Network Working Group R. Housley Internet-Draft Vigil Security Intended status: Standards Track S. Turner Expires: 15 April 2023 sn3rd J. P. Mattsson D. Migault Ericsson 12 October 2022 X.509 Certificate Extension for 5G Network Function Types draft-ietf-lamps-5g-nftypes-05 Abstract This document specifies the certificate extension for including Network Function Types (NFTypes) for the 5G System in X.509v3 public key certificates as profiled in RFC 5280. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 15 April 2023. Copyright Notice Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved. Housley, et al. Expires 15 April 2023 [Page 1] Internet-Draft 5G NFType in X.509 Certificates October 2022 This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Network Functions Certificate Extension . . . . . . . . . . . 3 4. ASN.1 Module . . . . . . . . . . . . . . . . . . . . . . . . 3 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 5 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 9.1. Normative References . . . . . . . . . . . . . . . . . . 5 9.2. Informative References . . . . . . . . . . . . . . . . . 6 Appendix A. Appendix A. NFType Strings . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 1. Introduction The 3rd Generation Partnership Project (3GPP) has specified several Network Functions (NFs) as part of the service-based architecture within the 5G System. The 49 NF types that are defined for 3GPP Release 17 listed in Table 6.1.6.3.3-1 of [TS29.510], and each NF type is identified by a short ASCII string. Operators of 5G systems make use of an internal PKI to identify interface instances in the NFs in a 5G system. X.509v3 public key certificates [RFC5280] are used, and the primary function of a certificate is to bind a public key to the identity of an entity that holds the corresponding private key, known as the certificate subject. The certificate subject and the subjectAltName certificate extension can be used to support identity-based access control decisions. This document specifies the NFTypes certificate extension to support role-based access control decisions by providing a list of NF Types associated with the certificate subject. The NFTypes certificate extension can be used by operators of 5G systems or later. Housley, et al. Expires 15 April 2023 [Page 2] Internet-Draft 5G NFType in X.509 Certificates October 2022 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 3. Network Functions Certificate Extension This section specifies the NFTypes certificate extension, which provides a list of NF Types associated with the certificate subject. The NFTypes certificate extension MAY be included in public key certificates [RFC5280]. The NFTypes certificate extension MUST be identified by the following object identifier: id-pe-nftypes OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-pe(1) TBD1 } This extension MUST NOT be marked critical. The NFTypes extension MUST have the following syntax: NFTypes ::= SEQUENCE SIZE (1..MAX) OF NFType NFType ::= IA5String (SIZE (1..32)) The NFTypes MUST contain at least one NFType. The NFTypes MUST NOT contain the same NFType more than once. The NFTypes MUST contain only an ASCII string, MUST contain at least one ASCII character, and MUST NOT contain more than 32 ASCII characters. The NFType uses the IA5String type to permit inclusion of the underscore character ('_'), which is not part of the PrintableString character set. 4. ASN.1 Module This section provides an ASN.1 module [X.680] for the NFTypes certificate extension, and it follows the conventions established in [RFC5912] and [RFC6268]. Housley, et al. Expires 15 April 2023 [Page 3] Internet-Draft 5G NFType in X.509 Certificates October 2022 NFTypeCertExtn { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-nftype(TBD2) } DEFINITIONS IMPLICIT TAGS ::= BEGIN IMPORTS EXTENSION FROM PKIX-CommonTypes-2009 -- RFC 5912 { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-pkixCommon-02(57) } ; -- NFTypes Certificate Extension ext-NFType EXTENSION ::= { SYNTAX NFTypes IDENTIFIED BY id-pe-nftype } -- NFTypes Certificate Extension OID id-pe-nftype OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-pe(1) TBD1 } -- NFTypes Certificate Extension Syntax NFTypes ::= SEQUENCE SIZE (1..MAX) OF NFType NFType ::= IA5String (SIZE (1..32)) END 5. Security Considerations The Security Considerations of [RFC5280] are applicable to this document. Some of the ASCII strings that specify the NF Types are standard. See Appendix A for values defined in 3GPP. Additionally, an operator MAY assign its own NF Types for use in their own network. Since the NF Type is used for role-based access control decisions, an operator- assigned NF Type MUST NOT overlap with a value already defined in the Housley, et al. Expires 15 April 2023 [Page 4] Internet-Draft 5G NFType in X.509 Certificates October 2022 commonly defined set. Use of the same ASCII string by two different operators for different roles could lead to confusion or incorrect access control decisions. The mechanism for an operator to determine whether an ASCII string associate with a NF Type is unique across operators is outside the scope of this document. The certificate extension supports many different forms of role-based access control to support the diversity of activities that NFs are trusted to perform in the overall system. Different levels of confidence that the NFTypes are proper assigned might be needed to contribute to the overall security of the 5G system. For example, more confidence might be needed to make access control decisions related to a scarce resource than implementation of filtering policies. As a result, different operators might have different trust models for NFTypes certificate extension. 6. Privacy Considerations In some security protocols, such as TLS 1.2 [RFC5246], certificates are exchanged in the clear. In other security protocols, such as TLS 1.3 [RFC8446], the certificates are encrypted. The inclusion of NFType certificate extension can help an observer determine which systems are of most interest based on the plaintext certificate transmission. 7. IANA Considerations For the NFType certificate extension in Section 3, IANA is requested to assign an object identifier (OID) for the certificate extension. The OID for the certificate extension should be allocated in the "SMI Security for PKIX Certificate Extension" registry (1.3.6.1.5.5.7.1). For the ASN.1 Module in Section 4, IANA is requested to assign an object identifier (OID) for the module identifier. The OID for the module should be allocated in the "SMI Security for PKIX Module Identifier" registry (1.3.6.1.5.5.7.0). 8. Acknowledgements Many thanks to Ben Smeets, Michael Li, and Roman Danyliw for their review and comments. 9. References 9.1. Normative References Housley, et al. Expires 15 April 2023 [Page 5] Internet-Draft 5G NFType in X.509 Certificates October 2022 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley, R., and W. Polk, "Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [TS23.003] 3rd Generation Partnership Project, "Technical Specification Group Core Network and Terminals; Numbering, addressing and identification (Release 17)", 3GPP TS:23.003 V17.5.0 , March 2022, . [TS29.510] 3rd Generation Partnership Project, "5G System; Network Function Repository Services; Stage 3 (Release 17)", 3GPP TS:29.510 V17.5.0 , March 2022, . [TS33.310] 3rd Generation Partnership Project, "Network Domain Security (NDS); Authentication Framework (AF) (Release 17)", 3GPP TS:33.310 V17.2.0 , March 2022, . [X.680] ITU-T, "Information technology -- Abstract Syntax Notation One (ASN.1): Specification of basic notation", ITU-T Recommendation X.680, ISO/IEC 8824-1:2021, February 2021, . 9.2. Informative References [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, DOI 10.17487/RFC5246, August 2008, . Housley, et al. Expires 15 April 2023 [Page 6] Internet-Draft 5G NFType in X.509 Certificates October 2022 [RFC5912] Hoffman, P. and J. Schaad, "New ASN.1 Modules for the Public Key Infrastructure Using X.509 (PKIX)", RFC 5912, DOI 10.17487/RFC5912, June 2010, . [RFC6268] Schaad, J. and S. Turner, "Additional New ASN.1 Modules for the Cryptographic Message Syntax (CMS) and the Public Key Infrastructure Using X.509 (PKIX)", RFC 6268, DOI 10.17487/RFC6268, July 2011, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . [TS29.571] 3rd Generation Partnership Project, "5G System; Common Data Types for Service Based Interfaces; Stage 3 (Release 17)", 3GPP TS:29.571 V17.5.0 , March 2022, . Appendix A. Appendix A. NFType Strings Table 6.1.6.3.3-1 of [TS29.510] defines the ASCII strings for the NF Types specified in 3GPP documents, which are listed below in alphabetical order. This list is not exhaustive. "5G_DDNMF" "ICSCF" "SCEF" "5G_EIR" "IMS_AS" "SCP" "AANF" "LMF" "SCSAS" "ADRF" "MB-SMF" "SCSCF" "AF" "MB-UPF" "SEPP" "AMF" "MFAF" "SMF" "AUSF" "MME" "SMSF" "BSF" "N3IWF" "SOR_AF" "CBCF" "NEF" "SPAF" "CEF" "NRF" "TSCTSF" "CHF" "NSACF" "UCMF" "DCCF" "NSSAAF" "UDM" "DRA" "NSSF" "UDR" "EASDF" "NSWOF" "UDSF" "GBA_BSF" "NWDAF" "UPF" "GMLC" "PCF" "HSS" "PCSCF" Authors' Addresses Housley, et al. Expires 15 April 2023 [Page 7] Internet-Draft 5G NFType in X.509 Certificates October 2022 Russ Housley Vigil Security, LLC Herndon, VA, United States of America Email: housley@vigilsec.com Sean Turner sn3rd Washington, DC, United States of America Email: sean@sn3rd.com John Preuß Mattsson Ericsson Kista Sweden Email: john.mattsson@ericsson.com Daniel Migault Ericsson Saint Laurent, QC Canada Email: daniel.migault@ericsson.com Housley, et al. Expires 15 April 2023 [Page 8]