draft-ietf-krb-wg-anon-12.txt   rfc6112.txt 
NETWORK WORKING GROUP L. Zhu Internet Engineering Task Force (IETF) L. Zhu
Internet-Draft P. Leach Request for Comments: 6112 P. Leach
Updates: 4120, 4121 and 4556 Microsoft Corporation Updates: 4120, 4121, 4556 Microsoft Corporation
(if approved) S. Hartman Category: Standards Track S. Hartman
Intended status: Standards Track Painless Security ISSN: 2070-1721 Painless Security
Expires: March 3, 2011 August 30, 2010 April 2011
Anonymity Support for Kerberos Anonymity Support for Kerberos
draft-ietf-krb-wg-anon-12
Abstract Abstract
This document defines extensions to the Kerberos protocol to allow a This document defines extensions to the Kerberos protocol to allow a
Kerberos client to securely communicate with a Kerberos application Kerberos client to securely communicate with a Kerberos application
service without revealing its identity, or without revealing more service without revealing its identity, or without revealing more
than its Kerberos realm. It also defines extensions which allow a than its Kerberos realm. It also defines extensions that allow a
Kerberos client to obtain anonymous credentials without revealing its Kerberos client to obtain anonymous credentials without revealing its
identity to the Kerberos Key Distribution Center (KDC). This identity to the Kerberos Key Distribution Center (KDC). This
document updates RFC 4120, RFC 4121, and RFC 4556. document updates RFCs 4120, 4121, and 4556.
Status of this Memo
This Internet-Draft is submitted in full conformance with the Status of This Memo
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This is an Internet Standards Track document.
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on March 3, 2011. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6112.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4 2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Protocol Description . . . . . . . . . . . . . . . . . . . . . 6 4. Protocol Description . . . . . . . . . . . . . . . . . . . . . 5
4.1. Anonymity Support in AS Exchange . . . . . . . . . . . . . 6 4.1. Anonymity Support in AS Exchange . . . . . . . . . . . . . 5
4.1.1. Anonymous PKINIT . . . . . . . . . . . . . . . . . . . 7 4.1.1. Anonymous PKINIT . . . . . . . . . . . . . . . . . . . 6
4.2. Anonymity Support in TGS Exchange . . . . . . . . . . . . 8 4.2. Anonymity Support in TGS Exchange . . . . . . . . . . . . 7
4.3. Subsequent Exchanges and Protocol Actions Common to AS 4.3. Subsequent Exchanges and Protocol Actions Common to AS
and TGS for Anonymity Support . . . . . . . . . . . . . . 10 and TGS for Anonymity Support . . . . . . . . . . . . . . 9
5. Interoperability Requirements . . . . . . . . . . . . . . . . 11 5. Interoperability Requirements . . . . . . . . . . . . . . . . 10
6. GSS-API Implementation Notes . . . . . . . . . . . . . . . . . 11 6. GSS-API Implementation Notes . . . . . . . . . . . . . . . . . 10
7. PKINIT Client Contribution to the Ticket Session Key . . . . . 12 7. PKINIT Client Contribution to the Ticket Session Key . . . . . 11
7.1. Combinging Two protocol Keys . . . . . . . . . . . . . . . 13 7.1. Combining Two Protocol Keys . . . . . . . . . . . . . . . 12
8. Security Considerations . . . . . . . . . . . . . . . . . . . 14 8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
11.1. Normative References . . . . . . . . . . . . . . . . . . . 15 11.1. Normative References . . . . . . . . . . . . . . . . . . . 15
11.2. Informative References . . . . . . . . . . . . . . . . . . 16 11.2. Informative References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
In certain situations, the Kerberos [RFC4120] client may wish to In certain situations, the Kerberos [RFC4120] client may wish to
authenticate a server and/or protect communications without revealing authenticate a server and/or protect communications without revealing
the client's own identity. For example, consider an application the client's own identity. For example, consider an application that
which provides read access to a research database, and which permits provides read access to a research database and that permits queries
queries by arbitrary requestors. A client of such a service might by arbitrary requesters. A client of such a service might wish to
wish to authenticate the service, to establish trust in the authenticate the service, to establish trust in the information
information received from it, but might not wish to disclose the received from it, but might not wish to disclose the client's
client's identity to the service for privacy reasons. identity to the service for privacy reasons.
Extensions to Kerberos are specified in this document by which a Extensions to Kerberos are specified in this document by which a
client can authenticate the Key Distribution Center (KDC) and request client can authenticate the Key Distribution Center (KDC) and request
an anonymous ticket. The client can use the anonymous ticket to an anonymous ticket. The client can use the anonymous ticket to
authenticate the server and protect subsequent client-server authenticate the server and protect subsequent client-server
communications. communications.
By using the extensions defined in this specification, the client can By using the extensions defined in this specification, the client can
request an anonymous ticket where the client may reveal the client's request an anonymous ticket where the client may reveal the client's
identity to the client's own KDC, or the client can hide the client's identity to the client's own KDC, or the client can hide the client's
identity completely by using anonymous Public Key Cryptography for identity completely by using anonymous Public Key Cryptography for
Initial Authentication in Kerberos (PKINIT) as defined in Initial Authentication in Kerberos (PKINIT) as defined in
Section 4.1. Using the returned anonymous ticket, the client remains Section 4.1. Using the returned anonymous ticket, the client remains
anonymous in subsequent Kerberos exchanges thereafter to KDCs on the anonymous in subsequent Kerberos exchanges thereafter to KDCs on the
cross-realm authentication path, and to the server with which it cross-realm authentication path and to the server with which it
communicates. communicates.
In this specification, the client realm in the anonymous ticket is In this specification, the client realm in the anonymous ticket is
the anonymous realm name when anonymous PKINIT is used to obtain the the anonymous realm name when anonymous PKINIT is used to obtain the
ticket. The client realm is the client's real realm name if the ticket. The client realm is the client's real realm name if the
client is authenticated using the client's long term keys. Note that client is authenticated using the client's long-term keys. Note that
the membership of a realm can imply a member of the community the membership of a realm can imply a member of the community
represented by the realm. represented by the realm.
The interaction with Generic Security Service Application Program The interaction with Generic Security Service Application Program
Interface (GSS-API) is described after the protocol description. Interface (GSS-API) is described after the protocol description.
2. Conventions Used in This Document 2. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Definitions 3. Definitions
The anonymous Kerberos realm name is defined as a well-known realm The anonymous Kerberos realm name is defined as a well-known realm
name based on [KRBNAM], and the value of this well-known realm name name based on [RFC6111], and the value of this well-known realm name
is the literal "WELLKNOWN:ANONYMOUS". is the literal "WELLKNOWN:ANONYMOUS".
The anonymous Kerberos principal name is defined as a well-known The anonymous Kerberos principal name is defined as a well-known
Kerberos principal name based on [KRBNAM]. The value of the name- Kerberos principal name based on [RFC6111]. The value of the name-
type field is KRB_NT_WELLKNOWN [KRBNAM], and the value of the name- type field is KRB_NT_WELLKNOWN [RFC6111], and the value of the name-
string field is a sequence of two KerberosString components: string field is a sequence of two KerberosString components:
"WELLKNOWN", "ANONYMOUS". "WELLKNOWN", "ANONYMOUS".
The anonymous ticket flag is defined as bit 16 (with the first bit The anonymous ticket flag is defined as bit 16 (with the first bit
being bit 0) in the TicketFlags: being bit 0) in the TicketFlags:
TicketFlags ::= KerberosFlags TicketFlags ::= KerberosFlags
-- anonymous(16) -- anonymous(16)
-- TicketFlags and KerberosFlags are defined in [RFC4120] -- TicketFlags and KerberosFlags are defined in [RFC4120]
This is a new ticket flag that is used to indicate a ticket is an This is a new ticket flag that is used to indicate that a ticket is
anonymous one. an anonymous one.
An anonymous ticket is a ticket that has all of the following An anonymous ticket is a ticket that has all of the following
properties: properties:
o The cname field contains the anonymous Kerberos principal name. o The cname field contains the anonymous Kerberos principal name.
o The crealm field contains the client's realm name or the anonymous o The crealm field contains the client's realm name or the anonymous
realm name. realm name.
o The anonymous ticket contains no information that can reveal the o The anonymous ticket contains no information that can reveal the
client's identity. However the ticket may contain the client client's identity. However, the ticket may contain the client
realm, intermediate realms on the client's authentication path, realm, intermediate realms on the client's authentication path,
and authorization data that may provide information related to the and authorization data that may provide information related to the
client's identity. For example, an anonymous principal that is client's identity. For example, an anonymous principal that is
identifiable only within a particular group of users can be identifiable only within a particular group of users can be
implemented using authorization data and such authorization data, implemented using authorization data and such authorization data,
if included in the anonymous ticket, would disclose the client's if included in the anonymous ticket, would disclose the client's
membership of that group. membership of that group.
o The anonymous ticket flag is set. o The anonymous ticket flag is set.
The anonymous KDC option is defined as bit 16 (with the first bit The anonymous KDC option is defined as bit 16 (with the first bit
being bit 0) in the KDCOptions: being bit 0) in the KDCOptions:
KDCOptions ::= KerberosFlags KDCOptions ::= KerberosFlags
-- anonymous(16) -- anonymous(16)
-- KDCOptions and KerberosFlags are defined in [RFC4120] -- KDCOptions and KerberosFlags are defined in [RFC4120]
As described in Section 4, the anonymous KDC option is set to request As described in Section 4, the anonymous KDC option is set to request
an anonymous ticket in an Authentication Service (AS) request or an an anonymous ticket in an Authentication Service (AS) request or a
Ticket Granting Service (TGS) request. Ticket Granting Service (TGS) request.
4. Protocol Description 4. Protocol Description
In order to request an anonymous ticket, the client sets the In order to request an anonymous ticket, the client sets the
anonymous KDC option in an AS request or an TGS request. anonymous KDC option in an AS request or a TGS request.
The rest of this section is organized as follows: it first describes The rest of this section is organized as follows: it first describes
protocol actions specific to AS exchanges, then it describes those of protocol actions specific to AS exchanges, then it describes those of
TGS exchange. These are then followed by the decription of protocol TGS exchanges. These are then followed by the description of
actions common to both AS and TGS and those in subsequent exchanges. protocol actions common to both AS and TGS and those in subsequent
exchanges.
4.1. Anonymity Support in AS Exchange 4.1. Anonymity Support in AS Exchange
The client requests an anonymous ticket by setting the anonymous KDC The client requests an anonymous ticket by setting the anonymous KDC
option in an AS exchange. option in an AS exchange.
The Kerberos client can use the client's long term keys, or the The Kerberos client can use the client's long-term keys, the client's
client's X.509 certificates [RFC4556], or any other preauthenication X.509 certificates [RFC4556], or any other pre-authentication data,
data, to authenticate to the KDC and requests an anonymous ticket in to authenticate to the KDC and requests an anonymous ticket in an AS
an AS exchange where the client's identity is known to the KDC. exchange where the client's identity is known to the KDC.
If the client in the AS request is anonymous, the anonymous KDC If the client in the AS request is anonymous, the anonymous KDC
option MUST be set in the request. Otherwise, the KDC MUST return a option MUST be set in the request. Otherwise, the KDC MUST return a
KRB-ERROR message with the code KDC_ERR_BADOPTION. KRB-ERROR message with the code KDC_ERR_BADOPTION.
If the client is anonymous and the KDC does not have a key to encrypt If the client is anonymous and the KDC does not have a key to encrypt
the reply (this can happen when, for example, the KDC does not the reply (this can happen when, for example, the KDC does not
support PKINIT [RFC4556]), the KDC MUST return an error message with support PKINIT [RFC4556]), the KDC MUST return an error message with
the code KDC_ERR_NULL_KEY [RFC4120]. the code KDC_ERR_NULL_KEY [RFC4120].
When policy allows, the KDC issues an anonymous ticket. If the When policy allows, the KDC issues an anonymous ticket. If the
client name in the request is the anonymous principal, the client client name in the request is the anonymous principal, the client
realm (crealm) in the reply is the anonymous realm, otherwise the realm (crealm) in the reply is the anonymous realm, otherwise, the
client realm is the realm of the AS. According to [RFC4120] the client realm is the realm of the AS. According to [RFC4120], the
client name and the client realm in the EncTicketPart of the reply client name and the client realm in the EncTicketPart of the reply
MUST match with the corresponding client name and the client realm of MUST match with the corresponding client name and the client realm of
the anonymous ticket in the reply; the client MUST use the client the KDC reply; the client MUST use the client name and the client
name and the client realm returned in the KDC-REP in subsequent realm returned in the KDC-REP in subsequent message exchanges when
message exchanges when using the obtained anonymous ticket. using the obtained anonymous ticket.
Care MUST be taken by the KDC not to reveal the client's identity in Care MUST be taken by the KDC not to reveal the client's identity in
the authorization data of the returned ticket when populating the the authorization data of the returned ticket when populating the
authorization data in a returned anonymous ticket. authorization data in a returned anonymous ticket.
The AD-INITIAL-VERIFIED-CAS authorization data as defined in The AD-INITIAL-VERIFIED-CAS authorization data, as defined in
[RFC4556] contains the issuer name of the client certificate. This [RFC4556], contains the issuer name of the client certificate. This
authorization is not applicable and MUST NOT be present in the authorization is not applicable and MUST NOT be present in the
returned anonymous ticket when anonymous PKINIT is used. When the returned anonymous ticket when anonymous PKINIT is used. When the
client is authenticated (i.e. anonymous PKINIT is not used), if it is client is authenticated (i.e., anonymous PKINIT is not used), if it
undesirable to disclose such information about the client's identity, is undesirable to disclose such information about the client's
the AD-INITIAL-VERIFIED-CAS authorization data SHOULD be removed from identity, the AD-INITIAL-VERIFIED-CAS authorization data SHOULD be
the returned anonymous ticket. removed from the returned anonymous ticket.
The client can use the client keys to mutually authenticate with the The client can use the client keys to mutually authenticate with the
KDC, request an anonymous TGT in the AS request. And in that case, KDC and request an anonymous Ticket Granting Ticket (TGT) in the AS
the reply key is selected as normal according to Section 3.1.3 of request. In that case, the reply key is selected as normal,
[RFC4120]. according to Section 3.1.3 of [RFC4120].
4.1.1. Anonymous PKINIT 4.1.1. Anonymous PKINIT
This sub-section defines anonymity PKINIT. This sub-section defines anonymous PKINIT.
As described earlier in this section, the client can request an As described earlier in this section, the client can request an
anonymous ticket by authenticating to the KDC using the client's anonymous ticket by authenticating to the KDC using the client's
identity; alternatively without revealing the client's identity to identity; alternatively, without revealing the client's identity to
the KDC, the Kerberos client can request an anonymous ticket as the KDC, the Kerberos client can request an anonymous ticket as
follows: the client sets the client name as the anonymous principal follows: the client sets the client name as the anonymous principal
in the AS exchange and provides a PA_PK_AS_REQ pre-authentication in the AS exchange and provides PA_PK_AS_REQ pre-authentication data
data [RFC4556] where both the signerInfos field and the certificates [RFC4556] where the signerInfos field of the SignedData [RFC5652] of
field of the SignedData [RFC3852] of the PA_PK_AS_REQ are empty. the PA_PK_AS_REQ is empty, and the certificates field is absent.
Because the anonymous client does not have an associated asymmetric Because the anonymous client does not have an associated asymmetric
key pair, the client MUST choose the Diffie-Hellman key agreement key pair, the client MUST choose the Diffie-Hellman key agreement
method by filling in the Diffie-Hellman domain parameters in the method by filling in the Diffie-Hellman domain parameters in the
clientPublicValue [RFC4556]. This use of the anonymous client name clientPublicValue [RFC4556]. This use of the anonymous client name
in conjunction with PKINIT is referred to as anonymous PKINIT. If in conjunction with PKINIT is referred to as anonymous PKINIT. If
anonymous PKINIT is used, the realm name in the returned anonymous anonymous PKINIT is used, the realm name in the returned anonymous
ticket MUST be the anonymous realm. ticket MUST be the anonymous realm.
Upon receiving the anonymous PKINIT request from the client, the KDC Upon receiving the anonymous PKINIT request from the client, the KDC
processes the request according to Section 3.1.2 of [RFC4120]. The processes the request, according to Section 3.1.2 of [RFC4120]. The
KDC skips the checks for the client's signature and the client's KDC skips the checks for the client's signature and the client's
public key (such as the verification of the binding between the public key (such as the verification of the binding between the
client's public key and the client name), but performs otherwise- client's public key and the client name), but performs otherwise
applicable checks, and proceeds as normal according to [RFC4556]. applicable checks, and proceeds as normal, according to [RFC4556].
For example, the AS MUST check if the client's Diffie-Hellman domain For example, the AS MUST check if the client's Diffie-Hellman domain
parameters are acceptable. The Diffie-Hellman key agreement method parameters are acceptable. The Diffie-Hellman key agreement method
MUST be used and the reply key is derived according to Section MUST be used and the reply key is derived according to Section
3.2.3.1 of [RFC4556]. If the clientPublicValue is not present in the 3.2.3.1 of [RFC4556]. If the clientPublicValue is not present in the
request, the KDC MUST return a KRB-ERROR with the code request, the KDC MUST return a KRB-ERROR with the code
KDC_ERR_PUBLIC_KEY_ENCRYPTION_NOT_SUPPORTED [RFC4556]. If all goes KDC_ERR_PUBLIC_KEY_ENCRYPTION_NOT_SUPPORTED [RFC4556]. If all goes
well, an anonymous ticket is generated according to Section 3.1.3 of well, an anonymous ticket is generated, according to Section 3.1.3 of
[RFC4120] and a PA_PK_AS_REP [RFC4556] pre-authentication data is [RFC4120], and PA_PK_AS_REP [RFC4556] pre-authentication data is
included in the KDC reply according to [RFC4556]. If the KDC does included in the KDC reply, according to [RFC4556]. If the KDC does
not have an asymmetric key pair, it MAY reply anonymously or reject not have an asymmetric key pair, it MAY reply anonymously or reject
the authentication attempt. If the KDC replies anonymously, both the the authentication attempt. If the KDC replies anonymously, the
signerInfos field and the certificates field of the SignedData signerInfos field of the SignedData [RFC5652] of PA_PK_AS_REP in the
[RFC3852] of PA_PK_AS_REP in the reply are empty. The server name in reply is empty, and the certificates field is absent. The server
the anonymous KDC reply contains the name of the TGS. name in the anonymous KDC reply contains the name of the TGS.
Upon receipt of the KDC reply that contains an anonymous ticket and a Upon receipt of the KDC reply that contains an anonymous ticket and
PA_PK_AS_REP [RFC4556] pre-authentication data, the client can then PA_PK_AS_REP [RFC4556] pre-authentication data, the client can then
authenticate the KDC based on the KDC's signature in the authenticate the KDC based on the KDC's signature in the
PA_PK_AS_REP. If the KDC's signature is missing in the KDC reply PA_PK_AS_REP. If the KDC's signature is missing in the KDC reply
(the reply is anonymous), the client MUST reject the returned ticket (the reply is anonymous), the client MUST reject the returned ticket
if it cannot authenticate the KDC otherwise. if it cannot authenticate the KDC otherwise.
A KDC that supports anonymous PKINIT MUST indicate the support of A KDC that supports anonymous PKINIT MUST indicate the support of
PKINIT according to Section 3.4 of [RFC4556]. PKINIT, according to Section 3.4 of [RFC4556]. In addition, such a
KDC MUST indicate support for anonymous PKINIT by including a padata
element of padata-type PA_PKINIT_KX and empty padata-value when
including PA-PK-AS-REQ in an error reply.
When included in a KDC error, PA_PKINIT_KX indicates support for
anonymous PKINIT. As discussed in Section 7, when included in an AS-
REP, PA_PKINIT_KX proves that the KDC and client both contributed to
the session key for any use of Diffie-Hellman key agreement with
PKINIT.
Note that in order to obtain an anonymous ticket with the anonymous Note that in order to obtain an anonymous ticket with the anonymous
realm name, the client MUST set the client name as the anonymous realm name, the client MUST set the client name as the anonymous
principal in the request when requesting an anonymous ticket in an AS principal in the request when requesting an anonymous ticket in an AS
exchange. Anonymity PKINIT is the only way via which an anonymous exchange. Anonymity PKINIT is the only way via which an anonymous
ticket with the anonymous realm as the client realm can be generated ticket with the anonymous realm as the client realm can be generated
in this specification. in this specification.
4.2. Anonymity Support in TGS Exchange 4.2. Anonymity Support in TGS Exchange
The client requests an anonymous ticket by setting the anonymous KDC The client requests an anonymous ticket by setting the anonymous KDC
option in a TGS exchange, and in that request the client can use a option in a TGS exchange, and in that request the client can use a
normal Ticket Granting Ticket (TGT) with the client's identity, or an normal Ticket Granting Ticket (TGT) with the client's identity, or an
anonymous TGT, or an anonymous cross realm TGT. If the client uses a anonymous TGT, or an anonymous cross-realm TGT. If the client uses a
normal TGT, the client's identity is known to the TGS. normal TGT, the client's identity is known to the TGS.
Note that the client can completely hide the client's identity in an Note that the client can completely hide the client's identity in an
AS exchange using anonymous PKINIT as described in the previous AS exchange using anonymous PKINIT, as described in the previous
section. section.
If the ticket in the PA-TGS-REQ of the TGS request is an anonymous If the ticket in the PA-TGS-REQ of the TGS request is an anonymous
one, the anonymous KDC option MUST be set in the request. Otherwise, one, the anonymous KDC option MUST be set in the request. Otherwise,
the KDC MUST return a KRB-ERROR message with the code the KDC MUST return a KRB-ERROR message with the code
KDC_ERR_BADOPTION. KDC_ERR_BADOPTION.
When policy allows, the KDC issues an anonymous ticket. If the When policy allows, the KDC issues an anonymous ticket. If the
ticket in the TGS request is an anonymous one, the client name and ticket in the TGS request is an anonymous one, the client name and
the client realm are copied from that ticket; otherwise the ticket in the client realm are copied from that ticket; otherwise, the ticket
the TGS request is a normal ticket, the returned anonymous ticket in the TGS request is a normal ticket, the returned anonymous ticket
contains the client name as the anonymous principal and the client contains the client name as the anonymous principal and the client
realm as the true realm of the client. In all cases, according to realm as the true realm of the client. In all cases, according to
[RFC4120] the client name and the client realm in the EncTicketPart [RFC4120] the client name and the client realm in the EncTicketPart
of the reply MUST match with the corresponding client name and the of the reply MUST match with the corresponding client name and the
client realm of the anonymous ticket in the reply; the client MUST client realm of the anonymous ticket in the reply; the client MUST
use the client name and the client realm returned in the KDC-REP in use the client name and the client realm returned in the KDC-REP in
subsequent message exchanges when using the obtained anonymous subsequent message exchanges when using the obtained anonymous
ticket. ticket.
Care MUST be taken by the TGS not to reveal the client's identity in Care MUST be taken by the TGS not to reveal the client's identity in
the authorization data of the returned ticket. When propagating the authorization data of the returned ticket. When propagating
authorization data in the ticket or in the enc-authorization-data authorization data in the ticket or in the enc-authorization-data
field of the request, the TGS MUST ensure that the client field of the request, the TGS MUST ensure that the client
confidentiality is not violated in the returned anonymous ticket. confidentiality is not violated in the returned anonymous ticket.
The TGS MUST process the authorization data recursively according to The TGS MUST process the authorization data recursively, according to
Section 5.2.6 of [RFC4120] beyond the container levels such that all Section 5.2.6 of [RFC4120], beyond the container levels such that all
embedded authorization elements are interpreted. The TGS SHOULD NOT embedded authorization elements are interpreted. The TGS SHOULD NOT
populate identity-based authorization data into an anonymous ticket populate identity-based authorization data into an anonymous ticket
in that such authorization data typically reveals the client's in that such authorization data typically reveals the client's
identity. The specification of a new authorization data type MUST identity. The specification of a new authorization data type MUST
specify the processing rules of the authorization data when an specify the processing rules of the authorization data when an
anonymous ticket is returned. If there is no processing rule defined anonymous ticket is returned. If there is no processing rule defined
for an authorization data element or the authorization data element for an authorization data element or the authorization data element
is unknown, the TGS MUST process it when an anonymous ticket is is unknown, the TGS MUST process it when an anonymous ticket is
returned as follows: returned as follows:
o If the authorization data element may reveal the client's o If the authorization data element may reveal the client's
identity, it MUST be removed unless otherwise specified. identity, it MUST be removed unless otherwise specified.
o If the authorization data element, that could reveal's the o If the authorization data element, that could reveal the client's
client's identity. is intended to restrict the use of the ticket identity, is intended to restrict the use of the ticket or limit
or limit the rights otherwise conveyed in the ticket, it cannot be the rights otherwise conveyed in the ticket, it cannot be removed
removed in order to hide the client's identity. In this case, the in order to hide the client's identity. In this case, the
authentication attempt MUST be rejected, and the TGS MUST return authentication attempt MUST be rejected, and the TGS MUST return
an error message with the code KDC_ERR_POLICY. Note this is an error message with the code KDC_ERR_POLICY. Note this is
applicable to both critical and optional authorization data. applicable to both critical and optional authorization data.
o If the authorization data element is unknown, the TGS MAY remove o If the authorization data element is unknown, the TGS MAY remove
it, or transfer it into the returned anonymous ticket, or reject it, or transfer it into the returned anonymous ticket, or reject
the authentication attempt, based on local policy for that the authentication attempt, based on local policy for that
authorization data type unless otherwise specified. If there is authorization data type unless otherwise specified. If there is
no policy defined for a given unknown authorization data type, the no policy defined for a given unknown authorization data type, the
authentication MUST be rejected. The error code is KDC_ERR_POLICY authentication MUST be rejected. The error code is KDC_ERR_POLICY
when the authentication is rejected. when the authentication is rejected.
The AD-INITIAL-VERIFIED-CAS authorization data as defined in The AD-INITIAL-VERIFIED-CAS authorization data, as defined in
[RFC4556] contains the issuer name of the client certificate. If it [RFC4556], contains the issuer name of the client certificate. If it
is undesirable to disclose such information about the client's is undesirable to disclose such information about the client's
identity, the AD-INITIAL-VERIFIED-CAS authorization data SHOULD be identity, the AD-INITIAL-VERIFIED-CAS authorization data SHOULD be
removed from an anonymous ticket. removed from an anonymous ticket.
The TGS encodes the name of the previous realm into the transited The TGS encodes the name of the previous realm into the transited
field according to Section 3.3.3.2 of [RFC4120]. Based on local field, according to Section 3.3.3.2 of [RFC4120]. Based on local
policy, the TGS MAY omit the previous realm if the cross realm TGT is policy, the TGS MAY omit the previous realm, if the cross realm TGT
an anonymous one in order to hide the authentication path of the is an anonymous one, in order to hide the authentication path of the
client. The unordered set of realms in the transited field, if client. The unordered set of realms in the transited field, if
present, can reveal which realm may potentially be the realm of the present, can reveal which realm may potentially be the realm of the
client or the realm that issued the anonymous TGT. The anonymous client or the realm that issued the anonymous TGT. The anonymous
Kerberos realm name MUST NOT be present in the transited field of a Kerberos realm name MUST NOT be present in the transited field of a
ticket. The true name of the realm that issued the anonymous ticket ticket. The true name of the realm that issued the anonymous ticket
MAY be present in the transited field of a ticket. MAY be present in the transited field of a ticket.
4.3. Subsequent Exchanges and Protocol Actions Common to AS and TGS for 4.3. Subsequent Exchanges and Protocol Actions Common to AS and TGS for
Anonymity Support Anonymity Support
In both AS and TGS exchanges, the realm field in the KDC request is In both AS and TGS exchanges, the realm field in the KDC request is
always the realm of the target KDC, not the anonymous realm when the always the realm of the target KDC, not the anonymous realm when the
client requests an anonymous ticket. client requests an anonymous ticket.
Absent other information the KDC MUST NOT include any identifier in Absent other information, the KDC MUST NOT include any identifier in
the returned anonymous ticket that could reveal the client's identity the returned anonymous ticket that could reveal the client's identity
to the server. to the server.
Unless anonymous PKINIT is used, if a client requires anonymous Unless anonymous PKINIT is used, if a client requires anonymous
communication then the client MUST check to make sure that the ticket communication, then the client MUST check to make sure that the
in the reply is actually anonymous by checking the presence of the ticket in the reply is actually anonymous by checking the presence of
anonymous ticket flag in the flags field of the EncKDCRepPart. This the anonymous ticket flag in the flags field of the EncKDCRepPart.
is because KDCs ignore unknown KDC options. A KDC that does not This is because KDCs ignore unknown KDC options. A KDC that does not
understand the anonymous KDC option will not return an error, but understand the anonymous KDC option will not return an error, but
will instead return a normal ticket. will instead return a normal ticket.
The subsequent client and server communications then proceed as The subsequent client and server communications then proceed as
described in [RFC4120]. described in [RFC4120].
Note that the anonymous principal name and realm are only applicable Note that the anonymous principal name and realm are only applicable
to the client in Kerberos messages, the server cannot be anonymous in to the client in Kerberos messages, the server cannot be anonymous in
any Kerberos message per this specification. any Kerberos message per this specification.
A server accepting an anonymous service ticket may assume that A server accepting an anonymous service ticket may assume that
subsequent requests using the same ticket originate from the same subsequent requests using the same ticket originate from the same
client. Requests with different tickets are likely to originate from client. Requests with different tickets are likely to originate from
different clients. different clients.
Upon receipt of an anonymous ticket, the transited policy check is Upon receipt of an anonymous ticket, the transited policy check is
preformed in the same way as that of a normal ticket if the client's performed in the same way as that of a normal ticket if the client's
realm is not the anonymous realm; if the client realm is the realm is not the anonymous realm; if the client realm is the
anonymous realm, absent other information any realm in the anonymous realm, absent other information any realm in the
authentication path is allowed by the cross-realm policy check. authentication path is allowed by the cross-realm policy check.
5. Interoperability Requirements 5. Interoperability Requirements
Conforming implementations MUST support the anonymous principal with Conforming implementations MUST support the anonymous principal with
a non-anonymous realm, and they MAY support the anonymous principal a non-anonymous realm, and they MAY support the anonymous principal
with the anonymous realm using anonymous PKINIT. with the anonymous realm using anonymous PKINIT.
6. GSS-API Implementation Notes 6. GSS-API Implementation Notes
GSS-API defines the name_type GSS_C_NT_ANONYMOUS [RFC2743] to GSS-API defines the name_type GSS_C_NT_ANONYMOUS [RFC2743] to
represent the anonymous identity. In addition, Section 2.1.1 of represent the anonymous identity. In addition, Section 2.1.1 of
[RFC1964] defines the single string representation of a Kerberos [RFC1964] defines the single string representation of a Kerberos
principal name with the name_type GSS_KRB5_NT_PRINCIPAL_NAME. The principal name with the name_type GSS_KRB5_NT_PRINCIPAL_NAME. The
anonymous principal with the anonymous realm corresponds to the GSS- anonymous principal with the anonymous realm corresponds to the GSS-
API anonymous principal. A principal with the anonymous principal API anonymous principal. A principal with the anonymous principal
name and a non-anonymous realm is an authenticated principal, hence name and a non-anonymous realm is an authenticated principal; hence,
such a principal does not correspond to the anonymous principal in such a principal does not correspond to the anonymous principal in
GSS-API with the GSS_C_NT_ANONYMOUS name type. The [RFC1964] name GSS-API with the GSS_C_NT_ANONYMOUS name type. The [RFC1964] name
syntax for GSS_KRB5_NT_PRINCIPAL_NAME MUST be used for importing the syntax for GSS_KRB5_NT_PRINCIPAL_NAME MUST be used for importing the
anonymous principal name with a non-anonymous realm name and for anonymous principal name with a non-anonymous realm name and for
displaying and exporting these names. In addition, this syntax must displaying and exporting these names. In addition, this syntax must
be used along with the name type GSS_C_NT_ANONYMOUS for displaying be used along with the name type GSS_C_NT_ANONYMOUS for displaying
and exporting the anonymous principal with the anonymous realm. and exporting the anonymous principal with the anonymous realm.
At the GSS-API [RFC2743] level, an initiator/client requests the use At the GSS-API [RFC2743] level, an initiator/client requests the use
of an anonymous principal with the anonymous realm by asserting the of an anonymous principal with the anonymous realm by asserting the
skipping to change at page 12, line 13 skipping to change at page 11, line 27
"un-done". "un-done".
Portable initiators are RECOMMENDED to use default credentials Portable initiators are RECOMMENDED to use default credentials
whenever possible, and request anonymity only through the input whenever possible, and request anonymity only through the input
anon_req_flag [RFC2743] to GSS_Init_Sec_Context(). anon_req_flag [RFC2743] to GSS_Init_Sec_Context().
7. PKINIT Client Contribution to the Ticket Session Key 7. PKINIT Client Contribution to the Ticket Session Key
The definition in this section was motivated by protocol analysis of The definition in this section was motivated by protocol analysis of
anonymous PKINIT (defined in this document) in building tunneling anonymous PKINIT (defined in this document) in building tunneling
channels [FAST] and subsequent channel bindings. In order to enable channels [RFC6113] and subsequent channel bindings. In order to
applications of anonymous PKINIT to form channels, all enable applications of anonymous PKINIT to form channels, all
implementations of anonymous PKINIT need to meet the requirements of implementations of anonymous PKINIT need to meet the requirements of
this section. There is otherwise no connection to the rest of this this section. There is otherwise no connection to the rest of this
document. document.
PKINIT is useful for constructing tunneling channels. To ensure that PKINIT is useful for constructing tunneling channels. To ensure that
an attacker cannot create a channel with a given name, it is an attacker cannot create a channel with a given name, it is
desirable that neither the KDC nor the client can unilaterally desirable that neither the KDC nor the client unilaterally determine
determine the ticket session key. To achieve that end, a KDC the ticket session key. To achieve that end, a KDC conforming to
conforming to this definition MUST encrypt a randomly generated key, this definition MUST encrypt a randomly generated key, called the KDC
called the KDC contribution key, in the PA_PKINIT_KX padata (defined contribution key, in the PA_PKINIT_KX padata (defined next in this
next in this section). The KDC contribution key is then combined section). The KDC contribution key is then combined with the reply
with the reply key to form the ticket session key of the returned key to form the ticket session key of the returned ticket. These two
ticket. These two keys are then combined using the KRB-FX-CF2 keys are then combined using the KRB-FX-CF2 operation defined in
operation defined in Section 7.1, where K1 is the KDC contribution Section 7.1, where K1 is the KDC contribution key, K2 is the reply
key, K2 is the reply key, the input pepper1 is American Standard Code key, the input pepper1 is American Standard Code for Information
for Information Interchange (ASCII) [ASAX34] string "PKINIT", and the Interchange (ASCII) [ASAX34] string "PKINIT", and the input pepper2
input pepper2 is ASCII string "KeyExchange". is ASCII string "KeyExchange".
PA_PKINIT_KX 147 PA_PKINIT_KX 147
-- padata for PKINIT that contains an encrypted -- padata for PKINIT that contains an encrypted
-- KDC contribution key. -- KDC contribution key.
PA-PKINIT-KX ::= EncryptedData -- EncryptionKey PA-PKINIT-KX ::= EncryptedData -- EncryptionKey
-- Contains an encrypted key randomly -- Contains an encrypted key randomly
-- generated by the KDC (known as the KDC contribution key). -- generated by the KDC (known as the KDC contribution key).
-- Both EncryptedData and EncryptionKey are defined in [RFC4120] -- Both EncryptedData and EncryptionKey are defined in [RFC4120]
The PA_PKINIT_KX padata MUST be included in the KDC reply when The PA_PKINIT_KX padata MUST be included in the KDC reply when
anonymous PKINIT is used; it SHOULD be included if PKINIT is used anonymous PKINIT is used; it SHOULD be included if PKINIT is used
with the Diffie-Hellman key exchange but the client is not anonymous; with the Diffie-Hellman key exchange but the client is not anonymous;
it MUST NOT be included otherwise (e.g. when PKINIT is used with the it MUST NOT be included otherwise (e.g., when PKINIT is used with the
public key encryption as the key exchange). public key encryption as the key exchange).
The padata-value field of the PA-PKINIT-KX type padata contains the The padata-value field of the PA-PKINIT-KX type padata contains the
DER [X680] [X690] encoding of the Abstract Syntax Notation One DER [X.680] [X.690] encoding of the Abstract Syntax Notation One
(ASN.1) type PA-PKINIT-KX. The PA-PKINIT-KX structure is a (ASN.1) type PA-PKINIT-KX. The PA-PKINIT-KX structure is an
EncryptedData. The clear text data being encrypted is the DER EncryptedData. The cleartext data being encrypted is the DER-encoded
encoded KDC contribution key randomly generated by the KDC. The KDC contribution key randomly generated by the KDC. The encryption
encryption key is the reply key and the key usage number is key is the reply key and the key usage number is
KEY_USAGE_PA_PKINIT_KX (44). KEY_USAGE_PA_PKINIT_KX (44).
The client then decrypts the KDC contribution key and verifies the The client then decrypts the KDC contribution key and verifies the
ticket session key in the returned ticket is the combined key of the ticket session key in the returned ticket is the combined key of the
KDC contribution key and the reply key as described above. A KDC contribution key and the reply key as described above. A
conforming client MUST reject anonymous PKINIT authentication if the conforming client MUST reject anonymous PKINIT authentication if the
PA_PKINIT_KX padata is not present in the KDC reply or if the ticket PA_PKINIT_KX padata is not present in the KDC reply or if the ticket
session key of the returned ticket is not the combined key of the KDC session key of the returned ticket is not the combined key of the KDC
contribution key and the reply key when PA-PKINIT-KX is present in contribution key and the reply key when PA-PKINIT-KX is present in
the KDC reply. the KDC reply.
7.1. Combinging Two protocol Keys 7.1. Combining Two Protocol Keys
KRB-FX-CF2() combines two protocol keys based on the pseudo-random() KRB-FX-CF2() combines two protocol keys based on the pseudo-random()
function defined in [RFC3961]. function defined in [RFC3961].
Given two input keys, K1 and K2, where K1 and K2 can be of two Given two input keys, K1 and K2, where K1 and K2 can be of two
different enctypes, the output key of KRB-FX-CF2(), K3, is derived as different enctypes, the output key of KRB-FX-CF2(), K3, is derived as
follows: follows:
KRB-FX-CF2(protocol key, protocol key, octet string, KRB-FX-CF2(protocol key, protocol key, octet string,
octet string) -> (protocol key) octet string) -> (protocol key)
skipping to change at page 13, line 43 skipping to change at page 13, line 14
Where ^ denotes the exclusive-OR operation. PRF+() is defined as Where ^ denotes the exclusive-OR operation. PRF+() is defined as
follows: follows:
PRF+(protocol key, octet string) -> (octet string) PRF+(protocol key, octet string) -> (octet string)
PRF+(key, shared-info) -> pseudo-random( key, 1 || shared-info ) || PRF+(key, shared-info) -> pseudo-random( key, 1 || shared-info ) ||
pseudo-random( key, 2 || shared-info ) || pseudo-random( key, 2 || shared-info ) ||
pseudo-random( key, 3 || shared-info ) || ... pseudo-random( key, 3 || shared-info ) || ...
Here the counter value 1, 2, 3 and so on are encoded as a one-octet Here the counter value 1, 2, 3, and so on are encoded as a one-octet
integer. The pseudo-random() operation is specified by the enctype integer. The pseudo-random() operation is specified by the enctype
of the protocol key. PRF+() uses the counter to generate enough bits of the protocol key. PRF+() uses the counter to generate enough bits
as needed by the random-to-key() [RFC3961] function for the as needed by the random-to-key() [RFC3961] function for the
encryption type specified for the resulting key; unneeded bits are encryption type specified for the resulting key; unneeded bits are
removed from the tail. removed from the tail.
8. Security Considerations 8. Security Considerations
Since KDCs ignore unknown options, a client requiring anonymous Since KDCs ignore unknown options, a client requiring anonymous
communication needs to make sure that the returned ticket is actually communication needs to make sure that the returned ticket is actually
anonymous. This is because a KDC that that does not understand the anonymous. This is because a KDC that does not understand the
anonymous option would not return an anonymous ticket. anonymous option would not return an anonymous ticket.
By using the mechanism defined in this specification, the client does By using the mechanism defined in this specification, the client does
not reveal the client's identity to the server but the client not reveal the client's identity to the server but the client
identity may be revealed to the KDC of the server principal (when the identity may be revealed to the KDC of the server principal (when the
server principal is in a different realm than that of the client), server principal is in a different realm than that of the client),
and any KDC on the cross-realm authentication path. The Kerberos and any KDC on the cross-realm authentication path. The Kerberos
client MUST verify the ticket being used is indeed anonymous before client MUST verify the ticket being used is indeed anonymous before
communicating with the server, otherwise the client's identity may be communicating with the server, otherwise, the client's identity may
revealed unintentionally. be revealed unintentionally.
In cases where specific server principals must not have access to the In cases where specific server principals must not have access to the
client's identity (for example, an anonymous poll service), the KDC client's identity (for example, an anonymous poll service), the KDC
can define server principal specific policy that insure any normal can define server-principal-specific policy that ensures any normal
service ticket can NEVER be issued to any of these server principals. service ticket can NEVER be issued to any of these server principals.
If the KDC that issued an anonymous ticket were to maintain records If the KDC that issued an anonymous ticket were to maintain records
of the association of identities to an anonymous ticket, then someone of the association of identities to an anonymous ticket, then someone
obtaining such records could breach the anonymity. Additionally, the obtaining such records could breach the anonymity. Additionally, the
implementations of most (for now all) KDC's respond to requests at implementations of most (for now all) KDC's respond to requests at
the time that they are received. Traffic analysis on the connection the time that they are received. Traffic analysis on the connection
to the KDC will allow an attacker to match client identities to to the KDC will allow an attacker to match client identities to
anonymous tickets issued. Because there are plaintext parts of the anonymous tickets issued. Because there are plaintext parts of the
tickets that are exposed on the wire, such matching by a third party tickets that are exposed on the wire, such matching by a third-party
observer is relatively straightforward. A service that is observer is relatively straightforward. A service that is
authenticated by the anonymous principals may be able to infer the authenticated by the anonymous principals may be able to infer the
identity of the client by examining and linking quasi-static protocol identity of the client by examining and linking quasi-static protocol
information such as the IP address from which a request is received, information such as the IP address from which a request is received,
or by linking multiple uses of the same anonymous ticket. or by linking multiple uses of the same anonymous ticket.
Two mechanisms, the FAST facility with the hide-client-names option
in [RFC6113] and the Kerberos5 starttls option [STARTTLS], protect
the client identity so that an attacker would never be able to
observe the client identity sent to the KDC. Transport or network
layer security between the client and the server will help prevent
tracking of a particular ticket to link a ticket to a user. In
addition, clients can limit how often a ticket is reused to minimize
ticket linking.
The client's real identity is not revealed when the client is The client's real identity is not revealed when the client is
authenticated as the anonymous principal. Application servers MAY authenticated as the anonymous principal. Application servers MAY
reject the authentication in order to, for example, prevent reject the authentication in order to, for example, prevent
information disclosure or as part of Denial of Service (DOS) information disclosure or as part of Denial of Service (DoS)
prevention. Application servers MUST avoid accepting anonymous prevention. Application servers MUST avoid accepting anonymous
credentials in situations where they must record the client's credentials in situations where they must record the client's
identity; for example, when there must be an audit trail. identity; for example, when there must be an audit trail.
9. Acknowledgements 9. Acknowledgements
JK Jaganathan helped editing early revisions of this document. JK Jaganathan helped editing early revisions of this document.
Clifford Neuman contributed the core notions of this document. Clifford Neuman contributed the core notions of this document.
skipping to change at page 15, line 27 skipping to change at page 15, line 8
Miguel Garcia and Phillip Hallam-Baker reviewed the document and Miguel Garcia and Phillip Hallam-Baker reviewed the document and
provided helpful suggestions. provided helpful suggestions.
In addition, the following individuals made significant In addition, the following individuals made significant
contributions: Jeffrey Altman, Tom Yu, Chaskiel M Grundman, Love contributions: Jeffrey Altman, Tom Yu, Chaskiel M Grundman, Love
Hornquist Astrand, Jeffrey Hutzelman, and Olga Kornievskaia. Hornquist Astrand, Jeffrey Hutzelman, and Olga Kornievskaia.
10. IANA Considerations 10. IANA Considerations
This document defines a new 'anonymous' Kerberos well-known name and This document defines a new 'anonymous' Kerberos well-known name and
a new 'anonymous' Kerberos well-known realm based on [KRBNAM]. IANA a new 'anonymous' Kerberos well-known realm based on [RFC6111]. IANA
is requested to add these two values to the Kerberos naming has added these two values to the Kerberos naming registries that are
registries that are created in [KRBNAM]. created in [RFC6111].
11. References 11. References
11.1. Normative References 11.1. Normative References
[ASAX34] American Standards Institute, "American Standard Code for [ASAX34] American Standards Institute, "American Standard Code for
Information Interchange", ASA X3.4-1963, June 1963. Information Interchange", ASA X3.4-1963, June 1963.
[KRBNAM] Zhu, L., "Additional Kerberos Naming Constraints", [RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
draft-ietf-krb-wg-naming (work in progress), 2008. RFC 1964, June 1996.
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
RFC 1964, June 1996. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2743] Linn, J., "Generic Security Service Application Program
Requirement Levels", BCP 14, RFC 2119, March 1997. Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC2743] Linn, J., "Generic Security Service Application Program [RFC3961] Raeburn, K., "Encryption and Checksum Specifications for
Interface Version 2, Update 1", RFC 2743, January 2000. Kerberos 5", RFC 3961, February 2005.
[RFC3852] Housley, R., "Cryptographic Message Syntax (CMS)", [RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
RFC 3852, July 2004. Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
[RFC3961] Raeburn, K., "Encryption and Checksum Specifications for [RFC4556] Zhu, L. and B. Tung, "Public Key Cryptography for Initial
Kerberos 5", RFC 3961, February 2005. Authentication in Kerberos (PKINIT)", RFC 4556,
June 2006.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The [RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)",
Kerberos Network Authentication Service (V5)", RFC 4120, STD 70, RFC 5652, September 2009.
July 2005.
[RFC4556] Zhu, L. and B. Tung, "Public Key Cryptography for Initial [RFC6111] Zhu, L., "Additional Kerberos Naming Constraints",
Authentication in Kerberos (PKINIT)", RFC 4556, June 2006. RFC 6111, April 2011.
[X.680] "Abstract Syntax Notation One (ASN.1): Specification of
Basic Notation", ITU-T Recommendation X.680: ISO/IEC
International Standard 8824-1:1998, 1997.
[X.690] "ASN.1 encoding rules: Specification of Basic Encoding
Rules (BER), Canonical Encoding Rules (CER) and
Distinguished Encoding Rules (DER)", ITU-T Recommendation
X.690 ISO/IEC International Standard 8825-1:1998, 1997.
11.2. Informative References 11.2. Informative References
[FAST] Zhu, L. and S. Hartman, "A Generalized Framework for [RFC6113] Hartman, S. and L. Zhu, "A Generalized Framework for
Kerberos Pre-Authentication", Kerberos Pre-Authentication", RFC 6113, April 2011.
draft-ietf-krb-wg-preauth-framework (work in progress),
2008. [STARTTLS] Josefsson, S., "Using Kerberos V5 over the Transport
Layer Security (TLS) protocol", Work in Progress,
August 2010.
Authors' Addresses Authors' Addresses
Larry Zhu Larry Zhu
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
US US
Email: larry.zhu@microsoft.com EMail: larry.zhu@microsoft.com
Paul Leach Paul Leach
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
US US
Email: paulle@microsoft.com EMail: paulle@microsoft.com
Sam Hartman Sam Hartman
Painless Security Painless Security
Email: hartmans-ietf@mit.edu EMail: hartmans-ietf@mit.edu
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