rfc9809v2.txt   rfc9809.txt 
Internet Engineering Task Force (IETF) H. Brockhaus Internet Engineering Task Force (IETF) H. Brockhaus
Request for Comments: 9809 Siemens Request for Comments: 9809 Siemens
Category: Standards Track D. Goltzsche Category: Standards Track D. Goltzsche
ISSN: 2070-1721 Siemens Mobility ISSN: 2070-1721 Siemens Mobility
June 2025 July 2025
X.509 Certificate Extended Key Usage (EKU) for Configuration, Updates, X.509 Certificate Extended Key Usage (EKU) for Configuration, Updates,
and Safety-Critical Communication and Safety-Critical Communication
Abstract Abstract
RFC 5280 defines the Extended Key Usage (EKU) extension and specifies RFC 5280 defines the Extended Key Usage (EKU) extension and specifies
several extended key purpose identifiers (KeyPurposeIds) for use with several extended key purpose identifiers (KeyPurposeIds) for use with
that extension in X.509 certificates. This document defines that extension in X.509 certificates. This document defines
KeyPurposeIds for general-purpose and trust anchor configuration KeyPurposeIds for general-purpose and trust anchor configuration
skipping to change at line 205 skipping to change at line 205
described in Section 6. described in Section 6.
Systems or applications that verify the signature of a general- Systems or applications that verify the signature of a general-
purpose configuration file or trust anchor configuration file, the purpose configuration file or trust anchor configuration file, the
signature of a software or firmware update package, or the signature of a software or firmware update package, or the
authentication of a communication peer for safety-critical authentication of a communication peer for safety-critical
communication SHOULD require that corresponding KeyPurposeIds be communication SHOULD require that corresponding KeyPurposeIds be
specified by the EKU extension. If the certificate requester knows specified by the EKU extension. If the certificate requester knows
the certificate users are mandated to use these KeyPurposeIds, it the certificate users are mandated to use these KeyPurposeIds, it
MUST enforce their inclusion. Additionally, such a certificate MUST enforce their inclusion. Additionally, such a certificate
requester MUST ensure that the KeyUsage extension be set to requester MUST ensure that the Key Usage extension be set to
digitalSignature for signature verification, to keyEncipherment for digitalSignature for signature verification, to keyEncipherment for
public key encryption, and keyAgreement for key agreement. public key encryption, and keyAgreement for key agreement.
4. Including the Extended Key Purpose in Certificates 4. Including the Extended Key Purpose in Certificates
[RFC5280] specifies the EKU X.509 certificate extension for use on [RFC5280] specifies the EKU X.509 certificate extension for use on
end-entity certificates. The extension indicates one or more end-entity certificates. The extension indicates one or more
purposes for which the certified public key is valid. The EKU purposes for which the certified public key is valid. The EKU
extension can be used in conjunction with the Key Usage (KU) extension can be used in conjunction with the Key Usage (KU)
extension, which indicates the set of basic cryptographic operations extension, which indicates the set of basic cryptographic operations
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