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Internet Engineering Task Force (IETF) S. SantessonRequest for Comments: 6170 3xA SecurityUpdates:3709 R. HousleyCategory: Standards Track Vigil SecurityISSN: 2070-1721 S. Bajaj Symantec Corp. L. Rosenthol Adobe May 2011Internet X.509 Public Key Infrastructure -- Certificate ImageAbstract This document specifies a method to bind a visual representation of a certificate in the form of a certificate image to a public key certificate as defined inRFC 5280, by defining a new "otherLogos" image type according toRFC 3709.Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available inSection 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc6170.Copyright Notice Copyright (c) 2011 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject toBCP 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 Simplified BSD License.Santesson, et al. Standards Track [Page 1]

RFC 6170 Certificate Image May 2011Table of Contents1. Introduction ....................................................21.1. Terminology ................................................32. Certificate Image ...............................................33. LogotypeImageInfo ...............................................44. Embedded Images .................................................55. Certificate Image Formats .......................................65.1. PDF ........................................................65.2. SVG ........................................................65.3. PNG ........................................................76. Security Considerations .........................................77. Acknowledgements ................................................88. References ......................................................98.1. Normative References .......................................98.2. Informative References .....................................9Appendix A. ASN.1 Module .........................................10Appendix B. Example ..............................................111. Introduction This standard specifies how to bind a certificate image to a certificate (defined in [RFC5280]), providing a visual representation of that certificate using the Logotype extension defined in [RFC3709] and 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 (UI). Typical situations when a human needs to examine the visual representation of a certificate are: - A person establishes a 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.Santesson, et al. Standards Track [Page 2]

RFC 6170                    Certificate Image                   May 2011   The display of 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 the problem of labeling that data   in the UI and informing the human about the exact nature (semantics)   of that data.  It is also challenging for the application to   determine which identification attributes 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 a community logo and issuer logo, enhancing   the display of certificate information.  The syntax is extensible and   allows inclusion of new image types using the otherLogos structure.   This standard defines how to include a complete certificate image   using the extensibility mechanism ofRFC 3709.1.1.  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].2.  Certificate Image   This section defines the certificate image as a new otherLogos type   according toSection 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 3 }   When present, the certificate image MUST be 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   to 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:Santesson, et al.            Standards Track                    [Page 3]

RFC 6170                    Certificate Image                   May 2011   -  Certificate Context   -  Certificate Issuer   -  Certificate Subject   Certificate Context information is visual marks and/or textual   information that 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, graphical symbols, and elements -- represents a complete visual   representation of the certificate.  However, the visual   representation of Certificate Subject and Certificate Issuer   information from the certificate MUST have the same meaning as the   textual representation of that information in the certificate itself.   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:     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   NOTE: The referencedRFC 3066 in the structure above (fromRFC 3709)         is obsolete and is currently replaced byRFC 5646 [RFC5646].         The language tag may carry information about the language used         to express any textual elements within the image as well as any         audio information associated with the image.   When the optional LogotypeImageInfo is included with a certificate   image, the parameters shall be used with the following semantics and   restrictions.   xSize and ySize represent the recommended display size for the image.   When a value of 0 (zero) is present, no recommended display size is   specified.  When non-zero values are present and these values differSantesson, et al.            Standards Track                    [Page 4]

RFC 6170                    Certificate Image                   May 2011   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 the x and y ratio intact.   The resolution parameter is redundant for all image formats that are   relevant for certificate images and MUST NOT be specified.4.  Embedded Images   The certificate image otherLogos type defined in this specification   and all logotype types defined inRFC 3709 [RFC3709] MAY be stored   within the logotype extension using the "data" URL scheme defined inRFC 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 inRFC 3709 is included here   for convenience:      LogotypeDetails ::= SEQUENCE {         mediaType       IA5String, -- MIME media type name and optional                                    -- parameters (seeSection 5)         logotypeHash    SEQUENCE SIZE (1..MAX) OF HashAlgAndValue,         logotypeURI     SEQUENCE SIZE (1..MAX) OF IA5String }   The syntax of the "data" URL scheme defined inRFC 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      media type 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 settings that otherwise apply to URLs in         general.Santesson, et al.            Standards Track                    [Page 5]

RFC 6170                    Certificate Image                   May 2011   NOTE: Implementations need to be cautious about the size of images         included in a certificate in order to ensure that the size of         the certificate does not prevent the certificate from being         used as intended.5.  Certificate Image Formats   Implementations of this specification MUST support JPEG and GIF as   defined inRFC 3709 [RFC3709].  In addition to these mandatory-to-   implement formats, this specification specifies the use of the   Portable Document Format (PDF), Scalable Vector Graphics (SVG), and   Portable Network Graphics (PNG) as image formats.5.1.  PDF   A certificate image MAY be provided in the form of a Portable   Document Format (PDF) document according to [ISO32000] and 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 a certificate image, the following   MIME media type as specified in [RFC3778] MUST be used as mediaType   in LogotypeDetails:      application/pdf5.2.  SVG   A certificate image MAY be provided in the form of a Scalable Vector   Graphics (SVG) image, which MUST follow the SVG Tiny profile [SVGT]   with the following amendments:   -  The SVG image MUST NOT contain any Internationalized Resource      Identifier (IRI) references to information stored outside of the      SVG image of type B, C, or D, according toSection 14.1.4 of SVG      Tiny 1.2 [SVGT].   -  The SVG image MUST NOT contain any 'script' element, according toSection 15.2 of SVG Tiny 1.2 [SVGT].   -  The XML structure in the SVG file MUST use <LF> (linefeed 0x0A) as      the end-of-line (EOL) character when calculating a hash over the      SVG image.   The referenced SVG file MAY be provided in GZIP-compressed [RFC1952]   form as an SVGZ file.  In this case, the extension 'svgz' is used as   an alias for 'svg.gz' [RFC1952], i.e., octet streams of typeSantesson, et al.            Standards Track                    [Page 6]

RFC 6170 Certificate Image May 2011 image/svg+xml, subsequently compressed with gzip as specified in [SVGR]. The hash over the SVGZ file is calculated over the decompressed SVG content with canonicalized EOL characters (<LF>) as specified above. The following MIME media type, defined inAppendix M of [SVGT], MUST be included as mediaType in LogotypeDetails for all SVG and SVGZ images: image/svg+xml When the SVG image is embedded using the "data" URL scheme as defined inSection 4, SVG image data MUST be provided in SVGZ (GZIP compressed) form (i.e., it MUST NOT be provided in uncompressed SVG form). Compliant implementations of this specification SHOULD be able to process SVG images that are formatted according to this section.5.3. PNG If a certificate image is provided as a bitmapped image, the PNG [ISO15948] format SHOULD be used. PNG images are identified by the following mediaType in LogotypeDetails: image/png6. Security Considerations This document is based on and inherits all security considerations fromRFC 3709 [RFC3709]. In particular,RFC 3709 discusses several issues a Certificate Authority (CA) should take into consideration when evaluating a request to issue a certificate with a certificate image. Images incorporated according toRFC 3709 provide an additional possibility for a CA with bad intentions or bad security procedures to include false, conflicting, or malicious information to relying parties. Such a CA may, for example: - include information in graphical form that is in conflict with information in provided text-based attributes or other name forms, and - include malicious data that could exploit known security bugs in common software libraries used to render graphical images.Santesson, et al. Standards Track [Page 7]

RFC 6170 Certificate Image May 2011 This underlines the necessity for CAs to provide reliable services, and the relying party's responsibility and need to carefully select which CAs are trusted to provide public key certificates. This also underlines the general necessity for relying parties to use up-to-date software libraries to render or dereference data from external sources (such as certificates), to minimize risks related to processing potentially malicious data before the data has been adequately verified and validated. 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 an 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. Clients SHOULD verify that SVGT images meet all requirements listed inSection 5.2 and reject images that contain references to external data. CAs issuing certificates 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 a case, the accepted image may contain data that could help an attacker to obtain colliding certificates with identical certificate signatures. Certificates, and hence their certificate images, are commonly public objects and as such usually will not contain privacy-sensitive information. However, when a certificate image that is referenced from a certificate contains privacy-sensitive information, appropriate security controls should be in place to protect the privacy of that information. Details of such controls are outside the scope of this document.7. Acknowledgements The authors recognize valuable contributions from members of the PKIX working group, the CA Browser Forum, and James Manger, for their review and sample data.Santesson, et al. Standards Track [Page 8]

RFC 6170                    Certificate Image                   May 20118.  References8.1.  Normative References   [RFC1952]   Deutsch, P., "GZIP file format specification version               4.3",RFC 1952, May 1996.   [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate               Requirement Levels",BCP 14,RFC 2119, March 1997.   [RFC2397]   Masinter, L., "The "data" URL scheme",RFC 2397, August               1998.   [RFC3709]   Santesson, S., Housley, R., and T. Freeman, "Internet               X.509 Public Key Infrastructure: Logotypes in X.509               Certificates",RFC 3709, February 2004.   [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.   [RFC5646]   Phillips, A., Ed., and M. Davis, Ed., "Tags for               Identifying Languages",BCP 47,RFC 5646, September 2009.   [ISO15948]  ISO/IEC 15948:2004, "Information technology -- Computer               graphics and image processing -- Portable Network               Graphics (PNG): Functional specification", 2004.   [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.   [ISO32000]  ISO 32000-1:2008, "Document management -- Portable               document format -- Part 1: PDF 1.7", April 2008.   [SVGT]      W3C Recommendation, "Scalable Vector Graphics (SVG) Tiny               1.2 Specification", December 2008.8.2.  Informative References   [RFC3778]   Taft, E., Pravetz, J., Zilles, S., and L. Masinter, "The               application/pdf Media Type",RFC 3778, May 2004.   [SVGR]      "Media Type Registration for image/svg+xml",http://dev.w3.org/SVG/profiles/1.1F2/master/mimereg.html.Santesson, et al.            Standards Track                    [Page 9]

RFC 6170                    Certificate Image                   May 2011Appendix A.  ASN.1 Module   CERT-IMAGE-MODULE { iso(1) identified-organization(3) dod(6)       internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)       id-mod-logotype-certimage(68) }   DEFINITIONS EXPLICIT TAGS ::=   BEGIN     EXPORTS ALL;   -- export all items from this module       id-logo-certImage  OBJECT IDENTIFIER  ::=             { iso(1) identified-organization(3) dod(6) internet(1)             security(5) mechanisms(5) pkix(7) id-logo(20) 3 }   ENDSantesson, et al.            Standards Track                   [Page 10]

RFC 6170                    Certificate Image                   May 2011Appendix B.  Example   The following example stores an embedded svgz-encoded SVG image using   the "data" URL scheme.      data:image/svg+xml;base64,H4sICLXutU0AA0NlcnRJbWFnZURlbW8uc3ZnANVa      W2/bOBZ+n19BqBigwdoS7xK9jmeapB0EWHQHzez2WZZoR1tZMiQ5jvvr95CSL7Gl1E      m8C9d9iERSPOd85+O5EB3+9jhL0YMuyiTPLh3iYgfpLMrjJJteOv/661M/cFBZhVkc      pnmmL50sd34b/TIsH6YoiS+da11UySSJwkqj21k41Q6CDbNyUMSTS+e+quYDz1sul+      6SuXkx9YhSysPUo7QPK/rlKqvCx35Wvmu+a/uGYow9EOigh0Qvr/LHSwcjjDjGiGHQ      914n0/sKlMf4Vwctk7i6X7/sGEYdNA5L/WeRT5IUDKmSbLVWNoo2cqNCh1XyoKN8Ns      uz0iqwVW8Qb1fOF0Vqp+PI06me6awqPeISzxn9goYzXYVxWIUWpfWLCMwcGoLpgy83      n8wzGkbR4GtefENmMBznC7DEroKpOBpM8mIWVqPEYGtA+BvoMfS2E5uF1Wqu7R6FLv      NFEelWReNolpiV3l2VpGntMW9nk6RKdf0+9BrFrMbeVuWhtzbHvMR6UlobPyVpBWjX      Bk7six2vH5nCwY6nXCo5xb7YusvFVPqCOGh16fSxSxglmPkScLfvmDDmC4FlDc1wov      8IF2WZhNlVumgEPRliimDD3PhGPyTgUUMC6lKqKAjxaptq1boUJvQFsvi+LOJyxZkP      E/vCwHuAmXmoj1AarnRBatzqkbv7cK5Ls2ORfwM/vsOG5lURZqXxOnDXPKZw5t5jVz      IhFKO0B6D6hARSXDR6Fzqq7H7mQeJAOQiUSPvFIrUHOfuui3zrFI5dYVeAmpcOcOb9      u63vLjae4kYX4yRifYPrTa2SlMigYdO+cEWeGADMLZLH96SH4R9xRYApl6q3Y02f+N      zlRAl+cZSKhB6qSIVa80fsqMnWOqZJpmsXwAPoyNaQ95uNIGasKPwhxGzQzOXzMIIz      BKabmLIil470zfSjWWn+kvpvLQ9g1l3yRIc8gukz0uysEcakcDfy3KMk+l0SOXlOop      ltJL7EPtUlzZfP4tnM70k8xkKCySt92MwfIXPoTe0pnu4dYbp7hJ/kxWySN0ey0o/1      qbiCsxDXJMWWo37QekBcAUFPSGkPCnUJF5wwBacDK5cGlEp4BC2lYoJcrNNGVc7DzI      qxT4CKsPlrAG8mL8whRejiQe9EmImIAoz3sds9NxP4RZEzugqzb7c3Q89u3WQKY9ae      gbsA/AUJB/bJs6pfJt9BHFEuk5DWITzOH5uZSThLUsDjQ5GE6RMsyihMTaQLfA6BIi      AQMAhnHHN1sd61WtUhDVJiuhkrdBXd740+hLB9Vm1HjQe4ywLOBLWOMMiyQAXNB8sm      9Gx2qdGgGkMG6wY8aLfqgH4dfnmrVc+pPrE/Z/QnZOs8C1Okb2/ggwLdxlDC1D6DFP      ZDD98txv8xQf5TEc7Ax6ZyaDf6BC4SylWKCMqtizp80+UMchATal63qHq0M3ZTs83O      b/XO6LYsFzpGVY5+iLxdWvwY+NaKoR/0iJIXL3dBjT2hG+wO+NXm53XStSh1eogfeo      jV35BTOaqh/cmPUe2Mdp91pQp2CjWOO2k7OamhjU1HB3DLGm66n6iajz4bqn2oICmN      FxDR/x2mC5s+rKhlkUA3Ne3P8lgP0qJfjf9uvu+HWXSfFwNoH4uqGUmTadYMtOc7yj      EEd9EUhkwEEOcDSHKQ+yhnSvUYRH8miQo2FK5TCjWZZGWKB8iHPud16wApnCvTOzjI      FAj9TQdCxa+ddOTizaa1xJvD0qMrKx+Ydaj6iwJQG0vaSdYWpTv4HwVRAP3Z6ONjOJ      unEIeKRVmhujpA2+wPmQR9WFQAFhh9bGQzFEXX+WwOnXq8pV35P2Acdn0pGebcMg7O      gQKaEdOKEAkFlk/9HuEKGBVwucc4AjnJ/LBYU09hVwWY1F0HlBUC2lbyIuYF58O8p+      adMwUt9YAoX/IwRtAC9NAdBAyGuEB3VR59u8/TGYx9/Xjz8bPB/Z/F9B0SghBK+4xx      fiwtr0GXECqedQQ9PRVpEAQ+26MidbGSmPm8RwRzcQsT17EPSmoorH3+av4Jcj78O/      vIp/uzMEkHKAE6/F7VHHSj8HddR0Q3ymcGZfRVjwfmOnNn3GuWR+FzhcPmPqiptHca      yacT28T8j3Cs0/LQCwo6J2iYxP4R58AsobjFegusoJhuq7VNS2evRPcqASvQki+gbk      BYwETNPt/1A2pT6UErR1zMzUITZRvF5Lp5basO1fk2U4aBSjkji8quL3cDyW7TpI3u      nxezMcSTNhQJhfpGctKgKN2Amo7/7ShSev4oXicPSYS+6GkCm9a1Qw3VEchCUA+z5H      tTcbQhK6F14YFUp+Yn7WgmzwpZCDf5DDiXT9B7U6RdHAHpdb7IqmLVjqZSLnTW61zj      Q7/G7D3hm9E846uTDZoNMADmLlm7IG2ieXfUtu1US9TeNGUHibE9Nv//2jRJGZfQmK      3v7ykJJOv1IXjBsDCPpmgWppe6sHxR3KVSQKqp+WIqammuJbtqkxZmMHry4oS/9pLh      dCXKq8uR0R+LDEqCKRxqc5VXdvPvIP+ggwR0RkyBfO9iKZvrWGAKVdz31cuocvoO/q      emClFMYEFEH7oI+vpkek4s4bCMBqK+5mHQUlDpE/oylpy+2/6pWXK31PEYagP04epV      1cE50UMy6IQZeQM7+Ol74Z+eHfpHNc7OjffQ/HeV0X8BopoDkGEkAAA=Santesson, et al.            Standards Track                   [Page 11]

RFC 6170                    Certificate Image                   May 2011Authors' 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   Symantec Corp.   350 Ellis Street   Mountain View, CA  94043   USA   EMail: siddharthietf@gmail.com   Leonard Rosenthol   3533 Sunset Way   Huntingdon Valley, PA  19006   USA   EMail: leonardr@adobe.comSantesson, et al.            Standards Track                   [Page 12]

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