Change:
Try to used KeyPurposeId (or key purpose, key purpose identifier, etc.), to express more accurately. Add some changes, related with restrictive expression of document signing KeyPurposeId, etc.
on the section 4, it seems better to change some of "EKU" to "KeyPurposeId" or "EKU values" to highlight following. excluded EKUs procedures checks, whether EKU values contain some OID(KeyPurpiseId), or absence of EKU extension. permitted EKU procedures check, whether EKU values contain some OID(KeyPurposeId).
Current expression on "Excluded EKUs procedure " and "Permitted EKU procedure" seems unclear about whether that procedure prohibits or allows, existence of certain key purpose identifier in the extended key usage value (partial match), OR certain set of key purpose identifier is on key usage value(exact match). my intension was the former. I will review, and will fix that expression if it were unclear. In addition, I will add "restrictions set is derived and implemented from (or configured with) the policy to which the implementation conforms." to clarify policy handling by RP or implementer.

Discussion:
Abstract <del> RFC 5280 specifies several extended key usages for X.509 certificates.  This document defines a general purpose document signing extended key usage for X.509 public key certificates which restricts the usage of the certificates for document signing. </del> <ins> RFC5280 specifies several extended key purpose identifiers (KeyPurposeIds) for X.509 certificates.  This document defines a general purpose document signing KeyPurposeId for inclusion in the Extended Key Usage (EKU) extension of X.509 public key certificates. Document Signing applications may require that the EKU extension be present and that a document signing KeyPurposeId be indicated in order for the certificate to be acceptable to that Document Signing application. </ins> 1. <del> RFC5280 specifies several extended key usages for X.509 certificates. In addition, several extended key usage had been added RFC7299 as public Object Identifier (OID) under the IANA repository.  While usage of any extended key usage is bad practice for publicly trusted certificates, there are no public and general extended key usage explicitly assigned for Document Signing certificates.  The current practice is to use id-kp-emailProtection, id-kp-codeSigning or vendor defined OID for general document signing purposes. </del> <ins> RFC5280 specifies several extended key purpose identifiers (KeyPurposeIds) for X.509 certificates.  In addition, several KeyPurposeIds have been addedRFC7299 under the IANA repository "SMI Security for PKIX Extended Key Purpose".  While usage of the "anyExtendedKeyUsage" KeyPurposeId is bad practice for publicly trusted certificates, there is no public and general KeyPurposeId explicitly assigned for Document Signing.  The current practice is to use id-kp-emailProtection, id-kp-codeSigning or a vendor-defined KeyPurposeId for general document signing purposes. </ins> In circumstances where code signing and S/MIME certificates are also widely used for document signing, the technical or policy changes

cryptographic agility on the document signing ecosystem and vice versa. <del> There is no issue if the vendor defined OIDs are used in a PKI (or a trust program) governed by the vendor.  However, if the OID is used outside of the vendor governance, the usage can easily become out of control (e.g. - When the end user encounters vendor defined OIDs, they might want to ask that vendor about use of the certificate, however, the vendor may not know about the particular use. - If the issuance of the cert is not under the control of the OID owner, there is no way for the OID owner to know what the impact will be if any change is made to the OID in question, and it would restrict vendor's choice of OID management. etc.). </del> <ins> There is no issue if the vendor-defined KeyPurposeIds are used in a PKI (or a trust program) governed by the vendor.  However, if the KeyPurposeId is used outside of vendor governance, the usage can easily become out of control (e.g. - When the end user encounters vendor-defined KeyPurposeIds, they might want to ask that vendor about use of the certificate, however, the vendor may not know about the particular use. - If the issuance of the cert is not under the control of the KeyPurposeId owner, there is no way for the KeyPurposeId owner to know what the impact will be if any change is made to the KeyPurposeId in question, and it would restrict vendor's choice of OID management.  etc.). </ins> <del> Therefore, it is not favorable to use a vendor defined EKU for signing a document that is not governed by the vendor. </del> <ins> Therefore, it is not favorable to use a vendor-defined KeyPurposeId for signing a document that is not governed by the vendor. </ins> <del> This document defines a general Document Signing extended key purpose identifier. </del> <ins> This document defines a extended key purpose identifier for Document Signing. </ins> 2.

3. This specification defines the KeyPurposeId id-kp-documentSigning. <del> Inclusion of this KeyPurposeId in a certificate indicates that the use of any Subject names in the certificate is restricted to use by a document signing. Term of "Document Sign" in this document is digitally sign contents that are consumed by people.  To be more precise, contents are intended to be shown to person with printable or displayable form by means of services or software, rather than processed by machines. </del> <ins> As described in RFC5280, If the Extended Key Usage extension is present, then the certificate MUST only be used for one of the purposes indicated.  RFC5280 also describes that If multiple key purposes are indicated the application need not recognize all purposes indicated, as long as the intended purpose is present. Document Signing applications MAY require that the Extended Key Usage extension be present and that a id-kp-documentSigning be indicated in order for the certificate to be acceptable to that Document Signing application. The term "Document Signing" in this document refers to digitally signing contents that are consumed by people.  To be more precise, contents are intended to be shown to a person with printable or displayable form by means of services or software, rather than processed by machines. </ins> 3.1. <del> RFC5280 specifies the EKU X.509 certificate extension for use in the </del> <ins> RFC5280 specifies the EKU X.509 certificate extension for use on the </ins> Internet.  The extension indicates one or more purposes for which the certified public key is valid.  The EKU extension can be used in <del> conjunction with the key usage extension, which indicates how the public key in the certificate is used, in a more basic cryptographic way. </del> <ins> conjunction with the key usage extension, which indicates the set of basic cryptographic operations for which the certified key may be used. </ins> The EKU extension syntax is repeated here for convenience: This specification defines the KeyPurposeId id-kp-documentSigning. Inclusion of this KeyPurposeId in a certificate indicates that the <del> use of any Subject names in the certificate is restricted to use by a document signing service or a software (along with any usages allowed by other EKU values). </del> <ins> public key encoded in the certificate has been certified to be used for cryptographic operations on contents that are consumed by people. </ins> 4. RFC8358 specifies the conventions for digital signatures on Internet- Drafts.  This is one of the intended use cases for the general <del> document signing EKU described in this document.  RFC8358 uses CMS to digitally sign a wide array of files such as ASCII, PDF, EPUB, HTML etc.  Currently, there are no specification regarding EKU for certificates signing those files except those which are defined by the software vendor. </del> <ins> document signing key purpose described in this document.  RFC8358 uses CMS to digitally sign a wide array of files such as ASCII, PDF, EPUB, HTML etc.  Currently, there are no specification regarding key purposes for certificates signing those files except those which are defined by the software vendor. </ins> The signed contents of Internet-Drafts are primarily intended to be consumed by people.  To be more precise, contents are intended to be shown to a person in a printable or displayable form by means of <del> services or software, rather than processed by machines.  To validate the digital signature on the contents that is intended to be consumed by people, implementations MAY perform the steps below as a certificate validation. The implementation MAY examine the Extended Key Usage value(s): </del> <ins> services or software, rather than processed by machines.  The digital signature on the contents is to indicate to the recipient of the contents that the content has not changed since it was signed by the identity indicated as the subject of the certificate.  To validate the digital signature which is signed on contents intended to be consumed by people, implementations MAY perform the steps below during certificate validation: The implementation MAY examine the KeyPurposeId(s) included in the Extended Key Usage extension as follows: A Restriction on Extended Key Usage is derived and implemented from (or configured with) the policy to which the implementation conforms. </ins> If there are no restrictions set for the relying party and the relying party software, the certificate is acceptable. If there are restrictions set for the replying party and relying <del> party software, proceed as following. Each Restriction on the EKUs can be "Excluded EKU" or "Permitted EKU" and handled. The procedure is intended to permit or prohibit presence of a certain EKU or complete absence of EKUs.  It is outside the scope of this document, but the relying party can permit or exclude combinations of EKU.  A consideration on prohibiting combination of EKUs is described in the security consideration section of this document. "Excluded EKU" is an EKU which the relying party or the relying party software prohibits.  Examples of "Excluded EKU" are, presence of anyExtendedKeyUsage or complete absence of EKU extension on a certificate.  If an EKU of the certificate meets the conditions set by the "Excluded EKU" restriction, the relying party or the relying party software rejects the certificate. "Permitted EKU" is an EKU which the relying party or the relying party software accepts.  Examples of "Permitted EKU" are, presence of this general document signing EKU and/or protocol specific document signing-type EKUs.  If an EKU of the certificate meets the condition set by a "Permitted EKU" restriction, the certificate is acceptable.  Otherwise, relying party or the relying party software rejects the certificate. When a single software has capability to process various data </del> <ins> party software, then process the KeyPurposeId(s) as described below. Each restriction on "Excluded KeyPurposeId" or "Permitted KeyPurposeId" is handled as described below. This procedure is intended to permit or prohibit presence of a certain KeyPurposeId or complete absence of KeyPurposeIds.  It is outside the scope of this document, but the relying party can permit or prohibit combinations of KeyPurposeIds.  A consideration on prohibiting combinations of KeyPurposeIds is described in the Security Considerations section of this document. "Excluded KeyPurposeId" is a KeyPurposeId which the relying party or the relying party software prohibits.  Examples of "Excluded KeyPurposeId" are, presence of the anyExtendedKeyUsage KeyPurposeId or complete absence of the EKU extension in a certificate.  If a KeyPurposeId of the certificate meets the conditions set by the "Excluded KeyPurposeId" restriction, the relying party or the relying party software rejects the certificate. Permitted KeyPurposeId procedure: : "Permitted KeyPurposeId" is a KeyPurposeId which the relying party or the relying party software accepts.  Examples of "Permitted KeyPurposeId" are, presence of this general document signing KeyPurposeId and/or protocol specific document signing- type KeyPurposeIds.  If a KeyPurposeId of the certificate meets the condition set by a "Permitted KeyPurposeId" restriction, the certificate is acceptable.  Otherwise, relying party or the relying party software rejects the certificate. When a single application has the capability to process various data </ins> formats, the software may choose to make the excluded and permitted decisions separately in accordance with the format it is handling <del> (e.g. text, pdf, etc). </del> <ins> (e.g.  text, pdf, etc). </ins> 5.

inserted in each certificate that is issued.  Unless certificates are governed by a vendor specific PKI (or trust program), certificates that indicate usage for document signing MAY include the id-kp- <del> documentSigning EKU extension.  This does not encompass the mandatory usage of the id-kp-documentSigning EKU in conjunction with the vendor specific EKU.  However, this does not restrict the CA from including multiple EKUs related to document signing. </del> <ins> documentSigning KeyPurposeId.  The inclusion of the id-kp- documentSigning KeyPurposeId does not preclude the inclusion of other KeyPurposeIds. </ins> 6. <del> The usage of id-kp-documentSigning EKU intends to prevent id-kp- emailProtection from being used for purposes other than email and id- kp-codeSigning used to sign objects other than binary codes.  This EKU does not introduce new security risks but instead reduces existing security risks by providing means to separate other EKUs used for communication protocols namely, TLS or S/MIME etc. in order to minimize the risk of cross protocol attacks. </del> <ins> The usage of id-kp-documentSigning KeyPurposeId is to provide an alternative to id-kp-emailProtection being used for non-email purposes and id-kp-codeSigning being used to sign objects other than binary code.  This extended key purpose does not introduce new security risks but instead reduces existing security risks by providing means to separate other extended key purposes used for communication protocols namely, TLS or S/MIME etc. in order to minimize the risk of cross-protocol attacks. </ins> <del> To reduce the risk of specific cross protocol attacks, the relying party or relying party software may additionaly prohibit use of specific combination of EKUs. </del> <ins> To reduce the risk of specific cross-protocol attacks, the relying party or relying party software may additionally prohibit use of specific combinations of KeyPurposeIds. </ins> While a specific protocol or signing scheme may choose to come up <del> with their own EKU, some may not have significant motive or resource to set up and manage thier own EKU.  This general document signing EKU may be used as a stop gap for those that intend to set up their own EKU or those who do not intend to set up an EKU but still would like to distinguish from other usage. Introduction of this id-kp-documentSigning EKU value does not </del> <ins> with their own KeyPurposeIds, some may not have significant motive or resources to set up and manage their own KeyPurposeIds.  This general document signing KeyPurposeId may be used as a stop-gap for those that intend to define their own KeyPurposeId or those who do not intend to set up an KeyPurposeId but still would like to distinguish document signing from other usages. Introduction of this id-kp-documentSigning KeyPurposeId does not </ins> introduce any new security or privacy concerns. 7. <del> This document requests that IANA make two assignments.  One for the id-kp-documentSigning object identifier (OID), as defined in ext, for the EKU from the "SMI Security for PKIX Extended Key Purpose" (1.3.6.1.5.5.7.3) registry.  Another for the id-mod-docsign-eku, as defined in Appendix A, for the ASN.1 module X.680 from the in the "SMI Security for PKIX Module Identifier" (1.3.6.1.5.5.7.0) registry. No further action is necessary by IANA. </del> <ins> This document requests that IANA make two assignments.  One assignment is for the addition of the id-kp-documentSigning object identifier (OID), as defined in ext, to the "SMI Security for PKIX Extended Key Purpose" (1.3.6.1.5.5.7.3) registry.  The other assignment is for the addition of the id-mod-docsign-eku ASN.1 module X.680 object identifier (OID), as defined in Appendix A, to the "SMI Security for PKIX Module Identifier" (1.3.6.1.5.5.7.0) registry.  No further action is necessary by IANA. </ins>