draft-ietf-krb-wg-clear-text-cred-02.txt   draft-ietf-krb-wg-clear-text-cred-03.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 August 15, 2011 Intended status: Standards Track September 23, 2011
Expires: February 16, 2012 Expires: March 26, 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-02 draft-ietf-krb-wg-clear-text-cred-03
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
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 16, 2012. This Internet-Draft will expire on March 26, 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
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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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 and MUST be ignored by the recipient if present. The be present and MUST be ignored by the recipient if present. The
cipher text (cipher) is a copy of the EncKrbCredPart as defined in cipher text (cipher) is a copy of the EncKrbCredPart as defined in
Section 5.8.1 [RFC4120] which is in clear text. Section 5.8.1 [RFC4120] which is in clear text.
4. Kerberos Encryption Type 0 Is Not An Encryption System 4. Kerberos Encryption Type 0 Is Not An Encryption System
The Kerberos Encryption Type 0 is an invalid value [RFC3961]. Layers The Kerberos Encryption Type 0 is an invalid value [RFC3961]. This
above the encryption layer are left to interpret its use in their own means that no [RFC3961] encryption type with value 0 will ever be
context specific manner. The use of encryption type 0 in the defined; no encryption or key management operations will use this
unencrypted form of the KRB-CRED is not to specify an encryption value. Layers above the encryption layer often transport encryption
type. In the context of the KRB-CRED it is a message specific types as integer values. These layers are free to use a 0 in an
indicator to be interpreted as the message is not encrypted. This encryption type integer as a flag or sentinal value or for other
approach was chosen due to existing Kerberos implementations which context-specific purposes. For example, section 3 of this
conform to this specification. specification defines the semantics of a 0 carried in the KRB-CRED
message's encryption type field. 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 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 attacker to possibility of modification of the KRB-CRED enables the attacker to
substitute the credentials. This can result in the recipient using substitute the credentials. This can result in the recipient using
the credentials of a client which was not intended. As a result, the the credentials of a client which was not intended. As a result, 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 to be known to each other. The transport MUST also established to be known to each other. The transport MUST also
provide confidentiality, integrity, and end to end security. provide confidentiality, integrity, and mutual authentication.
Examples of transports which MAY be securely used to transport an Examples of transports which MAY be securely used to transport an
unencrypted KRB-CRED message would include Transport Layer Security unencrypted KRB-CRED message would include Transport Layer Security
(TLS) [RFC5246] where mutual authentication has been established and (TLS) [RFC5246] where mutual authentication has been established and
those encoded within encrypted and signed SAML Security Assertion those encoded within encrypted and signed SAML Security Assertion
Markup Language (SAML) 2.0 [OASIS.saml-core-2.0-os] statement. Markup Language (SAML) 2.0 [OASIS.saml-core-2.0-os] statement.
6. 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.
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