Trade Working Group February 2004
INTERNET-DRAFT Masayuki Terada
NTT DoCoMo
Expires: August 2004 Ko Fujimura
NTT
Voucher Trading System Application Programming Interface (VTS-API)
<draft-ietf-trade-voucher-vtsapi-06.txt>
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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 to securely transfer vouchers, e.g., coupons, tickets, loyalty
points, and gift certificates; this process is often necessary in the
course of payment and/or delivery transactions.
Copyright (C) The Internet Society (2004). All Rights Reserved.
Acknowledgements
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The following persons, in alphabetic order, contributed substantially
to the material herein:
Donald Eastlake 3rd
Iguchi Makoto
Yoshitaka Nakamura
Ryuji Shoda
Table of Contents
Status of this Memo . . . . . . . . . . . . . . . . . . . . . . . 1
Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 1
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 3
2. Processing Model . . . . . . . . . . . . . . . . . . . . . 4
3. Design Overview . . . . . . . . . . . . . . . . . . . . . 6
4. Concepts . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Interface Definitions . . . . . . . . . . . . . . . . . . 7
5.1 VTSManager . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1.1 getParticipantRepository . . . . . . . . . . . . . . . . . 8
5.1.2 getVoucherComponentRepository . . . . . . . . . . . . . . 8
5.2 ParticipantRepository . . . . . . . . . . . . . . . . . . 8
5.2.1 lookup . . . . . . . . . . . . . . . . . . . . . . . . . . 9
5.3 Participant . . . . . . . . . . . . . . . . . . . . . . . 9
5.3.1 getIdentifier . . . . . . . . . . . . . . . . . . . . . . 9
5.3.2 getVTSAgent . . . . . . . . . . . . . . . . . . . . . . . 9
5.4 VTSAgent . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.4.1 login . . . . . . . . . . . . . . . . . . . . . . . . . . 10
5.4.2 logout . . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.4.3 prepare . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.4.4 issue . . . . . . . . . . . . . . . . . . . . . . . . . . 12
5.4.5 transfer . . . . . . . . . . . . . . . . . . . . . . . . . 13
5.4.6 consume . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.4.7 present . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.4.8 cancel . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.4.9 resume . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.4.10 create . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.4.11 delete . . . . . . . . . . . . . . . . . . . . . . . . . . 16
5.4.12 getContents . . . . . . . . . . . . . . . . . . . . . . . 17
5.4.13 getSessions . . . . . . . . . . . . . . . . . . . . . . . 17
5.4.14 getLog . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.4.15 addReceptionListener . . . . . . . . . . . . . . . . . . . 18
5.4.16 removeReceptionListener . . . . . . . . . . . . . . . . . 18
5.5 Session . . . . . . . . . . . . . . . . . . . . . . . . . 19
5.5.1 getIdentifier . . . . . . . . . . . . . . . . . . . . . . 19
5.5.2 getVoucher . . . . . . . . . . . . . . . . . . . . . . . . 19
5.5.3 getSender . . . . . . . . . . . . . . . . . . . . . . . . 19
5.5.4 getReceiver . . . . . . . . . . . . . . . . . . . . . . . 20
5.5.5 isPrepared . . . . . . . . . . . . . . . . . . . . . . . . 20
5.5.6 isActivated . . . . . . . . . . . . . . . . . . . . . . . 20
5.5.7 isSuspended . . . . . . . . . . . . . . . . . . . . . . . 20
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5.5.8 isCompleted . . . . . . . . . . . . . . . . . . . . . . . 20
5.6 Voucher . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.6.1 getIssuer . . . . . . . . . . . . . . . . . . . . . . . . 21
5.6.2 getPromise . . . . . . . . . . . . . . . . . . . . . . . 21
5.6.3 getCount . . . . . . . . . . . . . . . . . . . . . . . . . 21
5.7 VoucherComponentRepository . . . . . . . . . . . . . . . . 21
5.7.1 register . . . . . . . . . . . . . . . . . . . . . . . . . 22
5.8 VoucherComponent . . . . . . . . . . . . . . . . . . . . . 22
5.8.1 getIdentifier . . . . . . . . . . . . . . . . . . . . . . 22
5.8.2 getDocument . . . . . . . . . . . . . . . . . . . . . . . 23
5.9 ReceptionListener . . . . . . . . . . . . . . . . . . . . 23
5.9.1 arrive . . . . . . . . . . . . . . . . . . . . . . . . . . 24
5.10 Exceptions . . . . . . . . . . . . . . . . . . . . . . . . 24
6. Example Code . . . . . . . . . . . . . . . . . . . . . . . 25
7. Security Considerations . . . . . . . . . . . . . . . . . 26
8. Normative References . . . . . . . . . . . . . . . . . . . 27
9. Informative References . . . . . . . . . . . . . . . . . . 27
10. Author's Address . . . . . . . . . . . . . . . . . . . . . 28
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . . 28
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 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].
While VTSs 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, 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 at providing 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 the scope of this document is limited to the VTS
model, in which cash-like payment model is assumed and vouchers are
directly or indirectly transferred between 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
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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
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 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 of implementing 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 VTSs would utilize public
(asymmetric) key-based or shared (symmetric) key-based cryptographic
challenge-and-response protocols to trade vouchers securely,
centralized VTSs would utilize transactions that rewrite ownerships
of vouchers upon their database. It is therefore impractical to
define standard protocols for issuing, transferring, or redeeming
vouchers at this moment.
To provide implementation flexibility, this document assumes a
modular wallet architecture that allows multiple VTS to be added as
plug-ins. In this architecture, instead of specifying a standard
voucher transfer protocol, two specifications, i.e., Voucher
Component and VTS-API specifications, 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 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 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 redeem 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 database manipula-
tion with adequate access controls (in a centralized VTS). Finally,
a completion event is sent to the wallet systems or issuing/collect-
ing systems.
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This document describes the VTS-API specification. See [GVL] for the
Voucher Component specification that gives the syntax and semantics
for describing and interpreting 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 VTS. It brings more freedom
of VTS selection for issuers and application developers.
2) To provide an abstract and uniform API, this document intro-
duces 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 (negoti-
ation). This document assumes that the VTS to be used for
sending a voucher has settled before calling the VTS-APIs.
Negotiation can be done within the upper application layer
using other standards, e.g., [IOTP] or [ECML], if necessary.
4) Support only push-type voucher transfer interface in which
voucher transfer session is initiated by the transferor side.
Pull-type voucher transfer interface can be implemented on top
of the push-type VTS interface at 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 to use a VTS plug-in. All of the
objects needed to manipulate vouchers can be directly or indi-
rectly acquired via the VTSManager. A VTSManager maintains
the two repositories; a ParticipantRepository and a Voucher-
ComponentRepository described below.
ParticipantRepository
Provides the access points of Participants, which are to be
trading partners. A ParticipantRepository maintains Partici-
pants and acts as an "address book" of trading partners.
Participant
Represents a participant (such as issuers, holders, and
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collectors). A Participant knows how to obtain the corre-
sponding VTSAgent described below.
VTSAgent (extends Participant)
Provides the access point of vouchers in Valid Voucher Set
(VVS) that is logically managed by VTS. A VTSAgent provides a
means of manipulating vouchers held by its holder; basic trad-
ing 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 Participants, i.e., 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 of which all of the issuer
part and promise part of vouchers are the same. A Voucher
holds references to the Participant (issuer) who issued the
voucher and 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 Voucher-
ComponentRepository 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]).
ReceptionListener
Provides a listener function with regard to the receipt of a
voucher by VTSAgent to wallets or other applications that
implement this interface. (This interface may not be imple-
mented as part of 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.*;".
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5.1 VTSManager
public interface VTSManager
Provides the starting point to use 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 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.
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.
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The implementation of 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 representation of the trade partners and
issuers of vouchers. Anyone can retrieve objects implementing
Participant from the participant repository.
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:
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an object implementing VTSAgent.
5.4 VTSAgent
public interface VTSAgent extends Participant
Represents contact points to access vouchers in 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, or VTSSecurityException will be issue.
Before calling any trading method, i.e., issue(), transfer(),
consume(), and present(), the application must establish a session
by the prepare() method.
Sessions may often be suspended due to network failure 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.
Some VTSAgents may not have all of the trading methods; a voucher
collecting system doesn't require its VTSAgent to provide method
for issuing or creating vouchers. A VTSAgent returns
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 can be
given to the VTSAgent through this method. See 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 since 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
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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 since no authentication is required. Note that a PIN to
unlock the smartcard may be given through this depends on the
implementation.
Implementation Notes:
A VTS is responsible for providing secure ways for users to
login(); it is strongly recommended to utilize secure
communication channels such as [TLS] if secret or privacy
information is sent via networks. Fake server attacks including
so-called MITM (man-in-the-middle) must be considered as well.
Throws:
VTSSecurityException - if authentication fails.
5.4.2 logout
public void logout()
throws VTSException
Voids the authentication performed by the login() method.
After calling this method, calling any other method (except
login()) will cause 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 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
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centralized VTS implementation may start a transaction, while a
distributed VTS implementation may get, from the receiver, the
challenge needed to create an authentic response in the
following trading method.
If the VTSAgent has no ability to establish a session with the
specified receiver (permanent error), the VTSAgent throws an
InvalidParticipantExeption. If the VTSAgent can not establish a
session due to network failure (transient error), the VTSAgent
throws a CannotProceedException.
Parameters:
receiver - the trading partner who receives vouchers.
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"
corresponding 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).
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Parameters:
session - the session used by the issue transaction.
promise - the promise part of the voucher.
num - the number of vouchers to be issued.
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).
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:
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CannotProceedException - if the transaction cannot be successfully
completed.
FeatureNotAvailableException - if the VTSAgent does not provide
a means of transferring vouchers.
InsufficientVoucherException - if the VTSAgent doesn't 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
deletion to the receiver. 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 calling this method. 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).
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 doesn't have a
sufficient number of vouchers to consume.
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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 in order to give the
proof to the receiver as well as consume() if the VTS is
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 calling this method. The state
of the session will be "activated" when the vouchers are 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 doesn't 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
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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 isn't
cancelable.
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.
5.4.11 delete
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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 doesn't have
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.lang.Set getSessions()
throws VTSException
Returns a set of not-completed sessions prepared by the VTSAgent.
Returns:
the set of sessions prepared by the VTSAgent and not yet completed.
Throws:
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VTSSecurityException - if the VTSAgent cannot be authenticated
correctly.
5.4.14 getLog
public java.lang.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.
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:
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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 is transiently failed (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.
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()
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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 "prepared" state, or false.
5.5.6 isActivated
public boolean isActivated()
Verifies if the session is "activated".
Returns:
true if the session is in "activated" state, or false.
5.5.7 isSuspended
public boolean isSuspended()
Verifies if the session is "suspended".
Returns:
true if the session is in "suspended" state, or false.
5.5.8 isCompleted
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public boolean isCompleted()
Verifies if the session is "completed".
Returns:
true if the session is in "completed" state, or 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).
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.
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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.
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 it
is associated with an XML document that describes the promise made
by the issuer of the voucher, e.g., the 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
retrieve the document dynamically from the repository when the
getDocument() method is called.
5.8.1 getIdentifier
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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 to include the hash value of the voucher
component in the identifier to assure its 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.
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 that provides notification that a
VTSAgent has been received a voucher.
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When a voucher arrives at VTSAgent, the VTSAgent invokes 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 using VTS.
5.9.1 arrive
public void arrive(Session session)
Provides notification of the arrival of a voucher.
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 constructs the VTS-API.
CannotProceedException
This exception is thrown when a trading is interrupted due to
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 sup-
ported.
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InsufficientVoucherException
This exception is thrown when the number of the voucher is
less than the number specified to trade.
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 to proceed the operation.
VTSSecurityException
This exception is thrown when authentication fails or a method
which 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 corresponding 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).
}
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// 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();
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
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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 accesses 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 since it depends on VTS implementation, however, 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 helpful and 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. 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. "Docu-
ment Object Model (DOM) Level 1 Specification", W3C Recommendation,
October 1998, <http://www.w3.org/TR/1998/REC-DOM-Level-1-19981001/>
[GVL] K. Fujimura and M. Terada, "XML Voucher: Generic Voucher Lan-
guage", draft-ietf-trade-voucher-lang-06.txt, 2004.
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate Require-
ment Levels", BCP 14, RFC 2119, 1997.
9. Informative References
[ECML] J. W. Parsons and D. Eastlake "Electronic Commerce Modeling
Language (ECML) Version 2 Specification", draft-ietf-trade-
ecml2-spec-09.txt, 2004.
[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/>
[GPSF] G. Lacoste, B. Pfitzmann, M. Steiner, and M. Waidner (Eds.),
"SEMPER - Secure Electronic Marketplace for Europe," LNCS 1854,
Springer-Verlag, 2000.
[IOTP] D. Burdett, "Internet Open Trading Protocol - IOTP Version
M. Terada, K. Fujimura [Page 27]
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1.0", RFC 2801, 2000.
[JCC] T. Goldstein, "The Gateway Security Model in the Java Elec-
tronic 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/fips180-1/fip180-1.txt>
[VTS] K. Fujimura and D. Eastlake, "Requirements and Design for
Voucher Trading System (VTS)", RFC3506, 2003.
10. Author's Address
Masayuki Terada
NTT DoCoMo, Inc.
3-5 Hikari-no-oka, Yokosuka-shi, Kanagawa, 239-0847 JAPAN
Phone: +81-(0)46-840-3809
Fax: +81-(0)46-840-3364
Email: te@mml.yrp.nttdocomo.co.jp
Ko Fujimura
NTT Corporation
1-1 Hikari-no-oka, Yokosuka-shi, Kanagawa, 239-0847 JAPAN
Phone: +81-(0)46-859-3814
Fax: +81-(0)46-859-8329
Email: fujimura@isl.ntt.co.jp
Full Copyright Statement
Copyright (C) The Internet Society (2004). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this doc-
ument itself may not be modified in any way, such as by removing the
copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of develop-
ing Internet standards in which case the procedures for copyrights
defined in the Internet Standards process must be followed, or as
required to translate it into languages other than English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MER-
CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
M. Terada, K. Fujimura [Page 29]
