Designing a terminal
Pavel Tuček
2010, FI MU

Introduction
1.Micropayment scheme
2.Environment
3.Types of terminals
4.Other parts of system
5.Future work
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Micropayment scheme
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•Main participants:
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Environment for terminals
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Types of terminals
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•Types of terminals should be as few as possible! But one type is not enough.
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•Let’s split our micropayment scheme into two parts:
1.Broker’s relationship to users.
2.Broker’s relationship to vendors.
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•Motivation for this step is increasing trustworthiness of the whole system. In case there will be
only one terminal, users might doubt whether their communication with broker wasn’t monitored or
even intercepted by the vendor.
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Types of terminals
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•Terminal type #1 – Broker’s terminal (BT)
•BT is intended to be the center for customer care at the vendor’s site, but managed by broker.
This terminal must be online.
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Types of terminals
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•Terminal type #1 – Broker’s terminal (BT)
•BT is intended to be the center for customer care at the vendor’s site, but managed by broker.
This terminal must be online.
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•Functions depending on the payment scheme:
•user registration with broker,
•user certificate revocation by user upon key compromise.
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•Other functions:
•money recharging,
•account management,
•creating transaction logs.
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Types of terminals
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•Terminal type #2 – Vendor’s terminal (VT)
•VT is intended to be connected to a device which needs to be served by it. That might be a
printer, vending machines for hot and cold drinks, and snacks, etc. VT might be online or offline
according to the vendor’s infrastructure, but it will be definitely offline considering the
broker’s infrastructure.
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•Functions depending on the payment scheme:
•item purchase by user at vendor.
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Types of terminals
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•Terminal type #2 – Vendor’s terminal (VT)
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Types of terminals
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•Terminal type #2 – Vendor’s terminal (VT)
•VT is intended to be connected to a device which needs to be served by it. That might be a
printer, vending machines for hot and cold drinks, and snacks, etc. VT might be online or offline
according to the vendor’s infrastructure, but it will be definitely offline considering broker’s
infrastructure.
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•Other functions:
•picking coin per transaction,
•sending coins to vendor’s management server (VMS),
•creating transaction logs, error logs,…
•sending data to VMS (transaction logs, errors,…).
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Terminals’ specifications
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•Hardware requirements:
•card reader,
•display,
•input device (pin pad/keyboard/display),
•CPU,
•memory (RAM/ROM/flash),
•network component (industry standards1/Wi-Fi/BT/GSM/none),
•management connection (if talking about offline terminal: industry standards/USB/Wi-Fi/BT),
•smart card or TPM,
•connection to the served device.
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•1 ANT, 6LoWPAN, DASH7, ONE-NET, ZigBee, MiWi, Wibree and others.
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Terminals’ specifications
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•There are several candidates for the main CPU, but we can divide them into to groups.
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The x86 compatible CPUs (Intel Atom, AMD Athlon Neo, VIA Nano)
ARM-based CPUs or more precisely SoCs (TI's OMAP 3 series and Freescale's i.MX51 based on the
Cortex-A8 processor, or the Qualcomm Snapdragon and Marvell Armada 500/600 based on custom ARMv7
implementations)
The main difference is in design, while x86 compatible CPUs are CISC, the ARM-based CPUs are RISC.
This implies different size of chip (number of transistors) and it’s different power consumption.

Terminals’ specifications
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•Cryptographic requirements:
•certificate store,
•random number generator,
•SHA-2 family hash function,
•RSA algorithm,
•AES encryption.
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Other parts of system
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•Broker’s management server (BMS)
•BMS will be the management center for taking care of users and vendors. Most likely it will be an
information system or a server application.
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•Functions depending on the payment scheme:
•user certificate issuance by broker,
•vendor registration with broker,
•vendor certificate issuance by broker,
•user certificate revocation by broker,
•vendor certificate revocation by broker,
•vendor elimination from the system.
•Other functions:
•send data to all VMSs (broker’s blacklist,….)
•create transaction logs.
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Other parts of system
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•Vendor’s management server (VMS)
•VMS is intended to be the main center for the customer care at the vendor’s place. One of its
purposes is the management function for all VMSs and the other is communication with BMS. VMS will
be a computer/server with a special-purpose operating system.
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•Functions depending on the payment scheme:
•item claim by user at vendor,
•vendor certificate revocation by vendor upon key compromise.
•Other functions:
•collecting coins from all VTs,
•sending coins to BMS for redemption,
•sending data to all VTs (broker’s blacklist, vendor’s blacklist,….),
•managing vendor’s blacklist,
•VT certificate issuance,
•creating transaction logs.
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Other parts of system
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•Mobile broker’s terminal (MBT)
•An application with similar or same functionality as the Broker’s terminal has. Application will
be intended to use in mobile phones and personal computers equipped with smart card or smart card
reader.
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Future work
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1.Layout of the terminal mainboard.
2.Connections of single components in the terminal.
3.Temper resistance of the terminal.
4.Certification of the terminal.
5.Broker’s and vendor’s management servers.
6.Running 3rd party’s application in an untrustworthy environment.
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Questions
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•Questions are appreciated!
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Thanks
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•Thank you for attention!
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