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NETWORK WORKING GROUP L. Zhu
Internet-Draft P. Leach
Updates: 4120 (if approved) K. Jaganathan
Expires: January 17, 2007 Microsoft Corporation
July 16, 2006
Anonymity Support for Kerberos
draft-ietf-krb-wg-anon-01
Status of this Memo
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 becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on January 17, 2007.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document defines the use of anonymous Kerberos tickets for the
purpose of authenticating the servers and enabling secure
communication between a client and a server, without identifying the
client to the server.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Protocol Description . . . . . . . . . . . . . . . . . . . . . 5
5. GSS-API Implementation Notes . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
In certain situations or environments, the Kerberos [RFC4120] client
may wish to authenticate a server and/or protect communications
without revealing its own identity. For example, consider an
application which provides read access to a research database, and
which permits queries by arbitrary requestors. A client of such a
service might wish to authenticate the service, to establish trust in
the information received from it, but might not wish to disclose its
identity to the service for privacy reasons.
To accomplish this, a Kerberos mechanism is specified in this
document by which a client requests an anonymous ticket and use that
to authenticate the server and secure subsequent client-server
communications. This provides Kerberos with functional equivalence
to TLS [RFC2246] in environments where Kerberos is a more attractive
authentication mechanism.
Using this mechanism, the client has to reveal its identity in its
initial request to its own Key Distribution Center (KDC) [RFC4120],
and then it can remain anonymous thereafter to KDCs on the cross-
realm authentication path, if any, and to the server with which it
communicates.
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].
3. Definitions
The anonymous Kerberos realm name is a reserved realm name as defined
in [KRBNAM] and its value is the literal "RESERVED:ANONYMOUS".
The anonymous Kerberos principal name is a reserved Kerberos
principal name as defined in [KRBNAM], its name-type [RFC4120] is
KRB_NT_RESRVED [KRBNAM], and its name-string [RFC4120] is a sequence
of two KerberosString components: "RESERVED", "ANONYMOUS".
In this specification, only the client name or the client realm can
be anonymous; the server name or the server realm can not be
anonymous.
The transited field [RFC4120] of a ticket is an anonymous
authentication path if the tr-type field of the TransitedEncoding
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type [RFC4120] is NO-TRANSITED-INFO and the contents field is an
empty OCTET STRING.
NO-TRANSITED-INFO TBA
This transited encoding type indicates that there is no information
available about the authentication path.
The anonymous ticket flag is defined as bit TBA (with the first bit
being bit 0) in the TicketFlags:
TicketFlags ::= KerberosFlags
-- anonymous(TBA)
-- TicketFlags and KerberosFlags are defined in [RFC4120]
An anonymous ticket is a ticket that has all of the following
properties:
o The cname field [RFC4120] contains the anonymous Kerberos
principal name.
o The crealm field [RFC4120] contains either the realm name of the
client who made the request or the anonymous kerberos realm name,
based on the local policy of the KDC.
o The transited field [RFC4120] can contain either the client's
"normal" authentication path according to Section 3.3.3.2 of
[RFC4120] or the anonymous authentication path.
o It contains no information that can reveal the client's identity.
However the ticket can contain the client realm and the realms on
the authentication path, and the authorization data may provide
additional information of the client. For example, an anonymous
principal that is only identifiable within a particular group of
users can be implemented by using authorization data.
o The anonymous ticket flag is set.
Notes: The anonymous ticket flag MUST NOT be set by implementations
of this specification if the ticket is not an anonymous ticket. The
server principal name and the server realm in a cross-realm referral
TGT are not dependent on whether the client is the anonymous
principal or not.
The request-anonymous KDC option is defined as bit TBA (with the
first bit being bit 0) in the KDCOptions:
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KDCOptions ::= KerberosFlags
-- request-anonymous(TBA)
-- KDCOptions and KerberosFlags are defined in [RFC4120]
4. Protocol Description
In order to request an anonymous ticket, the client sets the request-
anonymous KDC option in an Authentication Exchange (AS) or Ticket
Granting Service (TGS) request [RFC4120]. The client can request an
anonymous TGT based on a normal TGT. Note that if the ticket in the
PA-TGS-REQ [RFC4120] is anonymous, the request-anonymous KDC option
MUST be set in the request.
When propagating authorization data, care MUST be taken by the TGS to
ensure that the client confidentiality is not violated: the TGS MUST
either fail the request or remove authorization data that may reveal
the client's identity. An optional authorization element unknown by
the TGS MUST be removed if it can be ignored (such as ones enclosed
in the AD-IF-RELEVANT or the AD-KDCIssued containers [RFC4120]). The
TGS can strip critical unknown authorization data if such data do not
convey any rights based on the requesting client's identity. Here is
a table of the known authorization-data elements, flagged with
whether they interfere with client anonymity and recommendations for
how to process them.
ad-type References Can Breach Confidentiality?
------------------------------------------------------------------
AD-IF-RELEVANT RFC4120 Yes, remove if unknown
AD-KDCIssued RFC4120 Yes, remove if unknown
AD-AND-OR RFC4120 Yes, remove if unknown
AD-MANDATORY-FOR-KDC RFC4120 Yes, fail the request if unknown
If it is inappropriate to remove an authorization element from the
TGS request in order to produce an anonymous ticket, the KDC MUST
return an error message with the code KDC_ERR_POLICY [RFC4120].
When policy allows, the KDC issues an anonymous ticket. The client
realm in the anonymous ticket can be the anonymous realm name based
on local policy. The client name and the client realm the
EncKDCRepPart of the reply [RFC4120] MUST match with the
corresponding client name and the client realm of the anonymous reply
ticket. The client then MUST use the client name and the client
realm returned in the EncKDCRepPart in subsequent message exchanges
when using that anonymous ticket.
If there is a key known by both the client and the KDC for encrypting
the KDC reply, the cname field in the request [RFC4120] can be
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anonymous. If the client is anonymous and the KDC does not have a
key to encrypt the reply, the KDC MUST return an error message with
the code KDC_ERR_NULL_KEY [RFC4120]. For AS exchange, if the reply
key is selected from the client keys (for example, as described in
Section 3.1.3 of [RFC4120]), then the client principal MUST NOT be
anonymous. The client can use the client keys to request an
anonymous TGT in the AS request. The anonymous client name, for
example, can be used in conjunction with PKINIT [RFC4556]. An
anonymous PKINIT client can authenticate the KDC based on the KDC
certificate. For TGS exchange, the reply key is selected according
to Section 3.3.3 of [RFC4120] as normal.
The KDC fills out the transited field of the anonymous ticket in the
reply as follows: If the service ticket in a TGS request is an
anonymous ticket with a "normal" authentication path, then the
authentication path in the reply ticket MUST also contain a "normal"
authentication path: the TGS MUST add the name of the previous realm.
However, if the service ticket in a TGS request is an anonymous
ticket with an anonymous authentication path, then the reply ticket
can contain either an anonymous authentication path or a "normal"
authentication path, based on the local policy of the KDC. Thus a
"normal" authentication path in an anonymous ticket can be a partial
path: it may not include all the intermediate realms on the
authentication path.
The KDC fills out the authtime field of the anonymous ticket in the
reply as follows: If the anonymous ticket is returned in an AS
exchange, the authtime field of the ticket contains the request time.
If the anonymous ticket is returned in a TGS exchange, the authtime
field contains the time of the initial authentication for the
principal who has made the request. An anonymous ticket can be
renewed, and the authtime field of a renewed ticket is the authtime
in the anonymous ticket that the renewed ticket was based on.
If a client requires anonymous communication then the client MUST
check to make sure that the ticket in the reply is actually anonymous
by checking the presence of the anonymous ticket flag. Because KDCs
ignore unknown KDC options, a KDC that does not understand the
request-anonymous KDC option will not return an error, but will
instead return a normal ticket.
The subsequent client and server communications then proceed as
described in [RFC4120]. No transited policy checking is needed for
the anonymous authentication path. However, transited policy checks
defined in Section 2.7 of [RFC4120] would apply to an anonymous
ticket that contains a "normal" authentication path.
A server accepting an anonymous service ticket may assume that
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subsequent requests using the same ticket originate from the same
client. Requests with different tickets are likely to originate from
different clients.
Interoperability and backward-compatibility notes: the KDC is given
the task of rejecting a request for an anonymous ticket when the
anonymous ticket is not acceptable by the server.
5. GSS-API Implementation Notes
At the GSS-API [RFC2743] level, the use of an anonymous principal by
the initiator/client requires a software change of the initiator/
client software (to assert the "anonymous" flag when calling
GSS_Init_Sec_Context().
GSS-API does not know or define "anonymous credentials", so the
(printable) name of the anonymous principal will rarely be used by or
relevant for the initator/client. The printable name is relevant for
the acceptor/server when performing an authorization decision based
on the name that pops up from GSS_Accept_Sec_Context() upon
successful security context establishment.
A GSS-API initiator MUST carefully check the resulting context
attributes from the initial call to GSS_Init_Sec_Context() when
requesting anonymity, because (as in the GSS-API tradition and for
backwards compatibility) anonymity is just another optional context
attribute. It could be that the mechanism doesn't recognize the
attribute at all or that anonymity is not available for some other
reasons -- and in that case the initiator must NOT send the initial
security context token to the acceptor, because it will likely reveal
the initiators identity to the acceptor, something that can rarely be
"un-done".
GSS-API defines the name_type GSS_C_NT_ANONYMOUS [RFC2743] to
represent the anonymous identity. In addition, Section 2.1.1 of
[RFC1964] defines the single string representation of a Kerberos
principal name with the name_type GSS_KRB5_NT_PRINCIPAL_NAME. For
the anonymous principals, the name component within the exportable
name as defined in Section 2.1.3 of [RFC1964] MUST signify the realm
name according to Section 2.1.1 of [RFC1964]. In this specification
only the client/initiator can be the anonymous identity.
Portable initiators are RECOMMENDED to use default credentials
whenever possible, and request anonymity only through the input
anon_req_flag [RFC2743] to GSS_Init_Sec_Context().
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6. Security Considerations
Since KDCs ignore unknown options [RFC4120], a client requiring
anonymous communication needs to make sure that the ticket is
actually anonymous. A KDC that that does not understand the
anonymous option would not return an anonymous ticket.
By using the mechanism defined in this specification, the client does
not reveal its identity to the server but its 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), and any
KDC on the cross-realm authentication path. The Kerberos client MUST
verify the ticket being used is indeed anonymous before communicating
with the cross-realm KDC or the server, otherwise the client's
identity may be revealed to the server unintentionally.
In cases where specific server principals must not have access to the
client's identity (for example, an anonymous poll service), the KDC
can define server principal specific policy that insure any normal
service ticket can NEVER be issued to any of these server principals.
If the KDC that issued an anonymous ticket were to maintain records
of the association of identities to an anonymous ticket, then someone
obtaining such records could breach the anonymity. Additionally, the
implementation of most (for now all) KDC's respond to requests at the
time that they are received. Traffic analasys on the connection to
the KDC will allow an attacket to match client identities to
anonymous tickets issued. Because there are plaintext parts of the
tickets that are exposed on the wire, such matching by a third party
observer is relatively straigtforward.
7. Acknowledgements
The authors would like to thank the following individuals for their
insightful comments and fruitful discussions: Sam Hartman, Clifford
Neuman, Martin Rex, Nicolas Williams, Jeffery Altman, Tom Yu,
Chaskiel M Grundman, Love Hoernquist Aestrand, and Jeffery Hutzelman.
8. IANA Considerations
No IANA actions are required for this document.
9. Normative References
[KRBNAM] Zhu, L., "Additonal Kerberos Naming Contraints",
draft-ietf-krb-wg-naming, work in progress.
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[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
RFC 1964, June 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2246] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
[RFC4556] Zhu, L. and B. Tung, "Public Key Cryptography for Initial
Authentication in Kerberos (PKINIT)", RFC 4556, June 2006.
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Authors' Addresses
Larry Zhu
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: lzhu@microsoft.com
Paul Leach
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: paulle@microsoft.com
Karthik Jaganathan
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: karthikj@microsoft.com
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Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2006). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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NETWORK WORKING GROUP L. Zhu
Internet-Draft P. Leach
Updates: 4120 (if approved) K. Jaganathan
Intended status: Standards Track Microsoft Corporation
Expires: April 14, 2007 October 11, 2006
Anonymity Support for Kerberos
draft-ietf-krb-wg-anon-02
Status of this Memo
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 becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on April 14, 2007.
Copyright Notice
Copyright (C) The Internet Society (2006).
Abstract
This document defines extensions to the Kerberos protocol for the
Kerberos client to authenticate the Kerberos Key Distribution Center
and the Kerberos server, without revealing the client's identity.
These extensions can be used to secure communication between the
anonymous client and the server.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Protocol Description . . . . . . . . . . . . . . . . . . . . . 5
5. GSS-API Implementation Notes . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Normative References . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
In certain situations, the Kerberos [RFC4120] client may wish to
authenticate a server and/or protect communications without revealing
its own identity. For example, consider an application which
provides read access to a research database, and which permits
queries by arbitrary requestors. A client of such a service might
wish to authenticate the service, to establish trust in the
information received from it, but might not wish to disclose its
identity to the service for privacy reasons.
Extensions to [RFC4120] are specified in this document by which a
client can authenticate the KDC and request an anonymous ticket. The
client can use the anonymous ticket to authenticate the server and
protect subsequent client-server communications. These extensions
provide Kerberos with functional equivalence to Transport Layer
Security (TLS) [RFC4346].
By using the extensions defined in this specification, the client MAY
reveal its identity in its initial request to its own KDC, but it can
remain anonymous thereafter to KDCs on the cross-realm authentication
path, and to the server with which it communicates.
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].
3. Definitions
The anonymous Kerberos realm name is a reserved realm name based on
[KRBNAM]. The value is the literal "RESERVED:ANONYMOUS".
The anonymous Kerberos principal name is a reserved Kerberos
principal name based on [KRBNAM]. The value of the name-type field
is KRB_NT_RESRVED [KRBNAM], and the value of the name-string field is
a sequence of two KerberosString components: "RESERVED", "ANONYMOUS".
Note that in this specification, the anonymous principal name and
realm are only applicable to the client in Kerberos messages, the
server MUST NOT be anonymous in any Kerberos message.
The transited field [RFC4120] of a ticket is an anonymous
authentication path if the tr-type field of the TransitedEncoding
type [RFC4120] is NO-TRANSITED-INFO and the contents field is an
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empty OCTET STRING.
NO-TRANSITED-INFO TBA
This means that no information of the authentication path is
disclosed.
The anonymous ticket flag is defined as bit TBA (with the first bit
being bit 0) in the TicketFlags:
TicketFlags ::= KerberosFlags
-- anonymous(TBA)
-- TicketFlags and KerberosFlags are defined in [RFC4120]
An anonymous ticket is a ticket that has all of the following
properties:
o The cname field [RFC4120] contains the anonymous Kerberos
principal name.
o The crealm field [RFC4120] contains either the client's realm name
or the anonymous realm name.
o The transited field [RFC4120] can contain either the client's
authentication path as described in Section 3.3.3.2 of [RFC4120]
or the anonymous authentication path.
o The anonymous ticket contains no information that can reveal the
client's identity. However the ticket MAY contain the client
realm and the realms on the authentication path, and authorization
data that MAY provide information related to the client's
identity. For example, an anonymous principal that is only
identifiable within a particular group of users can be implemented
using authorization data and such authorization data, if included
in the anonymous ticket, shall disclose the client's membership of
that group.
o The anonymous ticket flag is set.
The request-anonymous KDC option is defined as bit TBA (with the
first bit being bit 0) in the KDCOptions:
KDCOptions ::= KerberosFlags
-- request-anonymous(TBA)
-- KDCOptions and KerberosFlags are defined in [RFC4120]
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4. Protocol Description
In order to request an anonymous ticket, the client sets the request-
anonymous KDC option in an Authentication Exchange (AS) or Ticket
Granting Service (TGS) request [RFC4120]. The client can request an
anonymous TGT based on a normal TGT. If the client wishes to
authenticate the KDC anonymously, it sets the client name as
anonymous in the AS exchange and provides a PA_PK_AS_REQ pre-
authentication data [RFC4556] where both the signerInfos field and
the certificates field of the SignedData [RFC3852] of PA_PK_AS_REQ
are empty. Because the anonymous client does not have an associated
asymmetric key pair, the client MUST use the Diffie-Hellman key
agreement method by filling in the Diffie-Hellman domain parameters
in the clientPublicValue [RFC4556].
If the ticket in the PA-TGS-REQ [RFC4120] of the TGS request is
anonymous, or if the client in the AS request is anonymous, the
request-anonymous KDC option MUST be set in the request.
Upon receiving the AS request with a PA_PK_AS_REQ from the anonymous
client, the KDC skips the checks for the client's signature and the
client's public key (such as the verification of the binding between
the client's public key and the client name), but performs otherwise-
applicable checks, and proceeds as normal according to [RFC4556].
For example, the AS MUST check if the client's Diffie-Hellman domain
parameters are acceptable. The Diffie-Hellman key agreement method
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
request, the KDC MUST return a KRB-ERROR [RFC4120] with the code
KDC_ERR_PUBLIC_KEY_ENCRYPTION_NOT_SUPPORTED [RFC4556] and there is no
accompanying e-data. The client that made the anonymous request can
authenticate the KDC based on the KDC's signature in the reply. If
the KDC does not have an asymmetric key pair, it MAY reply
anonymously. In which case, both the signerInfos field and the
certificates field of the SignedData [RFC3852] of PA_PK_AS_REP in the
reply are empty. The server name in an anonymous reply contains the
name of the TGS. Upon receipt of an anonymous KDC reply, the client
MUST reject the returned ticket if it can not authenticate the KDC
otherwise.
The client can use its keys to mutually authenticate with the KDC,
and request an anonymous TGT in the AS request. And in that case,
the reply key is selected as normal according to Section 3.1.3 of
[RFC4120].
For the TGS exchange, the reply key is selected as normal according
to Section 3.3.3 of [RFC4120].
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When policy allows, the KDC issues an anonymous ticket. Based on
local policy, the client realm in the anonymous ticket can be the
anonymous realm name or the realm of the KDC. However, in all cases,
the client name and the client realm in the EncKDCRepPart of the
reply [RFC4120] MUST match with the corresponding client name and the
client realm of the anonymous ticket in the reply. The client MUST
use the client name and the client realm returned in the
EncKDCRepPart in subsequent message exchanges when using the obtained
anonymous ticket.
During the TGS request, when propagating authorization data, care
MUST be taken by the TGS to ensure that the client confidentiality is
not violated. The TGS MUST either fail the request or remove
authorization data that may reveal the client's identity. An
optional authorization element unknown by the TGS MUST be removed if
it can be ignored (such as ones enclosed in the AD-IF-RELEVANT
structure). The TGS can only strip critical unknown authorization
data if the ticket does not convey any rights such as those conveyed
by a KDCIssued authorization data element. If a ticket contains a
KDCIssued authorization data element, then no other authorization
data elements may be removed if they could serve to limit the rights
conveyed by the KDCIssued element. Here is a table of the known
authorization-data elements, tagged with whether they interfere with
client anonymity and recommendations for how to process them:
ad-type References Can Breach Confidentiality?
------------------------------------------------------------------
AD-IF-RELEVANT RFC4120 Yes, remove if unknown
AD-KDCIssued RFC4120 Yes, fail the request if unknown
AD-AND-OR RFC4120 Yes, remove if unknown
AD-MANDATORY-FOR-KDC RFC4120 Yes, fail the request if unknown
The KDC fills out the transited field of the anonymous ticket in the
reply as follows: If the service ticket in a TGS request is an
anonymous ticket with a "normal" authentication path, then the
authentication path in the reply ticket MUST also contain a "normal"
authentication path, the TGS MUST add the name of the previous realm.
However, if the service ticket in a TGS request is an anonymous
ticket with an anonymous authentication path, then the reply ticket
can contain either an anonymous authentication path or a "normal"
authentication path, based on local policy of the KDC. Thus a
"normal" authentication path in an anonymous ticket can be a partial
path, it may not include all the intermediate realms on the
authentication path.
The KDC fills out the authtime field of the anonymous ticket in the
reply as follows: If the anonymous ticket is returned in an AS
exchange, the authtime field of the ticket contains the request time.
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If the anonymous ticket is returned in a TGS exchange, the authtime
field contains the authtime of the ticket in the PA-TGS-REQ
[RFC4120]. An anonymous ticket can be renewed, and the authtime
field of a renewed ticket is the authtime in the anonymous ticket on
which the renewed ticket was based.
If it is inappropriate to remove an authorization element from the
TGS request in order to produce an anonymous ticket, the KDC MUST
return an error message with the code KDC_ERR_POLICY [RFC4120].
If the client is anonymous and the KDC does not have a key to encrypt
the reply, the KDC MUST return an error message with the code
KDC_ERR_NULL_KEY [RFC4120] and there is no accompanying e-data.
If a client requires anonymous communication then the client MUST
check to make sure that the ticket in the reply is actually anonymous
by checking the presence of the anonymous ticket flag. This is
because KDCs ignore unknown KDC options. A KDC that does not
understand the request-anonymous KDC option will not return an error,
but will instead return a normal ticket.
The subsequent client and server communications then proceed as
described in [RFC4120]. No transited policy checking is needed for
the anonymous authentication path. However, transited policy checks
defined in Section 2.7 of [RFC4120] would apply to an anonymous
ticket that contains a "normal" authentication path.
A server accepting an anonymous service ticket may assume that
subsequent requests using the same ticket originate from the same
client. Requests with different tickets are likely to originate from
different clients.
Interoperability and backward-compatibility notes: the KDC is given
the task of rejecting a request for an anonymous ticket when the
anonymous ticket is not acceptable by the server.
5. GSS-API Implementation Notes
At the GSS-API [RFC2743] level, the use of an anonymous principal by
the initiator/client requires the initiator/client to assert the
"anonymous" flag when calling GSS_Init_Sec_Context().
GSS-API does not know or define "anonymous credentials", so the
(printable) name of the anonymous principal will rarely be used by or
relevant for the initiator/client. The printable name is relevant
for the acceptor/server when performing an authorization decision
based on the name that pops up from GSS_Accept_Sec_Context() upon
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successful security context establishment.
A GSS-API initiator MUST carefully check the resulting context
attributes from the initial call to GSS_Init_Sec_Context() when
requesting anonymity, because (as in the GSS-API tradition and for
backwards compatibility) anonymity is just another optional context
attribute. It could be that the mechanism doesn't recognize the
attribute at all or that anonymity is not available for some other
reasons -- and in that case the initiator must NOT send the initial
security context token to the acceptor, because it will likely reveal
the initiators identity to the acceptor, something that can rarely be
"un-done".
GSS-API defines the name_type GSS_C_NT_ANONYMOUS [RFC2743] to
represent the anonymous identity. In addition, Section 2.1.1 of
[RFC1964] defines the single string representation of a Kerberos
principal name with the name_type GSS_KRB5_NT_PRINCIPAL_NAME. For
the anonymous principals, the name component within the exportable
name as defined in Section 2.1.3 of [RFC1964] MUST signify the realm
name according to Section 2.1.1 of [RFC1964]. Note that in this
specification only the client/initiator can be anonymous.
Portable initiators are RECOMMENDED to use default credentials
whenever possible, and request anonymity only through the input
anon_req_flag [RFC2743] to GSS_Init_Sec_Context().
6. Security Considerations
Since KDCs ignore unknown options [RFC4120], a client requiring
anonymous communication needs to make sure that the ticket is
actually anonymous. This is because a KDC that that does not
understand the anonymous option would not return an anonymous ticket.
By using the mechanism defined in this specification, the client does
not reveal its identity to the server but its 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), and any
KDC on the cross-realm authentication path. The Kerberos client MUST
verify the ticket being used is indeed anonymous before communicating
with the server, otherwise the client's identity may be revealed
unintentionally.
In cases where specific server principals must not have access to the
client's identity (for example, an anonymous poll service), the KDC
can define server principal specific policy that insure any normal
service ticket can NEVER be issued to any of these server principals.
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If the KDC that issued an anonymous ticket were to maintain records
of the association of identities to an anonymous ticket, then someone
obtaining such records could breach the anonymity. Additionally, the
implementations of most (for now all) KDC's respond to requests at
the time that they are received. Traffic analysis on the connection
to the KDC will allow an attacker to match client identities to
anonymous tickets issued. Because there are plaintext parts of the
tickets that are exposed on the wire, such matching by a third party
observer is relatively straightforward.
7. Acknowledgements
Clifford Neuman contributed the core notions of this document.
Martin Rex wrote the text for GSS-API considerations.
Nicolas Williams reviewed the GSS-API considerations section and
suggested ideas for improvements.
Sam Hartman and Nicolas Williams were great champions of this work.
In addition, the following individuals made significant
contributions: Jeffery Altman, Tom Yu, Chaskiel M Grundman, Love
Hoernquist Aestrand, and Jeffery Hutzelman.
8. IANA Considerations
Section 3 defines the anonymous Kerberos name and the anonymous
Kerberos realm based on [KRBNAM]. The IANA registry for [KRBNAM]
need to be updated to add references to this document.
9. Normative References
[KRBNAM] Zhu, L., "Additonal Kerberos Naming Contraints",
draft-ietf-krb-wg-naming, work in progress.
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
RFC 1964, June 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC3852] Housley, R., "Cryptographic Message Syntax (CMS)",
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Internet-Draft Kerberos Anonymity Support October 2006
RFC 3852, July 2004.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC4556] Zhu, L. and B. Tung, "Public Key Cryptography for Initial
Authentication in Kerberos (PKINIT)", RFC 4556, June 2006.
Authors' Addresses
Larry Zhu
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: lzhu@microsoft.com
Paul Leach
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: paulle@microsoft.com
Karthik Jaganathan
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: karthikj@microsoft.com
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Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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Copies of IPR disclosures made to the IETF Secretariat and any
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this standard. Please address the information to the IETF at
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Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
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NETWORK WORKING GROUP L. Zhu
Internet-Draft P. Leach
Updates: 4120 (if approved) K. Jaganathan
Intended status: Standards Track Microsoft Corporation
Expires: September 3, 2007 March 2, 2007
Anonymity Support for Kerberos
draft-ietf-krb-wg-anon-03
Status of this Memo
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 becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 3, 2007.
Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document defines extensions to the Kerberos protocol for the
Kerberos client to authenticate the Kerberos Key Distribution Center
and the Kerberos server, without revealing the client's identity.
These extensions can be used to secure communication between the
anonymous client and the server.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Protocol Description . . . . . . . . . . . . . . . . . . . . . 4
5. GSS-API Implementation Notes . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Normative References . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
In certain situations, the Kerberos [RFC4120] client may wish to
authenticate a server and/or protect communications without revealing
its own identity. For example, consider an application which
provides read access to a research database, and which permits
queries by arbitrary requestors. A client of such a service might
wish to authenticate the service, to establish trust in the
information received from it, but might not wish to disclose its
identity to the service for privacy reasons.
Extensions to [RFC4120] are specified in this document by which a
client can authenticate the Key Distribution Center (KDC) and request
an anonymous ticket. The client can use the anonymous ticket to
authenticate the server and protect subsequent client-server
communications. These extensions provide Kerberos with functional
equivalence to Transport Layer Security (TLS) [RFC4346].
By using the extensions defined in this specification, the client may
reveal its identity in its initial request to its own KDC, but it can
remain anonymous thereafter to KDCs on the cross-realm authentication
path, and to the server with which it communicates.
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].
3. Definitions
The anonymous Kerberos realm name is defined as a well-known realm
name based on [KRBNAM]. The value is the literal "WELLKNOWN:
ANONYMOUS". An anonymous Kerberos realm name MUST NOT be present in
the transited field [RFC4120] of a ticket.
The anonymous Kerberos principal name is defined as a well-known
Kerberos principal name based on [KRBNAM]. The value of the name-
type field [RFC4120] is KRB_NT_RESRVED [KRBNAM], and the value of the
name-string field [RFC4120] is a sequence of two KerberosString
components: "WELLKNOWN", "ANONYMOUS".
Note that in this specification, the anonymous principal name and
realm are only applicable to the client in Kerberos messages, the
server MUST NOT be anonymous in any Kerberos message.
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The anonymous ticket flag is defined as bit TBA (with the first bit
being bit 0) in the TicketFlags:
TicketFlags ::= KerberosFlags
-- anonymous(TBA)
-- TicketFlags and KerberosFlags are defined in [RFC4120]
An anonymous ticket is a ticket that has all of the following
properties:
o The cname field [RFC4120] contains the anonymous Kerberos
principal name.
o The crealm field [RFC4120] contains the client's realm name, or
the name of the realm that issued the initial ticket for the
client principal, or the anonymous realm name.
o The anonymous ticket contains no information that can reveal the
client's identity. However the ticket may contain the client
realm, intermediate realms on the client's authentication path,
and authorization data that may provide information related to the
client's identity. For example, an anonymous principal that is
identifiable only within a particular group of users can be
implemented using authorization data and such authorization data,
if included in the anonymous ticket, shall disclose the client's
membership of that group.
o The anonymous ticket flag is set.
The request-anonymous KDC option is defined as bit TBA (with the
first bit being bit 0) in the KDCOptions:
KDCOptions ::= KerberosFlags
-- request-anonymous(TBA)
-- KDCOptions and KerberosFlags are defined in [RFC4120]
As described in Section 4, the request-anonymous KDC option is set to
request an anonymous ticket.
4. Protocol Description
In order to request an anonymous ticket, the client sets the request-
anonymous KDC option in an Authentication Exchange (AS) or Ticket
Granting Service (TGS) request [RFC4120]. The client can request an
anonymous Ticket Granting Ticket (TGT) based on a normal TGT. Unless
otherwise specified, the client can obtain an anonymous ticket with
the anonymous realm name only by requesting an anonymous ticket in an
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AS exchange with the client realm set as anonymous in the request.
If the client wishes to authenticate the KDC anonymously, it sets the
client name as anonymous in the AS exchange and provides a
PA_PK_AS_REQ pre-authentication data [RFC4556] where both the
signerInfos field and the certificates field of the SignedData
[RFC3852] of the PA_PK_AS_REQ are empty. Because the anonymous
client does not have an associated asymmetric key pair, the client
MUST choose the Diffie-Hellman key agreement method by filling in the
Diffie-Hellman domain parameters in the clientPublicValue [RFC4556].
If the ticket in the PA-TGS-REQ [RFC4120] of the TGS request is
anonymous, or if the client in the AS request is anonymous, the
request-anonymous KDC option MUST be set in the request. Otherwise,
the KDC MUST return a KRB-ERROR message with the code
KDC_ERR_BADOPTION [RFC4120], and there is no accompanying e-data
defined in this document.
Upon receiving the AS request with a PA_PK_AS_REQ [RFC4556] from the
anonymous client, the KDC 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 public key (such as the verification of
the binding between the client's public key and the client name), but
performs otherwise-applicable checks, and proceeds as normal
according to [RFC4556]. For example, the AS MUST check if the
client's Diffie-Hellman domain parameters are acceptable. The
Diffie-Hellman key agreement method 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 request, the KDC MUST return
a KRB-ERROR [RFC4120] with the code
KDC_ERR_PUBLIC_KEY_ENCRYPTION_NOT_SUPPORTED [RFC4556] and there is no
accompanying e-data. If all goes 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 included in the KDC reply
according to [RFC4556]. If the KDC does not have an asymmetric key
pair, it MAY reply anonymously or reject the authentication attempt.
If the KDC replies anonymously, both the signerInfos field and the
certificates field of the SignedData [RFC3852] of PA_PK_AS_REP in the
reply are empty. The server 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
PA_PK_AS_REP [RFC4556] pre-authentication data, the client can then
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
(the reply is anonymous), the client MUST reject the returned ticket
if it cannot authenticate the KDC otherwise.
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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,
the reply key is selected as normal according to Section 3.1.3 of
[RFC4120].
For the TGS exchange, the reply key is selected as normal according
to Section 3.3.3 of [RFC4120].
When policy allows, the KDC issues an anonymous ticket. Based on
local policy, the client realm in the anonymous ticket can be the
anonymous realm name or the realm of the KDC. However, in all cases,
the client name and the client realm in the EncKDCRepPart of the
reply [RFC4120] MUST match with the corresponding client name and the
client realm of the anonymous ticket in the reply. The client MUST
use the client name and the client realm returned in the
EncKDCRepPart in subsequent message exchanges when using the obtained
anonymous ticket.
During the TGS request, when propagating authorization data, care
MUST be taken by the TGS to ensure that the client confidentiality is
not violated. If a anonymous ticket is returned, any authorization
element that may reveal the client's identity MUST be removed. The
authentication attempt MUST be rejected if there is an authorization
element that is intended to restrict the use of the ticket thus
cannot be removed or the local policy prevents the removal of an
authorization element, and this rule MUST be applied to all critical
and optional authorization data. An optional authorization element
unknown by the TGS MUST be removed if it does not potentially convey
any rights or limit the rights otherwise conveyed in the ticket. If
there is a critical unknown authorization element, unless this
element is encapsulated in a known authorization data element
amending the criticality of the elements it contains, authentication
MUST fail according to [RFC4120]. If it is inappropriate to remove
an authorization element from the TGS request in order to produce an
anonymous ticket, the KDC MUST return an error message with the code
KDC_ERR_POLICY [RFC4120], and there is no accompanying e-data defined
in this document.
The TGS MUST add the name of the previous realm according to Section
3.3.3.2 of [RFC4120]. If the client's realm is the anonymous realm,
the abbreviation forms [RFC4120] that build on the preceding name
cannot be used at the start of the transited encoding. The null-
subfield form (e.g., encoding ending with ",") [RFC4120] could not be
used next to the anonymous realm that can potentially be at the
beginning where the client realm is filled in.
The KDC fills out the authtime field of the anonymous ticket in the
reply as follows: If the anonymous ticket is returned in an AS
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exchange, the authtime field of the ticket contains the request time.
If the anonymous ticket is returned in a TGS exchange, the authtime
field contains the authtime of the ticket in the PA-TGS-REQ pre-
authentication data [RFC4120]. An anonymous ticket can be renewed,
and the authtime field of a renewed ticket is the authtime in the
anonymous ticket on which the renewed ticket was based.
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
support PKINIT [RFC4556]), the KDC MUST return an error message with
the code KDC_ERR_NULL_KEY [RFC4120] and there is no accompanying
e-data defined in this document.
If a client requires anonymous communication then the client MUST
check to make sure that the ticket in the reply is actually anonymous
by checking the presence of the anonymous ticket flag. This is
because KDCs ignore unknown KDC options. A KDC that does not
understand the request-anonymous KDC option will not return an error,
but will instead return a normal ticket.
The subsequent client and server communications then proceed as
described in [RFC4120].
A server accepting an anonymous service ticket may assume that
subsequent requests using the same ticket originate from the same
client. Requests with different tickets are likely to originate from
different clients.
5. GSS-API Implementation Notes
At the GSS-API [RFC2743] level, the use of an anonymous principal by
the initiator/client requires the initiator/client to assert the
"anonymous" flag when calling GSS_Init_Sec_Context().
GSS-API does not know or define "anonymous credentials", so the
(printable) name of the anonymous principal will rarely be used by or
relevant for the initiator/client. The printable name is relevant
for the acceptor/server when performing an authorization decision
based on the initiator name that is returned from the acceptor side
upon the successful security context establishment.
A GSS-API initiator MUST carefully check the resulting context
attributes from the initial call to GSS_Init_Sec_Context() when
requesting anonymity, because (as in the GSS-API tradition and for
backwards compatibility) anonymity is just another optional context
attribute. It could be that the mechanism doesn't recognize the
attribute at all or that anonymity is not available for some other
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reasons -- and in that case the initiator must NOT send the initial
security context token to the acceptor, because it will likely reveal
the initiators identity to the acceptor, something that can rarely be
"un-done".
GSS-API defines the name_type GSS_C_NT_ANONYMOUS [RFC2743] to
represent the anonymous identity. In addition, Section 2.1.1 of
[RFC1964] defines the single string representation of a Kerberos
principal name with the name_type GSS_KRB5_NT_PRINCIPAL_NAME. For
the anonymous principals, the name component within the exportable
name as defined in Section 2.1.3 of [RFC1964] MUST signify the realm
name according to Section 2.1.1 of [RFC1964]. Note that in this
specification only the client/initiator can be anonymous.
Portable initiators are RECOMMENDED to use default credentials
whenever possible, and request anonymity only through the input
anon_req_flag [RFC2743] to GSS_Init_Sec_Context().
6. Security Considerations
Since KDCs ignore unknown options [RFC4120], a client requiring
anonymous communication needs to make sure that the ticket is
actually anonymous. This is because a KDC that that does not
understand the anonymous option would not return an anonymous ticket.
By using the mechanism defined in this specification, the client does
not reveal its identity to the server but its 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), and any
KDC on the cross-realm authentication path. The Kerberos client MUST
verify the ticket being used is indeed anonymous before communicating
with the server, otherwise the client's identity may be revealed
unintentionally.
In cases where specific server principals must not have access to the
client's identity (for example, an anonymous poll service), the KDC
can define server principal specific policy that insure any normal
service ticket can NEVER be issued to any of these server principals.
If the KDC that issued an anonymous ticket were to maintain records
of the association of identities to an anonymous ticket, then someone
obtaining such records could breach the anonymity. Additionally, the
implementations of most (for now all) KDC's respond to requests at
the time that they are received. Traffic analysis on the connection
to the KDC will allow an attacker to match client identities to
anonymous tickets issued. Because there are plaintext parts of the
tickets that are exposed on the wire, such matching by a third party
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Internet-Draft Kerberos Anonymity Support March 2007
observer is relatively straightforward.
7. Acknowledgements
Clifford Neuman contributed the core notions of this document.
Ken Raeburn reviewed the document and provided suggestions for
improvements.
Martin Rex wrote the text for GSS-API considerations.
Nicolas Williams reviewed the GSS-API considerations section and
suggested ideas for improvements.
Sam Hartman and Nicolas Williams were great champions of this work.
In addition, the following individuals made significant
contributions: Jeffery Altman, Tom Yu, Chaskiel M Grundman, Love
Hoernquist Aestrand, and Jeffery Hutzelman.
8. IANA Considerations
Section 3 defines the anonymous Kerberos name and the anonymous
Kerberos realm based on [KRBNAM]. The IANA registry for [KRBNAM]
need to be updated to add references to this document.
9. Normative References
[KRBNAM] Zhu, L., "Additonal Kerberos Naming Contraints",
draft-ietf-krb-wg-naming, work in progress.
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
RFC 1964, June 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000.
[RFC3852] Housley, R., "Cryptographic Message Syntax (CMS)",
RFC 3852, July 2004.
[RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005.
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[RFC4346] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.1", RFC 4346, April 2006.
[RFC4556] Zhu, L. and B. Tung, "Public Key Cryptography for Initial
Authentication in Kerberos (PKINIT)", RFC 4556, June 2006.
Authors' Addresses
Larry Zhu
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: lzhu@microsoft.com
Paul Leach
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: paulle@microsoft.com
Karthik Jaganathan
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052
US
Email: karthikj@microsoft.com
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