draft-ietf-krb-wg-clear-text-cred-00.txt   draft-ietf-krb-wg-clear-text-cred-01.txt 
Network Working Group R. Yount Network Working Group R. Yount
Internet-Draft Carnegie Mellon University Internet-Draft Carnegie Mellon University
Intended status: Standards Track June 28, 2011 Intended status: Standards Track July 26, 2011
Expires: December 30, 2011 Expires: January 27, 2012
The Unencrypted Form Of Kerberos 5 KRB-CRED Message The Unencrypted Form Of Kerberos 5 KRB-CRED Message
draft-ietf-krb-wg-clear-text-cred-00 draft-ietf-krb-wg-clear-text-cred-01
Abstract Abstract
The Kerberos 5 KRB-CRED message is used to transfer Kerberos The Kerberos 5 KRB-CRED message is used to transfer Kerberos
credentials between applications. When used with a secure transport credentials between applications. When used with a secure transport
the unencrypted form of the KRB-CRED message may be desirable. This the unencrypted form of the KRB-CRED message may be desirable. This
document describes the unencrypted form of the KRB-CRED message. document describes the unencrypted form of the KRB-CRED message.
Status of this Memo Status of this Memo
skipping to change at page 1, line 33 skipping to change at page 1, line 33
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on December 30, 2011. This Internet-Draft will expire on January 27, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
1. Introduction 1. Introduction
There are applications which need to transfer Kerberos credentials There are applications which need to transfer Kerberos credentials
between them without having a prior relationship with established between them without having a prior relationship with established
Kerberos keys. When tranferred over a transport that provides Kerberos keys. When transferred over a transport that provides
confidentiality and integrity the unencrypted form of the KRB-CRED confidentiality and integrity, the unencrypted form of the KRB-CRED
message MAY be used. One application employing this method is the message MAY be used. One application employing this method is the
Security Assertion Markup Language (SAML) 2.0 Kerberos attribute transport mechanism described in section 2.8 of
[OASIS.saml-core-2.0-os] attribute transport. the SAML V2.0 Kerberos Attribute Profile
[sstc-saml-attribute-kerberos].
In the SAML application, the Identity Provider (IdP) somehow obtains In the SAML application, the Identity Provider (IdP) somehow obtains
a Kerberos service ticket from the Kerberos Key Distribution Center a Kerberos service ticket from the Kerberos Key Distribution Center
(KDC) when required by the SAML system and transfers the credential (KDC) when required by the SAML system and transfers the credential
to a Service Provider (SP) within an attribute statement. The SP can to a Service Provider (SP) within an attribute statement. The SP can
then use the credential to access a Kerberos protected service. then use the credential to access a Kerberos protected service.
The Kerberos 5 specification as described in [RFC4120] mentions the The Kerberos 5 specification as described in [RFC4120] mentions the
non-standard legacy use of unencypted KRB-CRED with Generic Security non-standard legacy use of unencrypted KRB-CRED with Generic Security
Services Application Programming Interface (GSS-API) [RFC1964] by the Services Application Programming Interface (GSS-API) [RFC1964] by the
MIT, Heimdal, and Microsoft Kerberos implementations. This document MIT, Heimdal, and Microsoft Kerberos implementations. This document
provides a formal specification of the unencrypted form of the KRB- provides a formal specification of the unencrypted form of the KRB-
CRED message. CRED message.
2. Requirements notation 2. Requirements notation
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. The Unencrypted Form Of The KRB-CRED 3. The Unencrypted Form Of The KRB-CRED
The unencrypted form of the KRB-CRED contains EncryptedData as The unencrypted form of the KRB-CRED contains EncryptedData as
defined in Section 5.2.9 [RFC4120]. The encryption type (etype) MUST defined in Section 5.2.9 [RFC4120]. The encryption type (etype) MUST
BE specified as 0. The optional key version number (kvno) SHOULD NOT BE specified as 0. The optional key version number (kvno) SHOULD NOT
be present. The cipher text (cipher) is a copy of the EncKrbCredPart be present and MUST be ignored by the recipient if present. The
as defined in Section 5.8.1 [RFC4120] which is in clear text. cipher text (cipher) is a copy of the EncKrbCredPart as defined in
Section 5.8.1 [RFC4120] which is in clear text.
4. Security Considerations 4. Kerberos Encryption Type 0 Is Not An Encryption System
The Kerberos Encryption Type 0 is an invalid value [RFC3961]. Layers
above the encryption layer are left to interpret its use in their own
context specific manner. The use of encryption type 0 in the
unencrypted form of the KRB-CRED is not to specify an encryption
type. In the context of the KRB-CRED it is a message specific
indicator to be interpreted as the message is not encrypted. This
approach was chosen due to existing Kerberos implementations which
conform to this specification.
5. Security Considerations
The KRB-CRED message contains sensitive information related to The KRB-CRED message contains sensitive information related to
Kerberos credentials being transferred, such as their secret session Kerberos credentials being transferred, such as their secret session
keys, client and server principal names, and validity period. keys, client and server principal names, and validity period.
Possession of this information, along with the ticket itself, would Possession of this information, along with the ticket itself, would
allow an attacker to impersonate the client named in the ticket. The allow an attacker to impersonate the client named in the ticket. The
possibility of modification of the KRB-CRED enables the substitution possibility of modification of the KRB-CRED enables the attacker to
of a credential by the attacker which can result in the recipients substitute the credentials. This can result in the recipient using
use the credentials of a client which was not intended. As a result, the credentials of a client which was not intended. As a result, the
the KRB-CRED message must be carefully safeguarded. KRB-CRED message must be carefully safeguarded.
The use of an unencrypted form of the KRB-CRED message MUST only be The use of an unencrypted form of the KRB-CRED message MUST only be
used with a transport where sender and recipient identities can been used with a transport where sender and recipient identities can been
established be known to each other and provides confidentiality and established to be known to each other. The transport MUST also
integrity. Examples of transports which MAY be securely used to provide confidentiality and integrity. Examples of transports which
transport an unencrypted KRB-CRED message would include Transport MAY be securely used to transport an unencrypted KRB-CRED message
Layer Security (TLS) [RFC5246] where mutual authentication has been would include Transport Layer Security (TLS) [RFC5246] where mutual
established and those encoded within encrypted and signed SAML authentication has been established and those encoded within
Security Assertion Markup Language (SAML) 2.0 encrypted and signed SAML Security Assertion Markup Language (SAML)
[OASIS.saml-core-2.0-os] statement. 2.0 [OASIS.saml-core-2.0-os] statement.
5. Acknowledgements 6. Acknowledgements
The following individuals have contributed to the development of this The following individuals have contributed to the development of this
specification. specification.
Thomas HardJono, Massachusetts Institute of Technology Thomas Hardjono, Massachusetts Institute of Technology
Josh Howlett, Individual Josh Howlett, Individual
Jeffrey Hutzelman, Carnegie Mellon University Jeffrey Hutzelman, Carnegie Mellon University
6. IANA Considerations 7. IANA Considerations
This memo includes no request to IANA. The reference for Kerberos encryption type 0 should be updated to
point to this document.
7. Normative References 8. References
8.1. Normative References
[OASIS.saml-core-2.0-os] [OASIS.saml-core-2.0-os]
Cantor, S., Kemp, J., Philpott, R., and E. Maler, Cantor, S., Kemp, J., Philpott, R., and E. Maler,
"Assertions and Protocol for the OASIS Security Assertion "Assertions and Protocol for the OASIS Security Assertion
Markup Language (SAML) V2.0", OASIS Standard saml-core- Markup Language (SAML) V2.0", OASIS Standard saml-core-
2.0-os, March 2005. 2.0-os, March 2005.
[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.
[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.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246, August 2008. (TLS) Protocol Version 1.2", RFC 5246, August 2008.
8.2. Informative References
[RFC3961] Raeburn, K., "Encryption and Checksum Specifications for
Kerberos 5", RFC 3961, February 2005.
[sstc-saml-attribute-kerberos]
Howlett, J. and T. Hardjono, "SAML V2.0 Kerberos Attribute
Profile Version 1.0, OASIS Security Services Draft, sstc-
saml-attribute-kerberos.odt (work in progress)",
December 2010.
Author's Address Author's Address
Russell J. Yount Russell J. Yount
Carnegie Mellon University Carnegie Mellon University
5000 Forbes Avenue 5000 Forbes Avenue
Pittsburgh, Pennsylvania 15213 Pittsburgh, Pennsylvania 15213
US US
Phone: +1 412 268 8391 Phone: +1 412 268 8391
Email: rjy@cmu.edu Email: rjy@cmu.edu
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