X.509 Certificate Extended Key Usage (EKU) for 5G Network Functions
draft-ietf-lamps-nf-eku-02
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9509.
|
|
|---|---|---|---|
| Authors | Tirumaleswar Reddy.K , Jani Ekman , Daniel Migault | ||
| Last updated | 2023-09-08 (Latest revision 2023-09-07) | ||
| Replaces | draft-reddy-lamps-jose-eku | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
GENART IETF Last Call review
by Elwyn Davies
Ready w/nits
INTDIR IETF Last Call review
by Benson Muite
Ready w/nits
|
||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Russ Housley | ||
| Shepherd write-up | Show Last changed 2023-07-23 | ||
| IESG | IESG state | Became RFC 9509 (Proposed Standard) | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Roman Danyliw | ||
| Send notices to | housley@vigilsec.com | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA expert review state | Reviews assigned | ||
| IANA expert review comments | The expert has approved the SMI Security for PKIX Extended Key Purpose registrations. |
draft-ietf-lamps-nf-eku-02
LAMPS WG T. Reddy
Internet-Draft J. Ekman
Intended status: Standards Track Nokia
Expires: 10 March 2024 D. Migault
Ericsson
7 September 2023
X.509 Certificate Extended Key Usage (EKU) for 5G Network Functions
draft-ietf-lamps-nf-eku-02
Abstract
RFC 5280 specifies several extended key purpose identifiers
(KeyPurposeIds) for X.509 certificates. This document defines
encrypting JSON objects in HTTP messages, JSON Web Token (JWT) and
signing the OAuth 2.0 access tokens KeyPurposeIds for inclusion in
the Extended Key Usage (EKU) extension of X.509 v3 public key
certificates used by Network Functions (NFs) for the 5G System.
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 10 March 2024.
Copyright Notice
Copyright (c) 2023 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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Extended Key Purpose for Network Functions . . . . . . . . . 4
4. Including the Extended Key Purpose in Certificates . . . . . 5
5. Implications for a Certification Authority . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 7
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
11.1. Normative References . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
The Operators of 5G systems make use of an internal PKI to generate
X.509 PKI certificates for the Network Functions (NFs) in a 5G
system. The certificates are used for the following purposes:
* Client and Server certificates for NFs in 5GC Service Based
Architecture (see Section 6.1.3c of [TS33.310])
* Client Credentials Assertion (CCA) is JSON Web Tokens (JWT)
[RFC7519] and is secured with digital signatures based on JSON Web
Signature (JWS) [RFC7515] (see Section 13.3.8.2 of [TS33.501]).
* Certificates for encrypting JSON objects in HTTP messages between
Security Edge Protection Proxies (SEPPs) using JSON Web Encryption
(JWE) [RFC7516] (Section 13.2.4.4 of [TS33.501]) and Section 6.3.2
of [TS33.210])
* Certificates for signing the OAuth 2.0 access tokens for service
authorization to grant temporary access to resources provided by
NF producers using JWS (see Section 13.4.1 of [TS33.501])
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[RFC5280] specifies several extended key purpose identifiers (EKU),
defined via KeyPurposeIds, for X.509 certificates. In addition, the
IANA repository "SMI Security for PKIX Extended Key Purpose"
[RFC7299] contains additional KeyPurposeIds. It's important to note
that using the anyExtendedKeyUsage KeyPurposeId, as defined in
Section 4.2.1.12 of [RFC7299], is generally considered a poor
practice. This is especially true for publicly trusted certificates,
whether they are multi-purpose or single-purpose, within the context
of 5G systems and the 5GC Service Based Architecture.
If the purpose of the issued certificates is not restricted, i.e.,
the type of operations for which a public key contained in the
certificate can be used are not specified, those certificates could
be used for another purpose than intended, violating the CA policies,
and increasing the risk of cross-protocol attacks. Failure to ensure
proper segregation of duties means that a NF who generates the
public/private keys and applies for a certificate to the operator CA,
could obtain a certificate which can be misused for tasks that this
NF is not entitled to perform. For example, a NF service consumer
could impersonate NF service producers using its certificate.
Another example, if the purpose of the certificate is for the NF
service consumer is to use it as a client certificate, the NF with
this client certificate and corresponding private key must not be
allowed to sign the CCA. When a NF service producer receives the
signed CCA from the NF service consumer, the NF would accept the
token even if CCA is signed with a certificate not issued for this
purpose.
The KeyPurposeId id-kp-serverAuth (Section 4.2.1.12 of [RFC5280]) can
be used to identify that the certificate is for a server (e.g., NF
service producer), and the KeyPurposeId id-kp-clientAuth
(Section 4.2.1.12 of [RFC5280]) can be used to identify that the
certificate is for a client (e.g., NF service consumer). However,
there is currently no KeyPurposeIds for the other usages of
certificates in 5G System. This document defines the Extended Key
Usage (EKU) extension of X.509 public key certificates for signing
the JWT Claims set using JWS, encrypting JSON objects in HTTP
messages using JWE, and signing the OAuth 2.0 access tokens using
JWS.
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Vendor-defined KeyPurposeIds used within a PKI governed by the vendor
or a group of vendors typically do not pose interoperability
concerns, as non-critical extensions can be safely ignored if
unrecognized. However, using or misusing KeyPurposeIds outside of
their intended vendor-controlled environment can lead to
interoperability issues. Therefore, it is advisable not to rely on
vendor-defined KeyPurposeIds. Instead, the specification defines
standard KeyPurposeIds to ensure interoperability across various
implementations.
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. Extended Key Purpose for Network Functions
This specification defines the KeyPurposeIds id-kp-jwt, id-kp-
httpContentEncrypt, id-kp-oauthAccessTokenSigning for respectively
signing the JWT Claims set of CCA using JWS, encrypting JSON objects
in HTTP messages between Security Edge Protection Proxies (SEPPs)
using JWE and signing the OAuth 2.0 access tokens for service
authorization to grant temporary access to resources provided by NF
producers using JWS. As described in [RFC5280], "[i]f the [Extended
Key Usage] extension is present, then the certificate MUST only be
used for one of the purposes indicated." [RFC5280] also notes that
"[i]f multiple [key] purposes are indicated the application need not
recognize all purposes indicated, as long as the intended purpose is
present."
Applications verifying the signature of a Client Credentials
Assertion (CCA) represented as JWT, decrypting JSON objects in HTTP
messages between Security Edge Protection Proxies (SEPPs) using JWE
or verifying the signature of an OAuth 2.0 access tokens for service
authorization to grant temporary access to resources provided by NF
producers using JWS MAY require corresponding KeyPurposeIds be
specified by the EKU extention. In addition, such application MUST
require the keyUsage extension be set to digitalSignature or
nonRepudiation (also designated as contentCommitment) for the
signature calculation and/or to keyEncipherment for encryption of the
secret key.
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4. Including the Extended Key Purpose in Certificates
[RFC5280] specifies the EKU X.509 certificate extension for use on
end entity certificates. The extension indicates one or more
purposes for which the certified public key is valid. The EKU
extension can be used in conjunction with the key usage extension,
which indicates the set of basic cryptographic operations for which
the certified key may be used. The EKU extension syntax is repeated
here for convenience:
ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId
KeyPurposeId ::= OBJECT IDENTIFIER
As described in [RFC5280], the EKU extension may, at the option of
the certificate issuer, be either critical or non-critical. The
inclusion of KeyPurposeId id-kp-jwt, id-kp-httpContentEncrypt, and
id-kp-oauthAccessTokenSigning in a certificate indicates that the
public key encoded in the certificate has been certified for use in
the following:
1. Validating the JWS Signature in JWT.
2. Encrypting JSON objects in HTTP messages (for example, encrypting
the CEK with the recipient's public key using the RSAES-OAEP
algorithm to produce the JWE Encrypted Key).
3. Signing OAuth 2.0 access tokens.
The distinction between JWS and JWE is determined by the KU that is
set to digitalSignature or nonRepudiation for JWS and keyEncipherment
for JWE.
id-kp OBJECT IDENTIFIER ::= {
iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) kp(3) }
id-kp-jwt OBJECT IDENTIFIER ::= { id-kp TBD1 }
id-kp-httpContentEncrypt OBJECT IDENTIFIER ::= { id-kp TBD2 }
id-kp-oauthAccessTokenSigning OBJECT IDENTIFIER ::= { id-kp TBD3 }
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5. Implications for a Certification Authority
The procedures and practices employed by a certification authority
MUST ensure that the correct values for the EKU extension as well as
the KU extension are inserted in each certificate that is issued.
The inclusion of the id-kp-jwt, id-kp-httpContentEncrypt and id-kp-
oauthAccessTokenSigning KeyPurposeIds does not preclude the inclusion
of other KeyPurposeIds.
6. Security Considerations
The Security Considerations of [RFC5280] are applicable to this
document. This extended key purpose does not introduce new security
risks but instead reduces existing security risks by providing means
to identify if the certificate is generated to sign the JWT Claims
Set, signing the OAuth 2.0 access tokens using JWS or to encrypt the
CEK in JWE for encrypting JSON objects in HTTP messages.
To reduce the risk of specific cross-protocol attacks, the relying
party or the relying party software may additionally prohibit use of
specific combinations of KeyPurposeIds. The procedure of using
Excluded KeyPurposeId and Permitted KeyPurposeId by an relying party
to permit or prohibit combinations of KeyPurposeIds is defined in
Section 4 of [RFC9336]. Examples of Excluded KeyPurposeId include
the presence of the anyExtendedKeyUsage KeyPurposeId or the complete
absence of the EKU extension in a certificate. Examples of Permitted
KeyPurposeId include the presence of id-kp-jwt, id-kp-
httpContentEncrypt or id-kp-oauthAccessTokenSigning KeyPurposeId.
7. 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 EKU
extension can help an observer determine the purpose of the
certificate. In addition, If the certificate is issued by a public
certification authority, the inclusion of EKU extension can help an
attacker to monitor the Certificate Transparency logs [RFC9162] to
identify the purpose of the certificate.
8. IANA Considerations
IANA is requested to register the following OIDs in the "SMI Security
for PKIX Extended Key Purpose" registry (1.3.6.1.5.5.7.3). This OID
is defined in Section 4.
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+=========+===============================+============+
| Decimal | Description | References |
+=========+===============================+============+
| TBD1 | id-kp-jwt | This-RFC |
+---------+-------------------------------+------------+
| TBD2 | id-kp-httpContentEncrypt | This-RFC |
+---------+-------------------------------+------------+
| TBD3 | id-kp-oauthAccessTokenSigning | This-RFC |
+---------+-------------------------------+------------+
Figure 1: Table 1
IANA is also requested to register the following ASN.1[X.680] module
OID in the "SMI Security for PKIX Module Identifier" registry
(1.3.6.1.5.5.7.0). This OID is defined in Appendix A.
+=========+==========================+============+
| Decimal | Description | References |
+=========+==========================+============+
| TBD4 | id-mod-nf-eku | This-RFC |
+---------+--------------------------+------------+
Figure 2: Table 2
9. Contributors
The following individuals have contributed to this document:
German Peinado
Nokia
Email: german.peinado@nokia.com
10. Acknowledgments
We would like to thank Corey Bonnell, Ilari Liusvaara, Carl Wallace,
Yoav Nir and Russ Housley for their useful feedback.
11. References
11.1. 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>.
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[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>.
[RFC7515] Jones, M., Bradley, J., and N. Sakimura, "JSON Web
Signature (JWS)", RFC 7515, DOI 10.17487/RFC7515, May
2015, <https://www.rfc-editor.org/info/rfc7515>.
[RFC7516] Jones, M. and J. Hildebrand, "JSON Web Encryption (JWE)",
RFC 7516, DOI 10.17487/RFC7516, May 2015,
<https://www.rfc-editor.org/info/rfc7516>.
[RFC7519] Jones, M., Bradley, J., and N. Sakimura, "JSON Web Token
(JWT)", RFC 7519, DOI 10.17487/RFC7519, May 2015,
<https://www.rfc-editor.org/info/rfc7519>.
[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>.
11.2. 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,
<https://www.rfc-editor.org/info/rfc5246>.
[RFC7299] Housley, R., "Object Identifier Registry for the PKIX
Working Group", RFC 7299, DOI 10.17487/RFC7299, July 2014,
<https://www.rfc-editor.org/info/rfc7299>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>.
[RFC9162] Laurie, B., Messeri, E., and R. Stradling, "Certificate
Transparency Version 2.0", RFC 9162, DOI 10.17487/RFC9162,
December 2021, <https://www.rfc-editor.org/info/rfc9162>.
[RFC9336] Ito, T., Okubo, T., and S. Turner, "X.509 Certificate
General-Purpose Extended Key Usage (EKU) for Document
Signing", RFC 9336, DOI 10.17487/RFC9336, December 2022,
<https://www.rfc-editor.org/info/rfc9336>.
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[TS23.501] "3rd Generation Partnership Project; Technical
Specification Group Services and System Aspects; System
architecture for the 5G System (5GS); Stage 2 (Release
18), 3GPP TS 23.501 V18.0.0 Dec 2022,",
<https://www.3gpp.org/ftp/Specs/
archive/23_series/23.501/23501-i00.zip>.
[TS33.210] "3rd Generation Partnership Project; Technical
Specification Group Services and System Aspects;Network
Domain Security (NDS); IP network layer security (Release
17), 3GPP TS 33.210 V17.1.0 Sept 2022,",
<https://www.3gpp.org/ftp/Specs/
archive/33_series/33.210/33210-h10.zip>.
[TS33.310] "3rd Generation Partnership Project; Technical
Specification Group Services and System Aspects; Network
Domain Security (NDS); Authentication Framework (AF)
(Release 17), 3GPP 33.310 V17.4.0, Sept 2022,",
<https://www.3gpp.org/ftp/Specs/
archive/33_series/33.310/33310-h40.zip>.
[TS33.501] "3rd Generation Partnership Project; Technical
Specification Group Services and System Aspects; Security
architecture and procedures for 5G system (Release 17), ,
3GPP TS:33.501 V17.7.0, Sept 2022,",
<https://www.3gpp.org/ftp/Specs/
archive/33_series/33.501/33501-h70.zip>.
[X.680] "ITU-T, "Information technology - Abstract Syntax Notation
One (ASN.1): Specification of basic notation", ITU-T
Recommendation X.680, February 2021.",
<https://www.itu.int/rec/T-REC-X.680>.
[X.690] "ITU-T, "Information technology - ASN.1 encoding rules:
Specification of Basic Encoding Rules (BER), Canonical
Encoding Rules (CER) and Distinguished Encoding Rules
(DER)", ITU-T Recommendation X.690, February 2021,",
<https://www.itu.int/rec/T-REC-X.690>.
Appendix A. ASN.1 Module
The following module adheres to ASN.1 specifications [X.680] and
[X.690].
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<CODE BEGINS>
NF-EKU
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-nf-eku (TBD4) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
-- OID Arc
id-kp OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) kp(3) }
-- Extended Key Usage Values
id-kp-jwt OBJECT IDENTIFIER ::= { id-kp TBD1 }
id-kp-httpContentEncrypt OBJECT IDENTIFIER ::= { id-kp TBD2 }
id-kp-oauthAccessTokenSigning OBJECT IDENTIFIER ::= { id-kp TBD3 }
END
<CODE ENDS>
Authors' Addresses
Tirumaleswar Reddy
Nokia
India
Email: kondtir@gmail.com
Jani Ekman
Nokia
Finland
Email: jani.ekman@nokia.com
Daniel Migault
Ericsson
Canada
Email: daniel.migault@ericsson.com
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