-AS-REQ

PA_PK_AS_REQ 16
PA-PK-AS-REP
PA_PK_AS_REP 17

PKINIT also makes use of the following new authorization data type:

AD-INITIAL-VERIFIED-CAS

AD_INITIAL_VERIFIED_CAS 9

PKINIT introduces the following new error codes:

KDC_ERR_CLIENT_NOT_TRUSTED 62
KDC_ERR_KDC_NOT_TRUSTED 63
KDC_ERR_INVALID_SIG 64
KDC_ERR_KEY_SIZE
KDC_ERR_DH_KEY_PARAMETERS_NOT_ACCEPTED 65
KDC_ERR_CERTIFICATE_MISMATCH 66
KDC_ERR_CANT_VERIFY_CERTIFICATE 70
KDC_ERR_INVALID_CERTIFICATE 71
KDC_ERR_REVOKED_CERTIFICATE 72
KDC_ERR_REVOCATION_STATUS_UNKNOWN 73
KDC_ERR_CLIENT_NAME_MISMATCH 75
KDC_ERR_INCONSISTENT_KEY_PURPOSE 76

PKINIT uses the following typed data types for errors:

TD-TRUSTED-CERTIFIERS

TD_TRUSTED_CERTIFIERS 104
TD-CERTIFICATE-INDEX
TD_INVLID_CERTIFICATES 105
TD-DH-PARAMETERS
TD_DH_PARAMETERS 109

PKINIT defines the following encryption types, for use in the AS-REQ
message (to to indicate acceptance of the corresponding encryption
Object Identifiers (OIDs) algorithms that
can used by Cryptographic Message Syntax (CMS) [RFC3852] messages in PKINIT):
the reply:

dsaWithSHA1-CmsOID 9
md5WithRSAEncryption-CmsOID 10
sha1WithRSAEncryption-CmsOID 11
rc2CBC-EnvOID 12
rsaEncryption-EnvOID (PKCS1 v1.5) 13
rsaES-OAEP-EnvOID (PKCS1 v2.0) 14
des-ede3-cbc-EnvOID 15

The above encryption types are used by the client only within the
KDC-REQ-BODY to indicate which Cryptographic Message Syntax (CMS)
[RFC3852] algorithms it supports. Their use within Kerberos
EncryptedData structures is not specified by this document.

The ASN.1 module for all structures defined in this document (plus
IMPORT statements for all imported structures) are is given in
Appendix A.

All structures defined in or imported into this document MUST be
encoded using Distinguished Encoding Rules (DER) [X690]. [X690] (unless
otherwise noted). All data structures wrapped carried in OCTET STRINGs must
be encoded according to the rules specified in corresponding
specifications.

Interoperability note: Some implementations may not be able to decode
wrapped CMS objects encoded with BER but not DER; specifically, they
may not be able to decode infinite length encodings. To maximize
interoperability, implementers SHOULD encode CMS objects used in
PKINIT with DER.

3.1.3 Algorithm Identifiers

PKINIT does not define, but does make use of, the following algorithm
identifiers.

PKINIT uses the following algorithm identifier identifiers for Diffie-Hellman
key agreement [RFC3279]:

dhpublicnumber (Diffie-Hellman modulo a prime p [RFC2631])
id-ecPublicKey (Elliptic Curve Diffie-Hellman [IEEE1363])

PKINIT uses the following signature algorithm identifiers [RFC3279]:

sha-1WithRSAEncryption (RSA with SHA1)
md5WithRSAEncryption (RSA with MD5)
id-dsa-with-sha1 (DSA with SHA1)

PKINIT uses the following encryption algorithm identifiers [RFC3447]
for encrypting the temporary key with a public key:

rsaEncryption (PKCS1 v1.5)
id-RSAES-OAEP (PKCS1 v2.0)

PKINIT uses the following algorithm identifiers [RFC3370][RFC3565]
for encrypting the KDC AS reply key with the temporary key:

des-ede3-cbc (three-key 3DES, CBC mode)
rc2-cbc (RC2, CBC mode)
id-aes256-CBC (AES-256, CBC mode)

3.2 PKINIT Pre-authentication Syntax and Use

This section defines the syntax and use of the various
pre-authentication fields employed by PKINIT.

3.2.1 Generation of Client Request

The initial authentication request (AS-REQ) is sent as per [CLAR]; in
addition, a pre-authentication field contains data signed by element, whose padata-type is
PA_PK_AS_REQ and whose padata-value contains the
client's private signature key, as follows: DER encoding of the
type PA-PK-AS-REQ, is included.

PA-PK-AS-REQ ::= SEQUENCE {
signedAuthPack [0] IMPLICIT OCTET STRING,
-- Contains a CMS type ContentInfo encoded
-- according to [RFC3852].
-- The contentType field of the type ContentInfo
-- is id-signedData (1.2.840.113549.1.7.2),
-- and the content field is a SignedData.
-- The eContentType field for the type SignedData is
-- id-pkauthdata (1.3.6.1.5.2.3.1), and the
-- eContent field contains the DER encoding of the
-- type AuthPack.
-- AuthPack is defined below.
trustedCertifiers [1] SEQUENCE OF TrustedCA OPTIONAL,
-- A list of CAs, trusted by the client, that can
-- be used as the trust anchor to validate KDC certificates.
kdcCert the KDC's
-- signature.
-- Each TrustedCA identifies a CA or a CA
-- certificate (thereby its public key).
kdcPkId [2] IMPLICIT OCTET STRING
OPTIONAL,
-- Contains a CMS type IssuerAndSerialNumber SignerIdentifier encoded
-- according to [RFC3852].
-- Identifies Identifies, if present, a particular KDC certificate, if the
-- public key that the client already has it. has.
...
}

DHNonce ::= OCTET STRING

TrustedCA ::= CHOICE SEQUENCE {
caName [1] [0] IMPLICIT OCTET STRING,
-- Contains a PKIX type Name encoded according to
-- [RFC3280].
issuerAndSerial
-- Specifies the CA distinguished subject name.
certificateSerialNumber [1] INTEGER OPTIONAL,
-- Specifies the certificate serial number.
-- The defintion of the certificate serial number
-- is taken from X.509 [X.509-97].
subjectKeyIdentifier [2] IMPLICIT OCTET STRING, STRING OPTIONAL,
-- Contains Identifies the CA's public key by a key
-- identifier. When an X.509 certificate is
-- referenced, this key identifier matches the X.509
-- subjectKeyIdentifier extension value. When other
-- certificate formats are referenced, the documents
-- that specify the certificate format and their use
-- with the CMS type IssuerAndSerialNumber encoded must include details on matching the
-- according key identifier to [RFC3852]. the appropriate certificate
-- Identifies a specific CA certificate. field.
...
}

AuthPack ::= SEQUENCE {
pkAuthenticator [0] PKAuthenticator,
clientPublicValue [1] SubjectPublicKeyInfo OPTIONAL,
-- Defined in [RFC3280].
-- The pubic key value (the subjectPublicKey field
-- of the type SubjectPublicKeyInfo) MUST be encoded
-- according to [RFC3279].
-- Present only if the client wishes to use the
-- Diffie-Hellman key agreement method.
supportedCMSTypes [2] SEQUENCE OF AlgorithmIdentifier
OPTIONAL,
-- List of CMS encryption types supported by
-- client in order of (decreasing) preference.
clientDHNonce [3] DHNonce OPTIONAL,
-- Present only if the client indicates that it
-- wishes to cache reuse DH keys or to allow the KDC to
-- do so. so (see Section 3.2.3.1).
...
}

PKAuthenticator ::= SEQUENCE {
cusec [0] INTEGER (0..999999),
ctime [1] KerberosTime,
-- cusec and ctime are used as in [CLAR], for replay
-- prevention.
nonce [2] INTEGER (0..4294967295),
-- Chosen randomly; This nonce does not need to
-- match with the nonce in the KDC-REQ-BODY.
paChecksum [3] OCTET STRING,
-- Contains the SHA1 checksum, performed over
-- KDC-REQ-BODY.
...
}

The ContentInfo [RFC3852] structure for the signedAuthPack field is
filled out as follows:

1. The contentType field of the type ContentInfo is id-signedData
(as defined in [RFC3852]), and the content field is a SignedData
(as defined in [RFC3852]).

2. The eContentType field for the type SignedData is id-pkauthdata:
{ iso(1) org(3) dod(6) internet(1) security(5) kerberosv5(2)
pkinit(3) pkauthdata(1) }.

3. The eContent field for the type SignedData contains the DER
encoding of the type AuthPack.

4. The signerInfos field of the type SignedData contains a single
signerInfo, which contains the signature over the type AuthPack.

5. The certificates field of the type SignedData contains the
client's certificate and additional
certificates intended to facilitate certification path
construction, so that the KDC can
validate the client's certificate and verify the signature over the
type AuthPack. For path validation, these certificates SHOULD be
sufficient to construct at least one certification path from the
client certificate to one trust anchor acceptable by the KDC
[CAPATH]. The certificates field MUST NOT contain "root" CA
certificates.

6. The client's Diffie-Hellman public value (clientPublicValue) is
included if and only if the client wishes to use the
Diffie-Hellman key agreement method. For the Diffie-Hellman key
agreement method, implementations MUST support Oakley 1024-bit
MODP well-known group 2 [RFC2412] and SHOULD support Oakley
2048-bit MODP well-known group 14 and Oakley 4096-bit MODP
well-known group 16 [RFC3526]. They MAY support Oakley 185-bit
EC2N group 4 [RFC2412].

The Diffie-Hellman group field size should be chosen so as to provide
sufficient cryptographic security. The following table, based on
[LENSTRA], gives approximate comparable key sizes for symmetric-
and asymmetric-key cryptosystems based on the best-known
algorithms for attacking them.

Symmetric | ECC | DH/DSA/RSA
-------------+---------+------------
80 | 163 | 1024
112 | 233 | 2048
128 | 283 | 3072
192 | 409 | 7680
256 | 571 | 15360

Table 1: Comparable key sizes (in bits)

When Diffie-Hellma modulo a prime p is used, the exponents should
have at least twice as many bits as the symmetric keys that will
be derived from them [ODL99].

7. The client may wish to cache reuse DH keys or to allow the KDC to do
so. so
(see Section 3.2.3.1). If so, then the client includes the
clientDHNonce field. This nonce string needs to be as long as
the longest key length of the symmetric key types that the client
supports. This nonce MUST be chosen randomly.

3.2.2 Receipt of Client Request

Upon receiving the client's request, the KDC validates it. This
section describes the steps that the KDC MUST (unless otherwise
noted) take in validating the request.

The KDC looks for verifies the client's certificate signature in the signedAuthPack
(based on field
according to [RFC3852].

If, while validating the signerInfo) and validate this certificate.

If client's X.509 certificate [RFC3280], the
KDC cannot find build a certification path to validate the client's
certificate, it sends back an error of type a KRB-ERROR [CLAR] message with the code
KDC_ERR_CANT_VERIFY_CERTIFICATE. The accompanying e-data for this
error message is a TYPED-DATA (as defined in [CLAR]). For this error, the [CLAR]) that contains an
element whose data-type is TD-TRUSTED-CERTIFIERS, TD_TRUSTED_CERTIFIERS, and the whose
data-value is contains the DER encoding of

TrustedCertifiers the type
TD-TRUSTED-CERTIFIERS:

TD-TRUSTED-CERTIFIERS ::= SEQUENCE OF OCTET STRING TrustedCA
-- The OCTET STRING contains Identifies a PKIX type Name encoded list of CAs trusted by the KDC.
-- according Each TrustedCA identifies a CA or a CA
-- certificate (thereby its public key).

Upon receiving this error message, the client SHOULD retry only if it
has a different set of certificates (from those of the previous
requests) that form a certification path (or a partial path) from one
of the trust anchors selected by the KDC to [RFC3280]. its own certificate.

If, while processing the certification path, the KDC determines that
the signature on one of the certificates in the signedAuthPack field
is invalid, it returns an error of type a KRB-ERROR [CLAR] message with the code
KDC_ERR_INVALID_CERTIFICATE. The accompanying e-data for this error
message is a TYPED-DATA, TYPED-DATA that contains an element whose data-type is TD-CERTIFICATE-INDEX,
TD_INVALID_CERTIFICATES, and whose data-value is contains the DER
encoding of the index into the CertificateSet field, ordered as sent
by the client:

CertificateIndex type TD-INVALID-CERTIFICATES:

TD-INVALID-CERTIFICATES ::= SEQUENCE OF OCTET STRING
-- Contains Each OCTET STRING contains a CMS type
-- IssuerAndSerialNumber encoded
-- according to
-- [RFC3852].
-- Each IssuerAndSerialNumber of indentifies a
-- certificate (sent by the client) with an
-- invalid
-- signature.

If more than one X.509 certificate signature is invalid, the KDC MAY
send one TYPED-DATA element per invalid signature.

The

Based on local policy, the KDC SHOULD may also check whether any X.509
certificates in the client's certification path validating the client's
certificate have been revoked. If any of them have been revoked, the
KDC MUST return an error of type message with the code
KDC_ERR_REVOKED_CERTIFICATE; if the KDC attempts to determine the
revocation status but is unable to do so, it SHOULD return an error
of type
message with the code KDC_ERR_REVOCATION_STATUS_UNKNOWN. The
certificate or certificates affected are identified exactly as for an
the error of type code KDC_ERR_INVALID_CERTIFICATE (see above).

The client's public key is then used to verify the signature. If the
signature fails to verify, the KDC MUST return an error message with
the code KDC_ERR_INVALID_SIG. There is no accompanying e-data for
this error message.

In addition to validating the client's certificate, signature, the KDC MUST also
check that this certificate properly maps the client's public key used to verify the client's
signature is bound to the client's principal name as specified in the
AS-REQ as follows:

1. If the KDC has its own mapping from binding between either the name in client's
signature-verification public key or the client's certificate to a and
the client's Kerberos principal name, it uses that Kerberos name. binding.

2. Otherwise, if the client's X.509 certificate contains a
SubjectAltName extension with a Kerberos name KRB5PrincipalName (defined below)
in the otherName field, it uses binds the client's X.509 certificate to
that name.

The otherName field (of type AnotherName) in the SubjectAltName
extension MUST contain KRB5PrincipalName as defined below.

The type-id field of the type AnotherName is id-pksan:

id-pksan OBJECT IDENTIFIER ::=
{ iso(1) org(3) dod(6) internet(1) security(5) kerberosv5(2)
x509-sanan (2) }

The value field of the type AnotherName is the DER encoding of the
following ASN.1 type:

KRB5PrincipalName ::= SEQUENCE {
realm [0] Realm,
principalName [1] PrincipalName
}

If the KDC does not have its own mapping binding and there is no Kerberos
KRB5PrincipalName name present in the client's X.509 certificate, or and
if the Kerberos name in the request does not match the name
KRB5PrincipalName in the client's X.509 certificate (including the
realm name), the KDC MUST return an error message with the code
KDC_ERR_CLIENT_NAME_MISMATCH. There is no accompanying e-data for
this error.

Even if the client's certificate is validated and it is mapped to the
client's principal name, the KDC may decide not to accept the
client's certificate, depending on local policy. error message.

The KDC MAY require the presence of an Extended Key Usage (EKU)
KeyPurposeId [RFC3280] id-pkekuoid in the extensions field of the
client's X.509 certificate:

id-pkekuoid OBJECT IDENTIFIER ::=
{ iso(1) org(3) dod(6) internet(1) security(5) kerberosv5(2)
pkinit(3) pkekuoid(4) }
-- PKINIT client authentication.
-- Key usage bits that may MUST be consistent:
-- digitalSignature;
-- Key usage bits that MAY be consistent: digitalSignature
-- nonRepudiation, and (keyEncipherment or keyAgreement).

As a matter of local policy,

If this EKU is required but is missing, the KDC may decide to reject requests on
the basis MUST return an error
message of the absence or presence of specific EKU OIDs. code KDC_ERR_INCONSISTENT_KEY_PURPOSE. There is no
accompanying e-data for this error message. KDCs implementing this
requirement SHOULD also accept the EKU KeyPurposeId id-ms-sc-logon
(1.3.6.1.4.1.311.20.2.2) as meeting the requirement, as there are a
large number of X.509 client certificates deployed for use with
PKINIT which have this EKU.

The KDC MUST return the error code KDC_ERR_CLIENT_NOT_TRUSTED if

If for any other reasons, the client's certificate public key is not accepted.

Once the client's certificate is accepted,
the KDC can then verify
the client's signature over the type AuthPack according to [RFC3852].
If the signature fails to verify, the KDC MUST return an error
KDC_ERR_INVALID_SIG. There is no accompanying e-data for this error. message with the code
KDC_ERR_CLIENT_NOT_TRUSTED.

The KDC MUST check the timestamp to ensure that the request is not a
replay, and that the time skew falls within acceptable limits. The
recommendations for clock skew times in [CLAR] apply here. If the
check fails, the KDC MUST return error code KRB_AP_ERR_REPEAT or
KRB_AP_ERR_SKEW, respectively.

If the clientPublicValue is filled in, indicating that the client
wishes to use the Diffie-Hellman key agreement method, the KDC SHOULD
check to see if the key parameters satisfy its policy. If they do
not, it MUST return an error message with the code KDC_ERR_KEY_SIZE.
KDC_ERR_DH_KEY_PARAMETERS_NOT_ACCEPTED. The accompanying e-data is a TYPED-DATA,
TYPED-DATA that contains an element whose data-type is TD-DH-PARAMETERS,
TD_DH_PARAMETERS, and whose data-value is contains the DER encoding of
the following: type TD-DH-PARAMETERS:

TD-DH-PARAMETERS ::= SEQUENCE OF DomainParameters
-- Type DomainParameters is defined in [RFC3279]. DHDomainParameters
-- Contains a list of Diffie-Hellman group domain
-- parameters in decreasing preference order.

DHDomainParameters ::= CHOICE {
modp [0] DomainParameters,
-- Type DomainParameters is defined in [RFC3279].
ec [1] EcpkParameters,
-- Type EcpkParameters is defined in [RFC3279].
...
}

TD-DH-PARAMETERS contains a list of Diffie-Hellman group domain parameters
that the KDC supports in decreasing preference order, from which the
client should SHOULD pick one to retry the request.

The KDC MUST return error code KDC_ERR_CERTIFICATE_MISMATCH if

If the client included a kdcCert kdcPkId field in the PA-PK-AS-REQ and the
KDC does not have possess the corresponding certificate.

The key, the KDC MUST return error code KDC_ERR_KDC_NOT_TRUSTED ignore the
kdcPkId field as if the client did not include a kdcCert field, but did include one.

If the client included a trustedCertifiers field, and the KDC does
not possesses a certificate issued by the private key for any one of the listed certifiers. certifiers,
the KDC MUST ignore the trustedCertifiers field as if the client did
not include any.

If there is a supportedCMSTypes field in the AuthPack, the KDC must
check to see if it supports any of the listed types. If it supports
more than one of the types, the KDC SHOULD use the one listed first.
If it does not support any of them, it MUST return an error of type
KRB5KDC_ERR_ETYPE_NOSUPP. message
with the code KDC_ERR_ETYPE_NOSUPP [CLAR].

3.2.3 Generation of KDC Reply

Assuming that the client's request has been properly validated, the
KDC proceeds as per [CLAR], except as follows.

The KDC MUST set the initial flag and include an authorization data
element of type AD-INITIAL-VERIFIED-CAS ad-type [CLAR] AD_INITIAL_VERIFIED_CAS in the issued
ticket. The value is
an OCTET STRING containing ad-data [CLAR] field contains the DER encoding of InitialVerifiedCAs:

InitialVerifiedCAs the
type AD-INITIAL-VERIFIED-CAS:

AD-INITIAL-VERIFIED-CAS ::= SEQUENCE OF SEQUENCE {
ca [0] IMPLICIT OCTET STRING, TrustedCA
-- Contains Identifies the certification path based on which
-- the client certificate was validated.
-- Each TrustedCA identifies a PKIX type Name encoded according to CA or a CA
-- [RFC3280].
validated [1] BOOLEAN,
...
} certificate (thereby its public key).

The KDC MAY wrap AS wraps any AD-INITIAL-VERIFIED-CAS data in AD-IF-RELEVANT
containers if the list of CAs satisfies the KDC's AS' realm's local policy
(this corresponds to the TRANSITED-POLICY-CHECKED ticket flag
[CLAR]). Furthermore, any TGS must MUST copy such authorization data from
tickets used in a PA-TGS-REQ [CLAR] of the TGS-REQ to the resulting
ticket,
including and it can wrap or unwrap the data into or out-of the
AD-IF-RELEVANT container, depends on if present. the list of CAs satisfies the
TGS' realm's local policy.

Application servers that understand this authorization data type
SHOULD apply local policy to determine whether a given ticket bearing
such a type *not* contained within an AD-IF-RELEVANT container is
acceptable. (This corresponds to the AP server checking the
transited field when the TRANSITED-POLICY-CHECKED flag has not been
set [CLAR].) If such a data type is contained within an
AD-IF-RELEVANT container, AP servers MAY apply local policy to
determine whether the authorization data is acceptable.

The content of the AS-REP is otherwise unchanged from [CLAR]. The
KDC encrypts the reply as usual, but not with the client's long-term
key. Instead, it encrypts it with either a shared key derived from a
Diffie-Hellman exchange, or a generated encryption key. The contents
of the PA-PK-AS-REP indicate which key delivery method is used:

PA-PK-AS-REP ::= CHOICE {
dhInfo [0] DHRepInfo,
-- Selected when Diffie-Hellman key exchange is
-- used.
encKeyPack [1] IMPLICIT OCTET STRING,
-- Selected when public key encryption is used.
-- Contains a CMS type ContentInfo encoded
-- according to [RFC3852].
-- The contentType field of the type ContentInfo is
-- id-envelopedData (1.2.840.113549.1.7.3).
-- The content field is an EnvelopedData.
-- The contentType field for the type EnvelopedData
-- is id-signedData (1.2.840.113549.1.7.2).
-- The eContentType field for the inner type
-- SignedData (when unencrypted) is id-pkrkeydata
-- (1.2.840.113549.1.7.3) and the eContent field
-- contains the DER encoding of the type
-- ReplyKeyPack.

-- ReplyKeyPack is defined below. in Section 3.2.3.2.
...
}

KDCDHKeyInfo ::= SEQUENCE {
subjectPublicKey [0] BIT STRING,
-- KDC's DH public key, y = g^x mod p.
-- MUST be ASN.1 encoded as an INTEGER; key.
-- This encoding The DH pubic key value is then used as the contents
-- (i.e., the value) of this mapped to a BIT STRING field.
-- according to [RFC3279].
nonce [1] INTEGER (0..4294967295),
-- Contains the nonce in the PKAuthenticator of the
-- request if cached DH keys are NOT used, reused,
-- 0 otherwise.
dhKeyExpiration [2] KerberosTime OPTIONAL,
-- Expiration time for KDC's cached values, present key pair,
-- present if and only if cached DH keys are used. reused. If this
-- this field is omitted then the serverDHNonce field
-- field MUST also be omitted. See Section 3.2.3.1.
...
}

3.2.3.1 Using Diffie-Hellman Key Exchange

In this case, the PA-PK-AS-REP contains a DHRepInfo structure.

The ContentInfo [RFC3852] structure for the dhSignedData field is
filled in as follows:

1. The contentType field of the type ContentInfo is id-signedData
(as defined in [RFC3852]), and the content field is a SignedData
(as defined in [RFC3852]).

2. The eContentType field for the type SignedData is the OID value
for id-pkdhkeydata: { iso(1) org(3) dod(6) internet(1)
security(5) kerberosv5(2) pkinit(3) pkdhkeydata(2) }.

3. The eContent field for the type SignedData contains the DER
encoding of the type KDCDHKeyInfo.

4. The signerInfos field of the type SignedData contains a single
signerInfo, which contains the signature over the type
KDCDHKeyInfo.

5. The certificates field of the type SignedData contains the KDC's
certificate and additional
certificates intended to facilitate certification path
construction, so that the client can validate
the KDC's certificate and verify the KDC's signature
over the type KDCDHKeyInfo. This field may only be left empty if
the
client did include a kdcCert KDC public key specified by the kdcPkId field in the PA-PK-AS-REQ,
indicating that
PA-PK-AS-REQ was used for signing. Otherwise, for path
validation, these certificates SHOULD be sufficient to construct
at least one certification path from the client already has KDC certificate to one
trust anchor acceptable by the KDC's certificate. client [CAPATH]. The certificates
field MUST NOT contain "root" CA certificates.

6. If the client included the clientDHNonce field, then the KDC may
choose to reuse its DH keys. keys (see Section 3.2.3.1). If the server
reuses DH keys then it MUST include an expiration time in the
dhKeyExperiation field. Past the point of the expiration time,
the signature over the type DHRepInfo is considered
expired/invalid. When the server reuses DH keys then it MUST
include a serverDHNonce at least as long as the length of keys
for the symmetric encryption system used to encrypt the AS reply.
Note that including the serverDHNonce changes how the client and
server calculate the key to use to encrypt the reply; see below
for details. The KDC SHOULD NOT reuse DH keys unless the
clientDHNonce field is present in the request.

The reply key for use to decrypt the KDC AS reply [CLAR] key is derived as follows:

1. Both the KDC and the client calculate the shared secret value
DHKey:

DHKey = g^(xb * xa) mod as
follows:

a) When Diffie-Hellman modulo a prime p

where xb and xa are ([RFC2631]) is used, let
DHSharedSecret be the KDC's and client's private exponents,
respectively. DHKey, padded shared secret value.

b) When Elliptic Curve Diffie-Hellman (ECDH) (with each party
contributing one key pair) [IEEE1363] is used, let
DHSharedSecret be the x-coordinate of the shared secret value
(an elliptic curve point).

DHSharedSecret is first padded with leading zeros as needed to
make it as long as such that the modulus p,
size of DHSharedSecret in octets is the same as that of the
modulus, then represented as a string of octets in big-endian order (such that
order.

Implementation note: Both the size of DHKey in octets client and the KDC can cache the
triple (ya, yb, DHSharedSecret), where ya is the size of client's public
key and yb is the modulus p). KDC's public key. If both ya and yb are the
same in a later exchange, the cached DHSharedSecret can be used.

2. Let K be the key-generation seed length [KCRYPTO] of the KDC AS
reply key whose enctype is selected according to [CLAR].

3. Define the function octetstring2key() as follows:

octetstring2key(x) == random-to-key(K-truncate(
SHA1(0x00 | x) |
SHA1(0x01 | x) |
SHA1(0x02 | x) |
...
))

where x is an octet string; | is the concatenation operator; 0x00,
0x01, 0x02, etc., are each represented as a single octet;
random-to-key() is an operation that generates a protocol key from
a bitstring of length K; and K-truncate truncates its input to the
first K bits. Both K and random-to-key() are as defined in the
kcrypto profile [KCRYPTO] for the enctype of the KDC AS reply key.

4. When cached DH keys are used, reused, let n_c be the clientDHNonce, and n_k be
the serverDHNonce; otherwise, let both n_c and n_k be empty octet
strings.

5. The KDC AS reply key k is:

k = octetstring2key(DHKey octetstring2key(DHSharedSecret | n_c | n_k)

3.2.3.2 Using Public Key Encryption

In this case, the PA-PK-AS-REP contains a ContentInfo structure
wrapped in an OCTET STRING. The reply key for use to decrypt the KDC AS reply [CLAR] key is encrypted in the
encKeyPack field, which contains data of type ReplyKeyPack:

ReplyKeyPack ::= SEQUENCE {
replyKey [0] EncryptionKey,
-- Contains the session key used to encrypt the
-- enc-part field in the AS-REP.
nonce [1] INTEGER (0..4294967295),
-- Contains the nonce in the PKAuthenticator of the
-- request.
...
}

The ContentInfo [RFC3852] structure for the encKeyPack field is
filled in as follows:

1. The contentType field of the type ContentInfo is id-envelopedData
(as defined in [RFC3852]), and the content field is an
EnvelopedData (as defined in [RFC3852]).

2. The contentType field for the type EnvelopedData is
id-signedData: { iso (1) member-body (2) us (840) rsadsi (113549)
pkcs (1) pkcs7 (7) signedData (2) }.

3. The eContentType field for the inner type SignedData (when
decrypted from the encryptedContent field for the type
EnvelopedData) is id-pkrkeydata: { iso(1) org(3) dod(6)
internet(1) security(5) kerberosv5(2) pkinit(3) pkrkeydata(3) }.

4. The eContent field for the inner type SignedData contains the DER
encoding of the type ReplyKeyPack.

5. The signerInfos field of the inner type SignedData contains a
single signerInfo, which contains the signature over the type
ReplyKeyPack.

6. The certificates field of the inner type SignedData contains the
KDC's certificate and additional
certificates intended to facilitate certification path
construction, so that the client can validate the KDC's certificate and verify the KDC's signature
over the type ReplyKeyPack. This field may only be left empty if
the client included a kdcCert KDC public key specified by the kdcPkId field in the PA-PK-AS-REQ,
indicating that
PA-PK-AS-REQ was used for signing. Otherwise, for path
validation, these certificates SHOULD be sufficient to construct
at least one certification path from the client already has KDC certificate to one
trust anchor acceptable by the KDC's certificate. client [CAPATH]. The certificates
field MUST NOT contain "root" CA certificates.

7. The recipientInfos field of the type EnvelopedData is a SET which
MUST contain exactly one member of type KeyTransRecipientInfo.
The encryptedKey of this member contains the temporary key which
is encrypted using the client's public key.

8. The unprotectedAttrs or originatorInfo fields of the type
EnvelopedData MAY be present.

3.2.4 Receipt of KDC Reply

Upon receipt of the KDC's reply, the client proceeds as follows. If
the PA-PK-AS-REP contains the dhSignedData field, the client derives
the shared KDC AS reply key using the same procedure used by the KDC as
defined in Section 3.2.3.1. Otherwise, the message contains an encKeyPack, the
encKeyPack field, and the client decrypts and verifies extracts the temporary encryption
key in the encryptedKey field of the member KeyTransRecipientInfo,
and then uses that as the KDC AS reply key.

In either case, the client MUST validate the KDC's certificate and verify the signature in the
SignedData according to [RFC3852]. Unless the client can otherwise
prove that the KDC's certificate is
for the target KDC (i.e., the subject distinguished name in public key used to verify the KDC
certificate KDC's signature is bound
to the hostname or IP address of the KDC
authenticating target KDC, the client), it KDC's X.509 certificate MUST do the following to verify satisfy at least
one of the
responder's identity: follow two requirements:

1. The client checks to see if the included certificate contains a Subject Alternative Name (SAN)
extension [RFC3280] carrying a dNSName or
an iPAddress (if the KDC is specified by an IP address instead of
a name). If it does, it MUST check to see if and that name value matches that the
following name format:

_Service._Proto.Realm

Where the Service name is the string literal "kerberos", the
Proto can be "udp" or "tcp", and the Realm is the domain style
Kerberos realm name [CLAR] of the KDC it believes it target KDC. This name format
is communicating with, with
matching rules specified identical to the owner label format used in [RFC3280].

2. The client verifies that the KDC's DNS SRV
records for specifying the KDC location as described in [CLAR].
For example, the X.509 certificate MUST for the KDC of the Kerberos
realm "EXAMPLE.COM" would contain a dNSName value of
"_kerberos._tcp.EXAMPLE.COM" or "_kerberos._udp.EXAMPLE.COM".

2. The certificate contains the EKU KeyPurposeId [RFC3280] id-pkkdcekuoid:
id-pkkdcekuoid (defined below) and an SAN extension [RFC3280]
carrying an AnotherName whose type-id is id-pksan (as defined in
Section 3.2.2) and whose value contains a KRB5PrincipalName name,
and the realm name of that KRB5PrincipalName matches the realm
name of the target KDC.

id-pkkdcekuoid OBJECT IDENTIFIER ::=
{ iso(1) org(3) dod(6) internet(1) security(5) kerberosv5(2)
pkinit(3) pkkdcekuoid(5) }
-- Signing KDC responses.
-- Key usage bits that may MUST be consistent:
-- digitalSignature.

If no SAN id-pksan extension is present (but the id-pkkdcekuoid
EKU is) in the KDC's X.509 certificate, and the client has a
priori knowledge of the KDC's hostname (or IP address), the
client SHOULD accept the KDC's X.509 certificate if that
certificate contains an SAN extension carrying a dNSName and the
dNSName value matches the hostname (or the IP address) of the KDC
with which the client believes it is communicating.

Matching rules used for the dNSName value are specified in [RFC3280].

If all applicable checks are satisfied, the client then decrypts the
enc-part field of the KDC-REP in the AS_REP with AS-REP using the resulting KDC AS reply
key, and then proceeds as described in [CLAR].

Implementation note: CAs issuing KDC certificates SHOULD place all
"short" and "fully-qualified" Kerberos realm names of the KDC (one
per SAN extension) into the KDC certificate to allow maximum
flexibility.

3.3 Interoperability Requirements

The client MUST be capable of sending a set of certificates
sufficient to allow the KDC to construct a certification path for the
client's certificate, if the correct set of certificates is provided
through configuration or policy.

If the client sends all the X.509 certificates on a certification
path to a trust anchor acceptable by the KDC, and the KDC can not
verify the client's public key otherwise, the KDC MUST be able to
process path validation for the client's certificate based on the
certificates in the request.

The KDC MUST be capable of sending a set of certificates sufficient
to allow the client to construct a certification path for the KDC's
certificate, if the correct set of certificates is provided through
configuration or policy.

If the KDC sends all the X.509 certificates on a certification path
to a trust anchor acceptable by the client, and the client can not
verify the KDC's public key otherwise, the client MUST be able to
process path validation for the KDC's certificate based on the
certificates in the reply.

3.4 KDC Indication of PKINIT Support

If pre-authentication is required, but was not present in the
request, per [CLAR] an error message with the code
KDC_ERR_PREAUTH_FAILED is returned and a METHOD-DATA object will be
stored in the e-data field of the KRB-ERROR message to specify which
pre-authentication mechanisms are acceptable. The KDC can then
indicate the support of PKINIT by including a PA-PK-AS-REQ an empty element whose
padata-type is PA_PK_AS_REQ in that METHOD-DATA object.

Otherwise if it is required by the KDC's local policy that the client
must be pre-authenticated using the pre-authentication mechanism
specified in this document, but no PKINIT pre-authentication was
present in the request, an error message with the code
KDC_ERR_PREAUTH_FAILED SHOULD be returned.

KDCs MUST leave the padata-value field of PA-PK-AS-REQ entry the PA_PK_AS_REQ element in
the KRB-ERROR's METHOD-DATA empty (i.e., send a zero-length OCTET
STRING), and clients MUST ignore this and any other value. Future
extensions to this protocol may specify other data to send instead of
an empty OCTET STRING.

4. Security Considerations

PKINIT raises certain security considerations beyond those that can
be regulated strictly in protocol definitions. We will address them
in this section.

PKINIT extends the cross-realm model to the public-key
infrastructure. Users of PKINIT must understand security policies
and procedures appropriate to the use of Public Key Infrastructures. Infrastructures
[RFC3280].

Standard Kerberos allows the possibility of interactions between
cryptosystems of varying strengths; this document adds interactions
with public-key cryptosystems to Kerberos. Some administrative
policies may allow the use of relatively weak public keys. Using
such keys to wrap data encrypted under stronger conventional
cryptosystems may be inappropriate.

PKINIT requires keys for symmetric cryptosystems to be generated.
Some such systems contain "weak" keys. For recommendations regarding
these weak keys, see [CLAR].

PKINIT uses allows the use of the same RSA key pair for encryption and
signing when doing RSA encryption based key delivery. This is not
recommended usage of RSA keys [RFC3447], by using DH based key
delivery this is avoided.

Care should be taken in how certificates are chosen for the purposes
of authentication using PKINIT. Some local policies may require that
key escrow be used for certain certificate types. Deployers of
PKINIT should be aware of the implications of using certificates that
have escrowed keys for the purposes of authentication. Because
signing only certificates are normally not escrowed, by using DH
based key delivery this is avoided.

PKINIT does not provide for a "return routability" test to prevent
attackers from mounting a denial-of-service attack on the KDC by
causing it to perform unnecessary and expensive public-key
operations. Strictly speaking, this is also true of standard
Kerberos, although the potential cost is not as great, because
standard Kerberos does not make use of public-key cryptography. By
using DH based key delivery and reusing DH keys, the necessary crypto
processing cost per request can be minimized.

The syntax for the AD-INITIAL-VERIFIED-CAS authorization data does
permit empty SEQUENCEs to be encoded. Such empty sequences may only
be used if the KDC itself vouches for the user's certificate.

5. Acknowledgements

The following people have made significant contributions to this
draft: Paul Leach, Phil Hallin, Kelvin Yiu, Kristin Lauter, Sam Hartman, Love Hornquist
Astrand, Ken Raeburn, Nicolas Williams, John Wray, Jonathan Trostle,
Tom Yu, Jeffrey Hutzelman, David Cross, Dan Simon and Karthik
Jaganathan.

Special thanks to Clifford Neuman, Mat Matthew Hur and Sasha Medvinsky
who wrote earlier versions of this document.

The authors are indebt to the Kerberos working group chair Jeffrey
Hutzelman who kept track of various issues and was enormously helpful
during the creation of this document.

Some of the ideas on which this document is based arose during
discussions over several years between members of the SAAG, the IETF
CAT working group, and the PSRG, regarding integration of Kerberos
and SPX. Some ideas have also been drawn from the DASS system.
These changes are by no means endorsed by these groups. This is an
attempt to revive some of the goals of those groups, and this
document approaches those goals primarily from the Kerberos
perspective.

Lastly, comments from groups working on similar ideas in DCE have
been invaluable.

6. IANA Considerations

This document has no actions for IANA.

7. References

7.1 Normative References

[CLAR] RFC-Editor: To be replaced by RFC number for draft-ietf-
krb-wg-kerberos-clarifications. Work in Progress.

[IEEE1363]
IEEE, "Standard Specifications for Public Key
Cryptography", IEEE 1363, 2000.

[KCRYPTO] RFC-Editor: To be replaced by RFC number for draft-ietf-
krb-wg-crypto. Work in Progress.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2412] Orman, H., "The OAKLEY Key Determination Protocol",
RFC 2412, November 1998.

[RFC2631] Rescorla, E., "Diffie-Hellman Key Agreement Method",
RFC 2631, June 1999.

[RFC3279] Bassham, L., Polk, W. and R. Housley, "Algorithms and
Identifiers for the Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 3279, April 2002.

[RFC3280] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet
X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.

[RFC3370] Housley, R., "Cryptographic Message Syntax (CMS)
Algorithms", RFC 3370, August 2002.

[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.

[RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential (MODP)
Diffie-Hellman groups for Internet Key Exchange (IKE)",
RFC 3526, May 2003.

[RFC3565] Schaad, J., "Use of the Advanced Encryption Standard (AES)
Encryption Algorithm in Cryptographic Message Syntax
(CMS)", RFC 3565, July 2003.

[RFC3852] Housley, R., "Cryptographic Message Syntax (CMS)",
RFC 3852, July 2004.

[X.509-97] ITU-T. Recommendation X.509: The Directory - Authentication
Framework. 1997.

[X690] ASN.1 encoding rules: Specification of Basic Encoding
Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER), ITU-T Recommendation
X.690 (1997) | ISO/IEC International Standard
8825-1:1998.

7.2 Informative References

[CAPATH] RFC-Editor: To be replaced by RFC number for draft-ietf-
pkix-certpathbuild. Work in Progress.

[LENSTRA] Lenstra, A. and E. Verheul, "Selecting Cryptographic Key
Sizes", Journal of Cryptology 14 (2001) 255-293.

[ODL99] Odlyzko, A., "Discrete logarithms: The past and the
future, Designs, Codes, and Cryptography (1999)".

Authors' Addresses

Brian Tung
USC Information Sciences Institute
4676 Admiralty Way Suite 1001, Marina del Rey CA
Marina del Rey, CA 90292
US

Email: brian@isi.edu

Larry Zhu
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US

Email: lzhu@microsoft.com

Appendix A. PKINIT ASN.1 Module
KerberosV5-PK-INIT-SPEC {
iso(1) identified-organization(3) dod(6) internet(1)
security(5) kerberosV5(2) modules(4) pkinit(5)
} DEFINITIONS EXPLICIT TAGS ::= BEGIN

IMPORTS
SubjectPublicKeyInfo, AlgorithmIdentifier
FROM PKIX1Explicit88 { iso (1)
identified-organization (3) dod (6) internet (1)
security (5) mechanisms (5) pkix (7) id-mod (0)
id-pkix1-explicit (18) }
-- As defined in RFC 3280.

DomainParameters

DomainParameters, EcpkParameters
FROM PKIX1Algorithms88 { iso(1)
identified-organization(3) dod(6)
internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-pkix1-algorithms(17) }
-- As defined in RFC 3279.

KerberosTime, TYPED-DATA, PrincipalName, Realm, EncryptionKey
FROM KerberosV5Spec2 { iso(1) identified-organization(3)
dod(6) internet(1) security(5) kerberosV5(2)
modules(4) krb5spec2(2) } ;

id-pkinit OBJECT IDENTIFIER ::=
{ iso (1) org (3) dod (6) internet (1) security (5)
kerberosv5 (2) pkinit (3) }

id-pkauthdata OBJECT IDENTIFIER ::= { id-pkinit 1 }
id-pkdhkeydata OBJECT IDENTIFIER ::= { id-pkinit 2 }
id-pkrkeydata OBJECT IDENTIFIER ::= { id-pkinit 3 }
id-pkekuoid OBJECT IDENTIFIER ::= { id-pkinit 4 }
id-pkkdcekuoid OBJECT IDENTIFIER ::= { id-pkinit 5 }

pa-pk-as-req INTEGER ::= 16
pa-pk-as-rep INTEGER ::= 17

ad-initial-verified-cas INTEGER ::= 9

td-trusted-certifiers INTEGER ::= 104
td-certificate-index
td-invalid-certificates INTEGER ::= 105
td-dh-parameters INTEGER ::= 109

PA-PK-AS-REQ ::= SEQUENCE {
signedAuthPack [0] IMPLICIT OCTET STRING,
-- Contains a CMS type ContentInfo encoded
-- according to [RFC3852].

-- The contentType field of the type ContentInfo
-- is id-signedData (1.2.840.113549.1.7.2),
-- and the content field is a SignedData.
-- The eContentType field for the type SignedData is
-- id-pkauthdata (1.3.6.1.5.2.3.1), and the
-- eContent field contains the DER encoding of the
-- type AuthPack.
-- AuthPack is defined below.
trustedCertifiers [1] SEQUENCE OF TrustedCA OPTIONAL,
-- A list of CAs, trusted by the client, that can
-- be used as the trust anchor to validate KDC certificates.
kdcCert the KDC's
-- signature.
-- Each TrustedCA identifies a CA or a CA
-- certificate (thereby its public key).
kdcPkId [2] IMPLICIT OCTET STRING
OPTIONAL,
-- Contains a CMS type IssuerAndSerialNumber SignerIdentifier encoded
-- according to [RFC3852].
-- Identifies Identifies, if present, a particular KDC certificate, if the
-- public key that the client already has it. has.
...
}

DHNonce ::= OCTET STRING

TrustedCA ::= CHOICE SEQUENCE {
caName [1] [0] IMPLICIT OCTET STRING,
-- Contains a PKIX type Name encoded according to
-- [RFC3280].
issuerAndSerial
-- Identifies a CA.
-- Prefer the sid field below if that is available.
certificateSerialNumber [1] INTEGER OPTIONAL,
-- Specifies the certificate serial number.
-- The defintion of the certificate serial number
-- is taken from X.509 [X.509-97].
subjectKeyIdentifier [2] IMPLICIT OCTET STRING, STRING OPTIONAL,
-- Contains Identifies the CA's public key by a key
-- identifier. When an X.509 certificate is
-- referenced, this key identifier matches the X.509
-- subjectKeyIdentifier extension value. When other
-- certificate formats are referenced, the documents
-- that specify the certificate format and their use
-- with the CMS type IssuerAndSerialNumber encoded must include details on matching the
-- according key identifier to [RFC3852]. the appropriate certificate
-- Identifies a specific CA certificate. field.
...
}
AuthPack ::= SEQUENCE {
pkAuthenticator [0] PKAuthenticator,
clientPublicValue [1] SubjectPublicKeyInfo OPTIONAL,
-- Defined in [RFC3280].
-- The pubic key value (the subjectPublicKey field
-- of the type SubjectPublicKeyInfo) MUST be encoded
-- according to [RFC3279].
-- Present only if the client wishes to use the
-- Diffie-Hellman key agreement method.
supportedCMSTypes [2] SEQUENCE OF AlgorithmIdentifier
OPTIONAL,
-- List of CMS encryption types supported by
-- client in order of (decreasing) preference.
clientDHNonce [3] DHNonce OPTIONAL,
-- Present only if the client indicates that it
-- wishes to cache reuse DH keys or to allow the KDC to
-- do so.
...
}

TrustedCertifiers

TD-TRUSTED-CERTIFIERS ::= SEQUENCE OF OCTET STRING TrustedCA
-- The OCTET STRING contains Identifies a PKIX type Name encoded list of CAs trusted by the KDC.
-- according to [RFC3280].

CertificateIndex Each TrustedCA identifies a CA or a CA
-- certificate (thereby its public key).

TD-INVALID-CERTIFICATES ::= SEQUENCE OF OCTET STRING
-- Contains Each OCTET STRING contains a CMS type
-- IssuerAndSerialNumber encoded
-- according to
-- [RFC3852].
-- Each IssuerAndSerialNumber indentifies a
-- certificate (sent by the client) with an invalid
-- signature.

KRB5PrincipalName ::= SEQUENCE {
realm [0] Realm,
principalName [1] PrincipalName
}

InitialVerifiedCAs

DHRepInfo ::= SEQUENCE {
dhSignedData [0] IMPLICIT OCTET STRING,
-- Contains a CMS type ContentInfo encoded according
-- to [RFC3852].
-- The contentType field of the type ContentInfo is
-- id-signedData (1.2.840.113549.1.7.2), and the
-- content field is a SignedData.
-- The eContentType field for the type SignedData is
-- id-pkdhkeydata (1.3.6.1.5.2.3.2), and the
-- eContent field contains the DER encoding of the
-- type KDCDHKeyInfo.
-- KDCDHKeyInfo is defined below.
serverDHNonce [1] DHNonce OPTIONAL
-- Present if and only if dhKeyExpiration is
-- present.
}
KDCDHKeyInfo ::= SEQUENCE {
subjectPublicKey [0] BIT STRING,
-- KDC's DH public key, y = g^x mod p.
-- MUST be ASN.1 encoded as an INTEGER; key.
-- This encoding The DH pubic key value is then used as the contents
-- (i.e., the value) of this mapped to a BIT STRING field.
-- according to [RFC3279].
nonce [1] INTEGER (0..4294967295),
-- Contains the nonce in the PKAuthenticator of the
-- request if cached DH keys are NOT used, reused,
-- 0 otherwise.
dhKeyExpiration [2] KerberosTime OPTIONAL,
-- Expiration time for KDC's cached values, present key pair,
-- present if and only if cached DH keys are used. reused. If this
-- this field is omitted then the serverDHNonce field
-- field MUST also be omitted.
...
}

TD-DH-PARAMETERS ::= SEQUENCE OF DomainParameters DHDomainParameters
-- Contains a list of Diffie-Hellman group domain
-- parameters in decreasing preference order.

DHDomainParameters ::= CHOICE {
modp [0] DomainParameters,
-- Type DomainParameters is defined in [RFC3279].
ec [1] EcpkParameters,
-- Type EcpkParameters is defined in [RFC3279].
...
}
END

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