INTERNET-DRAFT Donald E. Eastlake 3rd
CyberCash
Expires: 28 July 1996 29 January 1996
Application Level Internet Payment Syntax
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Status of This Document
This draft, file name draft-eastlake-internet-payment-01.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> or the ietf-payments mailing list
<ietf-pay@imc.org>.
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
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``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
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munnari.oz.au (Pacific Rim), or ftp.is.co.za (Africa).
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Abstract
The Internet is becoming an increasingly commercial arena in which
information is being bought and sold and payments are rendered for
services and data delivered within the Internet and 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
commerce in applications level data and services Proposed
specifications are given for how this syntax fits into and enables
commerce in the data and services rendered by the World Wide Web,
FTP, Telnet, SMTP, and DNS protocols.
Acknowledgments
The contributions of the following persons to this draft are
gratefully acknowledged:
Brian Boesch <boesch@cybercash.com>
Phillip Hallam-Baker <hallam@w3.org>
Dave Kristol <dmk@allegra.att.com>
David S. Raggett <dsg@w3.org>.
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Table of Contents
Status of This Document....................................1
Abstract...................................................2
Acknowledgments............................................2
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, Receipts, and Errors..........................9
3.1 Payment Strings........................................9
3.2 Receipt Strings........................................9
3.3 Message Flow and Payer Private Information............10
3.4 Refunds...............................................10
3.5 Errors................................................10
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 Tags................................12
4.4 HTML Form Price Tags..................................13
4.5 Payments and Receipts Via Miscellaneous Headers.......14
4.6 Payments and Receipts Via PEP.........................15
4.7 Web Proxies...........................................16
5. Use in File Transfer Protocol..........................18
6. Use in Telnet..........................................19
7. Use in Simple Message Transfer Protocol................20
8. The Domain Name System.................................22
9. Protocols to Which Payment is not Applicable...........24
9.1 The ECHO, DISCARD, and CHARGEN Services...............24
9.2 The Finger Service....................................24
9.3 The Auth Service......................................25
10. Security Considerations...............................26
References................................................27
Author's Address..........................................27
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1. Introductions
Commerce in applications level data and services on the Internet
requires a means to (1) indicate prices and acceptable methods of
payment, (2) tender payment, and (3) issue a receipt acknowledging
payment or notification if payment fails.
This document specifies a character string syntax for these three
items.
1.1 Applications Level Applicability
Payment facilities could be applied at a number of levels. This
specification is concerned only with applications level provision of
data items and services. It does not 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
services.
This proposed syntax is concerned with such matters as payment for
access to a web page, upload of a file via ftp, 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 require it. 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
payments.
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 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 8 specify a standard for inclusion of these items
in transactions for the World Wide Web (HTTP/HTML), File Transfer
Protocol (FTP), Telnet, Simple Message Transfer Protocol (SMTP), and
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the Domain Name System (DNS) protocols.
Section 9 lists some protocols to which application level payment
systems should not be applied.
Section 10 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 payment 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) and will commonly include one or more prices.
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 to eight letter
currency codes, or any valid domain name containing at least two
labels. (ISO 4217 codes normally consist of the two letter country
code followed by a letter mnemonic for the major unit of currency.)
Currency codes are case insensitive. Codes of one, two, or more than
eight letters appearing in the place of a currency code are reserved
for future definition.
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 and may optionally have a "+"
or "-" immediately followed by an integer scaling exponent. Any
number of digits of precision and any size exponent may be provided
but payment systems may define how many digits and what range they
utilize.
Some examples:
2.34gbp 2 pounds and 34 pence sterling
79+0ALL seventy nine Albanian Leks
123456-5cad one dollar 23 and 456 thousandths cents Canadian
0.125usd one eighth of a US dollar
2.2 Payment System Strings
Payment system strings consist of the payment system name, an equal
sign, and any payment system specific information (such as what
account within that payment system the payment should be made payable
to).
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Payment system names are either case insensitive four to twelve
letter names registered with IANA or a URL [RFC 1738] and are
terminated by an equal sign. Codes occurring in the place of payment
system names consisting of one to three letter or more than twelve
letters are reserved for future definition.
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 equal sign 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 or
private use, any URL may be used.
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 an arbitrary
donation or a payment system and account to which they can attempt to
charge indefinite amounts or payment for a service which will vary
with the amount of the payment. Where meaningful, it is recommended
that a price be listed that is a reasonable ceiling such that if
costs exceed it, 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.
For example:
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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 fixed by collecting 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, Receipts, and Errors
The sections below describe encoding of payments and receipts and the
inclusion of error messages in the payment or receipt context.
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 equal sign terminated 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 non-null payment specific information.
Only one such full payment system string can occur in a payment or
receipt.
The content and/or encoding of the payment system specific
information would normally differ between the price tag, payment, and
receipt contexts but this is a matter only of concern to the payment
system.
3.1 Payment Strings
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:
foocash=29Uso+Oa/e92micHd4s3
The payment system used in the payment is selected from among those
in the price tag since those are known to be supported by the seller.
Payment systems will commonly 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.
3.2 Receipt Strings
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:
barsys=8n7VtC2+uL341/==
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Payment systems will commonly include, in the payment system specific
information of a receipt, an indication of how much the receipt is
for and some type of serial or transaction number so that
retransmission of a message containing the receipt will not result in
confusion.
3.3 Message Flow and Payer Private Information
For some payment systems, the buyer, instead of sending a payment to
the seller, actually completes payment based on the price tag and
simply sends to the seller a receipt string, as described above,
proving that they have paid.
For payment systems where the payment is sent to the seller,
provision SHOULD be made for a small amount of arbitrary payer
private information to be provided in the payment message by the
buyer and returned to the buyer by the seller in the receipt.
3.4 Refunds
Depending on payment system details, refunds may not be available or
they can be implemented in two ways. 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 systems, both refund techniques might be available.
In others, refunding may not be possible.
3.5 Errors
Errors in formatting 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 within a payment
system in a price tag may be reported in a payment or receipt. Great
care must be taken to be sure to avoid any situation that could
result in an endless loop of receipts.
Errors outside of payment systems, such as receiving a payment via an
unknown payment system or syntax errors that make it impossible to
determine a payment system, should be reported via the normal error
mechanism of the protocol within which the payments are embedded (see
sections below).
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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 small payments
which might reasonably be incurred on a "per web page" basis or the
like.
In the Web, a price is indicated by a COST parameter or by a payment
required error response. As described below, a COST parameter can
occur within an anchor, HTML document header, or several places in a
FORM. Payment and receipts can be included with HTTP requests and
payments using headers.
4.1 Web Browser User Interface
[the user interface material could be moved to an appendix]
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 0.15usd 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
heavyweight 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 or other
operation that occurs when following that link. Note, however, that
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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 payment.
The cost is given by a COST parameter in the anchor. For example:
<A COST="0.10usd 0.17cad paymentsystem=xxxxxx foocash=yyyyyy"
HREF="http://mercenary.com/goodies">
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 Tags
The cost for accessing an HTML page and the default cost for
accessing any anchors or forms within the page can be included in the
header. For example:
<HTML>
<head><title>Mating Habits of the Red Breasted Geek</title>
<meta http-equiv="www-cost" content="0.05usd xxxsys=on93h5M+pll=">
<cost> 0.75usd 0.99cad xxxsys=A8jne8W2/sw== </cost></head>
<body> ... </body></HTML>
An attempt to get such a document from a payment aware server without
payment of at least 5 cents via the xxxsys payment system 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.
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The <cost>...</cost> item in the head indicates that all anchors and
forms on the page should be considered to have a price of 75 cents US
or 99 cents Canadian via the xxxsys payment system unless otherwise
indicated.
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="xxxsys=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>
</form>
The COST associated with the form is a base price (which may be
defaulted from a <cost> item in the document header), 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 that applies only if no
item is selected. When an item is selected, it overrides 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, or the COST parameters can contain
payment system name(s) without payment specific information to cause
price information to add to the amount for the designated payment
system(s). 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 payment system field used in calculating the payment
for 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
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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
form.
4.5 Payments and Receipts Via Miscellaneous Headers
[This section defines payments and receipts using existing HTTP
header fields and one new such field. As an alternative, section 4.6
defines then using PEP.]
Payment can accompany an HTTP request by including a payment line in
the message header. This consists of the "ChargeTo:" 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: xxxcash=A8jne8W2/sw==
ChargeTo: foocash= barsys=
The first example is in the form of a payment via the xxxcash system.
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: xxxcash=b93njexW2/swq4==
There are 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.
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 can be returned, in
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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 it 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
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.
4.6 Payments and Receipts Via PEP
[This section is just a direct translation of section 4.5 into PEP
[draft-khare-http-pep-00.txt]. Probably needs more work to fully
take advantage of PEP.]
Payment can accompany an HTTP request by including a payment line in
the message header. This consists of a "Protocol: {payment ...}"
header where "..." is a payment system string.
It is also possible to use the Accept-protocol header 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:
Protocol: { payment xxxcash=A8jne8W2/sw== }
Accept-protocol: { payment foocash= barsys= }
The first example is in the form of a payment via the xxxcash system.
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 a "Protocol: { receipt
...}" header where "..." is a payment system string. For example:
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Protocol: { receipt xxxcash=b93njexW2/swq4== }
There are cases where a larger payment is collected initially and the
unused portion refunded or where adjustments are required after a
purchase. Because of this, payment and receipt protocol and accept-
protocol headers are both allowed in both HTTP requests and
responses.
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 can be returned, in
which case there must be a "Protocol: { cost xxx }" response header
field analogous to the "www-authenticate:" header field for a "401
unauthorized"" response. The xxx field inside the protocol:cost
header 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 it 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
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
[This section needs more work and the scoping provision of PEP
[draft-khare-http-pep-00.txt] would almost certainly prove helpful.]
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 payment header and the OPTIONS 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 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 and corrected. In any case, if the proxy can cache a copy,
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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 free
copying of information for which the owner wished to impose a charge.
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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, via the 332 or 532 reply codes, that an
ACCT command be sent. 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.)
SUMMARY
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 or during 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
(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 off a host or user from the normal flow of
mail. It seems unlikely that most individuals or mailing lists would
be willing to pay to send mail to such an addressee. 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
following:
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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 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.)
SUMMARY
Price Tags - in new 332 reply.
Payments - in new ACCT command.
Receipts - in new 233, 433, and 533 replies.
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8. The Domain Name System
The Domain Name System (DNS) is currently 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. For
such uses DNS data is public and charges SHOULD NOT be imposed for
DNS queries.
However, new uses of DNS, including dynamic update (draft-ietf-
dnsind-dynDNS-*.txt), and particularly burdensome operations such as
zone transfers of a large zone to other than a secondary, may warrant
charges.
Payment information is all communicated via the PAY RR. The type for
the PAY RR is <TBD> and its structre is as follows:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| subtype | /
+--+--+--+--+--+--+--+--+ /
/ data /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
The subtype indicates what the data is as follows:
0 - reserved.
1 - price tag.
2 - payment string.
3 - receipt string.
4-254 - available for IANA allocation.
255 - reserved.
PAY RRs occur in a zone and master file only under the zone name as a
price tag indicating the fee for a zone transfer to anyone other than
a zone secondary server.
Payment can be tendered with any request by including an appropriate
PAY RR in the additional information section. WARNING: do not do
this unless you are sure the server you are communicating with
understands payments. Most current servers will ignore any request
with a non-emplty additional information section.
A receipt or price tag can be rendered by including an appropriate
PAY RR in the additional inforamtion section of a reply. Error code
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<tbd> indicates payment is required and MUST be accompanied by a
price tag PAY RR.
(See RFCs 1034, 1035, drafat-ietf-dnsind-dynDNS-*.txt)
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9. Protocols to Which Payment is not Applicable
Some protocols are inappropriate for the addition of payment
mechanisms. Either they are sufficiently basic to the operation of
the network or provide sufficiently light-weight access to public
information or are so simple there is no obvious way to add
extensions. Some of these protocols, listed below, SHOULD NOT make
use of this syntax or impose prices or payments. This does not imply
that there are not many more protocols for which it would be
inappropriate to define payment extensions.
9.1 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. In any case, there really aren't any protocol
hooks in these services on which to attach payment.
9.2 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. In any case, the information returned
by finger is free form text making it difficult to flag a payment
requirement.
(See RFC 1288.)
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9.3 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 is attempting to mislead 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.)
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10. 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) and connection (IPSEC, IPv6)
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 is 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 confirm 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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References
[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",
05/01/1983.
[RFC 855] - J. Postel, J. Reynolds, "Telnet Protocol specification",
05/01/1983.
[RFC 959] - J. Postel, J. Reynolds, "File Transfer Protocol",
10/01/1985.
Author's Address
Donald E. Eastlake, 3rd
CyberCash, Inc.
318 Acton Street
Carlisle, MA 01741 USA
Telephone: +1 508 287 4877
+1 508 371 7148 (fax)
+1 703-620-4200 (main office, Reston, Virginia, USA)
email: dee@cybercash.com
Expiration and File Name
This draft expires 28 July 1996.
Its file name is draft-eastlake-internet-payment-01.txt.
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Appendix A: Initial Payment System Names
This is an 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
added]
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 or <n>*<m>
to indicate n or more but not more than m repetitions; n defaults to
0.
;prices
isocurrency = alpha alpha alpha
ietfcurrency = 4*8alpha
privatecurrency = 2*127[ dns-label "." ]
currency = isocurrency | ietfcurrency | privatecurrency
digits = 1*digit
decimal = "." | ","
number = digits | digits decimal *digit
exponent = "+" digits | "-" digits
cost = number currency | number exponent currency
;payment system strings
ianapaysys = 4*12alpha
privatepaysys = url
paysysname = ianapaysys | url
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"
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alpha = lowalpha | hialpha
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
"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
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