--- 1/draft-ietf-lamps-documentsigning-eku-01.txt 2022-03-07 09:13:21.352279213 -0800 +++ 2/draft-ietf-lamps-documentsigning-eku-02.txt 2022-03-07 09:13:21.372279709 -0800 @@ -1,29 +1,33 @@ LAMPS Working Group T. Ito Internet-Draft SECOM CO., LTD. Intended status: Standards Track T. Okubo -Expires: 3 September 2022 DigiCert, Inc. +Expires: 8 September 2022 DigiCert, Inc. S. Turner sn3rd - 2 March 2022 + 7 March 2022 General Purpose Extended Key Usage (EKU) for Document Signing X.509 Certificates - draft-ietf-lamps-documentsigning-eku-01 + draft-ietf-lamps-documentsigning-eku-02 Abstract - 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. + 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. About This Document This note is to be removed before publishing as an RFC. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-ietf-lamps-documentsigning- eku/. Discussion of this document takes place on the Limited Additional @@ -42,239 +46,262 @@ 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 3 September 2022. + This Internet-Draft will expire on 8 September 2022. Copyright Notice Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved. 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 + 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 - 3. Extended Key usage for DocumentSigning . . . . . . . . . . . 3 - 3.1. Extended Key Usage Values for Document Signing . . . . . 4 - 4. Using the Document Signing EKU in a Certificate . . . . . . . 4 - 5. Implications for a Certification Authority . . . . . . . . . 5 + 3. Extended Key Purpose for Document Signing . . . . . . . . . . 4 + 3.1. Including the Extended Key Purpose for Document Signing in + Certificates . . . . . . . . . . . . . . . . . . . . . . 4 + 4. Using the Extended Key Purpose for Document Signing in a + Certificate . . . . . . . . . . . . . . . . . . . . . . . 5 + 5. Implications for a Certification Authority . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 - 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 - 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 - 8.1. Normative References . . . . . . . . . . . . . . . . . . 6 + 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 + 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 + 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 7 - Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 7 + Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 8 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction - [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. + [RFC5280] specifies several extended key purpose identifiers + (KeyPurposeIds) for X.509 certificates. In addition, several + KeyPurposeIds have been added [RFC7299] 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. In circumstances where code signing and S/MIME certificates are also widely used for document signing, the technical or policy changes that are made to code signing and S/MIME certificates may cause unexpected behaviors or have an adverse impact such as decreased cryptographic agility on the document signing ecosystem and vice versa. - 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 + 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.). - Therefore, it is not favorable to use a vendor defined EKU for - signing a document that is not governed by the vendor. + Therefore, it is not favorable to use a vendor-defined KeyPurposeId + for signing a document that is not governed by the vendor. - This document defines a general Document Signing extended key purpose - identifier. + This document defines a extended key purpose identifier for Document + Signing. 2. Conventions and Definitions 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 usage for DocumentSigning +3. Extended Key Purpose for Document Signing This specification defines the KeyPurposeId id-kp-documentSigning. - 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 humans. To be more precise, contents are - intended to be shown to human with printable or displayable form by - means of services or software, rather than processed by machines. + 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. -3.1. Extended Key Usage Values for Document Signing + 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. - [RFC5280] specifies the EKU X.509 certificate extension for use in + 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. + +3.1. Including the Extended Key Purpose for Document Signing in + Certificates + + [RFC5280] specifies the EKU X.509 certificate extension for use on the Internet. 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 how the - public key in the certificate is used, in a more basic cryptographic - way. + 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 This specification defines the KeyPurposeId id-kp-documentSigning. 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 service or a software (along with any usages allowed - by other EKU values). + public key encoded in the certificate has been certified to be used + for cryptographic operations on contents that are consumed by people. id-kp OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) 3 } - id-kp-documentSigning OBJECT IDENTIFIER ::= { id-kp XX } -4. Using the Document Signing EKU in a Certificate +4. Using the Extended Key Purpose for Document Signing in a Certificate [RFC8358] specifies the conventions for digital signatures on Internet-Drafts. This is one of the intended use cases for the - general 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. + general 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. 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 - 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. + 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 Extended Key Usage value(s): + 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. 1. If there are no restrictions set for the relying party and the relying party software, the certificate is acceptable. 2. If there are restrictions set for the replying party and relying - party software, proceed as following. + party software, then process the KeyPurposeId(s) as described + below. - Each Restriction on the EKUs can be "Excluded EKU" or "Permitted - EKU" and handled. + Each restriction on "Excluded KeyPurposeId" or "Permitted + KeyPurposeId" is handled as described below. - 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. + 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 EKUs procedure: "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. + Excluded KeyPurposeId procedure: "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 EKU procedure: "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. + Permitted KeyPurposeId procedure: - When a single software has capability to process various data + : "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 formats, the software may choose to make the excluded and permitted decisions separately in accordance with the format it is handling (e.g. text, pdf, etc). 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 are 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- - 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. + documentSigning KeyPurposeId. The inclusion of the id-kp- + documentSigning KeyPurposeId does not preclude the inclusion of other + KeyPurposeIds. 6. Security Considerations - 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. + 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. - 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. + 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. While a specific protocol or signing scheme may choose to come up - 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. + 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 EKU value does not + Introduction of this id-kp-documentSigning KeyPurposeId does not introduce any new security or privacy concerns. 7. IANA Considerations - This document requests that IANA make two assignments. One for the - id-kp-documentSigning object identifier (OID), as defined in - Section 3.1, 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. + 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 Section 3.1, 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. 8. References 8.1. 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, . @@ -298,21 +325,21 @@ Working Group", RFC 7299, DOI 10.17487/RFC7299, July 2014, . [RFC8358] Housley, R., "Update to Digital Signatures on Internet- Draft Documents", RFC 8358, DOI 10.17487/RFC8358, March 2018, . Appendix A. ASN.1 Module The following ASN.1 module provides the complete definition of the - Document Signing EKU. + Document Signing KeyPurposeId. DocSignEKU { iso(1) identified-organization(3) dod(6) internet(1) security(5) mechanisms(5) pkix(7) id-mod(0) id-mod-docsign-eku(TBD1) } DEFINITIONS EXPLICIT TAGS ::= BEGIN -- EXPORTS ALL --