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Versions: 00 01                                                         
INTERNET-DRAFT                                    Donald E. Eastlake 3rd
Updates RFC 821, 854, 959                                      CyberCash
Expires: 6 January 1996                                      7 July 1995

              An Application Level Internet Payment Syntax
              -- ----------- ----- -------- ------- ------

Status of This Document

   This draft, file name draft-eastlake-internet-payment-00.txt, is
   intended to be become one or more Proposed Standard RFCs.
   Distribution of this document is unlimited. Comments should be sent
   to the author <dee@cybercash.com>.

   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 ds.internic.net, nic.nordu.net, ftp.isi.edu,
   munnari.oz.au, or ftp.is.co.za.

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   The Internet is becoming an increasingly commercial arena in which
   information is being bought and sold and payments are rendered for
   goods and services to be delivered outside of the Internet.  Thus
   far, the protocols and format used for such payments have been ad hoc
   and proprietary.

   This draft proposes a uniform application level syntax to support
   such commerce. Specific specifications are given for how this syntax
   fits into the World Wide Web, FTP, Telnet, and SMTP.


   The contributions of the following persons to this draft are
   gratefully acknowledged:

      Brian Boesch <boesch@cybercash.com>
      Phillip Hallam-Baker <hallam@w3.org>
      David S. Raggett <dsg@w3.org>.

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Table of Contents

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


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

      1. Introductions...........................................4
      1.1 Applications Level Applicability.......................4
      1.2 Overview of this document..............................4

      2. Price Tags..............................................6
      2.1 Prices.................................................6
      2.2 Payment System Strings.................................6
      2.3 Price Tags.............................................7

      3. Payments and Receipts...................................9

      4. Use in the World Wide Web..............................11
      4.1 Web Browser User Interface............................11
      4.2 Anchor Embedded Costs.................................11
      4.3 Page Header Price Tag.................................12
      4.4 HTML Form Price Tags..................................13
      4.5 Web Payments and Receipts.............................13
      4.6 Payment Required Error................................14
      4.7 Web Proxies...........................................15

      5. Use in File Transfer Protocol..........................16

      6. Use in Telnet..........................................17

      7. Use in Simple Message Transfer Protocol................18

      8. Protocols to Which Payment is not Applicable...........20
      8.1 The Domain Name System................................20
      8.2 The Finger Service....................................20
      8.3 The Auth Service......................................20
      8.4 The ECHO, DISCARD, and CHARGEN Services...............21

      9. Security Considerations................................22

      Author's Address..........................................23
      Expiration and File Name..................................23

      Appendix A: Initial Payment System Names..................24

      Appendix B: Simplified BNF................................25

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1. Introductions

   Applications level Internet commerce requires a means to (1) indicate
   prices and acceptable methods of payment, (2) tender payment, and (3)
   issue a receipt acknowledging payment or indicate if payment fails.

   This document specifies a character string syntax for these three

1.1 Applications Level Applicability

   Payment facilities could be applied at a number of levels.  This
   specification is concerned only with applications level data items
   and services.  It does not in any way concern itself with network
   level packets or quality of service nor does it concern itself
   directly with transport level connections or quantity or quality of
   service except as these transport level measures impact application

   This proposed syntax is concerned with such matters as access to a
   web page page, storage of a file, initiation of a telnet session, or
   conducting an extensive WAIS search.  These are generally user
   visible and meaningful data objects or tasks.

   Within most legal systems, the owners of such data objects and/or the
   owners of the facilities used to present such objects or perform such
   tasks are frequently entitled to require some recompense if they
   choose to do so.  This document does not concern itself with the
   morality of such laws or requirements but merely provides a syntax
   whereby cooperating entities may speak at that level about prices and

   There is no requirement that the "currencies" used with this syntax
   be the usually recognized national or international currencies.  For
   example, some transactions could be denominated in frequent flyer
   miles or other private artificial unit.

1.2 Overview of this document

   Sections 2 and 3 below define a basic syntactic framework for price
   tags, payments, and receipts.

   Sections 4 through 7 specify a standard for inclusion of these items
   in transactions for the World Wide Web (HTTP/HTML), File Transfer
   Protocol (FTP), Telnet, and the Simple Message Transfer Protocol

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   Section 8 lists some protocols to which application level payment
   systems should not be applied.

   Section 9 discusses security considerations.

   Appendix A is an initial list of payment systems that are or are
   planned to be usable via this syntax.

   Appendix B gives a semi-formal BNF-like description of the syntax.

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2. Price Tags

   A uniform price tag format is needed to indicate when payment is due,
   how much, and what methods are acceptable by the seller.  Such a
   price tag must include the specification of one or more acceptable
   payment systems (with a provision for payment system specific
   information where needed) and will almost always include one or more

   Sections 2.1 and 2.2 below describe prices and payment system strings
   and Section 2.3 assembles these for complete price tags.

2.1 Prices

   Prices are encoded as character strings consisting of a number
   followed by a currency code.

   These currency codes are the three letter ISO 4217 codes, Internet
   Assigned Number Authority (IANA) registered four letter or longer
   currency codes, or private use currency codes starting with "x-".
   (ISO 4217 code normally consist of the two letter country code
   followed by a letter mnemonic for the major unit of currency.)
   Currency codes are case insensitive. One and two letter codes
   appearing in the place of a country code are reserved for future use.

   The number preceding the currency designation is the quantity of
   major units of that currency.  It may optionally have a decimal point
   and additional decimal fraction digits for specifying minor unit or
   fractions of units.  (Some currencies, such as US Dollars or British
   Pounds have minor units (cents and pennies). Others, such as Japanese
   Yen and Italian Lira do not.)  Fractional digits may continue
   indefinitely after the decimal point but payment systems may define
   how many digits they utilize.

   Somes examples:

      2.34gbp, 79ALL, 1.23456cad, 0.125usd

   which signify 2 pounds and 34 pence sterling, seventy nine Albanian
   Leks, one dollar and 23 and 456 thousandths cents Canadian, and one
   eighth of a US dollar.

2.2 Payment System Strings

   Payment system strings consist of the payment system name, a colon,
   and any payment system specific information (such as what account

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   within that payment system the payment should be made payable to).

   Payment system names are case insensitive, four or more letters long,
   and are indicated by a terminating colon.  One to three letter codes
   occurring in the place of payment system names are reserved for
   future use.

   Payment system specific information must be encoded so that it
   contains no internal spaces or unusual characters as described in
   Appendix B.  It is up to the named payment system to encode and
   decode any information it requires so as to fit within this syntax.
   Use of the base64 encoding defined in RFC 1521 is recommended.  The
   payment system specific information, if any, appears immediately
   after the payment system name and colon and is terminated by white
   space or the end of the price tag character string.

   A registry of payment system names is maintained by IANA.  Initial
   payment system names are listed in Appendix A.  For experimental use
   pursuant to bilateral agreement between the parties involved payment
   system name starting with "x-" may be used. No names of this form
   will be officially registered.

2.3 Price Tags

   A complete price tag consists of a string of white space separated
   prices and payment system strings.  There must be at least one
   payment system string present.

   Normally there will also be at least one price.  However, there are
   circumstances under which the cost of a service in highly
   unpredictable and the seller is, in effect, requesting a payment
   system and account to which they can attempt to charge indefinite
   amounts.  Under these circumstances, it is recommended that a price
   be listed which is a reasonable ceiling such that if costs exceed
   that, the seller which have to present another price tag; however, it
   is permitted to omit the price and list only a payment system in a
   price tag.

   Payment systems SHOULD provide a means for a limited amount of
   arbitrary seller information to be included in the payment system
   specific part of a price tag and be returned to the seller within a
   payment message based on that price tag.

   A price appearing after a payment system string applies only to that
   system.  Putting a price before the first payment system specific
   information makes that price a default for every payment system
   specified.  The default can be overridden by specifying a different
   amount for that currency after a particular payment system.

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   For example:

      33.45all foocash:xxxx 22eTb barsys:yyyy 9.999ghC

   indicates that payment of twenty two Ethiopian Birrs via the foocash
   payment system or 9.999 Ghanaian Cedis via the barsys system or 33.45
   Albania Leks via either system is acceptable.

   In cases where the cost of the service is not known in advance, the
   price can be an estimate, deposit request, or the like, with any
   overpayment refunded.  Underpayment can be collected by requesting an
   additional payment from the client.  In the absence of trust between
   the parties, frequent small payments may be required.

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3. Payments and Receipts

   After encountering a price tag, either initially, during a session,
   or in conjunction with a "payment required" error, an application
   needs some method of tendering payment.  This is done with a payment
   system string with the same syntax as described in Section 2.2 above.
   For example:


   The payment system used in the payment is selected from among those
   in the price tag as those are known to be supported by the seller.
   Payment systems will normally include in the payment system specific
   information some sort of serial or transaction number so that
   retransmission of a message containing the string will not result in
   duplicate payment.

   Normally the seller will provide a receipt for the amount of money
   actually collected or a message indicating payment failure or error.
   This will be via a receipt character string which is also simply in
   the form of a payment system string.  For example:


   Payment systems will normally include in the payment system specific
   information of a receipt, in addition to an indication of how much
   the receipt is for, some type of serial or transaction number, so
   that retransmission of a message containing the receipt will not
   result in confusion.

   A null payment or receipt string is explicitly permitted in most
   contexts as a way for an entity to indicate merely that it is payment
   syntax aware.

   One or more payment system names in isolation are permitted in a
   payment or receipt context but only as a way to indicate that a
   particular payment system is understood.  Any actual payment or
   receipt must have a colon and non-null payment specific information.
   Only one such full payment system string can occur in a payment or

   Depending of payment system details, a refund can be implemented in
   two way.  It can be a payment message from the seller to the buyer,
   normally leading to a receipt from the buyer to the seller.  Or the
   seller may be able to directly refund to the buyer's account or the
   like and simply send the buyer a receipt.  In some payment system,
   both refund techniques might be available.  In others, refunding may
   not be possible.

   The content and/or encoding of the payment system specific

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   information would normally differ between the price tag, payment, and
   receipt contexts but this is a matter only of concern to the payment
   system.  Errors in formating or the like that are internal to a
   payment or receipt should generally be handled by being logged and/or
   reported by an error message encoded into a receipt.  Errors in a
   price tag may be reported in a payment or receipt.  Great care should
   be taken to be sure to avoid any situation that could result in an
   endless loop of receipts.

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4. Use in the World Wide Web

   The World Wide Web is a rapidly evolving system for information
   interaction that is being increasingly used for commerce.  It is
   particularly well suited for the inclusion of payment systems,
   especially any designed for efficient handling of very small payments
   which might reasonably be incurred on a "per web page" basis or the

   In the Web, a price is indicated by a COST parameter, as described
   below, which can occur within an anchor, HTML document header, or
   several places in a FORM. Payment can be included with any HTTP
   request using the "ChargeTo:" header.  A receipt can be included in
   any HTTP reply using the "Receipt:" header.

4.1 Web Browser User Interface

   It is important that small payments be closely integrated into the
   browser user interface.  An expected mode of operation will be one of
   many small payments so the overhead associated with each must be
   small.  It is unacceptable for the user to necessarily interact with
   a separate screen or window to approve each small payment although a
   user who wishes to do so should have that option.

   The user should be able to establish some threshold (default perhaps
   around 0.1usd or equivalent) such that actions incurring that charge
   or less are semi-automatic.  That is, no special approval action is
   required, although color coding or the like should be used to
   distinguish toll links from free links, an optional sound could be
   made when any money is sent, or other clues used to give the user a
   feel for what is going on.

   To avoid spending an unexpectedly large amount in small pieces,
   possibly a bank graphic or the like should be displayed to show how
   much cash is still available to the browser before the user will have
   to take action.  The act of refilling the bank would be a more heavy
   weight operation requiring user interaction or, to get a default
   amount, at least user approval.

4.2 Anchor Embedded Costs

   A cost can appear in an anchor.  This is a very strong hint that
   payment of the indicated amount should accompany the GET operation
   that occurs when following that link.  Note, however, that it is
   ultimately up to the server being hit to determine if payment is
   adequate or to follow the course it chooses for different levels of

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   The cost is given by a COST parameter in the anchor.  For example:

      <A COST="paymentsystem:xxxxxx 0.10usd 0.17cad"
      Great stuff for one thin dime! </A>

   It is recommended that toll links be shown in a different color or
   type style from toll-free links.  Browsers may wish to go further and
   indicate different cost levels, particularly costs above or below any
   "automatic approval" level the user has. When the user has their
   pointer over the link, the browser may wish to display the payment
   particulars in a similar way to that in which it displays the URL.
   (Such a display could be filtered to the currency and/or payment
   system(s) actually available to the user.)

   Notice that the cost, if any, indicated by the anchor text ("Great
   stuff..." above) could be different from the actual "COST=" parameter
   which controls the payment sent with the request.  In turn, the
   "COST=" amount could be different from what the server really wants.
   Or the server may provide different data or services for different
   payment amount.  Such variable payment schemes may be better handled
   with a FORM as described below.

4.3 Page Header Price Tag

   The cost for accessing an HTML page can be included in the header.
   For example:

      <head><title>Mating Habits of the Red Breasted Geek</title>
      <cost> 0.75usd 0.99cad cybercash:A8jne8W2/sw== </cost></head>
      <body> ... </body></HTML>

   An attempt to get such a document without payment or with inadequate
   payment should fail (see Payment Required Error section below).  A
   second attempt with payment will be required.  This could be done in
   a manner similar to an access restriction failure followed by a
   second attempt with access authorization information.

   Implementing page header cost requires that the HTML for a web page
   be partly understood by the server, at least through the head, but
   this is necessary to implement the "title:" and "link:" response
   entity header fields anyway.

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4.4 HTML Form Price Tags

   A cost can be associated with a form and with multiple choice items
   within the form.  For example:

   <form COST="CyberCash:A8jne8W2/sw== 0.75usd 0.99cad" ACTION=POST>

   Miscellaneous text, etc.

   <input type="radio" name="extras" value="omit">plain vanilla
   <input type="radio" name="extras" value="include"
        COST="0.25usd 0.40cad">chocolate fudge

   <p>Your quality of service: <select name="quality">
   <option value="bronze"> Low<p>
   <option value="silver" cost="0.10usd 0.17cad"> Medium<p>
   <option value="gold" cost="0.20usd 0.34cad">
   High<p> </select>

   The COST associated with the form is a base price to which any
   multiple choice item costs are added.  The form level COST may be
   omitted and COSTs can still appear with multiple choice items.  The
   COST associated with a "select" is a default which applies only if no
   item is selected.  When an item is selected, it over-rides the
   selection level cost and become the price component added into the
   total form price for that selection.

   The normally required payment system string can be omitted from some
   of the form COST parameters, in which case any prices add to the
   amount for all payment systems.  But one or more payment systems and
   their payment system specific parameters must be determinable if any
   payment is to be sent.  The payment system specific information
   associated with the last encountered instance of a payment system
   field in processing the form is used.  If no payment system field is
   encountered, then no payment will be sent with the request even
   though "COST=" parameters are present.

   As with anchor costs, it is desirable to indicate the cost of
   multiple choice items by color coding and the cost of activating the
   form by color coding the submit button.  Note that the submit button
   could change from free to toll or the like as choices are made in the

4.5 Web Payments and Receipts

   Any HTTP request can be accompanied with payment by including a
   payment line in the message header.  This consists of the "ChargeTo:"

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   header label followed by a payment system string; however,
   "ChargeTo:" can appear with one or more bare payment system names for
   the purpose of indicating that the browser understands those systems
   without conveying any actual payment.  Examples:

      ChargeTo:  cybercash:A8jne8W2/sw==

      ChargeTo:  foocash barsys

   The first example is in the form of a payment via cybercash.  The
   second example is an indication by the sender that it understands the
   foocash and barsys payment systems.

   The browser should keep track of such actual payments it has sent and
   re-send the identical payment if the request needs to be retried with
   access authorization information or due to a transient error, rather
   than sending additional funds.

   The collection of payment or the specifics of the failure of a
   tendered payment are indicated back to the customer by a receipt line
   in the response header.  This consists of the "receipt:" header label
   followed by a payment system string.  For example:

      Receipt: cybercash:A8jne8W2/sw==

   There cases where a larger payment is collected initially and the
   unused portion refunded or where adjustments are required after a
   purchase.  Because of this, ChargeTo and Receipt headers are both
   allowed in both HTTP requests and responses.

4.6 Payment Required Error

   If an HTTP request arrives without sufficient payment (or with none
   at all) and payment is required by the server, the server can simply
   provide a web page with limited or no actual information and possibly
   one or more links with COST parameters embedded in them.
   Alternatively, a "402 payment required" error is returned in which
   case there must be a "www-cost:" response header field analogous to
   the "www-authenticate:" header field for a "401 unauthorized""
   response.  The value of the www-cost field is the same as for the
   COST parameter described above.

   This is similar to an access restriction error in that the browser
   can just try again with payment included the way they can try again
   with access information. It may be possible to combine these by
   returning a 402 error with the HTML accompanying the error having a
   link with a COST parameter pointing to the originally sought item.
   This would combine automatic charging for browsers that have 402

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   error processing implemented with a convenient way for the user to
   re-request with payment for browsers that understand anchor COST
   parameters but do not automatically handle 402 errors.

4.7 Web Proxies

   When information that has an owner and price is being cached and
   served to multiple different users by a proxy, the payments should be
   requested by the proxy. The safest thing for the proxy to do is to
   send payment to the entity it retrieved the data from using an HTTP
   request with a ChargeTo header and the PAYMENT method.

   If the proxy understands the payment system well enough and there are
   no firewall problems, the proxy may be able to collect the payment
   and directly transfer funds to the information owner.

   It is not expected that proxy payment collection will be perfect.
   There will initially be many dumb proxies that don't understand
   payment and there may be proxies that deliberately avoid collecting
   and forwarding payment.  But any large scale avoidance of payment
   will be noticed.  In any case, if the proxy can cache a copy, so
   could the user, who could then give copies to all his friends.  The
   ease of automatically making small payments for information through
   this syntax is hoped to produce a net reduction in unauthorized
   information copying.

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5. Use in File Transfer Protocol

   An FTP server may wish to charge for a file transfer (either way) or
   for an FTP session.

   It may do so by requesting that an ACCT command be sent via the 332
   or 532 reply codes.  332 is used to indicate that a received command
   is being held in abeyance pending receipt of an ACCT while 532
   indicates that a received command has been abandoned due to lack of
   payment and an ACCT command needs to be sent before attempting the
   command again.

   Price tags are indicated in the 332 or 532 text by a string at the
   beginning of the form

      <COST="foocash:xxxxx 0.05usd">

   in the 332 or 532 text, i.e., a literal "<COST=" followed by a string
   conforming to the definition herein of a price tag, followed by a
   ">".  The word "cost" is case insensitive.  Arbitrary additional text
   may be included after the price tag.

   A payment can be send by simply including a payment string, as
   defined in section 3, after the ACCT command.

   A successful receipt is rendered by returning a 233 reply with a
   receipt payment system string as the beginning of its text.  A
   payment failure receipt is rendered by returning a 433 or 533 reply
   depending on whether the failure is transient or permanent.  In
   either case, the receipt string can be terminated by white space and
   additional text human readable text placed after the receipt string
   in the reply.

   (See RFC 959.)


      Price Tags - in existing 332 and 532 replies.
      Payments - in existing ACCT command.
      Receipts - in new 233, 433, and 533, replies.

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6. Use in Telnet

   A host may wish to charge for a Telnet session.  Telnet option code
   [TBD] is used to initially negotiate agreement of the two parties to
   speak about payment.  As with other Telnet options, either side can
   sent IAC WILL xxx, in response to which an IAC DO xxx indicates
   agreement and an IAC DON'T xxx indicate refusal.  Or a party can send
   IAC DO xxx to which IAC WILL xxx indicates agreement and an IAC WON'T
   xxx indicates refusal.

   After agreement to speak about payment has been reached, Telnet
   subnegotiation strings can be exchanged, bracketed with IAC SB and
   IAC SE.  The initial subnegotiation byte indicates the type of
   payment message following in the rest of the subnegotiation byte
   string as follows:

        Byte  Meaning
        ----  -------

         01    Price-tag
         02    Payment
         03    Receipt

   If desired, arbitrary binary representations may be used for payment
   system specific information after the colon terminating the system
   name in payments and receipts (as long as bytes with value 255 are
   doubled as per the Telnet standard). Termination can be unambiguously
   determined by the IAC SE sequence.  However, price tags must stick
   with the ASCII syntax given herein as they must be parsed by systems
   that may not understand any particular payment system.

   (See RFCs 854, 855.)

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7. Use in Simple Message Transfer Protocol

   A host or user may wish to charge for the receipt of mail. This is
   accomplished via the new 332 reply code.  This is an interim success
   code that indicates that further information is required to complete
   a pending command.  Note that use of 332 after the SMTP RCPT command
   would be a simple way to implement any particular user requiring
   payment for mail to be delivered to them and its use after the MAIL
   command would be a simple way to implement a system requiring payment
   for mail from all or certain sources (although this information is
   easy to forge).

   Payment is indicated by the new ACCT command.  This is followed by a
   payment string as defined in section 3 above.

   Charging for mail may cut a host or user off from the normal flow of
   mail.  It seems unlikely that most individuals or mailing lists would
   be willing to pay to send mail to an address. However, it is easy to
   envision cases where a service for which it would be reasonable to
   charge is requested via email.  Or there may be individuals who do
   want to substantially cut themselves off from most mail or mail from
   certain senders.

   SMTP servers that speak ESMTP (see RFC 1651) may optionally give the
   new EHLO keyword ACCT.  However, ESMTP is designed for servers to
   list features to be optionally invoked by clients.  It is not really
   appropriate as a means for servers to indicate features that they
   will *require* of clients.

   In any case, it is believed that no negotiation is necessary for an
   SMTP server to use the new 332 reply code.  RFC 821 is clear that the
   receipt of any 3xx reply code after a MAIL, RCPT, etc. command is to
   be considered an error.  This is the appropriate understanding for an
   SMTP client that does not understand payment when an SMTP server
   requires payment.

   The rules and state diagrams in RFC-821 are hereby amended and the
   state diagram for MAIL, RCPT, SEND, SOML, and SAML is modified to the

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                                    1     +---+  1,3
        FLOW FOR             +----------->| E |<-----+
        PAYMENT AWARE        |            +---+      |
        SMTP SERVER          |                       |
                             |      2     +---+   2  |
                             +----------->| S |<-----+
                             |            +---+      |
                             |                       |
                             |                       |
            +---+   cmd    +---+  3   +---+  ACCT  +---+
            | B |--------->| W |----->|   |------->| W |
            +---+          +---+      +---+        +---+
                             |                       |
                             |     4,5    +---+  4,5 |
                             +----------->| F |<-----+

   A successful receipt is rendered by returning the new 233 reply with
   a receipt payment system string as the beginning of its text.  A
   payment failure receipt is rendered by returning the new 433 or 533
   replies depending on whether the failure is transient or permanent.
   In either case, the receipt string can be terminated by white space
   and additional text human readable text placed after the receipt
   string in the reply.

   The middle digit 3 in SMTP reply codes is reserved for accounting,
   corresponding to its existing use in FTP.

   (See RFCs 821, 1651.)


      Price Tags - in new 332 reply.
      Payments - in new ACCT command.
      Receipts - in new 233, 433, and 533 replies.

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8. Protocols to Which Payment is not Applicable

   Some protocols are sufficiently basic to the operation of the network
   or provide sufficiently light-weight access to public information
   that attempts to impose application level payment would be
   inappropriate.  Some of these protocols, listed below, SHOULD NOT
   make use of this syntax or impose prices or payments.

8.1 The Domain Name System

   Part of the philosophy of the Domain Name System (DNS) is that it
   contains public information and generally gives the same answers to
   all inquirers.  It is used for such fundamental purposes as
   translating domain names (such as tam.cybercash.com) into IP
   addresses or specifying SMTP mail backup and routing servers.  As
   such, charges SHOULD NOT be imposed for DNS queries.

   (See RFCs 1034, 1035.)

8.2 The Finger Service

   Finger is an optional information service intended to permit remote
   users to learn a limited amount of information about a user or users
   on an Internet host.  Information such as the time they last logged
   in or contents of their ".plan" file.  There are serious security
   considerations involved in allowing finger access to a host and hosts
   are free to decide how much such access, if any, they will provide.

   In some cases, finger servers have been set up to act as information
   retrieval or reporting mechanisms, but this was not the designed
   purpose of finger and, in most cases, there are better mechanisms to
   provide such access.

   If finger access is provided because a site wishes to be open,
   charges SHOULD NOT be imposed.

   (See RFC 1288.)

8.3 The Auth Service

   This service, when implemented, allows a remote host to determine the
   user associated with a TCP connection.  It is intended as a security
   and auditing tool although it is weak in the face of anyone with
   direct access to the TPC or IP level who was attempting to mislead

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   it.  Implementation is optional.

   Those who chose to provide this service are doing so to cooperate in
   such security or auditing at some sacrifice in the privacy of their
   users.  Charging for this service makes little sense in this context.

   (See RFC 931.)

8.4 The ECHO, DISCARD, and CHARGEN Services

   These are light weight services intended for network maintenance.
   ECHO echoes the packet sent to it (see RFC 862), DISCARD throws away
   packets sent to it but maintains the connection (see RFC 863), and
   CHARGEN generates an infinite number of random characters and sends
   them until the calling party disconnects (see RFC 864).

   Hosts are free to decide which, if any, of these three services they
   wish to provide (although ECHO is Recommended), but SHOULD NOT impose
   any charges for them.

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9. Security Considerations

   Getting authorization to construct payments may, depending on the
   payment system, require the user to enter a passphrase. For example,
   a passphrase might be required at the beginning of their session to
   unlock a private key. Thus the user could be vulnerable to Trojan
   horse web browsers, ftp clients,  telnet clients, etc., as they are
   to many other types of Trojan horse applications.  Use of "secure"
   application distribution with signed executables, checksums, virus
   detection, etc., should be encouraged.

   An adversary may be able to observe or modify traffic to and from an
   application.  Payment systems should be designed so that such
   observation results in minimal loss of privacy and such observation
   or modification can not result in hijacking a payment.  Note that an
   adversary that has complete control over application communications
   can pretend to be a merchant just as it could by controlling an end
   node.  However, such impersonation from an end node may be easier to
   trace and control than impersonation at an unknown point along the
   communications path.  Message (MOSS, SHTTP, etc.) and connection
   (IPSEC, IPv6, SSL, etc.) security protocols are available to help
   protect the communications path.

   On receipt of an advance payment, a server is capable of charging the
   user regardless of whether the server actually provides the data or
   services being charged for. A server could even send back an error
   message but keep and use the payment.  Some means of automatically
   logging payments that result in a software or human detectable
   failure to deliver should be implemented so these can be examined for
   patterns or cross checked with payment system statements of account.

   A merchant can withhold and fail to send back to the user a receipt.
   Applications should assume any payment sent will be collected
   regardless of whether they get a receipt back.

   With payment systems, a monetary cost can sometimes be associated
   with downloaded data.  Caching algorithms may wish to take this into
   account and cache costly data in preference to free data.  Servers
   should accept the identical data request from the same net entity for
   a reasonable amount of time even if the payment being presented
   appears to be a duplicate. Transient errors may have prevented use of
   the data previously downloaded for that request.

   A bad client application could generate payments exceeding the funds
   or authorization available to it.  Servers should verify payments
   promptly and be cautious of extending services or goods unless they
   can confirms that payment is good.  Applications and payment systems
   should be designed to limit the amount of funds a rogue application
   could transfer.

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   [ISO 4217] - Codes for the representation of currencies and funds

   [RFC 821] - J. Postel, "Simple Mail Transfer Protocol", 08/01/1982.

   [RFC 854] - J. Postel, J. Reynolds, "Telnet option specifications",

   [RFC 855] - J. Postel, J. Reynolds, "Telnet Protocol specification",

   [RFC 959] - J. Postel, J. Reynolds, "File Transfer Protocol",

Author's Address

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

   Telephone:   +1 508 287 4877
                +1 703-620-4200 (main office, Reston, Virginia, USA)
   email:       dee@cybercash.com

Expiration and File Name

   This draft expires 28 December 1995.

   Its file name is draft-eastlake-internet-payment-00.txt.

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Appendix A: Initial Payment System Names

   This is the initial alphabetic list of the initial registered payment
   system names that intend to be usable via this syntax.

   [send email to author, dee@cyercash.com, if you would like to be

    Company Name         Email Contact         Home Page
    ------------         -------------         ---------
    Payment System Name  -  (brief description)

   CyberCash, Inc.       info@cybercash.com  http://www.cybercash.com
   cybercash  -  (credit card)
   cash       -  (cash)

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Appendix B: Simplified BNF

   This is a BNF-like description of the Payment Protocol syntax syntax,
   using the conventions of RFC822, except that "|" is used to designate
   alternatives, and brackets [] are used around optional or repeated
   elements. Briefly, literals are quoted with "", optional elements are
   enclosed in [brackets], and elements may be preceded with <n>* to
   designate n or more repetitions of the following element; n defaults
   to 0.


   isocurrency        = alpha alpha alpha
   ietfcurrency       = 4*alpha
   privatecurrency    = "x-" 4*alpha
   currency           = isocurrency | ietfcurrency | privatecurrency
   digits             = 1*digit
   decimalpoint       = "." | ","
   number             = digits | digits decimalpoint *digit

   cost               = number currency

   ;payment system strings

   ianapaysys     = 4*alpha
   privatepaysys  = "x-" 4*alpha
   paysysname     = ianapaysys | privatepaysys

   paysys         = paysysname ":" *uchar

   ;price tag

   pricetag = *sp paysys *[ 1*sp cost | 1*sp paysys ] *sp |
              *sp *[ cost 1*sp | paysys 1*sp ] paysys *sp

   ;miscellaneous definitions

   lowalpha       = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" |
                    "i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" |
                    "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" |
                    "y" | "z"
   hialpha        = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" |
                    "I" | "J" | "K" | "L" | "M" | "N" | "O" | "P" |
                    "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" |
                    "Y" | "Z"
   alpha          = lowalpha | hialpha
   digit          = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |

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                    "8" | "9"
   other          = "$" | "-" | "_" | "." | "+" | "/" | "=" | "@"
   hex            = digit | "A" | "B" | "C" | "D" | "E" | "F" |
                    "a" | "b" | "c" | "d" | "e" | "f"
   escape         = "%" hex hex
   sp             = " "
   uchar          = alpha | digit | other | extra | escape

Eastlake                                                       [Page 26]