INTERNET-DRAFT                     Mapping ISO 7812 Numbers into the DNS
                                                           February 1998
                                                     Expires August 1998

       Mapping ISO 7812 Card Numbers into the Domain Name System
       ------- --- ---- ---- ------- ---- --- ------ ---- ------

                         Donald E. Eastlake 3rd

Status of This Document

   This draft, file name draft-eastlake-card-map-01.txt, is intended to
   be become an Informational RFC concerning utilization of the Domain
   Name System (DNS) to support automated location of ISO 7812 financial
   transaction identification card related facilities in the Internet.
   Distribution of this document is unlimited. Comments should be sent
   to the SET protocol development mailing list <> or
   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).

Donald E. Eastlake 3rd                                          [Page 1]

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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  to locate financial transaction card related
   facilities on the Internet by mapping ISO 7812 derived card numbers
   into domain names within in the domain.


   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

          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. Domain Maintenance Agency.................11

      5. Security Considerations................................12

      Author's Address..........................................13
      Expiration and File Name..................................13

      Appendix: Initial Brand Pointers..........................14

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 cardholder.  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 automatic way, given a card number, to 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 like 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.

   A means of automatically mapping such identification numbers into
   domain names in most cases 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 contact
   facilities on the Internet for that card.  Thus web browsers/wallets
   could 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 is to locate SET Certification

   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 been updated to have a URL
   or for which the URL has changed due to bank mergers or splits or a
   previously registered card for which the certificate is expiring but
   the card is still valid, when access to the current URL is
   inconvenient. There may be cases where the URL has changed since a
   card was printed due to DNS changes.  Furthermore, in certification
   authority interaction, the user will be required to supply their PAN

Donald E. Eastlake 3rd                                          [Page 4]

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   in any case and the requirement that they manually enter a URL means
   additional effort and opportunity for error. (Note also that PANs
   have a built in check digit to catch most typographical errors while
   URLs do not.)

   Similar consideration will apply to location of some other facilities
   on the Internet.

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
   are 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 lookup mechanism when the
   numbers and prefixes/suffixes are variable length. In this regard, it
   is important to remember that more specific names always 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 gnerated internally by software in an automatic

   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 future point some BIN
   numbers starting with 37 would be assigned to a different brand.  If
   you are looking up card number 37012345678 (not a valid American
   Express number), you could do a retrieval with a name like (to avoid exposing the credit card, no more than six
   digits may be included in the query). A wild card RR with the name
   *.7.3.xz 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 *. wild card,
   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 *.7.3.xy wild card since it does not match the more
   exact wildcard.

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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, usually by
   truncating the identification number to its first six digits, (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 idetnfication number is always 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 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 truncating and
   reversing the number 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 names can be automatically
   generated from a card number and need not be exposed to ordinary

   Appendix A 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

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   not belonging to the block brand.  So there will probably be under
   1,000 entries in the subdomain.

   Since there are only a few tens of thousands of banks of significance
   in the world for financial transaction cards, there should be well
   under 100,000 entries in the subdomain.

   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), numbers
   within these large blocks can be carved out by more specific entries
   for other brands where necessary.

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 registration form request to be sent and a registration form
   returned which the user fills in.  The completed registration form is
   submitted in a certificate request message to which there is a
   response which can include the certificate or indicate it will be
   issued later or indicate a failure.  The registration form response
   message can also be a referral to another CA site rather than a
   registration form.

   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/Registration-Initiation which activates a SET

   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 ".SET-".  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 accommodate arrangements such as a default
   certification authority for a brand with specific CAs for some BINs

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   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 "/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 /cardholderCInitRequest.

      Suffix to Domain Name            Action

      /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, <httl://>.

3.3 Financial Institutions Not On Line

   Some numbers are allocated to institutions that do not have a network
   presence.  To avoid 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 normally be generated.  In
   other cases, it may be possible for a brand to fill in for an issuer
   or the like.

3.4 BIN Ambiguity

   For the purposes of 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.

   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

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   (see section 4) 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.

   The cases where a URL is derived to access certification authority
   facilities, and the BIN is ambiguous, are not logically different
   from the home page case but use a different implementation.  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 identification number.  The registration form response can
   have, instead of a registration form, a referral to a different URL.
   Thus, the "CA" could be simply a secure referral program that uses as
   much of the identification number as it wishes, possibly more than
   the fist six digits, to determine where to forward the cardholder
   application.  This referral CA could be, as in the home page case,
   run by multiple banks or a brand or the maintenance
   agency (see section 4).

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4. Domain Maintenance Agency

   For full operational deployment of the domain, a
   maintenance agency for the DNS information, and possibly additional
   delegated agencies for subdomains, will need to be identified.

   A possibility is an existing company engaged in domain name
   registration activities or a newly created organization for this
   purpose.  Also, the American Bankers Association (ABA) is the world
   ISO 7812 registration agency and so is a natural possibility.

   Funding for maintenance should not be a problem.  Current going rates
   for large scale domain registration are $35 (US) or equivalent (NSI
   fee less 30% infrastructure fund deduction, rate change for
   registration in multiple third level domains under, it
   is hard to see how the annual cost for domain registration could be
   such that it would exclude any noticeable financial institution
   wishing to participate.

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5. 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 DNS were subverted.

   Care should be taken in making DNS queries that the entire
   identification number is NOT used as this would expose the card
   number within the Internet.  No more than the initial six digits,
   which constitute the BIN for the purposes of this document, can be


   [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.
        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.

Donald E. Eastlake 3rd                                         [Page 12]

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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 August 1998.

   Its file name is draft-eastlake-card-map-01.txt.

Donald E. Eastlake 3rd                                         [Page 13]

INTERNET-DRAFT                     Mapping ISO 7812 Numbers into the DNS

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.

Donald E. Eastlake 3rd                                         [Page 14]