Network Working Group                                         R. Housley
Internet-Draft                                            Vigil Security
Intended status: Standards Track                               S. Turner
Expires: 25 December 2022                                          sn3rd
                                                          J. P. Mattsson
                                                              D. Migault
                                                                Ericsson
                                                            23 June 2022


       X.509 Certificate Extension for 5G Network Function Types
                   draft-housley-lamps-3g-nftypes-00

Abstract

   This document specifies the certificate extension for including
   Network Function Typess (NFTypes) for the 5G System in X.509v3 public
   key certificates as profiled in RFC 5280.

Status of This Memo

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   This Internet-Draft will expire on 25 December 2022.

Copyright Notice

   Copyright (c) 2022 IETF Trust and the persons identified as the
   document authors.  All rights reserved.











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   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.  Certificate Subject Identification  . . . . . . . . . . . . .   3
   4.  Network Functions Certificate Extension . . . . . . . . . . .   4
   5.  ASN.1 Module  . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Appendix A.  NFType Strings  . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

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 as short ASCII string.

   X.509v3 public key certificates [RFC5280] are used to identify
   interface instances in the NFs in a 5G system.  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, which
   provides a list of NF Types associated with the certificate subject.
   The NFTypes certificate extension can be used to support role-based
   access control decisions.






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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.  Certificate Subject Identification

   The Network Domain Security (NDS) Authentication Framework (AF) for
   3GPP Release 17 [TS33.310] provides several patterns for certificate
   subject names.  For example, the certificate subject name for an NF
   instance follows one of these patterns:

     (c=<country>), o=<Organization Name>, cn=<Some distinguishing name>

     cn=<hostname>, (ou=<servers>), dc=<domain>, dc=<domain>

   When either pattern is used, the cn= portion is a DirectoryString;
   however, Section 4.1.2.6 of [RFC5280], limits the character set to
   either PrintableString or UTF8String.  Note that the PrintableString
   has a much more limited set of characters that can be represented.

   When the first pattern is used, the o= portion of the name contains
   the home domain as specified in [TS23.003] to identify the public
   land mobile network, and it takes the following form:

     5gc.mnc<MNC>.mcc<MCC>.3gppnetwork.org

   where MNC designates the Mobile Network Code, and MCC designates the
   Mobile Country Code.

   The certificates are expected to include the SubjectAltName
   certificate extension that contains a fully qualified domain name
   (FQDN), where the FQDN designates the NF as defined in [TS23.003].
   For example, the SubjectAltName certificate extension for an NF
   instance implementing the AMF might include these FQDNs:

     amf1.cluster1.net2.amf.5gc.mnc012.mcc345.3gppnetwork.org

     amf1.callback.cluster1.net2.amf.5gc.mnc012.mcc345.3gppnetwork.org

   The certificates for entities that can act as TLS clients or servers
   are also expected to include a uniformResourceIdentifier in the
   SubjectAltName certificate extension that contains the NF Instance ID
   as specified in Clause 5.3.2 of [TS29.571].  For example, the
   SubjectAltName certificate extension for an NF Instance ID might be:



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     urn:uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6

   Following these patterns facilitates the use of the certificate
   subject and the subjectAltName certificate extension to support
   identity-based access control decisions.

   When the second pattern is used, the dc= portion of the name contains
   a single domain component.  For example, hostname.example.net would
   appear in the certificate subject as:

     cn=hostname, dc=example, dc=net

4.  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 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 only the ASCII strings.

   The NFTypes MUST contain at least one NFType.

   The NFTypes MUST NOT contain the same NFType more than once.

   Each NFType MUST contain at least one ASCII character, and each
   NFType MUST NOT contain more than 32 ASCII characters.

   The NFType is of type IA5String to permit inclusion of the character
   underscore character ('_'), which is not part of the PrintableString
   character set.






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5.  ASN.1 Module

   This appendix provides an ASN.1 module [X.680] for the NFTypes
   certificate extension, and it follows the conventions established in
   [RFC5912] and [RFC6268].

   <CODE BEGINS>
     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
   <CODE ENDS>

6.  Security Considerations

   The Security Considerations of [RFC5280] are applicable to this
   document.



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   The ASCII strings that specify the NF Types are not standard; an
   operator MAY build its own NF Type.  Since the NF Type is used for
   role-based access control decisions, the operator that specifies
   their own ASCII string for an NF Type MUST ensure that the new NF
   Type does not match an existing one.

7.  IANA Considerations

   For the NFType certificate extension in Section 4, 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 5, 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 and Michael Li for their review and
   comments.

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [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,
              <https://www.3gpp.org/ftp/Specs/
              archive/29_series/29.510/29510-h50.zip>.




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   [TS33.310] 3rd Generation Partnership Project, "Network Domain
              Security (NDS); Authentication Framework (AF) (Release
              17)", 3GPP TS:33.310 V17.2.0 , March 2022,
              <https://www.3gpp.org/ftp/Specs/
              archive/33_series/33.310/33310-h20.zip>.

   [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,
              <https://www.itu.int/rec/T-REC-X.680>.

9.2.  Informative References

   [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,
              <https://www.rfc-editor.org/info/rfc5912>.

   [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,
              <https://www.rfc-editor.org/info/rfc6268>.

   [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,
              <https://www.3gpp.org/ftp/Specs/
              archive/23_series/23.003/23003-h50.zip>.

   [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,
              <https://www.3gpp.org/ftp/Specs/
              archive/29_series/29.571/29571-h50.zip>.

Appendix A.  Appendix A.  NFType Strings

   Each NFType is identified by an ASCII string.  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.








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       "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

   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





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