draft-ietf-kitten-pkinit-freshness-00.txt   draft-ietf-kitten-pkinit-freshness-01.txt 
Kitten Working Group M. Short, Ed. Kitten Working Group M. Short, Ed.
Internet-Draft S. Moore Internet-Draft S. Moore
Intended status: Standards Track P. Miller Intended status: Standards Track P. Miller
Expires: July 26, 2015 Microsoft Corporation Expires: September 7, 2015 Microsoft Corporation
January 22, 2015 March 6, 2015
Public Key Cryptography for Initial Authentication in Kerberos (PKINIT) Public Key Cryptography for Initial Authentication in Kerberos (PKINIT)
Freshness Extension Freshness Extension
draft-ietf-kitten-pkinit-freshness-00 draft-ietf-kitten-pkinit-freshness-01
Abstract Abstract
This document describes how to further extend the Public Key This document describes how to further extend the Public Key
Cryptography for Initial Authentication in Kerberos (PKINIT) Cryptography for Initial Authentication in Kerberos (PKINIT)
extension [RFC4556] to exchange an opaque data blob which a KDC can extension [RFC4556] to exchange an opaque data blob which a KDC can
validate to ensure that the client is currently in possession of the validate to ensure that the client is currently in possession of the
private key during a PKInit AS exchange. private key during a PKInit AS exchange.
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
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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 July 26, 2015. This Internet-Draft will expire on September 7, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the Copyright (c) 2015 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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1.1. Kerberos message flow using KRB_AS_REQ without pre- 1.1. Kerberos message flow using KRB_AS_REQ without pre-
authentication . . . . . . . . . . . . . . . . . . . . . 3 authentication . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Message Exchanges . . . . . . . . . . . . . . . . . . . . . . 3 2. Message Exchanges . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Generation of KRB_AS_REQ Message . . . . . . . . . . . . 4 2.1. Generation of KRB_AS_REQ Message . . . . . . . . . . . . 4
2.2. Generation of KRB_ERROR Message . . . . . . . . . . . . . 4 2.2. Generation of KRB_ERROR Message . . . . . . . . . . . . . 4
2.3. Generation of KRB_AS_REQ Message . . . . . . . . . . . . 4 2.3. Generation of KRB_AS_REQ Message . . . . . . . . . . . . 4
2.4. Receipt of KRB_AS_REQ Message . . . . . . . . . . . . . . 4 2.4. Receipt of KRB_AS_REQ Message . . . . . . . . . . . . . . 4
2.5. Receipt of second KRB_ERROR Message . . . . . . . . . . . 5 2.5. Receipt of second KRB_ERROR Message . . . . . . . . . . . 5
3. PreAuthentication Data Types . . . . . . . . . . . . . . . . 5 3. PreAuthentication Data Types . . . . . . . . . . . . . . . . 5
4. PA-AS-FRESHNESS-REQUEST . . . . . . . . . . . . . . . . . . . 5 4. Extended PKAuthenticator . . . . . . . . . . . . . . . . . . 5
5. PA-AS-FRESHNESS . . . . . . . . . . . . . . . . . . . . . . . 5 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
6. Extended PKAuthenticator . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. Interoperability Considerations . . . . . . . . . . . . . . . 6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 7 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10. Interoperability Considerations . . . . . . . . . . . . . . . 7 9.1. Normative References . . . . . . . . . . . . . . . . . . 6
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 9.2. Informative References . . . . . . . . . . . . . . . . . 7
11.1. Normative References . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction 1. Introduction
The Kerberos PKINIT extension [RFC4556] defines two schemes for using The Kerberos PKINIT extension [RFC4556] defines two schemes for using
asymmetric cryptography in a Kerberos preauthenticator. One uses asymmetric cryptography in a Kerberos preauthenticator. One uses
Diffie-Hellman key exchange and the other depends on public key Diffie-Hellman key exchange and the other depends on public key
encryption. The public key encryption scheme is less commonly used encryption. The public key encryption scheme is less commonly used
for two reasons: for two reasons:
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4. The KDC receives and validates the KRB_AS_REQ as specified in 4. The KDC receives and validates the KRB_AS_REQ as specified in
Section 3.2.2 [RFC4556] then additionally validates the freshness Section 3.2.2 [RFC4556] then additionally validates the freshness
token. token.
5. The KDC and client continue as specified in [RFC4120] and 5. The KDC and client continue as specified in [RFC4120] and
[RFC4556]. [RFC4556].
2.1. Generation of KRB_AS_REQ Message 2.1. Generation of KRB_AS_REQ Message
The client indicates support of freshness tokens by adding a PA-AS- The client indicates support of freshness tokens by adding a
FRESHNESS-REQUEST padata type. PA_AS_FRESHNESS padata type with an empty octet string as the padata-
value.
2.2. Generation of KRB_ERROR Message 2.2. Generation of KRB_ERROR Message
The KDC will respond by adding a PA-AS-FRESHNESS padata type with the The KDC will respond by adding a PA_AS_FRESHNESS padata type with the
freshness token to the METHOD-DATA object. freshness token as the padata-value to the METHOD-DATA object.
2.3. Generation of KRB_AS_REQ Message 2.3. Generation of KRB_AS_REQ Message
After the client receives the KRB-ERROR message containing a After the client receives the KRB-ERROR message containing a
freshness token, it extracts the PA-AS-FRESHNESS padata value as an freshness token, it extracts the PA_AS_FRESHNESS padata-value field
opaque data blob. The PA-AS-FRESHNESS padata value SHALL then be of the PA_DATA structure as an opaque data blob. The PA_AS_FRESHNESS
added as an opaque blob in the freshnessToken field when the client padata-value field of the PA_DATA structure SHALL then be added as an
generates the PKAuthenticator for the PA_PK_AS_REQ message. This opaque blob in the freshnessToken field when the client generates the
ensures that the freshness token value will be included in the signed PKAuthenticator for the PA_PK_AS_REQ message. This ensures that the
data portion of the KRB_AS_REQ value. freshness token value will be included in the signed data portion of
the KRB_AS_REQ value.
2.4. Receipt of KRB_AS_REQ Message 2.4. Receipt of KRB_AS_REQ Message
After validating the PA_PK_AS_REQ message normally, the KDC will After validating the PA_PK_AS_REQ message normally, the KDC will
validate the PA-AS-FRESHNESS padata value in an implementation validate the freshnessToken value in the PKAuthenticator in an
specific way. If the freshness token is not valid, the KDC MUST implementation specific way. If the freshness token is not valid,
return KDC_ERR_PREAUTH_FAILED with PA-AS-FRESHNESS. Since the the KDC MUST return KDC_ERR_PREAUTH_FAILED with PA_AS_FRESHNESS.
freshness tokens are validated by KDCs in the same realm, Since the freshness tokens are validated by KDCs in the same realm,
standardizing the contents of the freshness token is not a concern standardizing the contents of the freshness token is not a concern
for interoperability. for interoperability.
2.5. Receipt of second KRB_ERROR Message 2.5. Receipt of second KRB_ERROR Message
Clients SHOULD retry in the cases when receiving a Clients SHOULD retry in the cases when receiving a
KDC_ERR_PREAUTH_FAILED KRB_ERROR message which includes a freshness KDC_ERR_PREAUTH_FAILED KRB_ERROR message which includes a freshness
token where there is a possibility that there was too much delay token where there is a possibility that there was too much delay
between the client receiving the freshness token and sending the between the client receiving the freshness token and sending the
PA_PK_AS_REQ message. PA_PK_AS_REQ message.
3. PreAuthentication Data Types 3. PreAuthentication Data Types
The following are the new PreAuthentication data types: The following are the new PreAuthentication data types:
+-------------------------+-------------------+ +----------------------+-------------------+
| Padata and Data Type | Padata-type Value | | Padata and Data Type | Padata-type Value |
+-------------------------+-------------------+ +----------------------+-------------------+
| PA_AS_FRESHNESS_REQUEST | TBD | | PA_AS_FRESHNESS | TBD |
| PA_AS_FRESHNESS | TBD | +----------------------+-------------------+
+-------------------------+-------------------+
4. PA-AS-FRESHNESS-REQUEST
The PA-AS-FRESHNESS-REQUEST indicates support for freshness tokens:
PA-AS-FRESHNESS-REQUEST ::= NULL
5. PA-AS-FRESHNESS
The PA-AS-FRESHNESS structure specifies a freshness token:
PA-AS-FRESHNESS ::= OCTET STRING 4. Extended PKAuthenticator
6. Extended PKAuthenticator
The PKAuthenticator structure specified in Section 3.2.1 [RFC4556] is The PKAuthenticator structure specified in Section 3.2.1 [RFC4556] is
extended to include a new freshnessToken as follows: extended to include a new freshnessToken as follows:
PKAuthenticator ::= SEQUENCE { PKAuthenticator ::= SEQUENCE {
cusec [0] INTEGER (0..999999), cusec [0] INTEGER (0..999999),
ctime [1] KerberosTime, ctime [1] KerberosTime,
-- cusec and ctime are used as in [RFC4120], for -- cusec and ctime are used as in [RFC4120], for
-- replay prevention. -- replay prevention.
nonce [2] INTEGER (0..4294967295), nonce [2] INTEGER (0..4294967295),
-- Chosen randomly; this nonce does not need to -- Chosen randomly; this nonce does not need to
-- match with the nonce in the KDC-REQ-BODY. -- match with the nonce in the KDC-REQ-BODY.
paChecksum [3] OCTET STRING OPTIONAL, paChecksum [3] OCTET STRING OPTIONAL,
-- MUST be present. -- MUST be present.
-- Contains the SHA1 checksum, performed over -- Contains the SHA1 checksum, performed over
-- KDC-REQ-BODY. -- KDC-REQ-BODY.
..., ...,
freshnessToken [4] PA-AS-FRESHNESS OPTIONAL, freshnessToken [4] OCTET STRING OPTIONAL,
-- MUST be present if sent by KDC -- PA_AS_FRESHNESS padata value as recieved from the
-- KDC. MUST be present if sent by KDC
... ...
} }
7. Acknowledgements 5. Acknowledgements
Henry B. Hotz, Nico Williams, Sam Hartman, Tom Yu, Martin Rex, and Henry B. Hotz, Nico Williams, Sam Hartman, Tom Yu, Martin Rex, and
Douglas E. Engert were key contributors to the discover of the Douglas E. Engert were key contributors to the discover of the
freshness issue in PKINIT. freshness issue in PKINIT.
Greg Hudson, Nathan Ide, Benjamin Kaduk, Magnus Nystrom Nico Williams Greg Hudson, Nathan Ide, Benjamin Kaduk, Magnus Nystrom, Nico
and Tom Yu reviewed the document and provided suggestions for Williams and Tom Yu reviewed the document and provided suggestions
improvements. for improvements.
8. IANA Considerations 6. IANA Considerations
IANA is requested to assign numbers for PA_AS_FRESHNESS listed in the IANA is requested to assign numbers for PA_AS_FRESHNESS listed in the
Kerberos Parameters registry Pre-authentication and Typed Data as Kerberos Parameters registry Pre-authentication and Typed Data as
follows: follows:
+------+-------------------------+------------+ +------+-----------------+------------+
| Type | Value | Reference | | Type | Value | Reference |
+------+-------------------------+------------+ +------+-----------------+------------+
| TBD | PA_AS_FRESHNESS_REQUEST | [This RFC] | | TBD | PA_AS_FRESHNESS | [This RFC] |
| TBD | PA_AS_FRESHNESS | [This RFC] | +------+-----------------+------------+
+------+-------------------------+------------+
9. Security Considerations 7. Security Considerations
The freshness token SHOULD include signing, encrypting or sealing The freshness token SHOULD include signing, encrypting or sealing
data from the KDC to determine authenticity and prevent tampering. data from the KDC to determine authenticity and prevent tampering.
Kerberos error messages are not integrity protected unless Kerberos error messages are not integrity protected unless
authenticated using Kerberos FAST [RFC6113]. Even if FAST is authenticated using Kerberos FAST [RFC6113]. Even if FAST is
required to provide integrity protection, a different KDC would not required to provide integrity protection, a different KDC would not
be able to validate freshness tokens without some kind of shared be able to validate freshness tokens without some kind of shared
database. database.
10. Interoperability Considerations 8. Interoperability Considerations
Since the client treats the KDC provided data blob as opaque, Since the client treats the KDC provided data blob as opaque,
changing the contents will not impact existing clients. Thus changing the contents will not impact existing clients. Thus
extensions to the freshness token do not impact client extensions to the freshness token do not impact client
interoperability. interoperability.
11. References 9. References
11.1. Normative References 9.1. Normative References
[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.
[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.
[RFC5349] Zhu, L., Jaganathan, K., and K. Lauter, "Elliptic Curve [RFC5349] Zhu, L., Jaganathan, K., and K. Lauter, "Elliptic Curve
Cryptography (ECC) Support for Public Key Cryptography for Cryptography (ECC) Support for Public Key Cryptography for
Initial Authentication in Kerberos (PKINIT)", RFC 5349, Initial Authentication in Kerberos (PKINIT)", RFC 5349,
September 2008. September 2008.
11.2. Informative References 9.2. Informative References
[RFC6113] Hartman, S. and L. Zhu, "A Generalized Framework for [RFC6113] Hartman, S. and L. Zhu, "A Generalized Framework for
Kerberos Pre-Authentication", RFC 6113, April 2011. Kerberos Pre-Authentication", RFC 6113, April 2011.
Authors' Addresses Authors' Addresses
Michiko Short (editor) Michiko Short (editor)
Microsoft Corporation Microsoft Corporation
USA USA
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