draft-ietf-krb-wg-anon-01.txt   draft-ietf-krb-wg-anon-02.txt 
NETWORK WORKING GROUP L. Zhu NETWORK WORKING GROUP L. Zhu
Internet-Draft P. Leach Internet-Draft P. Leach
Updates: 4120 (if approved) K. Jaganathan Updates: 4120 (if approved) K. Jaganathan
Expires: January 17, 2007 Microsoft Corporation Intended status: Standards Track Microsoft Corporation
July 16, 2006 Expires: April 14, 2007 October 11, 2006
Anonymity Support for Kerberos Anonymity Support for Kerberos
draft-ietf-krb-wg-anon-01 draft-ietf-krb-wg-anon-02
Status of this Memo Status of this Memo
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This Internet-Draft will expire on January 17, 2007. This Internet-Draft will expire on April 14, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
This document defines the use of anonymous Kerberos tickets for the This document defines extensions to the Kerberos protocol for the
purpose of authenticating the servers and enabling secure Kerberos client to authenticate the Kerberos Key Distribution Center
communication between a client and a server, without identifying the and the Kerberos server, without revealing the client's identity.
client to the server. These extensions can be used to secure communication between the
anonymous client and the server.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3 2. Conventions Used in This Document . . . . . . . . . . . . . . 3
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Protocol Description . . . . . . . . . . . . . . . . . . . . . 5 4. Protocol Description . . . . . . . . . . . . . . . . . . . . . 5
5. GSS-API Implementation Notes . . . . . . . . . . . . . . . . . 7 5. GSS-API Implementation Notes . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9. Normative References . . . . . . . . . . . . . . . . . . . . . 8 9. Normative References . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11 Intellectual Property and Copyright Statements . . . . . . . . . . 11
1. Introduction 1. Introduction
In certain situations or environments, the Kerberos [RFC4120] client In certain situations, the Kerberos [RFC4120] client may wish to
may wish to authenticate a server and/or protect communications authenticate a server and/or protect communications without revealing
without revealing its own identity. For example, consider an its own identity. For example, consider an application which
application which provides read access to a research database, and provides read access to a research database, and which permits
which permits queries by arbitrary requestors. A client of such a queries by arbitrary requestors. A client of such a service might
service might wish to authenticate the service, to establish trust in wish to authenticate the service, to establish trust in the
the information received from it, but might not wish to disclose its information received from it, but might not wish to disclose its
identity to the service for privacy reasons. identity to the service for privacy reasons.
To accomplish this, a Kerberos mechanism is specified in this Extensions to [RFC4120] are specified in this document by which a
document by which a client requests an anonymous ticket and use that client can authenticate the KDC and request an anonymous ticket. The
to authenticate the server and secure subsequent client-server client can use the anonymous ticket to authenticate the server and
communications. This provides Kerberos with functional equivalence protect subsequent client-server communications. These extensions
to TLS [RFC2246] in environments where Kerberos is a more attractive provide Kerberos with functional equivalence to Transport Layer
authentication mechanism. Security (TLS) [RFC4346].
Using this mechanism, the client has to reveal its identity in its By using the extensions defined in this specification, the client MAY
initial request to its own Key Distribution Center (KDC) [RFC4120], reveal its identity in its initial request to its own KDC, but it can
and then it can remain anonymous thereafter to KDCs on the cross- remain anonymous thereafter to KDCs on the cross-realm authentication
realm authentication path, if any, and to the server with which it path, and to the server with which it communicates.
communicates.
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 a reserved realm name as defined The anonymous Kerberos realm name is a reserved realm name based on
in [KRBNAM] and its value is the literal "RESERVED:ANONYMOUS". [KRBNAM]. The value is the literal "RESERVED:ANONYMOUS".
The anonymous Kerberos principal name is a reserved Kerberos The anonymous Kerberos principal name is a reserved Kerberos
principal name as defined in [KRBNAM], its name-type [RFC4120] is principal name based on [KRBNAM]. The value of the name-type field
KRB_NT_RESRVED [KRBNAM], and its name-string [RFC4120] is a sequence is KRB_NT_RESRVED [KRBNAM], and the value of the name-string field is
of two KerberosString components: "RESERVED", "ANONYMOUS". a sequence of two KerberosString components: "RESERVED", "ANONYMOUS".
In this specification, only the client name or the client realm can Note that in this specification, the anonymous principal name and
be anonymous; the server name or the server realm can not be realm are only applicable to the client in Kerberos messages, the
anonymous. server MUST NOT be anonymous in any Kerberos message.
The transited field [RFC4120] of a ticket is an anonymous The transited field [RFC4120] of a ticket is an anonymous
authentication path if the tr-type field of the TransitedEncoding authentication path if the tr-type field of the TransitedEncoding
type [RFC4120] is NO-TRANSITED-INFO and the contents field is an type [RFC4120] is NO-TRANSITED-INFO and the contents field is an
empty OCTET STRING. empty OCTET STRING.
NO-TRANSITED-INFO TBA NO-TRANSITED-INFO TBA
This transited encoding type indicates that there is no information This means that no information of the authentication path is
available about the authentication path. disclosed.
The anonymous ticket flag is defined as bit TBA (with the first bit The anonymous ticket flag is defined as bit TBA (with the first bit
being bit 0) in the TicketFlags: being bit 0) in the TicketFlags:
TicketFlags ::= KerberosFlags TicketFlags ::= KerberosFlags
-- anonymous(TBA) -- anonymous(TBA)
-- TicketFlags and KerberosFlags are defined in [RFC4120] -- TicketFlags and KerberosFlags are defined in [RFC4120]
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 [RFC4120] contains the anonymous Kerberos o The cname field [RFC4120] contains the anonymous Kerberos
principal name. principal name.
o The crealm field [RFC4120] contains either the realm name of the o The crealm field [RFC4120] contains either the client's realm name
client who made the request or the anonymous kerberos realm name, or the anonymous realm name.
based on the local policy of the KDC.
o The transited field [RFC4120] can contain either the client's o The transited field [RFC4120] can contain either the client's
"normal" authentication path according to Section 3.3.3.2 of authentication path as described in Section 3.3.3.2 of [RFC4120]
[RFC4120] or the anonymous authentication path. or the anonymous authentication path.
o It contains no information that can reveal the client's identity. o The anonymous ticket contains no information that can reveal the
However the ticket can contain the client realm and the realms on client's identity. However the ticket MAY contain the client
the authentication path, and the authorization data may provide realm and the realms on the authentication path, and authorization
additional information of the client. For example, an anonymous data that MAY provide information related to the client's
principal that is only identifiable within a particular group of identity. For example, an anonymous principal that is only
users can be implemented by using authorization data. 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. 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 The request-anonymous KDC option is defined as bit TBA (with the
first bit being bit 0) in the KDCOptions: first bit being bit 0) in the KDCOptions:
KDCOptions ::= KerberosFlags KDCOptions ::= KerberosFlags
-- request-anonymous(TBA) -- request-anonymous(TBA)
-- KDCOptions and KerberosFlags are defined in [RFC4120] -- KDCOptions and KerberosFlags are defined in [RFC4120]
4. Protocol Description 4. Protocol Description
In order to request an anonymous ticket, the client sets the request- In order to request an anonymous ticket, the client sets the request-
anonymous KDC option in an Authentication Exchange (AS) or Ticket anonymous KDC option in an Authentication Exchange (AS) or Ticket
Granting Service (TGS) request [RFC4120]. The client can request an Granting Service (TGS) request [RFC4120]. The client can request an
anonymous TGT based on a normal TGT. Note that if the ticket in the anonymous TGT based on a normal TGT. If the client wishes to
PA-TGS-REQ [RFC4120] is anonymous, the request-anonymous KDC option authenticate the KDC anonymously, it sets the client name as
MUST be set in the request. 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].
When propagating authorization data, care MUST be taken by the TGS to If the ticket in the PA-TGS-REQ [RFC4120] of the TGS request is
ensure that the client confidentiality is not violated: the TGS MUST anonymous, or if the client in the AS request is anonymous, the
either fail the request or remove authorization data that may reveal request-anonymous KDC option MUST be set in the request.
the client's identity. An optional authorization element unknown by
the TGS MUST be removed if it can be ignored (such as ones enclosed Upon receiving the AS request with a PA_PK_AS_REQ from the anonymous
in the AD-IF-RELEVANT or the AD-KDCIssued containers [RFC4120]). The client, the KDC skips the checks for the client's signature and the
TGS can strip critical unknown authorization data if such data do not client's public key (such as the verification of the binding between
convey any rights based on the requesting client's identity. Here is the client's public key and the client name), but performs otherwise-
a table of the known authorization-data elements, flagged with applicable checks, and proceeds as normal according to [RFC4556].
whether they interfere with client anonymity and recommendations for For example, the AS MUST check if the client's Diffie-Hellman domain
how to process them. 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].
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-type References Can Breach Confidentiality?
------------------------------------------------------------------ ------------------------------------------------------------------
AD-IF-RELEVANT RFC4120 Yes, remove if unknown AD-IF-RELEVANT RFC4120 Yes, remove if unknown
AD-KDCIssued RFC4120 Yes, remove if unknown AD-KDCIssued RFC4120 Yes, fail the request if unknown
AD-AND-OR RFC4120 Yes, remove if unknown AD-AND-OR RFC4120 Yes, remove if unknown
AD-MANDATORY-FOR-KDC RFC4120 Yes, fail the request 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
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 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 reply as follows: If the service ticket in a TGS request is an
anonymous ticket with a "normal" authentication path, then the anonymous ticket with a "normal" authentication path, then the
authentication path in the reply ticket MUST also contain a "normal" authentication path in the reply ticket MUST also contain a "normal"
authentication path: the TGS MUST add the name of the previous realm. authentication path, the TGS MUST add the name of the previous realm.
However, if the service ticket in a TGS request is an anonymous However, if the service ticket in a TGS request is an anonymous
ticket with an anonymous authentication path, then the reply ticket ticket with an anonymous authentication path, then the reply ticket
can contain either an anonymous authentication path or a "normal" can contain either an anonymous authentication path or a "normal"
authentication path, based on the local policy of the KDC. Thus a authentication path, based on local policy of the KDC. Thus a
"normal" authentication path in an anonymous ticket can be a partial "normal" authentication path in an anonymous ticket can be a partial
path: it may not include all the intermediate realms on the path, it may not include all the intermediate realms on the
authentication path. authentication path.
The KDC fills out the authtime field of the anonymous ticket in the 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 reply as follows: If the anonymous ticket is returned in an AS
exchange, the authtime field of the ticket contains the request time. exchange, the authtime field of the ticket contains the request time.
If the anonymous ticket is returned in a TGS exchange, the authtime If the anonymous ticket is returned in a TGS exchange, the authtime
field contains the time of the initial authentication for the field contains the authtime of the ticket in the PA-TGS-REQ
principal who has made the request. An anonymous ticket can be [RFC4120]. An anonymous ticket can be renewed, and the authtime
renewed, and the authtime field of a renewed ticket is the authtime field of a renewed ticket is the authtime in the anonymous ticket on
in the anonymous ticket that the renewed ticket was based 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 If a client requires anonymous communication then the client MUST
check to make sure that the ticket in the reply is actually anonymous check to make sure that the ticket in the reply is actually anonymous
by checking the presence of the anonymous ticket flag. Because KDCs by checking the presence of the anonymous ticket flag. This is
ignore unknown KDC options, a KDC that does not understand the because KDCs ignore unknown KDC options. A KDC that does not
request-anonymous KDC option will not return an error, but will understand the request-anonymous KDC option will not return an error,
instead return a normal ticket. but 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]. No transited policy checking is needed for described in [RFC4120]. No transited policy checking is needed for
the anonymous authentication path. However, transited policy checks the anonymous authentication path. However, transited policy checks
defined in Section 2.7 of [RFC4120] would apply to an anonymous defined in Section 2.7 of [RFC4120] would apply to an anonymous
ticket that contains a "normal" authentication path. ticket that contains a "normal" authentication path.
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.
Interoperability and backward-compatibility notes: the KDC is given Interoperability and backward-compatibility notes: the KDC is given
the task of rejecting a request for an anonymous ticket when the the task of rejecting a request for an anonymous ticket when the
anonymous ticket is not acceptable by the server. anonymous ticket is not acceptable by the server.
5. GSS-API Implementation Notes 5. GSS-API Implementation Notes
At the GSS-API [RFC2743] level, the use of an anonymous principal by At the GSS-API [RFC2743] level, the use of an anonymous principal by
the initiator/client requires a software change of the initiator/ the initiator/client requires the initiator/client to assert the
client software (to assert the "anonymous" flag when calling "anonymous" flag when calling GSS_Init_Sec_Context().
GSS_Init_Sec_Context().
GSS-API does not know or define "anonymous credentials", so the GSS-API does not know or define "anonymous credentials", so the
(printable) name of the anonymous principal will rarely be used by or (printable) name of the anonymous principal will rarely be used by or
relevant for the initator/client. The printable name is relevant for relevant for the initiator/client. The printable name is relevant
the acceptor/server when performing an authorization decision based for the acceptor/server when performing an authorization decision
on the name that pops up from GSS_Accept_Sec_Context() upon based on the name that pops up from GSS_Accept_Sec_Context() upon
successful security context establishment. successful security context establishment.
A GSS-API initiator MUST carefully check the resulting context A GSS-API initiator MUST carefully check the resulting context
attributes from the initial call to GSS_Init_Sec_Context() when attributes from the initial call to GSS_Init_Sec_Context() when
requesting anonymity, because (as in the GSS-API tradition and for requesting anonymity, because (as in the GSS-API tradition and for
backwards compatibility) anonymity is just another optional context backwards compatibility) anonymity is just another optional context
attribute. It could be that the mechanism doesn't recognize the attribute. It could be that the mechanism doesn't recognize the
attribute at all or that anonymity is not available for some other attribute at all or that anonymity is not available for some other
reasons -- and in that case the initiator must NOT send the initial reasons -- and in that case the initiator must NOT send the initial
security context token to the acceptor, because it will likely reveal security context token to the acceptor, because it will likely reveal
the initiators identity to the acceptor, something that can rarely be the initiators identity to the acceptor, something that can rarely be
"un-done". "un-done".
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. For principal name with the name_type GSS_KRB5_NT_PRINCIPAL_NAME. For
the anonymous principals, the name component within the exportable the anonymous principals, the name component within the exportable
name as defined in Section 2.1.3 of [RFC1964] MUST signify the realm 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 name according to Section 2.1.1 of [RFC1964]. Note that in this
only the client/initiator can be the anonymous identity. specification only the client/initiator can be anonymous.
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().
6. Security Considerations 6. Security Considerations
Since KDCs ignore unknown options [RFC4120], a client requiring Since KDCs ignore unknown options [RFC4120], a client requiring
anonymous communication needs to make sure that the ticket is anonymous communication needs to make sure that the ticket is
actually anonymous. A KDC that that does not understand the actually anonymous. This is because a KDC that that does not
anonymous option would not return an anonymous ticket. understand the 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 its identity to the server but its identity may be not reveal its identity to the server but its identity may be
revealed to the KDC of the server principal (when the server revealed to the KDC of the server principal (when the server
principal is in a different realm than that of the client), and any principal is in a different realm than that of the client), and any
KDC on the cross-realm authentication path. The Kerberos client MUST KDC on the cross-realm authentication path. The Kerberos client MUST
verify the ticket being used is indeed anonymous before communicating verify the ticket being used is indeed anonymous before communicating
with the cross-realm KDC or the server, otherwise the client's with the server, otherwise the client's identity may be revealed
identity may be revealed to the server unintentionally. 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 insure 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
implementation of most (for now all) KDC's respond to requests at the implementations of most (for now all) KDC's respond to requests at
time that they are received. Traffic analasys on the connection to the time that they are received. Traffic analysis on the connection
the KDC will allow an attacket 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 straigtforward. observer is relatively straightforward.
7. Acknowledgements 7. Acknowledgements
The authors would like to thank the following individuals for their Clifford Neuman contributed the core notions of this document.
insightful comments and fruitful discussions: Sam Hartman, Clifford
Neuman, Martin Rex, Nicolas Williams, Jeffery Altman, Tom Yu, Martin Rex wrote the text for GSS-API considerations.
Chaskiel M Grundman, Love Hoernquist Aestrand, and Jeffery Hutzelman.
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 8. IANA Considerations
No IANA actions are required for this document. 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 9. Normative References
[KRBNAM] Zhu, L., "Additonal Kerberos Naming Contraints", [KRBNAM] Zhu, L., "Additonal Kerberos Naming Contraints",
draft-ietf-krb-wg-naming, work in progress. draft-ietf-krb-wg-naming, work in progress.
[RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism", [RFC1964] Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
RFC 1964, June 1996. RFC 1964, June 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. 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 [RFC2743] Linn, J., "Generic Security Service Application Program
Interface Version 2, Update 1", RFC 2743, January 2000. 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 [RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
Kerberos Network Authentication Service (V5)", RFC 4120, Kerberos Network Authentication Service (V5)", RFC 4120,
July 2005. 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 [RFC4556] Zhu, L. and B. Tung, "Public Key Cryptography for Initial
Authentication in Kerberos (PKINIT)", RFC 4556, June 2006. Authentication in Kerberos (PKINIT)", RFC 4556, June 2006.
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
skipping to change at page 11, line 5 skipping to change at page 11, line 5
Email: paulle@microsoft.com Email: paulle@microsoft.com
Karthik Jaganathan Karthik Jaganathan
Microsoft Corporation Microsoft Corporation
One Microsoft Way One Microsoft Way
Redmond, WA 98052 Redmond, WA 98052
US US
Email: karthikj@microsoft.com Email: karthikj@microsoft.com
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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
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to the rights, licenses and restrictions contained in BCP 78, and
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Internet Society. Administrative Support Activity (IASA).
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