PKIX Working Group S. Santesson (AddTrust)
INTERNET-DRAFT R. Housley (RSA Laboratories)
Expires August 2002 February 2002
Internet X.509 Public Key Infrastructure
Logotypes in X.509 certificates
<draft-ietf-pkix-logotypes-01.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
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Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This document contains an initial outline of a standard for attaching
logotypes to certificates. The draft includes background discussions
around different aspects of problems and solutions, forming a
starting point for the creation of a complete standard.
Please send comments on this document to the ietf-pkix@imc.org
mailing list.
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Table of Contents
1 Introduction ................................................. 3
1.1 Are human recognition concepts relevant ................... 4
1.2 Combination of verification techiques ..................... 5
2 Different types of logotypes in certificates.................. 5
3 Technical solutions .......................................... 6
3.1 General ....................................... 6
3.2 Type of certificates ...................................... 7
3.3 Logotype placement ........................................ 8
3.3.1 Qualifier .............................................. 8
3.3.2 Issuer and Subject Alt Names ........................... 8
3.3.3 New extension .......................................... 9
3.3.4 Conclusion ............................................. 10
4 Use in Clients ............................................... 10
5 Security considerations ...................................... 10
6 References ................................................... 12
7 Intellectual Property Right .................................. 12
Appendices
A. ASN.1 definitions ........................................... 13
B. Author Addresses ............................................ 13
C. Full Copyright Statement .................................... 13
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1 Introduction
The basic function of a certificate is to bind a public key to the
identity of an entity (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 PKI has developed
certificates far beyond this functionality in order to meet the needs
from modern global networks and heterogeneous IT structures.
One driver of the evolution from simple certificate formats to more
complex structures is the need to distinguish between different
certificate concepts, such as assurance level, policies, appropriate
key usage, 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.
Systematic processing is necessary to determine whether a particular
certificate meets the predefined prerequisites for an intended usage.
Even though the information objects in certificates are appropriate
and effective for machine processing, they are poor instruments for a
corresponding human trust and recognition process.
The human prefers to structure information into categories and
symbols. Most humans associate complex structures of reality with
easy 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 accept when accepting a
service, instead they most commonly act in trust based on 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 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 identify the holder as a particular person or as member of
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.
Since certificates play an equivalent role in electronic exchanges,
we examine the inclusion of logotypes in certificates.
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1.1 Are human recognition concepts relevant?
The answer depends the manner in which certiciates are used. Are
certificates visible or invisible to human users? Will the
certificates be used in open environments?
If certificates are to be used in open environments and in
applications that brings the user in conscious contact with the
result of a certificate-based identification process, then human
recognition is highly relevant, and it may be a necessity.
Examples of sucha applications include:
- Web server identification where a user identifies the owner of the
web site.
- 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).
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
however two major problems.
1) The function to view a certificate is often rather hard to find
for a non-technical user.
2) The presentation of the certificate is rather technical and not
user friendly. Further it contains no graphic symbols and
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. However, many applications are structured to
hide certificates from users. The application designers do not want
to expose certificates to users at all.
1.2 Combination of verification techiques
Can the concepts of systematic certification path verification and
human recognition be combined in any sensible manner?
Systematic certification path verification determines whether the
end-entity certificate can be verified according to defined policy.
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The systematic processing provides assurance that the certificate is
a valid document. 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 function decisions. Some access control decisions may be made
by a systematic process, but others, depending on the application
context, involve the human user.
In some situations, the human user is the sole handler of the post
certification path 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. As we have seen, 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 interfer with each other. These issues are discussed in
the Security Considerations section.
1.3 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 RFC 2119 [STDWORDS].
2 Different types of logotypes in certificates
This draft suggests standardization of 3 logotype types.
1) Concept logotype
2) Issuer organization logotype
3) Subject organization logotype
The concept logotype - is the general mark for a service concept for
entity identification and certificate issuance. Many issuers may use
the concept logotypes to co-brand with a global concept in order to
gain global recognition of its local service provision. This type of
concept branding is very common in credit card business where local
independent card issuers issue cards within a globally branded
concept (such as VISA and MasterCard).
Issuer organization logotype - is a logotype representing the
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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.
3 Technical solution
3.1 General
There is no need to significantly increase the size of the
certificate by including logotype image data in a certificate.
Rather, a URI identifying the location to the logotype image and a
one-way hash of the referenced data is included in the certificate.
Applications may enhance processing and off-line functionality by
cashing logotype data.
The URI defines the file format for the logotype image.
The solution explicitly identifies the one-way hash function
employed.
The general structure for logotype data is:
LogotypeData ::= SEQUENCE {
typeOfLogotype TypeOfLogotype,
hashAlgorithm AlgorithmIdentifier,
logotypeDataHash OCTET STRING,
logotypeDataUri IA5String OPTIONAL }
TypeOflogotype ::= CHOICE {
predefinedLogotypeType PredefinedLogotypeType,
logotypeTypeID OBJECT IDENTIFIER }
PredefinedLogotypeType ::= INTEGER {
subject-organization-logotype(0),
issuer-organization-logotype(1)
concept-logotype(2) }
The predefined logotype types are:
subject-organization-logotype, if used, SHALL be used to include a
logotype of the subject organization. The logotype SHALL be
consistent with, and require the presence of, an organization name
stored in the organization attribute in the subject field.
issuer-organization-logotype, if used, SHALL be used to include a
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logotype of the issuer organization. The logotype SHALL be consistent
with, and require the presence of, an organization name stored in the
organization attribute in the issuer field.
Concept-logotype, if used, SHALL be used to include a logotype
representing the concept under which the issuer claims to issue this
certificate.
A concept may be shared within a network of certification authority
(CA) services, provided by one or several independent CA
organizations.
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 concept logotype, are
relationships claimed by the issuer. The policy under which the
issuer checks these logotypes is outside the scope of this standard.
Any URI pointing to a file containing the logotype data SHALL include
a file extension defining the image file format (i.e. .GIF, .TIF,
.TIFF, .JPG, .JPEG, etc.).
3.2 Type of certificates
Logotypes according to the present model may be used in 3 types of
certificates:
- Self-signed CA certificates (root certificates)
- Intermediate CA certificates
- End-entity certificates
A reason to constrain inclusion of logotypes to end-entity
certificates would be to exclude the aspect of logotypes from path
processing issues, where a path validating service would want to
check consistency of logotypes in a certification path.
However, as discussed above, logotypes are not aimed to be part of
certification path validation or any type of systematic processing
since its sole purpose is to enhance display of a single particular
certificate to a user regardless of its position or function in a
certification path.
Logotypes should not be an active component in path processing, and
logotypes should be allowed in all types of certificates, at the
discretion of the CA.
3.3 Logotype placement
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So far, there have been 3 solutions discussed regarding the placement
of the logotype data in certificates.
- Inclusion in a policy qualifier
- Inclusion in Issuer and Subject Alternative names extensions
- Inclusion in a separate private extension
3.3.1 Qualifier
This solution would include logotype data as a newly defined policy
qualifier.
Pros:
- This solution provides a mechanism to directly control the use and
display of logotypes under a particular policy
Cons:
- Current practice and standards (RFC 2459) recommends against use of
qualifiers
- This is generally considered to be a major hack and stretch of
semantics, since this type of data doesn't qualify a policy in any
way.
3.3.2 Issuer and Subject Alt Names
This solution would use the other name form to include;
- issuer and concept logotypes in the issuer alt name extension;
and,
- subject organization logo in the subject alt name extension.
Pros:
- This mechanism could possibly enable cross certifying CAs to deny
any subordinate CA the right to include logotypes in descending end
entity certificates by listing the logotypes name form in
excludedSubtrees.
Cons:
- Logotypes are not a name form and should not be treated as a
displayable name.
- It is generally understood that it should be possible to apply
general name constraint mechanisms (as described in RFC 2459 as
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well as son-of-2459) to names in the subject and issuer alt name
extension. This is not possible to do with logotypes since it is
not a name form.
- This split storage of logotype data into 2 different locations,
which may make life worse for applications with no interest in
logotypes.
- It is generally agreed that inclusion of logotype data by no means
should be regarded as critical data. This may interfere with the
criticality policy of the alt name extensions, especially if the
certificate has no attributes in the subject field, forcing the
subject alt name to be set to critical.
- This usage would possibly interfere with the resolution between
IETF and ITU-T regarding use of permitted subtrees.
- Since this solution may break current implementations it would
possibly block adoption of logotypes.
3.3.3 New extension
logotypeInfo EXTENSION ::= {
SYNTAX LogotypeSyntax
IDENTIFIED BY id-pe-logotypeInfo }
id-pe-logotypeInfo OBJECT IDENTIFIER ::= {id-pe XX}
LogotypeSyntax ::= SEQUENCE OF LogotypeData
Pros:
- This is the cleanest solution.
- Do not impact on legacy implementations.
Cons:
- This solution activates the issue whether this extension may be
abused by a CA who include logotypes (in EE certificates) that
violates the intention of a name constraints set by a chaining CA.
This issue is addressed in the security consideration section
below.
3.3.4 Conclusion
We must not destroy current structures. We must not create problems
and confusion.
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Only the private extension solution satisfies both of these desires.
Therefore, the private extension should be selected.
4 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 certificatin path is successfully validated, the replying
party must trust 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. Current standards do not provide any
mechanism for cross-certifying CAs to constrain subordinate CAs from
including private extensions (see security considerations).
Consequently, if relying party software accepts a CA, then it should
be prepared to (unquestioningly) display the associated logos to its
human user, given that it is configured to do so.
5 Security considerations
Logotypes are even worse than names regarding the possibility to
securely and accurately define what is, and what is not, a legitimate
logotype of an organization. There is a whole legal structure around
this issue that doesn't need repetition in this document.
As logotypes are hard (and sometimes expensive) to verify, this
increases the possibility of errors related to falsely assigning
wrong logotypes to organizations.
This is not a new issue for electronic identification instruments.
It is already dealt with in numerous 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.
There is a new problem related to electronic identification
instruments in the form of certificates. Certification paths may
impose constraints that are systematically checked during
certification path processing, which, in theory, may be violated by
logotypes.
Certification path processing does not, should not, and will never be
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able to control the inclusion of logotype data in certificates. That
is, a parent CA may constraint subordinate CAs to only issue
certificates to end-entities within a limited name space. A
potentially bad CA may comply with this name constraint and still
include a subject organization logotype. The the parent CA has no
means of preventing logotype data inclusion since there is no
mechanism to prevent subordinate CAs from including new extensions.
This is not unique to the logotype extension. No technical means are
provides for constraining subordinate CAs to a particular certificate
profile.
The controls available to a parent CA to protect itself from rogue
subordinate CAs are nontechnical. They include:
- Contractual agreements of suitable behaviour, including
terms of liability and severance pay in case of material
breach.
- Control mechanisms and procedures to monitor and
follow-up behaviour of subordinate CAs.
- Use of certificate policies to declare 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.
This issue cannot be given an easy and absolute technical solution.
Maybe the correct response is to surrender to the fact that involved
parties must settle some aspects of PKI outside the scope of
technical controls, and to clearly identify and communicate the
associated risks.
6 References
[STDWORDS] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", March 1997.
[RFC 2459] R. Housley, W. Ford, W. Polk, and D.Solo, "Internet X.509
Public Key Infrastructure: Certificate and CRL Profile", January
1999.
7 Intellectual Property Rights
The IETF takes no position regarding the validity or scope of any
intellectual property or other rights that might be claimed to
pertain to the implementation or use of the technology described in
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this document or the extent to which any license under such rights
might or might not be available; neither does it represent that it
has made any effort to identify any such rights. Information on the
IETF's procedures with respect to rights in standards-track and
standards related documentation can be found in BCP-11. Copies of
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rights by implementors or users of this specification can be obtained
from the IETF Secretariat.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights which may cover technology that may be required to practice
this standard. Please address the information to the IETF Executive
Director.
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APPENDICES
A. ASN.1 definitions
TBD
B. Author Addresses
Stefan Santesson
AddTrust AB
P.O. Box 465
S-201 24 Malmoe
Sweden
stefan@addtrust.com
Russell Housley
RSA Laboratories
918 Spring Knoll Drive
Herndon, VA 20170
USA
rhousley@rsasecurity.com
C. Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. In addition,
the ASN.1 modules presented in Appendices A and B may be used in
whole or in part without inclusion of the copyright notice.
However, this document itself may not be modified in any way, such
as by removing the copyright notice or references to the Internet
Society or other Internet organizations, except as needed for the
purpose of developing Internet standards in which case the
procedures for copyrights defined in the Internet Standards process
shall be followed, or as required to translate it into languages
other than English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns. This
document and the information contained herein is provided on an "AS
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IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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