Milan / Paylink System Manual Issue 1.5 29 January 2020
CONFIDENTIAL
Not to be disclosed without prior written permission from Aardvark Embedded Solutions Ltd
Page 24 of 71
Complex Dispenser (Recycler) Operations (1.12.3)
Introduction
The original Paylink model was based around the concept of independent acceptors and dispensers,
with the main specification for a dispenser being the MCL / cctalk hopper.
The advent of bill / note recyclers has meant that the Paylink model has had to be enhanced to
include these. The approach adopted has been based around the idea that bill / note recycler (and
the coin changer MDB device) is a combination in a single unit of an acceptor and number of
dispensers.
Outside of their core function, Complex Dispensers can have many more operational states, rather
than just running / errored. In addition, whilst the error reporting system is the same as for simpler
devices, there can be more details than the 12 or so pre-defined Paylink errors. The approach taken
is that an appropriate simple error is reported, and the RawEvent byte details the exact error reported
by the device. This section describes the operational characteristics of the devices, details on the
reporting of events / faults are detailed in the appropriate subsection of the Events (Faults / Auditing)
Section.
Security
The connections used by Paylink fall into three categories, cctalk, MDB and RS232. These
communications systems tend to match up with three different markets:
RS232 is used with a number of protocols to connect expensive bill acceptors / recyclers for
applications that are typically in expensive, secure enclosures. Any interference with this
connection will generally tend to be visible to the Paylink application.
MDB is used in very cheap systems, typically vending machines. The connection is vulnerable to
interference, but the amounts of money involved tend to be low.
cctalk is a very versatile system, which can be used in high value applications. The connection is
relatively vulnerable to interference and so encryption is very frequently used to provide
security. The security option chosen for Paylink cctalk is DES encryption, which involves the
exchange of local, random keys.
Paylink has, as a philosophy, the idea that it will connect to anything. Using DES encryption in
general for a bill and a coin acceptor do not therefore make sense and people wishing to create a
fully secure system using these are referred to the DES Paylink system (which is closed down and
secure)
A DES bill recycler however makes sense, as the locked down aspect here is in the peripheral -
Paylink can connect to any recycler, but the recycler will only communicate with Paylink. Given the
vulnerability to high value fraud of a cctalk recycler, Paylink therefore insists that any cctalk recyclers
that can support DES encryption must be used with DES encryption turned on.
DES Key Exchange
Before using a DES based device, Paylink has to acquire and store the random DES key provided by
the device. Paylink automatically checks at device discovery whether it has a correct key, and if it
hasn’t Paylink goes into key exchange mode.
A Paylink device in key exchange mode flashes the green LED at twice the normal frequency, and a
device waiting for a key exchange is visible to the application with the ACCEPTOR_NO_KEY bit set in
the AcceptorBlock.Status field.
The mechanism for triggering a key exchange is unique to each manufacturer / device.
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