5.3 COMMUNICATION PROTOCOLS
5.3.1 ENCRYPTED SSP (eSSP)
eSSP is a secure serial interface specifically designed to address the problems experienced
by cash systems in gaming machines. Problems such as acceptor swapping,
reprogramming acceptors and line tapping are all addressed.
The interface uses a master slave model, the host machine is the master and the
peripherals (note acceptor, coin acceptor or coin hopper) are the slaves.
Data transfer is over a multi-drop bus using clock asynchronous serial transmission with
simple open collector drivers. The integrity of data transfers is ensured through the use of
16 bit CRC checksums on all packets.
A Diffie-Hellman key exchange is used to allow the host machine and SMART hopper to
jointly establish a shared secret key over an insecure communications channel. The
encryption algorithm used is AES with a 128-bit key; this provides a very high level of
security.
IMPORTANT: All transactions with the SMART Hopper must be encrypted to prevent
dispense commands being recorded and replayed by an external device.
For detailed information and full protocol specification please refer to SSP Interface
Specification (ITL Drawing GA138), this is available from the ITL website www.innovative-
technology.co.uk.
For a list of SMART Hopper specific commands see Appendix C – ESSP Commands.
Examples of communications between host machine and SMART Hopper are shown in
Appendix D – Example ESSP Communications
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