draft-ietf-lamps-documentsigning-eku-01.txt   draft-ietf-lamps-documentsigning-eku-02.txt 
LAMPS Working Group T. Ito LAMPS Working Group T. Ito
Internet-Draft SECOM CO., LTD. Internet-Draft SECOM CO., LTD.
Intended status: Standards Track T. Okubo Intended status: Standards Track T. Okubo
Expires: 3 September 2022 DigiCert, Inc. Expires: 8 September 2022 DigiCert, Inc.
S. Turner S. Turner
sn3rd sn3rd
2 March 2022 7 March 2022
General Purpose Extended Key Usage (EKU) for Document Signing X.509 General Purpose Extended Key Usage (EKU) for Document Signing X.509
Certificates Certificates
draft-ietf-lamps-documentsigning-eku-01 draft-ietf-lamps-documentsigning-eku-02
Abstract Abstract
RFC 5280 specifies several extended key usages for X.509 RFC5280 specifies several extended key purpose identifiers
certificates. This document defines a general purpose document (KeyPurposeIds) for X.509 certificates. This document defines a
signing extended key usage for X.509 public key certificates which general purpose document signing KeyPurposeId for inclusion in the
restricts the usage of the certificates for document signing. 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 About This Document
This note is to be removed before publishing as an RFC. This note is to be removed before publishing as an RFC.
Status information for this document may be found at Status information for this document may be found at
https://datatracker.ietf.org/doc/draft-ietf-lamps-documentsigning- https://datatracker.ietf.org/doc/draft-ietf-lamps-documentsigning-
eku/. eku/.
Discussion of this document takes place on the Limited Additional Discussion of this document takes place on the Limited Additional
skipping to change at page 2, line 10 skipping to change at page 2, line 15
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." 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 Notice
Copyright (c) 2022 IETF Trust and the persons identified as the Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/ Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document. license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License. provided without warranty as described in the Revised BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Extended Key usage for DocumentSigning . . . . . . . . . . . 3 3. Extended Key Purpose for Document Signing . . . . . . . . . . 4
3.1. Extended Key Usage Values for Document Signing . . . . . 4 3.1. Including the Extended Key Purpose for Document Signing in
4. Using the Document Signing EKU in a Certificate . . . . . . . 4 Certificates . . . . . . . . . . . . . . . . . . . . . . 4
5. Implications for a Certification Authority . . . . . . . . . 5 4. Using the Extended Key Purpose for Document Signing in a
Certificate . . . . . . . . . . . . . . . . . . . . . . . 5
5. Implications for a Certification Authority . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 7 Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 8
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
[RFC5280] specifies several extended key usages for X.509 [RFC5280] specifies several extended key purpose identifiers
certificates. In addition, several extended key usage had been added (KeyPurposeIds) for X.509 certificates. In addition, several
[RFC7299] as public Object Identifier (OID) under the IANA KeyPurposeIds have been added [RFC7299] under the IANA repository
repository. While usage of any extended key usage is bad practice "SMI Security for PKIX Extended Key Purpose". While usage of the
for publicly trusted certificates, there are no public and general "anyExtendedKeyUsage" KeyPurposeId is bad practice for publicly
extended key usage explicitly assigned for Document Signing trusted certificates, there is no public and general KeyPurposeId
certificates. The current practice is to use id-kp-emailProtection, explicitly assigned for Document Signing. The current practice is to
id-kp-codeSigning or vendor defined OID for general document signing use id-kp-emailProtection, id-kp-codeSigning or a vendor-defined
purposes. KeyPurposeId for general document signing purposes.
In circumstances where code signing and S/MIME certificates are also In circumstances where code signing and S/MIME certificates are also
widely used for document signing, the technical or policy changes widely used for document signing, the technical or policy changes
that are made to code signing and S/MIME certificates may cause that are made to code signing and S/MIME certificates may cause
unexpected behaviors or have an adverse impact such as decreased unexpected behaviors or have an adverse impact such as decreased
cryptographic agility on the document signing ecosystem and vice cryptographic agility on the document signing ecosystem and vice
versa. versa.
There is no issue if the vendor defined OIDs are used in a PKI (or a There is no issue if the vendor-defined KeyPurposeIds are used in a
trust program) governed by the vendor. However, if the OID is used PKI (or a trust program) governed by the vendor. However, if the
outside of the vendor governance, the usage can easily become out of KeyPurposeId is used outside of vendor governance, the usage can
control (e.g. - When the end user encounters vendor defined OIDs, easily become out of control (e.g. - When the end user encounters
they might want to ask that vendor about use of the certificate, vendor-defined KeyPurposeIds, they might want to ask that vendor
however, the vendor may not know about the particular use. - If the about use of the certificate, however, the vendor may not know about
issuance of the cert is not under the control of the OID owner, there the particular use. - If the issuance of the cert is not under the
is no way for the OID owner to know what the impact will be if any control of the KeyPurposeId owner, there is no way for the
change is made to the OID in question, and it would restrict vendor's 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.). choice of OID management. etc.).
Therefore, it is not favorable to use a vendor defined EKU for Therefore, it is not favorable to use a vendor-defined KeyPurposeId
signing a document that is not governed by the vendor. for signing a document that is not governed by the vendor.
This document defines a general Document Signing extended key purpose This document defines a extended key purpose identifier for Document
identifier. Signing.
2. Conventions and Definitions 2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. 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. 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 As described in [RFC5280], If the Extended Key Usage extension is
that are consumed by humans. To be more precise, contents are present, then the certificate MUST only be used for one of the
intended to be shown to human with printable or displayable form by purposes indicated. [RFC5280] also describes that If multiple key
means of services or software, rather than processed by machines. 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 Internet. The extension indicates one or more purposes for which
the certified public key is valid. The EKU extension can be used in the certified public key is valid. The EKU extension can be used in
conjunction with the key usage extension, which indicates how the conjunction with the key usage extension, which indicates the set of
public key in the certificate is used, in a more basic cryptographic basic cryptographic operations for which the certified key may be
way. used.
The EKU extension syntax is repeated here for convenience: The EKU extension syntax is repeated here for convenience:
ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId ExtKeyUsageSyntax ::= SEQUENCE SIZE (1..MAX) OF KeyPurposeId
KeyPurposeId ::= OBJECT IDENTIFIER KeyPurposeId ::= OBJECT IDENTIFIER
This specification defines the KeyPurposeId id-kp-documentSigning. This specification defines the KeyPurposeId id-kp-documentSigning.
Inclusion of this KeyPurposeId in a certificate indicates that the Inclusion of this KeyPurposeId in a certificate indicates that the
use of any Subject names in the certificate is restricted to use by a public key encoded in the certificate has been certified to be used
document signing service or a software (along with any usages allowed for cryptographic operations on contents that are consumed by people.
by other EKU values).
id-kp OBJECT IDENTIFIER ::= id-kp OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1) { iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) 3 } security(5) mechanisms(5) pkix(7) 3 }
id-kp-documentSigning OBJECT IDENTIFIER ::= { id-kp XX } 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 [RFC8358] specifies the conventions for digital signatures on
Internet-Drafts. This is one of the intended use cases for the Internet-Drafts. This is one of the intended use cases for the
general document signing EKU described in this document. [RFC8358] general document signing key purpose described in this document.
uses CMS to digitally sign a wide array of files such as ASCII, PDF, [RFC8358] uses CMS to digitally sign a wide array of files such as
EPUB, HTML etc. Currently, there are no specification regarding EKU ASCII, PDF, EPUB, HTML etc. Currently, there are no specification
for certificates signing those files except those which are defined regarding key purposes for certificates signing those files except
by the software vendor. those which are defined by the software vendor.
The signed contents of Internet-Drafts are primarily intended to be The signed contents of Internet-Drafts are primarily intended to be
consumed by people. To be more precise, contents are 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 shown to a person in a printable or displayable form by means of
services or software, rather than processed by machines. To validate services or software, rather than processed by machines. The digital
the digital signature on the contents that is intended to be consumed signature on the contents is to indicate to the recipient of the
by people, implementations MAY perform the steps below as a contents that the content has not changed since it was signed by the
certificate validation. 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 1. If there are no restrictions set for the relying party and the
relying party software, the certificate is acceptable. relying party software, the certificate is acceptable.
2. If there are restrictions set for the replying party and relying 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 Each restriction on "Excluded KeyPurposeId" or "Permitted
EKU" and handled. KeyPurposeId" is handled as described below.
The procedure is intended to permit or prohibit presence of a This procedure is intended to permit or prohibit presence of a
certain EKU or complete absence of EKUs. It is outside the scope certain KeyPurposeId or complete absence of KeyPurposeIds. It is
of this document, but the relying party can permit or exclude outside the scope of this document, but the relying party can
combinations of EKU. A consideration on prohibiting combination permit or prohibit combinations of KeyPurposeIds. A
of EKUs is described in the security consideration section of consideration on prohibiting combinations of KeyPurposeIds is
this document. described in the Security Considerations section of this
document.
Excluded EKUs procedure: "Excluded EKU" is an EKU which the Excluded KeyPurposeId procedure: "Excluded KeyPurposeId" is a
relying party or the relying party software prohibits. KeyPurposeId which the relying party or the relying party
Examples of "Excluded EKU" are, presence of software prohibits. Examples of "Excluded KeyPurposeId" are,
anyExtendedKeyUsage or complete absence of EKU extension on a presence of the anyExtendedKeyUsage KeyPurposeId or complete
certificate. If an EKU of the certificate meets the absence of the EKU extension in a certificate. If a
conditions set by the "Excluded EKU" restriction, the relying KeyPurposeId of the certificate meets the conditions set by
party or the relying party software rejects the certificate. 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 Permitted KeyPurposeId procedure:
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 : "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 formats, the software may choose to make the excluded and permitted
decisions separately in accordance with the format it is handling decisions separately in accordance with the format it is handling
(e.g. text, pdf, etc). (e.g. text, pdf, etc).
5. Implications for a Certification Authority 5. Implications for a Certification Authority
The procedures and practices employed by a certification authority The procedures and practices employed by a certification authority
MUST ensure that the correct values for the EKU extension are MUST ensure that the correct values for the EKU extension are
inserted in each certificate that is issued. Unless certificates are inserted in each certificate that is issued. Unless certificates are
governed by a vendor specific PKI (or trust program), certificates governed by a vendor specific PKI (or trust program), certificates
that indicate usage for document signing MAY include the id-kp- that indicate usage for document signing MAY include the id-kp-
documentSigning EKU extension. This does not encompass the mandatory documentSigning KeyPurposeId. The inclusion of the id-kp-
usage of the id-kp-documentSigning EKU in conjunction with the vendor documentSigning KeyPurposeId does not preclude the inclusion of other
specific EKU. However, this does not restrict the CA from including KeyPurposeIds.
multiple EKUs related to document signing.
6. Security Considerations 6. Security Considerations
The usage of id-kp-documentSigning EKU intends to prevent id-kp- The usage of id-kp-documentSigning KeyPurposeId is to provide an
emailProtection from being used for purposes other than email and id- alternative to id-kp-emailProtection being used for non-email
kp-codeSigning used to sign objects other than binary codes. This purposes and id-kp-codeSigning being used to sign objects other than
EKU does not introduce new security risks but instead reduces binary code. This extended key purpose does not introduce new
existing security risks by providing means to separate other EKUs security risks but instead reduces existing security risks by
used for communication protocols namely, TLS or S/MIME etc. in order providing means to separate other extended key purposes used for
to minimize the risk of cross protocol attacks. 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 To reduce the risk of specific cross-protocol attacks, the relying
party or relying party software may additionaly prohibit use of party or relying party software may additionally prohibit use of
specific combination of EKUs. specific combinations of KeyPurposeIds.
While a specific protocol or signing scheme may choose to come up While a specific protocol or signing scheme may choose to come up
with their own EKU, some may not have significant motive or resource with their own KeyPurposeIds, some may not have significant motive or
to set up and manage thier own EKU. This general document signing resources to set up and manage their own KeyPurposeIds. This general
EKU may be used as a stop gap for those that intend to set up their document signing KeyPurposeId may be used as a stop-gap for those
own EKU or those who do not intend to set up an EKU but still would that intend to define their own KeyPurposeId or those who do not
like to distinguish from other usage. 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. introduce any new security or privacy concerns.
7. IANA Considerations 7. IANA Considerations
This document requests that IANA make two assignments. One for the This document requests that IANA make two assignments. One
id-kp-documentSigning object identifier (OID), as defined in assignment is for the addition of the id-kp-documentSigning object
Section 3.1, for the EKU from the "SMI Security for PKIX Extended Key identifier (OID), as defined in Section 3.1, to the "SMI Security for
Purpose" (1.3.6.1.5.5.7.3) registry. Another for the id-mod-docsign- PKIX Extended Key Purpose" (1.3.6.1.5.5.7.3) registry. The other
eku, as defined in Appendix A, for the ASN.1 module [X.680] from the assignment is for the addition of the id-mod-docsign-eku ASN.1 module
in the "SMI Security for PKIX Module Identifier" (1.3.6.1.5.5.7.0) [X.680] object identifier (OID), as defined in Appendix A, to the
registry. No further action is necessary by IANA. "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. References
8.1. Normative References 8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>. <https://www.rfc-editor.org/rfc/rfc2119>.
skipping to change at page 7, line 32 skipping to change at page 8, line 16
Working Group", RFC 7299, DOI 10.17487/RFC7299, July 2014, Working Group", RFC 7299, DOI 10.17487/RFC7299, July 2014,
<https://www.rfc-editor.org/rfc/rfc7299>. <https://www.rfc-editor.org/rfc/rfc7299>.
[RFC8358] Housley, R., "Update to Digital Signatures on Internet- [RFC8358] Housley, R., "Update to Digital Signatures on Internet-
Draft Documents", RFC 8358, DOI 10.17487/RFC8358, March Draft Documents", RFC 8358, DOI 10.17487/RFC8358, March
2018, <https://www.rfc-editor.org/rfc/rfc8358>. 2018, <https://www.rfc-editor.org/rfc/rfc8358>.
Appendix A. ASN.1 Module Appendix A. ASN.1 Module
The following ASN.1 module provides the complete definition of the 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) DocSignEKU { iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0) security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-docsign-eku(TBD1) } id-mod-docsign-eku(TBD1) }
DEFINITIONS EXPLICIT TAGS ::= DEFINITIONS EXPLICIT TAGS ::=
BEGIN BEGIN
-- EXPORTS ALL -- -- EXPORTS ALL --
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