U-PAI: A Universal Payment Application Interface

A paper from Second USENIX Workshop on Electronic Commerce,

USENIX, Oakland, CA

March 21, 2000 presented by steve 2

Outline

Introduction API Definitions Sample Ecash Proxy Conclusions

March 21, 2000 presented by steve 3

Introduction

Many payment mechanisms nowadayse.g. First Virtual, CyberCash, Ecash, SET,…

The most significant difference is the order of steps required to execute a payment

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Introduction (2)

Diversity of payment mechanisms stymied the progress of electronic commercecustomers must maintain accounts with

several different payment mechanismsno standard way for payment mechanisms to

interact with application software

March 21, 2000 presented by steve 5

U-PAI

U-PAI, a universal payment application interfaceGoal: define a common set of functions that

act as a layer of abstraction between application software and payment mechanisms

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U-PAI abstracts payment mechanism internals

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API Definitions

CORBA specification in ISL of Xerox PARCs ILU

Three main objects:AccountHandlePCR (Payment Control Record)Monitor

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AccountHandle

This instance is a representation of a real-world account

The user wishes to start making electronic payments with the account

Query balance and credit limits on the account

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Analogy to clarify the notion of accounts and AccountHandle

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AccountHandle (2)

Internal fields:BalanceCreditLimitAccountTypeTransferAccountTypesFromTransferAccountTypesTo…

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AccountHandle (3)

Methods:OpenAccount(PropertySet acctinfo): AnyCreateAccount(PropertySet acctinfo): AnyCloseAccount()DeleteAccount()

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PCR (Payment Control Record)

This instance is a representation of a single payment transaction

the locus of control for all activities regarding that payment

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PCR (2)

Internal fields:RefID, ContextIDAmountDestAccountHandle, SourceAccountHandleStatusMonitorList…

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PCR (3)

Methods:StartTransfer()TryToAbortTransfer()UpdateStatus(StatusEntry stat)

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Monitor

To supplement the status tracking feature of a PCR

Internal field: status Method: Notify(PCR p, StatusEntry s)

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Sample Ecash Proxy

An electronic “coin”-based payment mechanism

Provides anonymity for the purchaser U-PAI interacts with ecash at the level of

the user operations

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Ecash

E-cash/UNIX Pay Command

Coins transferred by e-cash

Payment Complete?

Accept deposit? (E-cash protocol)

Yes

Coins transferred by e-cash

Merchant Application

Customer Application

Merchant E-cash ClientBank

E-cash Server

Customer E-cash Client

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(c) Update Status(c) Update Status

(d) Notify(d) Notify(a) StartTransfer

(b) StartTransfer

Request and send Host/Port Info

Merchant E-cash Client

Merchant E-cash AccountHandle

Payment Control Record

Merchant Monitor

Customer Monitor

Application

Customer E-cash AccountHandle

Customer E-cash Client Bank

E-cash Server

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Conclusions

U-PAI allows a variety of payment mechanisms to be accessed by the same interface

U-PAI only covers the basic functionality of accounts and payments

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The EndThe End