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Network Working Group S. Santesson
Request for Comments: 3709 Microsoft
Category: Standards Track R. Housley
Vigil Security
T. Freeman
Microsoft
February 2004
Internet X.509 Public Key Infrastructure:
Logotypes in X.509 Certificates
Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document specifies a certificate extension for including
logotypes in public key certificates and attribute certificates.
Santesson, et al. Standards Track [Page 1]
RFC 3709 Logotypes in X.509 Certificates February 2004
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Certificate-based Identification . . . . . . . . . . . . 3
1.2. Selection of Certificates. . . . . . . . . . . . . . . . 4
1.3. Combination of Verification Techniques . . . . . . . . . 5
1.4. Terminology. . . . . . . . . . . . . . . . . . . . . . . 6
2. Different types of logotypes in Certificates . . . . . . . . . 6
3. Logotype Data. . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Logotype Extension . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Extension Format . . . . . . . . . . . . . . . . . . . . 7
4.2. Other Logotypes. . . . . . . . . . . . . . . . . . . . . 11
5. Type of Certificates . . . . . . . . . . . . . . . . . . . . . 12
6. Use in Clients . . . . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations. . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . 15
9. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . 16
10.2. Informative References . . . . . . . . . . . . . . . . . 16
A. ASN.1 Module . . . . . . . . . . . . . . . . . . . . . . . . . 17
B. Example Extension. . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
This specification supplements RFC 3280 [PKIX-1], which profiles
X.509 [X.509] certificates and certificate revocation lists (CRLs)
for use in the Internet.
The basic function of a certificate is to bind a public key to the
identity of an entity (the subject). From a strictly technical
viewpoint, this goal could be achieved by signing the identity of the
subject together with its public key. However, the art of Public-Key
Infrastructure (PKI) has developed certificates far beyond this
functionality in order to meet the needs of modern global networks
and heterogeneous IT structures.
Certificate users must be able to determine certificate policies,
appropriate key usage, assurance level, and name form constraints.
Before a relying party can make an informed decision whether a
particular certificate is trustworthy and relevant for its intended
usage, a certificate may be examined from several different
perspectives.
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RFC 3709 Logotypes in X.509 Certificates February 2004
Systematic processing is necessary to determine whether a particular
certificate meets the predefined prerequisites for an intended usage.
Much of the information contained in certificates is appropriate and
effective for machine processing; however, this information is not
suitable for a corresponding human trust and recognition process.
Humans prefer to structure information into categories and symbols.
Most humans associate complex structures of reality with easily
recognizable logotypes and marks. Humans tend to trust things that
they recognize from previous experiences. Humans may examine
information to confirm their initial reaction. Very few consumers
actually read all terms and conditions they agree to in accepting a
service, rather they commonly act on trust derived from previous
experience and recognition.
A big part of this process is branding. Service providers and
product vendors invest a lot of money and resources into creating a
strong relation between positive user experiences and easily
recognizable trademarks, servicemarks, and logotypes.
Branding is also pervasive in identification instruments, including
identification cards, passports, driver's licenses, credit cards,
gasoline cards, and loyalty cards. Identification instruments are
intended to identify the holder as a particular person or as a member
of the community. The community may represent the subscribers of a
service or any other group. Identification instruments, in physical
form, commonly use logotypes and symbols, solely to enhance human
recognition and trust in the identification instrument itself. They
may also include a registered trademark to allow legal recourse for
unauthorized duplication.
Since certificates play an equivalent role in electronic exchanges,
we examine the inclusion of logotypes in certificates. We consider
certificate-based identification and certificate selection.
1.1. Certificate-based Identification
The need for human recognition depends on the manner in which
certificates are used and whether certificates need to be visible to
human users. If certificates are to be used in open environments and
in applications that bring the user in conscious contact with the
result of a certificate-based identification process, then human
recognition is highly relevant, and may be a necessity.
Examples of such applications include:
- Web server identification where a user identifies the owner of
the web site.
Santesson, et al. Standards Track [Page 3]
RFC 3709 Logotypes in X.509 Certificates February 2004
- Peer e-mail exchange in B2B, B2C, and private communications.
- Exchange of medical records, and system for medical
prescriptions.
- Unstructured e-business applications (i.e., non-EDI
applications).
- Wireless client authenticating to a service provider.
Most applications provide the human user with an opportunity to view
the results of a successful certificate-based identification process.
When the user takes the steps necessary to view these results, the
user is presented with a view of a certificate. This solution has
two major problems. First, the function to view a certificate is
often rather hard to find for a non-technical user. Second, the
presentation of the certificate is too technical and is not user
friendly. It contains no graphic symbols or logotypes to enhance
human recognition.
Many investigations have shown that users of today's applications do
not take the steps necessary to view certificates. This could be due
to poor user interfaces. Further, many applications are structured
to hide certificates from users. The application designers do not
want to expose certificates to users at all.
1.2. Selection of Certificates
One situation where software applications must expose human users to
certificates is when the user must select a single certificate from a
portfolio of certificates. In some cases, the software application
can use information within the certificates to filter the list for
suitability; however, the user must be queried if more than one
certificate is suitable. The human user must select one of them.
This situation is comparable to a person selecting a suitable plastic
card from his wallet. In this situation, substantial assistance is
provided by card color, location, and branding.
In order to provide similar support for certificate selection, the
users need tools to easily recognize and distinguish certificates.
Introduction of logotypes into certificates provides the necessary
graphic.
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RFC 3709 Logotypes in X.509 Certificates February 2004
1.3. Combination of Verification Techniques
The use of logotypes will, in many cases, affect the users decision
to trust and use a certificate. It is therefore important that there
be a distinct and clear architectural and functional distinction
between the processes and objectives of the automated certificate
verification and human recognition.
Since logotypes are only aimed for human interpretation and contain
data that is inappropriate for computer based verification schemes,
the logotype extension MUST NOT be an active component in automated
certification path validation.
Automated certification path verification determines whether the
end-entity certificate can be verified according to defined policy.
The algorithm for this verification is specified in RFC 3280
[PKIX-1].
The automated processing provides assurance that the certificate is
valid. It does not indicate whether the subject is entitled to any
particular information, or whether the subject ought to be trusted to
perform a particular service. These are access control decisions.
Automatic processing will make some access control decisions, but
others, depending on the application context, involve the human user.
In some situations, where automated procedures have failed to
establish the suitability of the certificate to the task, the human
user is the final arbitrator of the post certificate verification
access control decisions. In the end, the human will decide whether
or not to accept an executable email attachment, to release personal
information, or follow the instructions displayed by a web browser.
This decision will often be based on recognition and previous
experience.
The distinction between systematic processing and human processing is
rather straightforward. They can be complementary. While the
systematic process is focused on certification path construction and
verification, the human acceptance process is focused on recognition
and related previous experience.
There are some situations where systematic processing and human
processing interfere with each other. These issues are discussed in
the Security Considerations section.
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RFC 3709 Logotypes in X.509 Certificates February 2004
1.4. 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 BCP 14, RFC 2119
[STDWORDS].
2. Different Types of Logotypes in Certificates
This specification defines the inclusion of three standard logotype
types.
1) Community logotype
2) Issuer organization logotype
3) Subject organization logotype
The community logotype - is the general mark for a community. It
identifies a service concept for entity identification and
certificate issuance. Many issuers may use a community logotype to
co-brand with a global community in order to gain global recognition
of its local service provision. This type of community branding is
very common in the credit card business, where local independent card
issuers include a globally recognized brand (such as VISA and
MasterCard).
Issuer organization logotype - is a logotype representing the
organization identified as part of the issuer name in the
certificate.
Subject organization logotype - is a logotype representing the
organization identified in the subject name in the certificate.
In addition to the standard logotype types, this specification
accommodates inclusion of other logotype types where each class of
logotype is defined by an object identifier. The object identifier
can be either locally defined or an identifier defined in section 4.2
of this document.
3. Logotype Data
This specification defines two types of logotype data: image data and
audio data. Implementations MUST support image data; however,
support for audio data is OPTIONAL.
There is no need to significantly increase the size of the
certificate by including image and audio data of logotypes. Rather,
a URI identifying the location to the logotype data and a one-way
hash of the referenced data is included in the certificate.
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RFC 3709 Logotypes in X.509 Certificates February 2004
Several image files, representing the same image in different
formats, sizes, and color palates, may represent each logotype image.
At least one of the image files representing a logotype SHOULD
contain an image within the size range of 60 pixels wide by 45 pixels
high, and 200 pixels wide by 150 pixels high.
Several audio files may further represent the same audio sequence in
different formats and resolutions. At least one of the audio files
representing a logotype SHOULD have a play time between 1 and 30
seconds.
If a logotype of a certain type (as defined in section 2) is
represented by more than one image file, then the image files MUST
contain variants of roughly the same image. Likewise, if a logotype
of a certain type is represented by more than one audio file, then
the audio files MUST contain variants of the same audio information.
A spoken message in different languages is considered a variation of
the same audio information. Compliant applications MUST NOT display
more than one of the images and MUST NOT play more than one of the
audio sequences for any logotype type at the same time.
A client MAY simultaneously display multiple logotypes of different
logotype types. For example, it may display one subject organization
logotype while also displaying a community logotype, but it MUST NOT
display multiple image variants of the same community logotype.
Each logotype present in a certificate MUST be represented by at
least one image data file.
Applications SHOULD enhance processing and off-line functionality by
caching logotype data.
4. Logotype Extension
This section specifies the syntax and semantics of the logotype
extension.
4.1. Extension Format
The logotype extension MAY be included in public key certificates
[PKIX-1] or attribute certificates [PKIX-AC]. The logotype extension
MUST be identified by the following object identifier:
id-pe-logotype OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-pe(1) 12 }
This extension MUST NOT be marked critical.
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RFC 3709 Logotypes in X.509 Certificates February 2004
Logotype data may be referenced through either direct or indirect
addressing. Clients MUST support both direct and indirect
addressing. Certificate issuing applications MUST support direct
addressing, and certificate issuing applications SHOULD support
indirect addressing.
The direct addressing includes information about each logotype in the
certificate, and URIs point to the image and audio data files.
Direct addressing supports cases where just one or a few alternative
images and audio files are referenced.
The indirect addressing includes one reference to an external hashed
data structure that contains information on the type, content, and
location of each image and audio file. Indirect addressing supports
cases where each logotype is represented by many alternative audio or
image files.
Both direct and indirect addressing accommodate alternative URIs to
obtain exactly the same item. This opportunity for replication is
intended to improve availability. Therefore, if a client is unable
to fetch the item from one URI, the client SHOULD try another URI in
the sequence. All URIs MUST use either the HTTP scheme (http://...)
or the FTP scheme (ftp://...) [URI]. At least one URI in each
sequence MUST use the HTTP scheme. Clients MUST support retrieval of
referenced LogoTypeData with HTTP/1.1 [HTTP/1.1]. Clients MAY
support retrieval using FTP [FTP].
The logotype extension MUST have the following syntax:
LogotypeExtn ::= SEQUENCE {
communityLogos [0] EXPLICIT SEQUENCE OF LogotypeInfo OPTIONAL,
issuerLogo [1] EXPLICIT LogotypeInfo OPTIONAL,
subjectLogo [2] EXPLICIT LogotypeInfo OPTIONAL,
otherLogos [3] EXPLICIT SEQUENCE OF OtherLogotypeInfo OPTIONAL }
LogotypeInfo ::= CHOICE {
direct [0] LogotypeData,
indirect [1] LogotypeReference }
LogotypeData ::= SEQUENCE {
image SEQUENCE OF LogotypeImage OPTIONAL,
audio [1] SEQUENCE OF LogotypeAudio OPTIONAL }
LogotypeImage ::= SEQUENCE {
imageDetails LogotypeDetails,
imageInfo LogotypeImageInfo OPTIONAL }
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RFC 3709 Logotypes in X.509 Certificates February 2004
LogotypeAudio ::= SEQUENCE {
audioDetails LogotypeDetails,
audioInfo LogotypeAudioInfo OPTIONAL }
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 }
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
LogotypeImageType ::= INTEGER { grayScale(0), color(1) }
LogotypeImageResolution ::= CHOICE {
numBits [1] INTEGER, -- Resolution in bits
tableSize [2] INTEGER } -- Number of colors or grey tones
LogotypeAudioInfo ::= SEQUENCE {
fileSize INTEGER, -- In octets
playTime INTEGER, -- In milliseconds
channels INTEGER, -- 1=mono, 2=stereo, 4=quad
sampleRate [3] INTEGER OPTIONAL, -- Samples per second
language [4] IA5String OPTIONAL } -- RFC 3066 Language Tag
OtherLogotypeInfo ::= SEQUENCE {
logotypeType OBJECT IDENTIFIER,
info LogotypeInfo }
LogotypeReference ::= SEQUENCE {
refStructHash SEQUENCE SIZE (1..MAX) OF HashAlgAndValue,
refStructURI SEQUENCE SIZE (1..MAX) OF IA5String }
-- Places to get the same "LTD" file
HashAlgAndValue ::= SEQUENCE {
hashAlg AlgorithmIdentifier,
hashValue OCTET STRING }
When using indirect addressing, the URI (refStructURI) pointing to
the external data structure MUST point to a binary file containing
the DER encoded data with the syntax LogotypeData. The referenced
file name SHOULD include a file extension of "LTD".
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RFC 3709 Logotypes in X.509 Certificates February 2004
At least one of the optional elements in the LogotypeExtn structure
MUST be present. Avoid the use of otherLogos whenever possible.
The LogotypeReference and LogotypeDetails structures explicitly
identify one or more one-way hash functions employed to authenticate
referenced data files. Clients MUST support the SHA-1 [SHS] one-way
hash function, and clients MAY support other one-way hash functions.
CAs MUST include a SHA-1 hash value for each referenced file,
calculated on the whole file, and CAs MAY include other one-way hash
values. Clients MUST compute a one-way hash value using one of the
identified functions, and clients MUST discard the logotype data if
the computed one-way hash function value does not match the one-way
hash function value in the certificate extension.
A MIME type is used to specify the format of the file containing the
logotype data. Implementations MUST support both the JPEG and GIF
image formats (with MIME types of "image/jpeg" and "image/gif"
[MEDIA], respectively). Animated images SHOULD NOT be used.
Implementations that support audio MUST support the MP3 audio format
(with a MIME type of "audio/mpeg" [AUDIO/MPEG]). MIME types MAY
include parameters.
When language is specified, the language tag MUST use the RFC 3066
[LANGCODES] syntax.
Logotype types defined in this specification are:
Community Logotype: If communityLogos is present, the logotypes
MUST represent one or more communities with which the certificate
issuer is affiliated. The communityLogos MAY be present in an end
entity certificate, a CA certificate, or an attribute certificate.
The communityLogos contains a sequence of Community Logotypes,
each representing a different community. If more than one
Community logotype is present, they MUST be placed in order of
preferred appearance. Some clients MAY choose to display a subset
of the present community logos; therefore the placement within the
sequence aids the client selection. The most preferred logotype
MUST be first in the sequence, and the least preferred logotype
MUST be last in the sequence.
Issuer Organization Logotype: If issuerLogo is present, the
logotype MUST represent the issuer's organization. The logotype
MUST be consistent with, and require the presence of, an
organization name stored in the organization attribute in the
issuer field (for either a public key certificate or attribute
certificate). The issuerLogo MAY be present in an end entity
certificate, a CA certificate, or an attribute certificate.
Santesson, et al. Standards Track [Page 10]
RFC 3709 Logotypes in X.509 Certificates February 2004
Subject Organization Logotype: If subjectLogo is present, the
logotype MUST represent the subject's organization. The logotype
MUST be consistent with, and require the presence of, an
organization name stored in the organization attribute in the
subject field (for either a public key certificate or attribute
certificate). The subjectLogo MAY be present in an end entity
certificate, a CA certificate, or an attribute certificate.
The relationship between the subject organization and the subject
organization logotype, and the relationship between the issuer and
either the issuer organization logotype or the community logotype,
are relationships asserted by the issuer. The policies and practices
employed by the issuer to check subject organization logotypes or
claims its issuer and community logotypes is outside the scope of
this document.
4.2. Other Logotypes
Logotypes identified by otherLogos (as defined in 4.1) can be used to
enhance the display of logotypes and marks that represent partners,
products, services, or any other characteristic associated with the
certificate or its intended application environment when the standard
logotype types are insufficient.
The conditions and contexts of the intended use of these logotypes
are defined at the discretion of the local client application.
The following other logotype types are defined in this document:
- Loyalty logotype
- Certificate Background logotype
OID Definitions:
id-logo OBJECT IDENTIFIER ::= { id-pkix 20 }
id-logo-loyalty OBJECT IDENTIFIER ::= { id-logo 1 }
id-logo-background OBJECT IDENTIFIER ::= { id-logo 2 }
A loyalty logotype, if present, MUST contain a logotype associated
with a loyalty program related to the certificate or its use. The
relation between the certificate and the identified loyalty program
is beyond the scope of this document. The logotype extension MAY
contain more than one Loyalty logotype.
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RFC 3709 Logotypes in X.509 Certificates February 2004
The certificate background logotype, if present, MUST contain a
graphical image intended as a background image for the certificate,
and/or a general audio sequence for the certificate. The background
image MUST allow black text to be clearly read when placed on top of
the background image. The logotype extension MUST NOT contain more
than one certificate background logotype.
5. Type of Certificates
Logotypes MAY be included in public key certificates and attribute
certificates at the discretion of the certificate issuer; however,
logotypes MUST NOT be part of certification path validation or any
type of automated processing. The sole purpose of logotypes is to
enhance the display of a particular certificate, regardless of its
position in a certification path.
6. Use in Clients
All PKI implementations require relying party software to have some
mechanism to determine whether a trusted CA issues a particular
certificate. This is an issue for certification path validation,
including consistent policy and name checking.
After a certification path is successfully validated, the replying
party trusts the information that the CA includes in the certificate,
including any certificate extensions. The client software can choose
to make use of such information, or the client software can ignore
it. If the client is unable to support a provided logotype, the
client MUST NOT report an error, rather the client MUST behave as
though no logotype extension was included in the certificate.
Current standards do not provide any mechanism for cross-certifying
CAs to constrain subordinate CAs from including private extensions
(see the security considerations section).
Consequently, if relying party software accepts a CA, then it should
be prepared to (unquestioningly) display the associated logotypes to
its human user, given that it is configured to do so. Information
about the logotypes is provided so that the replying party software
can select the one that will best meet the needs of the human user.
This choice depends on the abilities of the human user, as well as
the capabilities of the platform on which the replaying party
software is running. If none of the provided logotypes meets the
needs of the human user or matches the capabilities of the platform,
then the logotypes can be ignored.
A client MAY, subject to local policy, choose to display none, one,
or any number of the logotypes in the logotype extension.
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RFC 3709 Logotypes in X.509 Certificates February 2004
In many cases, a client will be used in an environment with a good
network connection and also used in an environment with little or no
network connectivity. For example, a laptop computer can be docked
with a high-speed LAN connection, or it can be disconnected from the
network altogether. In recognition of this situation, the client
MUST include the ability to disable the fetching of logotypes.
However, locally cached logotypes can still be displayed when the
user disables the fetching of additional logotypes.
A client MAY, subject to local policy, choose any combination of
audio and image presentation for each logotype. That is, the client
MAY display an image with or without playing a sound, and it MAY play
a sound with or without displaying an image. A client MUST NOT play
more than one logotype audio sequence at the same time.
The logotype is to be displayed in conjunction with other identity
information contained in the certificate. The logotype is not a
replacement for this identity information.
Care is needed when designing replying party software to ensure that
an appropriate context of logotype information is provided. This is
especially difficult with audio logotypes. It is important that the
human user be able to recognize the context of the logotype, even if
other audio streams are being played.
If the relying party software is unable to successfully validate a
particular certificate, then it MUST NOT display any logotype data
associated with that certificate.
7. Security Considerations
Implementations that simultaneously display multiple logotype types
(subject organization, issuer, community or other), MUST ensure that
there is no ambiguity as to the binding between the image and the
type of logotype that the image represents. "Logotype type" is
defined in section 2, and it refers to the type of entity or
affiliation represented by the logotype, not the type of binary
format.
Logotypes are very difficult to securely and accurately define.
Names are also difficult in this regard, but logotypes are even
worse. It is quite difficult to specify what is, and what is not, a
legitimate logotype of an organization. There is an entire legal
structure around this issue, and it will not be repeated here.
However, issuers should be aware of the implications of including
images associated with a trademark or servicemark before doing so.
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RFC 3709 Logotypes in X.509 Certificates February 2004
As logotypes can be difficult (and sometimes expensive) to verify,
the possibility of errors related to assigning wrong logotypes to
organizations is increased.
This is not a new issue for electronic identification instruments.
It is already dealt with in a number of similar situations in the
physical world, including physical employee identification cards.
Secondly, there are situations where identification of logotypes is
rather simple and straightforward, such as logotypes for well-known
industries and institutes. These issues should not stop those
service providers who want to issue logotypes from doing so, where
relevant.
It is impossible to prevent fraudulent creation of certificates by
dishonest or badly performing issuers, containing names and logotypes
that the issuer has no claim to or has failed to check correctly.
Such certificates could be created in an attempt to socially engineer
a user into accepting a certificate. The premise used for the
logotype work is thus that logotype graphics in a certificate are
trusted only if the certificate is successfully validated within a
valid path. It is thus imperative that the representation of any
certificate that fails to validate is not enhanced in any way by
using the logotype graphic.
Logotype data is fetched from a server when it is needed. By
watching activity on the network, an observer can determine which
clients are making use of certificates that contain particular
logotype data. This observation can potentially introduce privacy
issues. Since clients are expected to locally cache logotype data,
network traffic to the server containing the logotype data will not
be generated every time the certificate is used. In cases where
logotype data is not cashed, monitoring would reveal usage frequency.
In cases where logotype data is cached, monitoring would reveal when
a certain logotype image or audio sequence is used for the first
time.
Certification paths may also impose name constraints that are
systematically checked during certification path processing, which,
in theory, may be circumvented by logotypes.
Certificate path processing as defined in RFC 3280 [PKIX-1] does not
constrain the inclusion of logotype data in certificates. A parent
CA can constrain certification path validation such that subordinate
CAs cannot issue valid certificates to end-entities outside a limited
name space or outside specific certificate polices. A malicious CA
can comply with these name and policy requirements and still include
inappropriate logotypes in the certificates that it issues. These
certificates will pass the certification path validation algorithm,
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RFC 3709 Logotypes in X.509 Certificates February 2004
which means the client will trust the logotypes in the certificates.
Since there is no technical mechanism to prevent or control
subordinate CAs from including the logotype extension or its
contents, where appropriate, a parent CA could employ a legal
agreement to impose a suitable restriction on the subordinate CA.
This situation is not unique to the logotype extension.
The controls available to a parent CA to protect itself from rogue
subordinate CAs are non-technical. They include:
- Contractual agreements of suitable behavior, including terms of
liability in case of material breach.
- Control mechanisms and procedures to monitor and follow-up
behavior of subordinate CAs.
- Use of certificate policies to declare an assurance level of
logotype data, as well as to guide applications on how to treat
and display logotypes.
- Use of revocation functions to revoke any misbehaving CA.
There is not a simple, straightforward, and absolute technical
solution. Rather, involved parties must settle some aspects of PKI
outside the scope of technical controls. As such, issuers need to
clearly identify and communicate the associated risks.
8. IANA Considerations
Certificate extensions and attribute certificate extensions are
identified by object identifiers (OIDs). The OID for the extension
defined in this document was assigned from an arc delegated by the
IANA to the PKIX Working Group. No further action by the IANA is
necessary for this document or any anticipated updates.
9. Acknowledgments
This document is the result of contributions from many professionals.
The authors appreciate contributions from all members of the IETF
PKIX Working Group. We extend a special thanks to Al Arsenault,
David Cross, Tim Polk, Russel Weiser, Terry Hayes, Alex Deacon,
Andrew Hoag, Randy Sabett, Denis Pinkas, Magnus Nystrom, Ryan Hurst,
and Phil Griffin for their efforts and support.
Russ Housley thanks the management at RSA Laboratories, especially
Burt Kaliski, who supported the development of this specification.
The vast majority of the work on this specification was done while
Russ was employed at RSA Laboratories.
Santesson, et al. Standards Track [Page 15]
RFC 3709 Logotypes in X.509 Certificates February 2004
10. References
10.1. Normative References
[LANGCODES] Alvestrand, H., "Tags for Identification of Languages",
BCP 47, RFC 3066, January 2001.
[PKIX-1] Housley, R., Polk, W., Ford, W. and D. Solo, "Internet
X.509 Public Key Infrastructure: Certificate and
Certificate Revocation List (CRL) Profile", RFC 3280,
April 2002.
[PKIX-AC] Farrell, S. and R. Housley, "An Internet Attribute
Certificate Profile for Authorization", RFC 3281, April
2002.
[SHS] Federal Information Processing Standards Publication
(FIPS PUB) 180-1, Secure Hash Standard, 17 April 1995.
[Supersedes FIPS PUB 180 dated 11 May 1993.]
[STDWORDS] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[HTTP/1.1] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach P. and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[FTP] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, October 1985.
[URI] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform
Resource Identifiers (URI): Generic Syntax", RFC 2396,
August 1998.
[MEDIA] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
November 1996.
[AUDIO/MPEG] Nilsson, M., "The audio/mpeg Media Type", RFC 3003,
November 2000.
10.2. Informative References
[X.509] ITU-T Recommendation X.509 (2000) | ISO/IEC 9594-8:2001,
Information technology - Open Systems Interconnection -
The Directory: Public-key and attribute certificate
frameworks
Santesson, et al. Standards Track [Page 16]
RFC 3709 Logotypes in X.509 Certificates February 2004
APPENDIX A. ASN.1 Module
LogotypeCertExtn
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-mod-logotype(22) }
DEFINITIONS IMPLICIT TAGS ::=
BEGIN
IMPORTS
AlgorithmIdentifier FROM PKIX1Explicit88 -- RFC 3280
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-mod(0)
id-pkix1-explicit(18) };
-- Logotype Extension OID
id-pe-logotype OBJECT IDENTIFIER ::=
{ iso(1) identified-organization(3) dod(6) internet(1)
security(5) mechanisms(5) pkix(7) id-pe(1) 12 }
-- Logotype Extension Syntax
LogotypeExtn ::= SEQUENCE {
communityLogos [0] EXPLICIT SEQUENCE OF LogotypeInfo OPTIONAL,
issuerLogo [1] EXPLICIT LogotypeInfo OPTIONAL,
subjectLogo [2] EXPLICIT LogotypeInfo OPTIONAL,
otherLogos [3] EXPLICIT SEQUENCE OF OtherLogotypeInfo OPTIONAL }
LogotypeInfo ::= CHOICE {
direct [0] LogotypeData,
indirect [1] LogotypeReference }
LogotypeData ::= SEQUENCE {
image SEQUENCE OF LogotypeImage OPTIONAL,
audio [1] SEQUENCE OF LogotypeAudio OPTIONAL }
LogotypeImage ::= SEQUENCE {
imageDetails LogotypeDetails,
imageInfo LogotypeImageInfo OPTIONAL }
LogotypeAudio ::= SEQUENCE {
audioDetails LogotypeDetails,
audioInfo LogotypeAudioInfo OPTIONAL }
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RFC 3709 Logotypes in X.509 Certificates February 2004
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 }
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
LogotypeImageType ::= INTEGER { grayScale(0), color(1) }
LogotypeImageResolution ::= CHOICE {
numBits [1] INTEGER, -- Resolution in bits
tableSize [2] INTEGER } -- Number of colors or grey tones
LogotypeAudioInfo ::= SEQUENCE {
fileSize INTEGER, -- In octets
playTime INTEGER, -- In milliseconds
channels INTEGER, -- 1=mono, 2=stereo, 4=quad
sampleRate [3] INTEGER OPTIONAL, -- Samples per second
language [4] IA5String OPTIONAL } -- RFC 3066 Language Tag
OtherLogotypeInfo ::= SEQUENCE {
logotypeType OBJECT IDENTIFIER,
info LogotypeInfo }
LogotypeReference ::= SEQUENCE {
refStructHash SEQUENCE SIZE (1..MAX) OF HashAlgAndValue,
refStructURI SEQUENCE SIZE (1..MAX) OF IA5String }
-- Places to get the same "LTD" file
-- Note: The content of referenced "LTD" files is defined by the
-- LogotypeData type
HashAlgAndValue ::= SEQUENCE {
hashAlg AlgorithmIdentifier,
hashValue OCTET STRING }
-- Other logotype type OIDs
id-logo OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
dod(6) internet(1) security(5) mechanisms(5) pkix(7) 20 }
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RFC 3709 Logotypes in X.509 Certificates February 2004
id-logo-loyalty OBJECT IDENTIFIER ::= { id-logo 1 }
id-logo-background OBJECT IDENTIFIER ::= { id-logo 2 }
END
APPENDIX B. Example Extension
The following example displays a logotype extension containing one
Issuer logotype using direct addressing. The issuer logotype image
is of the type image/gif. The logotype image file is referenced
through 1 URI and the image is hashed by one sha1 hash value.
The values on the left are the ASN.1 tag and length, in hexadecimal.
30 106: SEQUENCE {
06 8: OBJECT IDENTIFIER '1 3 6 1 5 5 7 1 12'
04 94: OCTET STRING, encapsulates {
30 92: SEQUENCE {
A1 90: [1] {
A0 88: [0] {
30 86: SEQUENCE {
30 84: SEQUENCE {
30 82: SEQUENCE {
16 9: IA5String 'image/gif'
30 33: SEQUENCE {
30 31: SEQUENCE {
30 7: SEQUENCE {
06 5: OBJECT IDENTIFIER sha1 (1 3 14 3 2 26)
: }
04 20: OCTET STRING
: 8F E5 D3 1A 86 AC 8D 8E 6B C3 CF 80 6A D4 48 18
: 2C 7B 19 2E
: }
: }
30 34: SEQUENCE {
16 32: IA5String 'http://logo.example.com/logo.gif'
: }
: }
: }
: }
: }
: }
: }
: }
: }
Santesson, et al. Standards Track [Page 19]
RFC 3709 Logotypes in X.509 Certificates February 2004
Authors' Addresses
Stefan Santesson
Microsoft Denmark
Tuborg Boulevard 12
DK-2900 Hellerup
Denmark
EMail: stefans@microsoft.com
Russell Housley
Vigil Security, LLC
918 Spring Knoll Drive
Herndon, VA 20170
USA
EMail: housley@vigilsec.com
Trevor Freeman
Microsoft Corporation
One Microsoft Way
Redmond WA 98052
USA
EMail: trevorf@microsoft.com
Santesson, et al. Standards Track [Page 20]
RFC 3709 Logotypes in X.509 Certificates February 2004
Full Copyright Statement
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Santesson, et al. Standards Track [Page 21]