INTERNET-DRAFT                              ISO 7812 Numbers and the DNS
                                                              March 1998
                                                  Expires September 1998

            ISO 7812 Card Numbers and the Domain Name System
           --- ---- ---- ------- ---- --- ------ ---- ------

                         Donald E. Eastlake 3rd

Status of This Document

   This draft, file name draft-eastlake-card-map-02.txt, is intended to
   be become an Informational RFC concerning utilization of the Domain
   Name System (DNS) in automated location of ISO 7812 financial
   transaction identification card related facilities on the Internet.
   Distribution of this document is unlimited. Comments should be sent
   to the author.

   This document is an Internet-Draft.  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.  Internet-Drafts may be updated, replaced, or obsoleted by
   other documents at any time.  It is not appropriate to use Internet-
   Drafts as reference material or to cite them other than as a
   ``working draft'' or ``work in progress.''

   To learn the current status of any Internet-Draft, please check the
   1id-abstracts.txt listing contained in the Internet-Drafts Shadow
   Directories on (East USA), (West USA), (North Europe), (South Europe), (Pacific Rim), or (Africa).

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   There are a variety of web pages, servers, and the like, which
   holders of ISO 7812 based financial transaction identification cards
   may need to locate on the Internet.  For example, the SET protocol
   being developed by VISA, MasterCard, and others assumes that a
   cardholder can locate the appropriate certification authority to
   obtain a cardholder certificate.  This document proposes a method
   using the DNS as an important element in locating financial
   transaction card related facilities on the Internet by mapping ISO
   7812 number prefixes into domain names within in the


   The methods proposed herein are not, at the time of the issuance of
   this draft, endorsed by the credit card brands or associations.


   Suggestions from the following persons, listed in alphabetic order,
   have been incorporated in this document and are gratefully

          Doug Beattie, Electronic Commerce Consultants

          Brian Carpenter, IBM

          Roebert Elz, University of Melbourne

          Tony Lewis, VISA International

Donald E. Eastlake 3rd                                          [Page 2]

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Table of Contents

      Status of This Document....................................1


      Table of Contents..........................................3

      1. Introduction............................................4
      1.1 SET CA Location........................................4
      1.2 ISO 7812 Details.......................................5

      2. Inverse Number Mapping and Wildcards....................6

      3. Card Domain Names Specified.............................7
      3.1 Card Brand and Issuer Pointers.........................7
      3.2 SET Certification Authority (CA) Pointers..............8
      3.3 Financial Institutions Not On Line.....................9
      3.4 BIN Ambiguity..........................................9

      4. Security Considerations................................11

      Author's Address..........................................12
      Expiration and File Name..................................12

      Appendix: Initial Brand Pointers..........................13

Donald E. Eastlake 3rd                                          [Page 3]

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1. Introduction

   Financial transaction cards such as credit cards and debit cards are
   identified world wide by numbers issued in conjunction with ISO
   standard 7812 [ISO 7812-1]. In general, the leading digits of such
   card numbers, formally called the Issuer Identification Number (IIN),
   indicate the issuing institution and the remainder of the number
   identifies the individual card or account holder.  The institution
   prefix is sometimes referred to as the BIN (Bank Identification
   Number), although it applies to more than banks, and the entire
   number is somtimes known as the PAN (Primary Account Number), even
   though these numbers are also used for secondary and other account
   and identification numbers.  Card numbers are generally issued in
   connection with "brands" such as VISA, MasterCard, American Express,
   JCB, Discover, Dinners Club, Air Travel Card, etc.

   There has been no way, given a card number, to automatically find any
   Internet site related to the card issuer, the card brand, or other
   card facilities.  In particular, the SET protocol [SET] defined by
   VISA, MasterCard, and others, defines a means for cardholders, when
   required, to obtain X.509 compliant certificates to attest to the
   cardholder's authenticity but does not specify how to locate the
   appropriate certification authority.  Other protocol may require that
   other facilities based on card number be reached over the Internet.

   An means of automatically mapping such identification numbers into
   domain names means that as soon as a number is know (due to user
   account number entry or selection for a list of previous entered
   PANs, for example), the ability would be present to easily attempt to
   contact facilities on the Internet for that card.  Thus web
   browsers/wallets could, for example, provide "go to card brand", "get
   a SET certificate", "go to issuing bank",  etc., buttons whenever an
   IS 7812 identification number is known.

1.1 SET CA Location

   The most urgent potential need today is to locate SET Certification
   Authorities (CAs).

   In some cases, cardholders will be given URLs in mailings from the
   card issuer or on their card itself.  However, there will be other
   cases, such as older cards that have not had a CA URL added or a card
   for which the URL has changed due to bank mergers or splits or DNS
   changes.  Furthermore, in certification authority interaction, the
   user will be required to supply their full account number in any case
   and the requirement that they also manually enter a URL means
   additional effort and opportunity for error. Note also that ISO 7812
   account numbers have a built in check digit to catch most

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   typographical errors while URLs do not.

   The system described in this draft permits SET Certification
   Authority location without these problems.

1.2 ISO 7812 Details

   Formally, ISO 7812 identification card numbers are divided as

         1           2-6             7-v        last
      | MII | issuer identifier |           |             |
      +-----+-------------------+ account # | check digit |
      | issuer identification # |           |             |
      |         ISO 7812 identification number            |
        MII = Major Industry Identifier as follows
           0 - for ISO/TC 68 and other industry assignments
           1 - airlines
           2 - airlines  and other industry assignments
           3 - travel and entertainment
         4/5 - banking/financial
           6 - merchandizing and banking
           7 - petroleum
           8 - telecommunications and other industry assignments
           9 - for national assignment

   If the number starts with 9, the next three digits are the numeric
   country code as defined in ISO 3166 and the remainder of the number
   is as defined by that national standards body for that country.

   Account numbers are variable length up to a maximum of 12 digits.

   The check digit is calculated modulo 10 by the Luhn formula over all
   the preceeding digits as specified in ISO 7812.

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2. Inverse Number Mapping and Wildcards

   When numbers are allocated in lexically hierarchical blocks so that a
   prefix or suffix of digits is a meaningful division, the DNS wildcard
   feature can be used to provide a convenient delgation and lookup
   mechanism when the numbers and prefixes/suffixes are variable length.
   In this regard, it is important to remember that more specific names
   override less specific ones for DNS wildcards.

   Domain names start with the most significant label on the right and
   go to less significant labels as you go left while in card numbers
   the leading or left most digits are the most significant while the
   trailing or right most digits are less significant.  Thus, the digits
   must be reversed to match the card number and DNS naming systems and
   the digits must be interspersed with dots to provide hierarchical
   division into DNS domains.

   Note that the transformed, reversed card number need not be exposed
   to users but could be generated internally by software in an
   automatic fashion.

   For example, currently the American Express card brand is the only
   one using numbers starting with 37.  However, this is not a guarantee
   for all time and it could be that at some point BIN numbers starting
   with 37 would be assigned to a different brand.  If you are looking
   up facility "z" for card number 37012345678 (not a valid American
   Express number), you could do a retrieval with a name like A wild card RR with the name
   * would match this and would appear in the
   response with its name expanded to the specific name asked for, but
   only if there were no more specific name.  If there were a specific name, for instance, it would
   always be chosen in preference to the *.7.3.xz wildcard in this case
   because it is a more exact match.  On the other hand, if a retrieval
   were done for, it would get the more
   general * wild card since it does not match the
   more exact wildcard.  (The situation is generally somewhat more
   complex than indicted here because additional intermediate length
   wildcards may be needed.  See the Appendix for a more complete
   example zone.)

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3. Card Domain Names Specified

   Subdomains are defined within the domain for access to
   the brand, the SET certification authority, and the card issuer.
   Additional subdomains may be added if additional facilities
   differently indexed by the card number require access.

   To find a facility, you need to (1) get the BIN, (2) reverse the
   order of these digits, and (3) put a dot between each digit and add
   the appropriate facility suffix as shown below.  The financial
   transaction identification number MUST be truncated to avoid
   revealing the full number in the DNS queries.

   Sections 3.1 and 3.2 give further details on the facilities
   available, section 3.3 discusses what to do about banks which are not
   on line, and section 3.4 discusses what to do if the BIN is too
   specific or not specific enough.

   None of the facility pointers obtained via these means need be
   exclusive and these financial identification card related Internet
   facilities may have other names and URLs that will also work.  These
   facilities are intended to supplement, not necesarily replace, the
   direct communication of domain names and URLs from financial
   institutions to their customers.

3.1 Card Brand and Issuer Pointers

   The card brand and issuer home pages can be located by creating the
   numeric portion as above and appending "" or
   "" respectively.  A CNAME RR will be stored at
   that name pointing to the actual domain name for the home page.  A
   CNAME is chosen, rather than having specific "A" RRs pointing to
   host(s), "MX" RRs pointing to mail servers, etc., to minimize the
   update load on the domain.  Changes in the serving host,
   mail servers, etc., need only be made under the facility's domain
   name, which the CNAME points to, rather than also under

   For example, the brand for the card 551204..., a MasterCard card, can
   be found by browsing at and the
   issuer for the card 471922..., a VISA card, can be found by browsing
   at  These domain names can be
   automatically generated from a card number and need not be exposed to
   ordinary users.

   The Appendix shows possible initial content of the
   domain.  There are relatively few brands and they are allocated to
   moderately compact blocks of numbers with relatively few exceptions
   not belonging to the block brand. So there will probably be under

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   2,000 entries in the subdomain.

   Since there are only a few tens of thousands of banks and other
   issuers of significance in the world for financial transaction cards,
   there should be well under 200,000 entries in the

   Although at this time very large blocks of numbers are generally
   allocated to brands (for example almost all card numbers starting
   with 5 and 4 are MasterCard and Visa cards, respectively), some
   numbers within these large blocks may be carved out by more specific
   entries for other brands.

3.2 SET Certification Authority (CA) Pointers

   A very high level description of the cardholder certificate issuance
   procedure in SET [SET] is for a cardholderCInitRequest initialization
   message to be sent to the CA, an initialization response received,
   then a registrationFormRequest is sent to the CA and a either
   registration form returned which the user fills in or a referral to
   another CA is returned.  The completed registration form is submitted
   in a certificateRequest message to which there is a response which
   can include the certificate or indicate it will be issued later or
   indicate a failure.

   The above sequence can occur over a variety of transports [SET-EIG]
   including TCP and HTTP.  TCP would be to the SET well known port 257,
   unless some other port was mutually agreed on, but cardholder to CA
   communication is normally expected to be HTTP.  In HTTP, the sequence
   is usually preceded by a kick-off message from the CA which is of
   MIME type Application/SET-Registration-Initiation which activates a
   SET wallet.

   There are three pointers provided in connection with CAs, one for the
   CA general web page for browsing, one derived URL that can be hit to
   produce the SET certificate issuance kick-off message, and a derived
   URL that can be used to post the initial cardholderCInitRequest if a
   kick-off cycle is not needed.

   The certification authority home page can be found as described in
   3.1 above for brands and issuers, except that the suffix is

   A CNAME will also be used in this subdomain.  At this time it is not
   clear in how many cases a certification authority will correspond to
   a single BIN, to a brand, to blocks of BINs, or even to part of a BIN
   (see section 3.4).  Note that the wild card mechanism can easily

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   accommodate arrangements such as a default certification authority
   for a brand with specific CAs for some BINs within that brand.

   To determine the URLs to hit for the SET certificate issuance wake up
   message [SET-EIG], take the CA domain name as above, prefix it with
   "http://", and suffix it with "/SET-Registration-Initiation".  For
   some purposes, the wake up message may not be necessary.  In that
   case, the cardholderCInitRequest SET message [SET] can be POSTed
   directly to a similar URL but with the suffix of

       Suffix to Domain Name            Action

      /SET-Registration-Initiation     Certificate Request Wakeup
      /cardholderCInitRequest          SET msg to start cert. req.

   Note that no explicit DNS retrieval is necessary.  In initiating a
   cardholder certificate application for card number 8765432109, you
   mechanically transform the number into a URL and go.  In this case
   that would be, to start with a kick-off,


3.3 Financial Institutions Not On Line

   Some numbers are allocated to institutions that do not have a network
   presence.  In some of those cases, a wildcard will provide an
   appropriate pointer, say to a brand supplied bank lookup page that
   provides telephone number and address to contact the bank.  However,
   in cases where the next higher level wildcard would provide
   inappropriate pointers for such institutions, it will be necessary in
   some cases to add entries for such numbers which are CNAMEed to
   "" which will not exist.  Thus an appropriate
   error message will be generated.

3.4 BIN Ambiguity

   For the facilities under defined thus far in this
   document, the BIN is defined as the first six digits of the account
   number.  In many cases an issuer or certification authority is
   defined by fewer digits.  This is no problem as a wild card can be
   used to match all extensions of this shorter prefix.  However, cases
   where six digits are insufficient need special handling as describe
   below.  In the future, there might be facilities added under that are accessed via classes of ISO 7812 numbers not
   subject to this six digit security limitation.

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   If multiple institutions have decided to share a BIN, there are
   several ways it can be handled.  For the issuer web page either (1)
   the banks sharing the BIN can run a common web page with links to
   their individual pages on it or (2) if they are all the same brand,
   the brand can run such a multi-issuer referral page at the BIN or, in
   some cases, at a higher level wildcard or (3) in the unlikely event
   that they are different brands, the maintenance agency
   can run a page providing access to the different sub-BIN issuers.  A
   multiple issuer home page could just have names, icons, and links to
   the separate institutions or more complex indexing if it covered many
   banks.  While this problem in not expected to arise for the subdomain, similar solutions apply if it does.

   In the cases where a URL is derived to access SET certification
   authority facilities, and the BIN is ambiguous, a different
   implementation is used.  In particular, instead of a human looking at
   a web page, we may have an application trying to get a cardholder
   certificate.  However, when the registration process reaches the
   point of sending the CA a registration form request, that request is
   accompanied (securely) by the full account number.  The registration
   form response can have, instead of a registration form, a referral to
   a different URL.  Thus, the certification authority could be simply a
   secure referral program that uses as much of the identification
   number as it wishes, quite possibly more than the fist six digits, to
   determine where to forward the cardholder application.

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4. Security Considerations

   This document concerns a means to map ISO 7812 financial
   identification numbers into the Domain Name System (DNS) so that card
   related facilities on the Internet can be automatically located.  The
   security of the resulting pointers is dependent on the integrity of
   the maintenance agency and the security of the DNS,
   including the use of security extensions [RFC 2065].  However, note
   that when used in connection with SET certificate issuance, the SET
   security mechanisms provide strong protection against spoofing or
   compromise of sensitive information even if the DNS were subverted.

   For currently existing types of ISO 7812 numbers care should be taken
   in making DNS queries that an entire sensitive identification number
   is NOT used.  Since DNS queries are not encrypted, this would expose
   the card number within the Internet. No more than the initial six
   digits should be used.


   [ISO 3166] - Codes for the representation of names of countries.

   [ISO 7812-1] - Identification card - Identification of Issuers.

   [RFC 1034] - Domain Names - Concepts and Facilities, P. Mockapetris,
   November 1987

   [RFC 1035] - Domain Names - Implementation and Specifications, P.
   Mockapetris, November 1987.

   [RFC 2065] - Domain Name System Security Extensions, D. Eastlake, C.
   Kaufman, January 1997.

   [SET] - Secure Electronic Transaction (SET) Specification, Version
   1.0, May 31, 1997, available from <>.
        Book 1: Business Description
        Book 2: Programmer's Guide
        Book 3: Formal Protocol Definition

   [SET-EIG] - External Interface Guide to SET Secure Electronic
   Transaction, September 24, 1997, available from

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Author's Address

   Donald E. Eastlake 3rd
   CyberCash, Inc.
   318 Acton Street
   Carlisle, MA 01741 USA

   Telephone:   +1 978 287 4877
                +1 703 620-4200 (main office, Reston, VA)
   FAX:         +1 978 371 7148

Expiration and File Name

   This draft expires September 1998.

   Its file name is draft-eastlake-card-map-02.txt.

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Appendix: Initial Brand Pointers

   This table shows the initial brand name pointers that might be
   installed in the domain.

         Initial Name                  CNAME


   (MasterCard actually only has numbers starting with 51, 52, 53, 54,
   55, and 56 but until some other brand actually has cards issued with
   a number starting with a 5, there is no reason to go to any more
   detail in the wildcard.  JCB is actually 3528, not all of 35* but the
   same reasoning applies.)

Donald E. Eastlake 3rd                                         [Page 13]