INTERNET-DRAFT Stefan Santesson (3xA Security)
Intended Status: Proposed Standard Russ Housley (Vigil Security)
Expires October 2009 Siddharth Bajaj (VeriSign)
Leonard Rosenthol (Adobe)
April 2009
Internet X.509 Public Key Infrastructure:
Certificate Image
<draft-santesson-pkix-certimage-00.txt>
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Abstract
This document specifies a method to bind a visual representation of a
certificate in the form of a certificate image to a [RFC5280] public
key certificate by defining a new otherLogos image type according to
[RFC3709].
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1. Introduction
This standard specifies a Certificate Image that may be signed and
referenced by a certificate as a visual representation of that
certificate to humans.
This standard makes use of the certificate Logotype extension defined
in [RFC3709] and specifies the Certificate Image as a new otherLogos
type.
The purpose of the Certificate image is to enable a meaningful
informational and visual experience for a human user in situations
where a Graphical User Interface (GUI) of an application needs to
show a certificate to a user.
Typical situations when an application may want to show a certificate
to a human are:
- A person establishes contact with an authenticated entity, such
as a commercial web site or government service. The person wants
to see the authenticated identity of the service provider.
- A person consumes signed information such as a signed e-mail, a
signed document, or a signed contract. The person wants to see the
authenticated identity of the signer.
- A person is requested to authenticate to a service, or to sign
some information, and is requested to select an appropriate
certificate for the purpose. The person needs to see the available
certificates to understand what type of personal data they contain
and for what purpose they are intended.
Unless an application recognize the certificate type and has some
predefined display logic for the certificate it displays, it will
extremely hard for the application to provide meaningful information
about the certificate to humans. Some important reasons are:
- Many common attributes are not specific enough to identify their
information content. For example, the country attribute includes a
country identifier but does not define whether this represents a
country of residence, country of citizenship or something else.
The attribute SRIALNUMBER may contain any type of identifier such
as social security number, membership number or driver's license
number.
- Some name forms are suitable for human consumption and others
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for machine processing. It is extremely hard for a certificate
viewer to know exactly which name types that makes sense to a
human and how to label this information in the user interface.
RFC 3709 specifies how to bind images to a certificate, such as
community logo, issuer logo. RFC 3709 is also extensible and allows
inclusion of new image types using the other-Logos structure. This
extensibility is used in this standard to allow inclusion of a
complete certificate display image.
1.1 Outstanding issues
This section lists issues that should be resolved before publication
of the standard. When these issues are resolved, this section will be
deleted.
Issue: embedded images
RFC 3709 specifies how to reference images through a URL, but does
not specify any means to store referenced images in the
certificate itself. It will remain outside of the scope of this
specification to define any means to embed certificate images in
the certificate. However, a complementing standard could be
defined, specifying the syntax of URL references pointing to
images stored in a separate local extension embedded in the
certificate.
Issue: Image formats
This draft recommends that certificate images are stored in a
scalable format and specifically defines how to include images in
PDF/A [ISO19005] and SVG Tiny [SVGT1.2] format. A third popular
scalable vector graphic format VML (Vector graphic Markup
Language) is not a public standard. Nevertheless, some
implementers have chosen to support VML instead of SVG. It might
therefore be useful to specify how to reference a VML formatted
certificate image in an informational annex.
1.2 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2 Certificate Image
This section defines the Certificate Image as a new otherLogos type
as defined in section 4.1 of [RFC3709]
The Certificate Image otherLogos type is identified by the Object
Identifier (OID) id-logo-certimage.
id-pkix OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) }
id-logo OBJECT IDENTIFIER ::= { id-pkix 20 }
id-logo-certimage OBJECT IDENTIFIER ::= { id-logo TBD }
//* Note: TBD is to be replaced by a real OID before publication of
this draft *//
When present the Certificate Image MUST represent a complete visual
representation of the certificate. This means that the display of
this certificate image represents all information about the
certificate that the issuer subjectively defines as relevant to show
a typical human user within the typical intended use of the
certificate, giving adequate information about at least the following
three aspects of the certificate:
- Certificate Context
- Certificate Issuer
- Certificate Subject
Certificate Context information is visual marks and/or textual
information which helps the typical user to understand the typical
usage and/or purpose of the certificate
It is up to the issuer to decide what information in the form of text
and graphical symbols and elements, which represents a complete
visual representation of the certificate.
Applications providing a Graphical User Interface (GUI) to the
certificate user MAY present a Certificate Image according to this
standard in any given application interface, as the only visual
representation of a certificate.
3 LogotypeImageInfo
The optional LogotypeImageInfo structure is defined in [RFC3709] and
is included here for convenience:
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LogotypeImageInfo ::= SEQUENCE {
type [0] LogotypeImageType DEFAULT color,
fileSize INTEGER, -- In octets
xSize INTEGER, -- Horizontal size in pixels
ySize INTEGER, -- Vertical size in pixels
resolution LogotypeImageResolution OPTIONAL,
language [4] IA5String OPTIONAL } -- RFC 3066 Language Tag
When the optional LogotypeImageInfo is included with a certificate
image, the parameters shall be used with the following semantics and
restrictions.
xSize and ySize represents recommended display size for the image.
When a value of 0 (zero) is present, no recommended display size
specified.
Resolution MUST NOT be specified.
4 Certificate Image Formats
4.1 PDF
A Certificate Image MAY be provided in the form of a Portable
Document Format (PDF) document according to [ISO32000] following the
conventions defined in this section. When a certificate image is
formatted as a PDF document, it MUST also be formatted according to
the profile PDF/A [ISO19005].
When including a PDF document as Certificate Image, the following
MIME media type as specified in [RFC3778] MUST be used as mediaType
in Logotype Details:
application/pdf
4.2 SVG
A Certificate Image MAY be provided in the form of a Scalable Vector
Graphic (SVG) image, which MUST follow the SVG Tiny profile [SVGT1.2]
When including a PDF document as Certificate Image, the following
MIME media type defined in Appendix M of [SVGT1.2] MUST be used as
mediaType in Logotype Details:
image/svg+xml
The XML structure in the SVG file MUST use <LF> (linefeed 0x0A) as
end-of-line (EOL) character when calculating the hash over the SVG
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file. The referenced SVG file may be provided in compressed form, for
example as SVG.GZ or SVGZ. It is outside the scope of this
specification to specify any such compression algorithm. However,
after decompression the EOL characters of the SVG file MUST be
normalized according to this section before computing the hash of the
SVG file.
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5 Security Considerations
The security considerations of [RFC3709] apply also to this standard.
This standard makes it possible for a CA to issue a certificate with
a Certificate Image that is in conflict with other data included in
the certificate without the relying party application being able to
detect the delta.
A relying party application MUST decide that the certificate is valid
and trustworthy enough to provide a Certificate Image to the local
GUI before using it.
6 IANA Considerations
IANA considerations
7 References
7.1 Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation
List (CRL) Profile", RFC 5280, May 2008.
[RFC3709] S. Santesson, R. Housley, T. Freeman, "Internet X.509
Public Key Infrastructure Logotypes in X.509
Certificates", RFC 3709, February 2004.
[ISO32000] ISO 32000-1:2008, "Document management - Portable
document format" -- Part 1: PDF 1.7, April 2008.
[ISO19005] ISO 19005-1:2005, "Document Management - Electronic
document file format for long term preservation -
Part 1: Use of PDF 1.4 (PDF/A-1)", 2005.
[SVGT1.2] W3C Recommendation, "Scalable Vector Graphics (SVG)
Tiny 1.2 Specification", December 2008.
7.2 Informative References
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[RFC3778] E. Taft, J. Pravetz, S. Zilles, L. Masinter "The
application/pdf Media Type", RFC 3778, May 2004
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Authors' Addresses
Stefan Santesson
3xA Security (AAA-sec.com)
Bjornstorp 744
247 98 Genarp
Sweden
EMail: sts@aaa-sec.com
Russell Housley
Vigil Security, LLC
918 Spring Knoll Drive
Herndon, VA 20170
USA
EMail: housley@vigilsec.com
Siddharth Bajaj
VeriSign
685 East Middlefield rd
Mountain view, CA 94043
USA
Email: sbajaj@verisign.com
Leonard Rosenthol
3533 Sunset Way
Huntingdon Valley, PA 19006
USA
Email: leonardr@adobe.com
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Expires October 2009
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