INTERNET-DRAFT Stefan Santesson (3xA Security)
Intended Status: Proposed Standard Russ Housley (Vigil Security)
Updates: 3709 (once approved) Siddharth Bajaj (VeriSign)
Expires: June 7, 2010 Leonard Rosenthol (Adobe)
December 4, 2009
Internet X.509 Public Key Infrastructure - Certificate Image
<draft-ietf-pkix-certimage-04>
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/1id-abstracts.html
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
Copyright and License Notice
Copyright (c) 2009 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
(http://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 Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the BSD License.
Santesson et all. Expires June 7, 2010 [Page 1]
INTERNET DRAFT Certificate Image December 4, 2009
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].
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
2 Certificate Image . . . . . . . . . . . . . . . . . . . . . . . 5
3 LogotypeImageInfo . . . . . . . . . . . . . . . . . . . . . . . . 5
4 Certificate Image Formats . . . . . . . . . . . . . . . . . . . 6
4.1 PDF . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2 SVG . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2 PNG . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
5 Embedded images . . . . . . . . . . . . . . . . . . . . . . . . 7
6 Security Considerations . . . . . . . . . . . . . . . . . . . . 9
7 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 9
8 References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1 Normative References . . . . . . . . . . . . . . . . . . . 10
8.2 Informative References . . . . . . . . . . . . . . . . . . 10
Appendix A - "data" URL example . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
Santesson et all. Expires June 7, 2010 [Page 2]
INTERNET DRAFT Certificate Image December 4, 2009
1. Introduction
This standard specifies how to bind a Certificate Image, providing a
visual representation of a certificate, to that [RFC5280] certificate
using the Logotype extension defined in [RFC3709], specifying the
Certificate Image as a new otherLogos type.
The purpose of the Certificate image is to aid human interpretation
of a certificate by providing meaningful visual information to the
user interface.
Typical situations when a human needs to examine the visual
representation of a certificate are:
- A person establishes secured channel with an authenticated
service. The person needs to determine the identity of the service
based on the authenticated credentials.
- A person validates the signature on critical information, such
as signed executable code, and needs to determine the identity of
the signer based on the signer's certificate.
- A person is required to select an appropriate certificate to be
used when authenticating to a service or Identity Management
infrastructure. The person needs to see the available certificates
in order to distinguish between them in the selection process.
Display of a certificate information to humans is challenging due to
lack of well defined semantics for critical identity attributes.
Unless the application has out of band knowledge about a particular
certificate, the application will not know the exact nature of the
data stored in common identification attributes such as serialNumber,
organizationName, country, etc. Consequently the application can
display the actual data, but faces problem to label that data in the
UI, informing the human about the exact nature (semantics) of that
data. It is also challenging for the application to determine which
identification attribute that are important to display and how to
organize them in a logical order.
RFC 3709 [RFC3709] defines a certificate extension for binding images
to a certificate, such as community logo and issuer logo, enhancing
display of certificate information. The syntax is extensible and
allows inclusion of new image types using the other-Logos structure.
This standard defines how to include a complete certificate image
using the extensibility mechanism of RFC 3709.
Santesson et all. Expires June 7, 2010 [Page 3]
INTERNET DRAFT Certificate Image December 4, 2009
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].
Santesson et all. Expires June 7, 2010 [Page 4]
INTERNET DRAFT Certificate Image December 4, 2009
2 Certificate Image
This section defines the Certificate Image as a new otherLogos type
according to 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:
Santesson et all. Expires June 7, 2010 [Page 5]
INTERNET DRAFT Certificate Image December 4, 2009
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. When non-zero values are present and these values differ
from corresponding size values in the referenced image file, then the
referenced image SHOULD be scaled to fit within the size parameters
of LogotypeImageInfo, while keeping x and y ratio intact.
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 LogotypeDetails:
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]
The following MIME media type defined in Appendix M of [SVGT1.2] MUST
be used as mediaType in LogotypeDetails for SVG images:
image/svg+xml
Santesson et all. Expires June 7, 2010 [Page 6]
INTERNET DRAFT Certificate Image December 4, 2009
The SVG image file MUST NOT incorporate any external image data by
reference to an external SVG document, or by reference to an external
media source other than SVG. Doing so would incorporate image data
that is not covered by the logotypeHash value of the image.
Certificate using applications MUST reject any image that violates
this rule.
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
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.
4.2 PNG
If a certificate image is provided as a bit mapped image, the PNG
[ISO15948] format SHOULD be used.
PNG images are identified by the following mediaType in
LogotypeDetails:
image/png
5 Embedded images
The certificate image otherLogos type MAY be stored within the
logotype extension using the "data" URL scheme defined in RFC 2397
[RFC2397] if the logotype image is provided through direct
addressing, i.e. the image is referenced using the LogotypeDetails
structure.
The syntax of Logotype details defined in RFC 3709 is included here
for convenience:
LogotypeDetails ::= SEQUENCE {
mediaType IA5String, -- MIME media type name and optional
-- parameters
logotypeHash SEQUENCE SIZE (1..MAX) OF HashAlgAndValue,
logotypeURI SEQUENCE SIZE (1..MAX) OF IA5String }
Santesson et all. Expires June 7, 2010 [Page 7]
INTERNET DRAFT Certificate Image December 4, 2009
The syntax of the "data" URL Scheme defined in RFC 2397 is included
here for convenience:
dataurl := "data:" [ mediatype ] [ ";base64" ] "," data
mediatype := [ type "/" subtype ] *( ";" parameter ) data
:= *urlchar parameter := attribute "=" value
When including the image data in the logotype extension using the
"data" URL scheme the following conventions apply.
- the value of mediaType in LogotypeDetails MUST be identical to
the mediatype value in the "data" URL.
- The hash of the image MUST be included in logotypeHash and MUST
be calculated over the same data as it would have been, had the
image been referenced through a link to an external resource.
Note: As the "data" URL scheme is processed as a data source rather
than as a URL, the image data is typically not limited by any
URL length limit setting that otherwise apply to URLs in
general.
Note: Implementations need to be cautious about the the size of
images included in a certificate in order to ensure that the
size of the certificate does not prevent the certificate to be
used as intended.
Santesson et all. Expires June 7, 2010 [Page 8]
INTERNET DRAFT Certificate Image December 4, 2009
6 Security Considerations
This document is based on and inherits all security considerations
from RFC 3709 [RFC3709].
Referenced image files are hashed in order to bind the image to the
signature of the certificate. Some image types, such as SVG allow
part of the image to be collected from external source by
incorporating a reference to an external image file. If this feature
were used within a certificate image file, the hash of the image file
would only cover the URI reference to the external image file, but
not the referenced image data. To ensure that the hash of the
certificate image covers the whole image, implementations of this
standard MUST reject images that incorporate parts of the image by
reference to external image files.
CAs issuing certificate with embedded certificate images should be
cautious when accepting graphics from the certificate requestor for
inclusion in the certificate if the hash algorithm used to sign the
certificate is vulnerable to collision attacks. In such case the
accepted image may contain data that could help an attacker to obtain
colliding certificates with identical certificate signatures.
7 IANA Considerations
This document requires no actions from IANA.
Santesson et all. Expires June 7, 2010 [Page 9]
INTERNET DRAFT Certificate Image December 4, 2009
8 References
8.1 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
[RFC2397] L. Masinter, 'The "data" URL scheme' RFC 2397, August 1998
[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
[ISO15948] ISO/IEC 15948:2004, "Information technology - Computer
graphics and image processing -- Portable Network Graphics
(PNG): Functional specification", 2004
[SVGT1.2] W3C Recommendation, "Scalable Vector Graphics (SVG) Tiny
1.2 Specification", December 2008
8.2 Informative References
[RFC3778] E. Taft, J. Pravetz, S. Zilles, L. Masinter "The
application/pdf Media Type", RFC 3778, May 2004
Santesson et all. Expires June 7, 2010 [Page 10]
INTERNET DRAFT Certificate Image December 4, 2009
Appendix A - "data" URL example
The following example stores an embedded SVG image using the "data"
URL scheme.
data:image/svg+xml;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcm
cvMjAwMC9zdmciIHdpZHRoPSI0MDEiIGhlaWdodD0iODAxIiB2ZXJzaW9uPSIxLj
AiPg0KPHBhdGggc3R5bGU9ImZpbGw6bm9uZTsgc3Ryb2tlOiMwMDAwMDA7IHN0cm
9rZS13aWR0aDoxMDsiDQpkPSJNNDUsNWE0MCw0MCAwIDAgMSAtNDAsNDB2MzEwYT
QwLDQwIDAgMCAxIDQwLDQwaDMxMGE0MCw0MCAwIDAgMSA0MCwtNDB2LTMxMGE0MC
w0MCAwIDAgMSAtNDAsLTQweiIvPg0KPC9zdmc+DQo=
This example stores the following SVG image:
<svg xmlns="http://www.w3.org/2000/svg" width="401" height="801"
version="1.0">
<path style="fill:none; stroke:#000000; stroke-width:10;"
d="M45,5a40,40 0 0 1 -40,40v310a40,40 0 0 1 40,40h310a40,
40 0 0 1 40,-40v-310a40,40 0 0 1 -40,-40z"/>
</svg>
Santesson et all. Expires June 7, 2010 [Page 11]
INTERNET DRAFT Certificate Image December 4, 2009
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
Santesson et all. Expires June 7, 2010 [Page 12]
