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McCallum 6 Expires: November 17, 2016 Red Hat, Inc. 7 May 16, 2016 9 Authentication Indicator in Kerberos Tickets 10 draft-ietf-kitten-krb-auth-indicator-02 12 Abstract 14 This document specifies an extension in the Kerberos protocol 15 [RFC4120]. It defines a new authorization data type AD- 16 AUTHENTICATION-INDICATOR. The purpose of introducing this data type 17 is to include an indicator of the strength of a client's 18 authentication in the service tickets so that application services 19 can use it as an input into policy decisions. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at http://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on November 17, 2016. 38 Copyright Notice 40 Copyright (c) 2016 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (http://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 56 2. Document Conventions . . . . . . . . . . . . . . . . . . . . 2 57 3. AD Type Specification . . . . . . . . . . . . . . . . . . . . 2 58 4. Security Considerations . . . . . . . . . . . . . . . . . . . 3 59 5. References . . . . . . . . . . . . . . . . . . . . . . . . . 3 60 5.1. Normative References . . . . . . . . . . . . . . . . . . 3 61 5.2. Informative References . . . . . . . . . . . . . . . . . 4 62 Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 4 63 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 4 65 1. Introduction 67 Kerberos [RFC4120] allows secure interaction among users and services 68 over a network. It supports a variety of authentication mechanisms 69 using its pre-authentication framework [RFC6113]. The Kerberos 70 authentication service has been architected to support password based 71 authentication as well as multi-factor authentication using one-time 72 password devices or public key cryptography. Implementations that 73 have pre-authentication mechanisms offering significantly different 74 strengths of client authentication may choose to keep track of the 75 strength of the authentication used as an input into policy 76 decisions. 78 This document specifies a new authorization data type to convey 79 authentication strength to application services. Elements of this 80 type appear within an AD-CAMMAC [RFC7751] container. 82 2. Document Conventions 84 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 85 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 86 document are to be interpreted as described in RFC 2119 [RFC2119]. 88 3. AD Type Specification 90 The KDC MAY include the following authorization data element, wrapped 91 in AD-CAMMAC, in initial credentials, and copy it from a ticket- 92 granting ticket into service tickets: 94 AD-AUTHENTICATION-INDICATOR 97 95 The corresponding ad-data field contains the DER encoding of the 96 following ASN.1 type: 98 AD-AUTHENTICATION-INDICATOR ::= SEQUENCE OF UTF8String 100 Each UTF8String value is a short string that indicates that a 101 particular set of requirements was met during the initial 102 authentication. These strings are intended to be compared against 103 known values. They are not intended to store structured data. These 104 strings MAY be site-defined strings that do not contain a colon such 105 as the name of the Pre-Authentication mechanism used, or 106 alternatively URIs that reference a Level of Assurance Profile 107 [RFC6711]. 109 Authorization data elements of type AD-AUTHENTICATION-INDICATOR MUST 110 be included in an AD-CAMMAC container so that their contents can be 111 verified as originating from the KDC. Elements of type AD- 112 AUTHENTICATION-INDICATOR MAY safely be ignored by applications and 113 KDCs that do not implement this element. 115 4. Security Considerations 117 Elements of type AD-AUTHENTICATION-INDICATOR are wrapped in AD-CAMMAC 118 containers. AD-CAMMAC supersedes AD-KDC-ISSUED, and allows both 119 application services and the KDC to verify the authenticity of the 120 contained authorization data. 122 KDC implementations MUST use AD-CAMMAC verifiers as described in the 123 the security considerations of RFC 7751 [RFC7751] to ensure that AD- 124 AUTHENTICATION-INDICATOR elements are not modified by an attacker. 125 Application servers MUST validate the AD-CAMMAC container before 126 making authorization decisions based on AD-AUTHENTICATION-INDICATOR 127 elements. Application servers MUST NOT make authorization decisions 128 based on AD-AUTHENTICATION-INDICATOR elements which appear outside of 129 AD-CAMMAC containers. 131 Using multiple strings in AD-AUTHENTICATION-INDICATOR MAY lead to 132 ambiguity when a service tries to make a decision based on the AD- 133 AUTHENTICATION-INDICATOR values. This ambiguity can be avoided if 134 indicator values are always used as a positive indication of certain 135 requirements being met during the initial authentication. 137 5. References 139 5.1. Normative References 141 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 142 Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/ 143 RFC2119, March 1997, 144 . 146 [RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The 147 Kerberos Network Authentication Service (V5)", RFC 4120, 148 DOI 10.17487/RFC4120, July 2005, 149 . 151 [RFC6113] Hartman, S. and L. Zhu, "A Generalized Framework for 152 Kerberos Pre-Authentication", RFC 6113, DOI 10.17487/ 153 RFC6113, April 2011, 154 . 156 [RFC7751] Sorce, S. and T. Yu, "Kerberos Authorization Data 157 Container Authenticated by Multiple Message Authentication 158 Codes (MACs)", RFC 7751, DOI 10.17487/RFC7751, March 2016, 159 . 161 5.2. Informative References 163 [MS-SFU] Microsoft, "Kerberos Protocol Extensions: Service for User 164 and Constrained Delegation Protocol", January 2013, 165 . 167 [RFC6711] Johansson, L., "An IANA Registry for Level of Assurance 168 (LoA) Profiles", RFC 6711, DOI 10.17487/RFC6711, August 169 2012, . 171 Appendix A. ASN.1 Module 173 KerberosV5AuthenticationIndicators { 174 iso(1) identified-organization(3) dod(6) internet(1) 175 security(5) kerberosV5(2) modules(4) 176 authentication-indicators(9) 177 } DEFINITIONS EXPLICIT TAGS ::= BEGIN 179 AD-AUTHENTICATION-INDICATOR ::= SEQUENCE OF UTF8String 181 END 183 Appendix B. Acknowledgements 185 Dmitri Pal (Red Hat) 186 Simo Sorce (Red Hat) 187 Greg Hudson (MIT) 189 Authors' Addresses 191 Anupam Jain 192 Georgia Tech 193 225 North Ave NW 194 Atlanta, GA 30332 195 USA 197 EMail: ajain323@gatech.edu 199 Nathan Kinder 200 Red Hat, Inc. 201 444 Castro St. 202 Suite 500 203 Mountain View, CA 94041 204 USA 206 EMail: nkinder@redhat.com 208 Nathaniel McCallum 209 Red Hat, Inc. 210 100 East Davie Street 211 Raleigh, NC 27601 212 USA 214 EMail: npmccallum@redhat.com