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 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 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. Santesson, Housley Expires: August 2002 [Page 1] INTERNET DRAFT Logotypes in X.509 Certificates February 2002 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 Santesson, Housley Expires: August 2002 [Page 2] INTERNET DRAFT Logotypes in X.509 Certificates February 2002 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. Santesson, Housley Expires: August 2002 [Page 3] INTERNET DRAFT Logotypes in X.509 Certificates February 2002 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. Santesson, Housley Expires: August 2002 [Page 4] INTERNET DRAFT Logotypes in X.509 Certificates February 2002 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 Santesson, Housley Expires: August 2002 [Page 5] INTERNET DRAFT Logotypes in X.509 Certificates February 2002 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 Santesson, Housley Expires: August 2002 [Page 6] INTERNET DRAFT Logotypes in X.509 Certificates February 2002 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 Santesson, Housley Expires: August 2002 [Page 7] INTERNET DRAFT Logotypes in X.509 Certificates February 2002 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 Santesson, Housley Expires: August 2002 [Page 8] INTERNET DRAFT Logotypes in X.509 Certificates February 2002 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. Santesson, Housley Expires: August 2002 [Page 9] INTERNET DRAFT Logotypes in X.509 Certificates February 2002 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 Santesson, Housley Expires: August 2002 [Page 10] INTERNET DRAFT Logotypes in X.509 Certificates February 2002 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 Santesson, Housley Expires: August 2002 [Page 11] INTERNET DRAFT Logotypes in X.509 Certificates February 2002 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 claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain ageneral license or permission for the use of such proprietary 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. Santesson, Housley Expires: August 2002 [Page 12] INTERNET DRAFT Logotypes in X.509 Certificates February 2002 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. 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