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McCallum 6 Expires: April 1, 2017 Red Hat, Inc. 7 September 28, 2016 9 Authentication Indicator in Kerberos Tickets 10 draft-ietf-kitten-krb-auth-indicator-03 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 service tickets so that application services can 19 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 April 1, 2017. 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 . . . . . . . . . . . . . . . . . . . . . . . . . 4 60 5.1. Normative References . . . . . . . . . . . . . . . . . . 4 61 5.2. Informative References . . . . . . . . . . . . . . . . . 4 62 Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 5 63 Appendix B. Acknowledgements . . . . . . . . . . . . . . . . . . 5 64 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 66 1. Introduction 68 Kerberos [RFC4120] allows secure interaction among users and services 69 over a network. It supports a variety of authentication mechanisms 70 using its pre-authentication framework [RFC6113]. The Kerberos 71 authentication service has been architected to support password-based 72 authentication as well as multi-factor authentication using one-time 73 password devices, public-key cryptography and other pre- 74 authentication schemes. Implementations that offer pre- 75 authentication mechanisms supporting significantly different 76 strengths of client authentication may choose to keep track of the 77 strength of the authentication that was used, for use as an input 78 into policy decisions. 80 This document specifies a new authorization data type to convey 81 authentication strength information to application services. 82 Elements of this type MUST appear within an AD-CAMMAC [RFC7751] 83 container. This requirement exists to provide integrity protection 84 from man-in-the-middle attacks. 86 2. Document Conventions 88 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 89 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 90 document are to be interpreted as described in RFC 2119 [RFC2119]. 92 3. AD Type Specification 94 The KDC MAY include authorization data of ad-type 97, wrapped in AD- 95 CAMMAC, in initial credentials. The KDC MAY copy it from a ticket- 96 granting ticket into service tickets. 98 The corresponding ad-data field contains the DER encoding of the 99 following ASN.1 type: 101 AD-AUTHENTICATION-INDICATOR ::= SEQUENCE OF UTF8String 103 Each UTF8String value is a short string that indicates that a 104 particular set of requirements was met during the initial 105 authentication. These strings are intended to be compared against 106 known values. They are not intended to store structured data. Each 107 string MUST be either: 109 * A URI which references a Level of Assurance Profile [RFC6711] 111 * A site-defined string, which MUST NOT contain a colon, whose 112 meaning is determined by the realm administrator. 114 Authorization data elements of type AD-AUTHENTICATION-INDICATOR MUST 115 be included in an AD-CAMMAC container so that their contents can be 116 verified as originating from the KDC. Elements of type AD- 117 AUTHENTICATION-INDICATOR MAY safely be ignored by applications and 118 KDCs that do not implement this element. 120 4. Security Considerations 122 Elements of type AD-AUTHENTICATION-INDICATOR are wrapped in AD-CAMMAC 123 containers. AD-CAMMAC supersedes AD-KDC-ISSUED, and allows both 124 application services and the KDC to verify the authenticity of the 125 contained authorization data. 127 KDC implementations MUST use AD-CAMMAC verifiers as described in the 128 the security considerations of RFC 7751 [RFC7751] to ensure that AD- 129 AUTHENTICATION-INDICATOR elements are not modified by an attacker. 130 Application servers MUST validate the AD-CAMMAC container before 131 making authorization decisions based on AD-AUTHENTICATION-INDICATOR 132 elements. Application servers MUST NOT make authorization decisions 133 based on AD-AUTHENTICATION-INDICATOR elements which appear outside of 134 AD-CAMMAC containers. 136 Using multiple strings in AD-AUTHENTICATION-INDICATOR MAY lead to 137 ambiguity when a service tries to make a decision based on the AD- 138 AUTHENTICATION-INDICATOR values. This ambiguity can be avoided if 139 indicator values are always used as a positive indication of certain 140 requirements being met during the initial authentication. 142 5. References 144 5.1. Normative References 146 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 147 Requirement Levels", BCP 14, RFC 2119, 148 DOI 10.17487/RFC2119, March 1997, 149 . 151 [RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The 152 Kerberos Network Authentication Service (V5)", RFC 4120, 153 DOI 10.17487/RFC4120, July 2005, 154 . 156 [RFC6113] Hartman, S. and L. Zhu, "A Generalized Framework for 157 Kerberos Pre-Authentication", RFC 6113, 158 DOI 10.17487/RFC6113, April 2011, 159 . 161 [RFC7751] Sorce, S. and T. Yu, "Kerberos Authorization Data 162 Container Authenticated by Multiple Message Authentication 163 Codes (MACs)", RFC 7751, DOI 10.17487/RFC7751, March 2016, 164 . 166 5.2. Informative References 168 [MS-SFU] Microsoft, "Kerberos Protocol Extensions: Service for User 169 and Constrained Delegation Protocol", January 2013, 170 . 172 [RFC6711] Johansson, L., "An IANA Registry for Level of Assurance 173 (LoA) Profiles", RFC 6711, DOI 10.17487/RFC6711, August 174 2012, . 176 Appendix A. ASN.1 Module 178 KerberosV5AuthenticationIndicators { 179 iso(1) identified-organization(3) dod(6) internet(1) 180 security(5) kerberosV5(2) modules(4) 181 authentication-indicators(9) 182 } DEFINITIONS EXPLICIT TAGS ::= BEGIN 184 AD-AUTHENTICATION-INDICATOR ::= SEQUENCE OF UTF8String 186 END 188 Appendix B. Acknowledgements 190 Dmitri Pal (Red Hat) 191 Simo Sorce (Red Hat) 192 Greg Hudson (MIT) 194 Authors' Addresses 196 Anupam Jain 197 Georgia Tech 198 225 North Ave NW 199 Atlanta, GA 30332 200 USA 202 EMail: ajain323@gatech.edu 204 Nathan Kinder 205 Red Hat, Inc. 206 444 Castro St. 207 Suite 500 208 Mountain View, CA 94041 209 USA 211 EMail: nkinder@redhat.com 213 Nathaniel McCallum 214 Red Hat, Inc. 215 100 East Davie Street 216 Raleigh, NC 27601 217 USA 219 EMail: npmccallum@redhat.com