draft-ietf-lamps-documentsigning-eku-00.txt   draft-ietf-lamps-documentsigning-eku-01.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: 17 July 2022 DigiCert, Inc. Expires: 3 September 2022 DigiCert, Inc.
S. Turner S. Turner
sn3rd sn3rd
13 January 2022 2 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-00 draft-ietf-lamps-documentsigning-eku-01
Abstract Abstract
[RFC5280] specifies several extended key usages for X.509 RFC 5280 specifies several extended key usages for X.509
certificates. This document defines a general purpose document certificates. This document defines a general purpose document
signing extended key usage for X.509 public key certificates which signing extended key usage for X.509 public key certificates which
restricts the usage of the certificates for document signing. restricts the usage of the certificates for document signing.
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-
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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 17 July 2022. This Internet-Draft will expire on 3 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
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3 2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
3. Extended Key usage for DocumentSigning . . . . . . . . . . . 3 3. Extended Key usage for DocumentSigning . . . . . . . . . . . 3
3.1. Extended Key Usage Values for Document Signing . . . . . 4 3.1. Extended Key Usage Values for Document Signing . . . . . 4
4. Using the Document Signing EKU in a Certificate . . . . . . . 4 4. Using the Document Signing EKU in a Certificate . . . . . . . 4
5. Implications for a Certification Authority . . . . . . . . . 5 5. Implications for a Certification Authority . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Normative References . . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 7 Appendix A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . 7
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 7 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 usages for X.509
certificates. In addition, several extended key usage had been certificates. In addition, several extended key usage had been added
added[RFC7299] as public OID under the IANA repository. While usage [RFC7299] as public Object Identifier (OID) under the IANA
of any extended key usage is bad practice for publicly trusted repository. While usage of any extended key usage is bad practice
certificates, there are no public and general extended key usage for publicly trusted certificates, there are no public and general
explicitly assigned for Document Signing certificates. The current extended key usage explicitly assigned for Document Signing
practice is to use id-kp-emailProtection, id-kp-codeSigning or vendor certificates. The current practice is to use id-kp-emailProtection,
defined Object ID for general document signing purposes. id-kp-codeSigning or vendor defined OID 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 OIDs are used in a PKI (or a
trust program) governed by the vendor. However, if the OID is used trust program) governed by the vendor. However, if the OID is used
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they might want to ask that vendor about use of the certificate, they might want to ask that vendor about use of the certificate,
however, the vendor may not know about the particular use. - If the 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 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 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 change is made to the OID 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 EKU for
signing a document that is not governed by the vendor. signing a document that is not governed by the vendor.
This document defines a general Document Signing extended key usage. This document defines a general Document Signing extended key purpose
identifier.
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 usage for DocumentSigning
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[RFC5280] specifies the EKU X.509 certificate extension for use in [RFC5280] specifies the EKU X.509 certificate extension for use in
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 how the
public key in the certificate is used, in a more basic cryptographic public key in the certificate is used, in a more basic cryptographic
way. way.
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 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 document signing service or a software (along with any usages allowed
by other EKU values). 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 Document Signing EKU 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 EKU described in this document. [RFC8358]
uses CMS to digitally sign a wide array of files such as ASCII, PDF, uses CMS to digitally sign a wide array of files such as ASCII, PDF,
EPUB, HTML etc. Currently, there are no specification regarding EKU EPUB, HTML etc. Currently, there are no specification regarding EKU
for certificates signing those files except those which are defined for certificates signing those files except those which are defined
by the software vendor. 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 human. To be more precise, contents are intended to be consumed by people. To be more precise, contents are intended to be
shown to human 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. To validate
the digital signature which is signed to contents intended to be the digital signature on the contents that is intended to be consumed
consumed by human, implementations MAY perform the steps below as a by people, implementations MAY perform the steps below as a
certificate validation: certificate validation.
The implementation MAY examine the Extended Key Usage value(s): The implementation MAY examine the Extended Key Usage value(s):
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, proceed as following.
Each Restriction on the EKUs can be "Excluded EKU" or "Permitted EKU" Each Restriction on the EKUs can be "Excluded EKU" or "Permitted
and handled. EKU" and handled.
The procedure is intended to permit or prohibit presence of a certain The procedure is intended to permit or prohibit presence of a
EKU or complete absence of EKUs. It is outside the scope of this certain EKU or complete absence of EKUs. It is outside the scope
document, but the relying party can permit or prohibit conbinations of this document, but the relying party can permit or exclude
of EKU. A consideration on prohibiting combination of EKUs is combinations of EKU. A consideration on prohibiting combination
described in the security consideration section of this document. of EKUs is described in the security consideration section of
this document.
2.1. Excluded EKUs procedure "Excluded EKU" is an EKU which the Excluded EKUs procedure: "Excluded EKU" is an EKU which the
relying party or the relying party software prohibits. Examples of relying party or the relying party software prohibits.
"Excluded EKU" are, presence of anyEKU or complete absence of EKU Examples of "Excluded EKU" are, presence of
extension on a certificate. If an EKU of the certificate meets the anyExtendedKeyUsage or complete absence of EKU extension on a
conditions set by the "Excluded EKU" restriction, the relying party certificate. If an EKU of the certificate meets the
or the relying party software rejects the certificate. conditions set by the "Excluded EKU" restriction, the relying
party or the relying party software rejects the certificate.
2.2. Permitted EKU procedure "Permitted EKU" is an EKU which the Permitted EKU procedure: "Permitted EKU" is an EKU which the
relying party or the relying party software accepts. Examples of relying party or the relying party software accepts. Examples
"Permitted EKU" are, presence of this general document signing EKU of "Permitted EKU" are, presence of this general document
and/or protocol specific document signing-type EKUs. If an EKU of signing EKU and/or protocol specific document signing-type
the certificate meets the condition set by a "Permitted EKU" EKUs. If an EKU of the certificate meets the condition set by
restriction, the certificate is acceptable. Otherwise, relying party a "Permitted EKU" restriction, the certificate is acceptable.
or the relying party software rejects the certificate. Otherwise, relying party or the relying party software rejects
the certificate.
When a single software has capability to process various data When a single software has 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
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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 EKU extension. This does not encompass the mandatory
usage of the id-kp-documentSigning EKU in conjunction with the vendor usage of the id-kp-documentSigning EKU in conjunction with the vendor
specific EKU. However, this does not restrict the CA from including specific EKU. However, this does not restrict the CA from including
multiple EKUs related to document signing. 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 EKU intends to prevent id-kp-
emailProtection from being used for none-email purposes and id-kp- emailProtection from being used for purposes other than email and id-
codeSigning used to sign objects other than binary codes. This EKU kp-codeSigning used to sign objects other than binary codes. This
does not introduce new security risks but instead reduces existing EKU does not introduce new security risks but instead reduces
security risks by providing means to separate other EKUs used for existing security risks by providing means to separate other EKUs
communication protocols namely, TLS or S/MIME etc. in order to used for communication protocols namely, TLS or S/MIME etc. in order
minimize the risk of cross protocol attacks. 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 additionaly prohibit use of
specific combination of EKUs. specific combination of EKUs.
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 EKU, some may not have significant motive or resource
to set up and manage thier own EKU. This general document signing 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 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 own EKU or those who do not intend to set up an EKU but still would
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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 for the
id-kp-documentSigning object identifier (OID), as defined in id-kp-documentSigning object identifier (OID), as defined in
Section 3.1, for the EKU from the "SMI Security for PKIX Extended Key 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- 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 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) in the "SMI Security for PKIX Module Identifier" (1.3.6.1.5.5.7.0)
registry. No further action is necessary by IANA. registry. No further action is necessary by IANA.
8. Normative References 8. 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>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008, (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/rfc/rfc5280>. <https://www.rfc-editor.org/rfc/rfc5280>.
[RFC7299] Housley, R., "Object Identifier Registry for the PKIX
Working Group", RFC 7299, DOI 10.17487/RFC7299, July 2014,
<https://www.rfc-editor.org/rfc/rfc7299>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>. May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8358] Housley, R., "Update to Digital Signatures on Internet-
Draft Documents", RFC 8358, DOI 10.17487/RFC8358, March
2018, <https://www.rfc-editor.org/rfc/rfc8358>.
[X.680] ITU-T, "Information technology - Abstract Syntax Notation [X.680] ITU-T, "Information technology - Abstract Syntax Notation
One (ASN.1): Specification of basic notation", ISO/ One (ASN.1): Specification of basic notation", ISO/
IEC 8824-1:2015, November 2015. IEC 8824-1:2015, November 2015.
8.2. Informative References
[RFC7299] Housley, R., "Object Identifier Registry for the PKIX
Working Group", RFC 7299, DOI 10.17487/RFC7299, July 2014,
<https://www.rfc-editor.org/rfc/rfc7299>.
[RFC8358] Housley, R., "Update to Digital Signatures on Internet-
Draft Documents", RFC 8358, DOI 10.17487/RFC8358, March
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 EKU.
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) id-mod-docsign-eku(TBD1) } security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-docsign-eku(TBD1) }
DEFINITIONS EXPLICIT TAGS ::= DEFINITIONS EXPLICIT TAGS ::=
BEGIN BEGIN
-- EXPORTS ALL -- -- EXPORTS ALL --
-- IMPORTS NOTHING -- -- IMPORTS NOTHING --
-- OID Arc -- -- OID Arc --
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) kp(3) } security(5) mechanisms(5) pkix(7) kp(3) }
-- Document Signing Extended Key Usage -- -- Document Signing Extended Key Usage --
id-kp-documentSigning OBJECT IDENTIFIER ::= { id-kp TBD2 } id-kp-documentSigning OBJECT IDENTIFIER ::= { id-kp TBD2 }
END END
Acknowledgments Acknowledgments
We would like to thank Russ Housley for verifying the ASN.1 module. We would like to thank Russ Housley for verifying the ASN.1 module.
Authors' Addresses Authors' Addresses
Tadahiko Ito Tadahiko Ito
SECOM CO., LTD. SECOM CO., LTD.
Email: tadahiko.ito.public@gmail.com Email: tadahiko.ito.public@gmail.com
Tomofumi Okubo Tomofumi Okubo
DigiCert, Inc. DigiCert, Inc.
Email: tomofumi.okubo+ietf@gmail.com Email: tomofumi.okubo+ietf@gmail.com
Sean Turner Sean Turner
sn3rd sn3rd
Email: sean@sn3rd.com Email: sean@sn3rd.com
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