Network Working Group M. Terada

Network Working Group M. Terada
Request for Comments: 4154 NTT DoCoMo
Category: Informational K. Fujimura
NTT
September 2005

Voucher Trading System Application Programming Interface (VTS-API)

Status of This Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (2005).

IESG Note

This document is not a candidate for any level of Internet Standard.
This document specifies the Voucher Trading System Application
Programming Interface (VTS-API), which assumes that the VTS plug-in
is trusted by its user. The application making calls to VTS-API
ought to authenticate the VTS plug-in and securely bind the plug-in
with the VTS provider information specified in the Voucher Component.
However, this document does not specify an approach to application
authentication. The VTS-API should not be used without being
augmented by an application authentication mechanism.

Abstract

This document specifies the Voucher Trading System Application
Programming Interface (VTS-API). The VTS-API allows a wallet or
other application to issue, transfer, and redeem vouchers in a
uniform manner independent of the VTS implementation. The VTS is a
system for securely transferring vouchers; e.g., coupons, tickets,
loyalty points, and gift certificates. This process is often
necessary in the course of payment and/or delivery transactions.

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Table of Contents

1. Introduction ................................................. 3
2. Processing Model ............................................. 4
3. Design Overview .............................................. 6
4. Concepts ..................................................... 6
5. Interface Definitions ........................................ 8
5.1. VTSManager .............................................. 8
5.1.1. getParticipantRepository ......................... 8
5.1.2. getVoucherComponentRepository .................... 8
5.2. ParticipantRepository ................................... 9
5.2.1. lookup ........................................... 9
5.3. Participant ............................................. 9
5.3.1. getIdentifier .................................... 10
5.3.2. getVTSAgent ...................................... 10
5.4. VTSAgent ................................................ 10
5.4.1. login ............................................ 11
5.4.2. logout ........................................... 12
5.4.3. prepare .......................................... 12
5.4.4. issue ............................................ 13
5.4.5. transfer ......................................... 14
5.4.6. consume .......................................... 15
5.4.7. present .......................................... 16
5.4.8. cancel ........................................... 17
5.4.9. resume ........................................... 18
5.4.10. create .......................................... 18
5.4.11. delete .......................................... 19
5.4.12. getContents ..................................... 19
5.4.13. getSessions ..................................... 19
5.4.14. getLog .......................................... 20
5.4.15. addReceptionListener ............................ 20
5.4.16. removeReceptionListener ......................... 21
5.5. Session ................................................. 21
5.5.1. getIdentifier .................................... 21
5.5.2. getVoucher ....................................... 22
5.5.3. getSender ........................................ 22
5.5.4. getReceiver ...................................... 22
5.5.5. isPrepared ....................................... 22
5.5.6. isActivated ...................................... 23
5.5.7. isSuspended ...................................... 23
5.5.8. isCompleted ...................................... 23
5.6. Voucher ................................................. 23
5.6.1. getIssuer ........................................ 23
5.6.2. getPromise ....................................... 24
5.6.3. getCount ......................................... 24
5.7. VoucherComponentRepository .............................. 24
5.7.1. register ......................................... 24
5.8. VoucherComponent ........................................ 25

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5.8.1. getIdentifier .................................... 25
5.8.2. getDocument ...................................... 26
5.9. ReceptionListener ....................................... 26
5.9.1. arrive ........................................... 26
5.10. Exceptions ............................................. 27
6. Example Code ................................................. 28
7. Security Considerations ...................................... 29
8. Acknowledgements ............................................. 30
9. Normative References ......................................... 30
10. Informative References ....................................... 30

1. Introduction

This document specifies the Voucher Trading System Application
Programming Interface (VTS-API). The motivation and background of
the Voucher Trading System (VTS) are described in Requirements for
Generic Voucher Trading [VTS].

A voucher is a logical entity that represents a certain right, and it
is logically managed by the VTS. A voucher is generated by the
issuer, traded among users, and finally collected using VTS. The
terminology and model of the VTS are also described in [VTS].

VTSes can be implemented in different ways, such as a centralized
VTS, which uses a centralized online server to store and manage all
vouchers, or a distributed VTS, which uses per-user smartcards to
maintain the vouchers owned by each user. However, the VTS-API
allows a caller application to issue, transfer, and redeem vouchers
in a uniform manner independent of the VTS implementation. Several
attempts have been made to provide a generic payment API. Java
Commerce Client [JCC] and Generic Payment Service Framework [GPSF],
for example, introduce a modular wallet architecture that permits
diverse types of payment modules to be added as plug-ins and supports
both check-like/cash-like payment models. This document is inspired
by these approaches but its scope is limited to the VTS model, in
which the cash-like payment model is assumed and vouchers are
directly or indirectly transferred between the sender (transferor)
and receiver (transferee) via the VTS. This document is not intended
to support API for SET, e-check, or other payment schemes that do not
fit the VTS model.

Unlike the APIs provided in JCC and GPSF, which are designed to
transfer only monetary values, this API enables the transfer of a
wide range of values through the use of XML-based Generic Voucher
Language [GVL]. The monetary meaning of the voucher is interpreted
by the upper application layer using the information described in the
language. This approach makes it possible to provide a simpler API
in the voucher-transfer layer and enhances runtime efficiency. The

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API specification in this document is described in the Java language
syntax. Bindings for other programming languages may be completed in
a future version of this document or in separate related
specifications.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]

2. Processing Model

This section provides the processing model in which the VTS-API is
used. A part of the text in this section has been taken from the
Generic Voucher Language specification [GVL].

There are several ways to implement VTS. For discount coupons or
event tickets, for example, a smartcard-based distributed offline VTS
is often preferred, whereas for bonds or securities, a centralized
online VTS is preferred. While distributed VTSes would utilize
public (asymmetric) key-based or shared (symmetric) key-based
cryptographic challenge-and-response protocols to trade vouchers
securely, centralized VTSes would utilize transactions that rewrite
ownerships of vouchers on their database. Therefore, it is
impractical to define standard protocols for issuing, transferring,
or redeeming vouchers at this time.

To provide implementation flexibility, this document assumes a
modular wallet architecture that allows multiple VTSes to be added as
plug-ins. In this architecture, instead of specifying a standard
voucher transfer protocol, two specifications, Voucher Component and
VTS-API, are standardized (Figure 1).

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Sender wallet/Issuing system Receiver wallet/Collecting system
+---------------------------+ +---------------------------+
| | | |
| | Voucher Component | |
| | (Specifies VTS Provider and Promise) | |
| |-------------------------------------------------------->| |
| | | | | |
| | Intention to receive and payment (option) | |
| |<- - - - - - - - - - - - - - - - - - - - - - - - - - - - | |
| | | | | |
| | | | | |
| | Issue/transfer/ VTS | | VTS Register | |
| | redeem request plug-in | plug-in Listener(*1)| |
| |------------------>| | | |<------------------| |
| | (VTS API) |<- - - - - - - ->| (VTS API) | |
| | | VTS-specific | | |
| | | protocol if VTS | | |
| | | is distributed | | |
| | Result |<- - - - - - - ->| Notify(*2) | |
| |<------------------| | | |------------------>| |
+---------------------------+ +---------------------------+

(*1) Registration is optional. Note also that the VTS plug-ins are
usually pre-registered when the wallet or collecting system
is started.

(*2) If a listener is registered.

Figure 1. Wallet architecture with VTS plug-ins

In this architecture, a VTS provides a logical view of vouchers
called a Valid Voucher Set (VVS), which is a set that includes the
vouchers <I,P,H> managed by the VTS [VTS]. A user's wallet can
access (e.g., view, transfer, and redeem) the subset of the VVS that
includes a set of vouchers owned by the user by interacting with the
VTS plug-in via the VTS-API. Likewise, an issuing system can issue a
voucher and add it to the VVS, and a collecting system can be
notified of the redemption of vouchers via the VTS-API.

After a sender and a receiver agree on what vouchers are to be traded
and which VTS is to be used, the issuing system or wallet system
requests the corresponding VTS plug-in to permit the issue, transfer,
or redemption transactions to be performed via the VTS-API. The VTS
then logically rewrites the ownership of the vouchers on the VVS
using the VTS-specific protocol. Since the VTS is responsible for
preventing illegal acts on vouchers like forgery or reproduction, as
required in [VTS], the protocol would include a cryptographic
challenge-and-response (in a distributed VTS) or a transactional

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database manipulation with adequate access controls (in a centralized
VTS). Finally, a completion event is sent to the wallet systems or
issuing/collecting systems.

This document describes the VTS-API specification. See [GVL] for the
Voucher Component specification that gives the syntax and semantics
for describing and interpreting the meaning of vouchers.

3. Design Overview

We have adopted the following approach to specify the VTS-API.

1) Provide an abstract and uniform API that encapsulates the VTS
implementation. For example, a common API is provided for both
centralized and distributed VTSes. Issuers and application
developers have more freedom in VTS selection.

2) To provide an abstract and uniform API, this document
introduces an interface called VTSAgent that is associated with
a holder and provides methods to manipulate vouchers held by
its holder. Vouchers are accessed through the methods provided
by the VTSAgent.

3) Use existing standards for the VTS branding mechanism
(negotiation). This document assumes that the VTS to be used
for sending a voucher has settled the VTS-APIs are called.
Negotiation can be done within the upper application layer
using other standards (e.g., [IOTP] or [ECML]), if necessary.

4) Support only the push-type voucher transfer interface, in which
the voucher transfer session is initiated by the transferor
side. A pull-type voucher transfer interface can be
implemented on top of the push-type VTS interface at the
application level.

4. Concepts

The VTS-API consists of the following interfaces. A VTS is required
to implement all of the interfaces except ReceptionListener, which is
intended to be implemented by wallets or other applications that use
VTS.

VTSManager
Provides the starting point for using a VTS plug-in. All of
the objects needed to manipulate vouchers can be directly or
indirectly acquired via the VTSManager. A VTSManager maintains
the two repositories: a ParticipantRepository and a
VoucherComponentRepository, both of which are described below.

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ParticipantRepository
Provides the access points of participants that are to be
trading partners. A ParticipantRepository maintains
Participants and acts as an "address book" of trading partners.

Participant
Represents a participant (such as an issuer, a holder, or a
collector). A Participant interface knows how to obtain the
corresponding VTSAgent described below.

VTSAgent (extends Participant)
Provides the access point of vouchers in the Valid Voucher Set
(VVS) that is logically managed by the VTS. A VTSAgent
provides a means of manipulating vouchers held by its holder
according to basic trading methods; i.e., issue, transfer,
consume, and present. Before calling trading methods, the
application must create a Session, which is described below.

Session
Represents the logical connection established by the trade. A
Session has references to two Participant interfaces; i.e.,
those of the sender and the receiver. After trading methods
are called using a Session, the Session holds a reference to
the Vouchers to be traded.

Voucher
Represents one or more vouchers in which all of the issuer and
promise parts of the vouchers are the same. A Voucher holds
references to the Participant interface who issued the voucher
(issuer) and to a VoucherComponent (promise), which is
described below.

VoucherComponent
Represents a Voucher Component, described in [GVL]. It defines
the promise part of the voucher.

VoucherComponentRepository
Provides the access points of VoucherComponents. A
VoucherComponentRepository maintains VoucherComponents and acts
as a "voucher type book" managed by the VTS. This document
assumes that a set of VoucherComponents has been acquired and
stored in this repository. Delivery of VoucherComponents is
beyond the scope of this document. It may be delivered within
the VTS from the trading partners or manually acquired from a
trusted third party (see Section 3 of [GVL]).

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ReceptionListener
Provides a listener function with regard to the receipt of a
voucher by a VTSAgent to wallets or other applications that
implement this interface. (This interface may not be
implemented as part of the VTS.)

5. Interface Definitions

The interfaces defined in this document reside in the package named
"org.ietf.vts". Wallets or other applications that use this API,
should import this package as "import org.ietf.vts.*;".

5.1. VTSManager

public interface VTSManager

Provides the starting point for using a VTS plug-in.

All of the objects needed to manipulate vouchers can be directly
or indirectly acquired via a VTSManager so that wallets or other
applications can make the VTS available by instantiating an object
implementing this interface.

A class that implements the VTSManager interface must have a
public default constructor (a constructor without any parameters).
The VTS provides a name for such a constructor so that the
implementation class can bootstrap the interface.

5.1.1. getParticipantRepository

public ParticipantRepository getParticipantRepository()

Returns a repository that maintains Participants.

Returns:

the ParticipantRepository of the VTS, or null if no
ParticipantRepository is available.

5.1.2. getVoucherComponentRepository

public VoucherComponentRepository getVoucherComponentRepository()

Returns a repository that maintains VoucherComponents.

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Returns:

the VoucherComponentRepository of the VTS, or null if no
VoucherComponentRepository is available.

5.2. ParticipantRepository

public interface ParticipantRepository

Provides the access points of Participants. A
ParticipantRepository maintains Participants and acts as an
"address book" of trading partners.

The object implementing this interface maintains Participants (or
holds a reference to an object maintaining Participants), which
are to be trading partners.

The implementation of a ParticipantRepository may be either (an
adaptor to) "yellow pages", which is a network-wide directory
service like LDAP, or "pocket address book", which maintains only
personal acquaintances.

5.2.1. lookup

public Participant lookup(String id)

Retrieves the participant that has the specified id.

Returns:

the participant associated with the specified id, or null if the
id is null or the corresponding participant cannot be found.

5.3. Participant

public interface Participant

Represents the participants (such as issuers, holders, and
collectors).

This interface is used as a representation of the trade partners
and issuers of vouchers. Anyone can retrieve objects that
implement Participants from the participant repository.

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5.3.1. getIdentifier

public String getIdentifier()

Returns the identifier of the participant. Each participant must
have a unique identifier.

The identifier can be used for looking up and retrieving the
participant via the ParticipantRepository.

The format of the identifier is implementation-specific.

Returns:

the identifier string of the participant.

5.3.2. getVTSAgent

VTSAgent getVTSAgent()

Returns a VTSAgent, whose identifier is the same as the identifier
of the participant.

Returns:

an object that implements the VTSAgent.

5.4. VTSAgent

public interface VTSAgent extends Participant

Represents contact points to access vouchers in a Valid Voucher
Set (VVS) that is managed by the VTS.

Each VTSAgent is associated with a holder and provides a means for
managing vouchers owned by the holder. The holder must be
authenticated using the login() method before being called by any
other method, otherwise, a VTSSecurityException will be issued.

Before any trading method is called, e.g., issue(), transfer(),
consume(), and present(), the application must establish a session
by the prepare() method.

Due to network failure, sessions may often be suspended when the
voucher is sent via a network. The suspended sessions can be
restarted by the resume() method. Details on the state management
of a session are described in Section 5.5.

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Some VTSAgents may not have all of the trading methods; a voucher
collecting system doesn't require its VTSAgent to provide a method
for issuing or creating vouchers. A VTSAgent returns a
FeatureNotAvailableException when an unsupported method is
invoked.

5.4.1. login

public void login(String passphrase)
throws VTSException

Authenticates the VTSAgent. The passphrase is specified if the
VTS requires it for authentication, otherwise it must be null.
Nothing is performed if the VTSAgent has already been logged-in.
The authentication scheme is implementation-specific. Examples of
the implementation are as follows:

1) Vouchers are managed on a remote centralized server
(centralized VTS), which requires a password to login. In this
case, the application may prompt the user to input the password
and the password can be given to the VTSAgent through this
method. For further information, see the Implementation Notes
below.

2) Vouchers are managed on a remote centralized server
(centralized VTS), which requires challenge-and-response
authentication using smartcards held by users. In this case,
the passphrase may be null because access to the smartcard can
be done without contacting the application or user (i.e., the
VTSAgent receives the challenge from the server, sends the
challenge to the smartcard (within the VTS), and returns the
response from the smartcard to the server). Note that a PIN to
unlock the smartcard may be given through this method,
depending on the implementation.

3) Each user holds their own smartcard in which their own vouchers
are stored (distributed VTS). In this case, the passphrase may
be null because no authentication is required. Note that a PIN
to unlock the smartcard may be given, though this depends on
the implementation.

Implementation Notes:

A VTS is responsible for providing secure ways for users to
login(). It is strongly recommended that secure communication
channels such as [TLS] be used if secret or private information
is sent via networks. Fake server attacks, including the so-
called MITM (man-in-the-middle), must be considered as well.

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Throws:

VTSSecurityException - if authentication fails.

5.4.2. logout

public void logout()
throws VTSException

Voids the authentication performed by the login() method.

After this method is called, calling any other method (except
login()) will cause a VTSSecurityException.

The VTSAgent can login again by the login() method.

Throws:

VTSSecurityException - if the VTSAgent is not authenticated
correctly.

5.4.3. prepare

public Session prepare(Participant receiver)
throws VTSException

Establishes a session that is required for trading vouchers. The
trading partner who receives the vouchers is specified as the
receiver. The vouchers to be traded will be specified later (when
a trading method is called).

The establishment of a session is implementation-specific. A
centralized VTS implementation may start a transaction, while a
distributed VTS implementation may get the challenge needed to
create an authentic response from the receiver in the following
trading method.

If the VTSAgent does not have the ability to establish a session
with the specified receiver (permanent error), the VTSAgent throws
an InvalidParticipantExeption. If the VTSAgent cannot establish a
session due to network failure (transient error), the VTSAgent
throws a CannotProceedException.

Parameters:

receiver - the trading partner who receives vouchers.

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Returns:

an established session whose state is "prepared" (see Section
5.5).

Throws:

CannotProceedException - if the preparation of the session is
aborted (e.g., network failures).

FeatureNotAvailableException - if the VTSAgent does not provide
any trading methods.

InvalidParticipantException - if the specified participant is
invalid.

VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

5.4.4. issue

public void issue(Session session,
VoucherComponent promise,
java.lang.Number num)
throws VTSException

Issues vouchers. This method creates the specified number of
vouchers <this, promise, receiver> and adds them to the VVS. If
the VTS is distributed, this method would create a "response" that
corresponds to the challenge received in the prepare() method and
send it to the receiver. Note that the receiver is specified when
prepare() is called. Nothing is performed if the specified number
is 0.

The session MUST be "prepared" when calling this method. The
state of the session will be "activated" when the vouchers are
created, and it will be "completed" when the transaction is
successfully completed or "suspended" if the transaction is
interrupted abnormally (e.g., network failures).

Parameters:

session - the session used by the issue transaction.

promise - the promise part of the voucher.

num - the number of vouchers to be issued.

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Throws:

CannotProceedException - if the transaction cannot be successfully
completed.

FeatureNotAvailableException - if the VTSAgent does not provide a
means of issuing vouchers.

InvalidStateException - if the session is not "prepared".

VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

5.4.5. transfer

public void transfer(Session session,
Participant issuer,
VoucherComponent promise,
java.lang.Number num)
throws VTSException

Transfers vouchers. This method rewrites the specified number of
vouchers <issuer, promise, this> to <issuer, promise, receiver> in
the VVS; i.e., deletes the vouchers from the sender and stores
them for the receiver. Similar to issue(), this method would
create and send the response to the receiver if the VTS is
distributed. The VTSAgent must have sufficient vouchers in the
VVS. Nothing is performed if the specified number is 0.

The session MUST be "prepared" when calling this method. The
state of the session will be "activated" when the voucher are
retrieved from the sender, and it will be "completed" when the
transaction is successfully completed or "suspended" if the
transaction is interrupted abnormally (e.g., network failures).

If null is specified for the issuer parameter, it indicates "any
issuer". This method selects vouchers to be transferred from the
set of vouchers returned by the getContents(null, promise).

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Parameters:

session - the session used by the transfer transaction.

issuer - the issuer part of the voucher, or null.

promise - the promise part of the voucher.

num - the number of vouchers to be transferred.

Throws:

CannotProceedException - if the transaction cannot be successfully
completed.

FeatureNotAvailableException - if the VTSAgent does not provide a
means of transferring vouchers.

InsufficientVoucherException - if the VTSAgent does not have a
sufficient number of vouchers to transfer.

InvalidStateException - if the session is not "prepared".

VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

5.4.6. consume

public void consume(Session session,
Participant issuer,
VoucherComponent promise,
java.lang.Number num)
throws VTSException

Consumes vouchers. This method deletes the specified number of
vouchers <issuer, promise, this> from the VVS and notifies the
receiver of the deletion. Similar to issue() and transfer(), the
response would be created and sent to the receiver if the VTS is
distributed so that the receiver can obtain proof of the deletion.
The VTSAgent must have a sufficient number of vouchers in the VVS.
Nothing is performed if the specified number is 0.

The session MUST be "prepared" when this method is called. The
state of the session will be "activated" when the vouchers are
deleted, and it will be "completed" when the transaction is
successfully completed or "suspended" if the transaction is
interrupted abnormally (e.g., network failures).

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If null is specified for the issuer parameter, it indicates "any
issuer". This method selects vouchers to be consumed from the set
of vouchers returned by the getContents(null, promise).

Parameters:

session - the session used by the consume transaction.

issuer - the issuer part of the voucher, or null.

promise - the promise part of the voucher.

num - the number of vouchers to be consumed.

Throws:

CannotProceedException - if the transaction cannot be successfully
completed.

FeatureNotAvailableException - if the VTSAgent does not provide a
means of consuming vouchers.

InsufficientVoucherException - if the VTSAgent does not have a
sufficient number of vouchers to consume.

InvalidStateException - if the session is not "prepared".

VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

5.4.7. present

public void present(Session session,
Participant issuer,
VoucherComponent promise,
java.lang.Number num)
throws VTSException

Presents vouchers. This method shows that the sender has the
specified number of vouchers <issuer, promise, this> in the VVS to
the receiver of the session; no modification is performed to the
VVS. However, the response would be sent to the receiver as well
as consume() in order to prove that the VTS has been distributed.
The VTSAgent must have a sufficient number of vouchers in the VVS.
Nothing is performed if the specified number is 0.

The session MUST be "prepared" when this method is called. The
state of the session will be "activated" when the vouchers are

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retrieved, and it will be "completed" when the transaction is
successfully completed or "suspended" if the transaction is
interrupted abnormally (e.g., by network failures).

If null is specified for the issuer parameter, it indicates "any
issuer". This method selects vouchers to be presented from the
set of vouchers returned by the getContents(null, promise).

Parameters:

session - the session used by the present transaction.

issuer - the issuer part of the voucher, or null.

promise - the promise part of the voucher.

num - the number of the voucher to be presented.

Throws:

CannotProceedException - if the transaction cannot be successfully
completed.

InsufficientVoucherException - if the VTSAgent does not have a
sufficient number of vouchers to present.

InvalidStateException - if the session is not "prepared".

FeatureNotAvailableException - if the VTSAgent does not provide a
means of presenting vouchers.

VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

5.4.8. cancel

public void cancel(Session session)
throws VTSException

Releases the session. "Prepared" sessions MUST be canceled. An
implementation MAY be permitted to cancel "activated" or
"suspended" sessions.

Throws:

InvalidStateException - if the state of the session cannot be
canceled.

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VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

5.4.9. resume

public void resume(Session session)
throws VTSException

Restarts the session. Only "suspended" sessions can be resumed.
The state of the session will be re-"activated" immediately, and
it will be "completed" when the transaction is successfully
completed or "suspended" again if the transaction is interrupted
abnormally (e.g., network failures).

Throws:

CannotProceedException - if the transaction cannot be successfully
completed.

InvalidStateException - if the session is not "suspended".

VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

5.4.10. create

public void create(VoucherComponent promise, java.lang.Number num)
throws VTSException

Creates vouchers where the issuer is the VTSAgent itself. This
method creates the specified number of vouchers <this, promise,
this> and adds them to the VVS. Nothing is performed if the
specified number is 0.

Throws:

FeatureNotAvailableException - if the VTSAgent does not provide a
means of creating vouchers.

VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

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5.4.11. delete

public void delete(Participant issuer, VoucherComponent promise,
java.lang.Number num)
throws VTSException

Deletes vouchers. This method deletes the specified number of
vouchers <issuer, promise, this> from the VVS. The VTSAgent must
have sufficient vouchers in the VVS. Nothing is performed if the
specified number is 0.

Throws:

InsufficientVoucherException - if the VTSAgent does not have a
sufficient number of vouchers to delete.

VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

5.4.12. getContents

public java.util.Set getContents(Participant issuer,
VoucherComponent promise)
throws VTSException

Returns the set of vouchers whose issuer and promise both match
the issuer and promise specified in the parameters.

If null is specified for the issuer or promise parameter, it
indicates "any issuer" or "any promise", respectively. If null is
specified for both parameters, this method selects all vouchers
owned by the holder from the VVS.

Returns:

the set of vouchers held by the holder of the VTSAgent.

Throws:

VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

5.4.13. getSessions

public java.util.Set getSessions()
throws VTSException

Returns a set of incomplete sessions prepared by the VTSAgent.

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Returns:

the set of sessions prepared by the VTSAgent that are not yet
completed.

Throws:

VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

5.4.14. getLog

public java.util.Set getLog()
throws VTSException

Returns a set of completed sessions prepared or received by the
VTSAgent. This set represents the trading log of the VTSAgent. A
VTS may delete an old log eventually, so that the entire log may
not be returned; the amount of the log kept by the VTSAgent is
implementation-specific.

Returns:

the set of completed sessions prepared or received by the
VTSAgent.

Throws:

VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

5.4.15. addReceptionListener

public void addReceptionListener(ReceptionListener l)
throws VTSException

Adds a ReceptionListener to the listener list.

After a ReceptionListener l is registered by this method,
l.arrive() will be called whenever the VTSAgent receives a
voucher.

Nothing is performed if the specified listener is null.

Throws:

VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

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5.4.16. removeReceptionListener

public void removeReceptionListener(ReceptionListener l)
throws VTSException

Removes a ReceptionListener from the listener list.

Nothing is performed when the specified listener is null or not
registered.

Throws:

VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.

5.5. Session

public interface Session

Represents the logical connection established by the trade.
Sessions are established by VTSAgent#prepare().

A session has four states: prepared, activated, suspended, and
completed. The initial state of a session is "prepared", and the
session will be "activated" immediately when any of the trading
methods of VTSAgent is called. The "activated" session will be
"completed" after the trading method is successfully completed.
If the trading method fails transiently (e.g., network failure),
the session will be "suspended". Suspended sessions can be re-
"activated" and restarted by calling VTSAgent#resume().

A completed session may disappear from the VTSAgent; the session
will be collected by the GC unless other objects keep its
reference.

5.5.1. getIdentifier

public String getIdentifier()

Returns the identifier of the session. The generation scheme of
the identifier is implementation-specific. An implementation may
use a transaction ID as the identifier of the session.

Returns:

the string of the identifier of the session.

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5.5.2. getVoucher

public Voucher getVoucher()

Returns the voucher to be traded using the session, or returns
null if the session has not been activated.

Returns:

the voucher to be traded, or null if the state of the session is
"prepared".

5.5.3. getSender

public Participant getSender()

Returns the sender of the session (i.e., the creator who prepared
the session).

Returns:

the sender of the session.

5.5.4. getReceiver

public Participant getReceiver()

Returns the receiver of the session (i.e., the participant
specified when preparing the session (by the VTSAgent#prepare()
method)).

Returns:

the receiver of the session.

5.5.5. isPrepared

public boolean isPrepared()

Verifies if the session is "prepared".

Returns:

true if the session is in the "prepared" state, otherwise, false.

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5.5.6. isActivated

public boolean isActivated()

Verifies if the session is "activated".

Returns:

true if the session is in the "activated" state, otherwise, false.

5.5.7. isSuspended

public boolean isSuspended()

Verifies if the session is "suspended".

Returns:

true if the session is in the "suspended" state, otherwise, false.

5.5.8. isCompleted

public boolean isCompleted()

Verifies if the session is "completed".

Returns:

true if the session is in the "completed" state, otherwise, false.

5.6. Voucher

public interface Voucher

Represents voucher(s) described in [VTS]. An object implementing
this interface can represent more than one voucher if all of the
issuer part and the promise part of the vouchers are the same.

5.6.1. getIssuer

public Participant getIssuer()

Returns the issuer part of the voucher(s).

Returns:

the participant who issued the voucher(s).

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5.6.2. getPromise

public VoucherComponent getPromise()

Returns the promise part of the voucher(s).

Returns:

the voucher component that defines the promise of the voucher.

5.6.3. getCount

public java.lang.Number getCount()

Returns the number of the voucher(s).

Returns:

the positive (>0) number of the voucher(s).

5.7. VoucherComponentRepository

public interface VoucherComponentRepository

Maintains VoucherComponents.

An object implementing VoucherComponentRepository provides a means
of retrieving the voucher components that are the promises of
vouchers in the VVS.

Before issuing a voucher, the promise of the voucher must be
registered with this repository. The repository can be
implemented as either a network-wide directory service or personal
storage like the ParticipantRepository.

5.7.1. register

public VoucherComponent register(org.w3c.dom.Document document)

Creates a voucher component associated with the specified DOM
object and registers the voucher component with the repository.

A voucher component of the voucher to be issued must be registered
using this method.

Nothing is performed (and the method returns null) if the
specified document is null or the syntax of the document does not
conform to the VTS.

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The method returns the registered voucher component if the
specified DOM object has been already registered (no new voucher
component is created in this case).

Returns:

a registered voucher component associated with the specified
document, or null if the document is null or has wrong syntax.

5.8. VoucherComponent

public interface VoucherComponent

Represents the voucher component that defines the promise of the
voucher.

Each VoucherComponent object has its own unique identifier and is
associated with an XML document that describes the promise made by
the issuer of the voucher (e.g., goods or services can be claimed
in exchange for redeeming the voucher).

This interface can be implemented as sort of a "smart pointer" to
the XML document. An implementation may have a reference to a
voucher component repository instead of the voucher component, and
it may retrieve the document dynamically from the repository when
the getDocument() method is called.

5.8.1. getIdentifier

public String getIdentifier()

Returns the identifier of the voucher component. Each voucher
component must have a unique identifier. The identifier may be
used to check for equivalence of voucher components.

The format of the identifier is implementation-specific, however,
it is RECOMMENDED that the hash value of the voucher component in
the identifier be included to assure uniqueness. For generating
the hash value, it is desirable to use a secure hash function
(e.g., [SHA-1]) and to apply a canonicalization function (e.g.,
[EXC-C14N]) before applying the hash function to minimize the
impact of insignificant format changes to the voucher component,
(e.g., line breaks or character encoding).

Returns:

the identifier string of the voucher component.

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5.8.2. getDocument

public org.w3c.dom.Document getDocument()

Returns a Document Object Model [DOM] representation of the
document associated with the voucher component by the
VoucherComponentRepository#register() method.

The DOM object to be returned may be retrieved from a
VoucherComponentRepository on demand, instead of the
VoucherComponent always keeping a reference to the DOM object.

The VTS must guarantee that the getDocument method will eventually
return the DOM object, provided that the voucher associated with
the corresponding voucher component exists in the VVS.

Returns:

a DOM representation of the document associated with the voucher
component.

Throws:

DocumentNotFoundException - if the associated DOM object cannot be
retrieved.

5.9. ReceptionListener

public interface ReceptionListener extends java.util.EventListener

Provides a listener interface with a notification that a VTSAgent
has received a voucher.

When a voucher arrives at the VTSAgent, the VTSAgent invokes the
arrive() method of each registered ReceptionListener.
ReceptionListeners can obtain a Session object, which contains
information about the received voucher and the sender of the
voucher.

This interface is intended to provide a means of notifying a
wallet that "You have new vouchers", so that this interface may be
implemented by wallets or other applications that use VTS.

5.9.1. arrive

public void arrive(Session session)

Provides notification of the arrival of a voucher.

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After the listener is registered to a VTSAgent (by the
VTSAgent#addReceptionListener() method), the VTSAgent invokes this
method whenever it receives a voucher.

The specified session is equivalent to the session used by the
sender to trade the voucher. The state of the session is
"completed" when this method is called.

5.10. Exceptions

java.lang.Exception
+-- VTSException
+-- CannotProceedException
+-- DocumentNotFoundException
+-- FeatureNotAvailableException
+-- InsufficientVoucherException
+-- InvalidParticipantException
+-- InvalidStateException
+-- VTSSecurityException

VTSException
This is the superclass of all exceptions thrown by the methods in
the interfaces that construct the VTS-API.

CannotProceedException
This exception is thrown when a trading is interrupted by network
failures or other errors.

DocumentNotFoundException
This exception is thrown when the document associated with a
voucher component cannot be found.

FeatureNotAvailableException
This exception is thrown when the invoked method is not supported.

InsufficientVoucherException
This exception is thrown when the number of the voucher is less
than the number specified for trading.

InvalidParticipantException
This exception is thrown when the specified participant cannot be
located.

InvalidStateException
This exception is thrown when the state of the session is invalid
and the operation cannot proceed.

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VTSSecurityException
This exception is thrown when authentication fails, or when a
method that requires authentication in advance is called without
authentication.

6. Example Code

// Issue a voucher

VTSManager vts = new FooVTSManager();
ParticipantRepository addrBook = vts.getParticipantRepository();
VoucherComponentRepository vcr = vts.getVoucherComponentRepository();

Participant you = addrBook.lookup("http://example.org/foo");
// looks up a trading partner identified as
// "http://example.org/foo".
VTSAgent me = addrBook.lookup("myName").getVTSAgent();
// a short-cut name may be used if VTS implementation allows.

VoucherComponent promise = vcr.register(anXMLVoucherDocument);
// registers a voucher component that corresponds to the voucher
// to be issued.

try {
me.login();
// sets up the issuer's smartcard (assuming distributed VTS).
s = me.prepare(you);
// receives a challenge from the partner.
me.issue(s, promise, 1);
// sends a voucher using the received challenge.
me.logout();
} catch (VTSException e) {
// if an error (e.g., a network trouble) occurs...
System.err.println("Sorry.");
e.printStackTrace();
// this example simply prints a stack trace, but a real wallet
// may prompt the user to retry (or cancel).
}

// Transfer all my vouchers

VTSManager vts = new FooVTSManager();
ParticipantRepository addrBook = vts.getParticipantRepository();

Participant you = addrBook.lookup("8f42 5aab ffff cafe babe...");
// some VTS implementations would use a hash value of a public key
// (aka fingerprint) as an identifier of a participant.
VTSAgent me = addrBook.lookup("myName").getVTSAgent();

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try {
me.login();
Iterator i = me.getContents(null, null).iterator();

while (i.hasNext()) {
Voucher v = (Voucher) i.next();
s = me.prepare(you);
me.transfer(s, v.getIssuer(), v.getPromise(), v.getCount());
}

me.logout();
} catch (VTSException e) {
System.err.println("Sorry.");
e.printStackTrace();
}

// Register an incoming voucher notifier (biff)

VTSManager vts = new FooVTSManager();

ParticipantRepository addrBook = vts.getParticipantRepository();
VTSAgent me = addrBook.lookup("myName").getVTSAgent();

ReceptionListener listener = new ReceptionListener() {
public void arrive(Session s) {
System.out.println("You got a new voucher.");
}
};

try {
me.login();
me.addReceptionListener(listener);
me.logout();
} catch (VTSException e) {
System.err.println("Sorry.");
e.printStackTrace();
}

7. Security Considerations

Security is very important for trading vouchers. VTS implementations
are responsible for preventing illegal acts upon vouchers (as
described in [VTS]), as well as preventing malicious access from
invalid users and fake server attacks, including man-in-the-middle
attacks.

The means to achieve the above requirements are not specified in this
document because they depend on VTS implementation. However,

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securing communication channels (e.g., using TLS) between client VTS
plug-ins and the central server in a centralized VTS (as described in
5.4.1 login()), and applying cryptographic challenge-and-response
techniques in a distributed VTS are likely to be helpful and are
strongly recommended to implement a secure VTS.

This document assumes that the VTS plug-in is trusted by its user.
The caller application of a VTS should authenticate the VTS plug-in
and bind it securely using the VTS Provider information specified in
the Voucher Component. This document, however, does not specify any
application authentication scheme and it is assumed to be specified
by other related standards. Until various VTS systems are deployed,
it is enough to manually check and install VTS plug-ins like other
download applications.

8. Acknowledgements

The following persons, in alphabetic order, contributed substantially
to the material herein:

Donald Eastlake 3rd
Iguchi Makoto
Yoshitaka Nakamura
Ryuji Shoda

9. Normative References

[DOM] V. Apparao, S. Byrne, M. Champion, S. Isaacs, I. Jacobs,
A. Le Hors, G. Nicol, J. Robie, R. Sutor, C. Wilson, and
L. Wood. "Document Object Model (DOM) Level 1
Specification", W3C Recommendation, October 1998,
<http://www.w3.org/TR/1998/REC-DOM-Level-1-19981001/>

[GVL] Fujimura, K. and M. Terada, "XML Voucher: Generic Voucher
Language", RFC 4153, September 2005.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

10. Informative References

[ECML] Eastlake 3rd, D., "Electronic Commerce Modeling Language
(ECML) Version 2 Specification", RFC 4112, June 2005.

[EXC-C14N] J. Boyer, D. Eastlake, and J. Reagle, "Exclusive XML
Canonicalization Version 1.0", W3C Recommendation, July
2002, <http://www.w3.org/TR/2002/REC-xml-exc-c14n-
20020718/>

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RFC 4154 VTS-API September 2005

[GPSF] G. Lacoste, B. Pfitzmann, M. Steiner, and M. Waidner
(Eds.), "SEMPER - Secure Electronic Marketplace for
Europe," LNCS 1854, Springer-Verlag, 2000.

[IOTP] Burdett, D., "Internet Open Trading Protocol - IOTP
Version 1.0", RFC 2801, April 2000.

[JCC] T. Goldstein, "The Gateway Security Model in the Java
Electronic Commerce Framework", Proc. of Financial
Cryptography '97, 1997.

[SHA-1] Department of Commerce/National Institute of Standards and
Technology, "FIPS PUB 180-1. Secure Hash Standard. U.S.",
<http://csrc.nist.gov/publications/fips/fips180-2/
fips180-2withchangenotice.pdf>

[TLS] Dierks, T. and C. Allen, "The TLS Protocol Version 1.0",
RFC 2246, January 1999.

[VTS] Fujimura, K. and D. Eastlake, "Requirements and Design for
Voucher Trading System (VTS)", RFC 3506, March 2003.

Authors' Addresses

Masayuki Terada
NTT DoCoMo, Inc.
3-5 Hikari-no-oka, Yokosuka-shi, Kanagawa, 239-8536 JAPAN

Phone: +81-(0)46-840-3809
Fax: +81-(0)46-840-3705
EMail: [email protected]

Ko Fujimura
NTT Corporation
1-1 Hikari-no-oka, Yokosuka-shi, Kanagawa, 239-0847 JAPAN

Phone: +81-(0)46-859-3053
Fax: +81-(0)46-859-1730
EMail: [email protected]

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Full Copyright Statement

Copyright (C) The Internet Society (2005).

This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.

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Acknowledgement

Funding for the RFC Editor function is currently provided by the
Internet Society.

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