SG Intec Ltd & Co KG SG-Lock, Developer'S Manual

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3 Protecting Software with
SG-Lock
3.1 Introduction
The operation of SG-Lock as copy protection system is based on the call of
certain functions, that establish a connection between an easy to copy software
(that therefore has to be protected) and the practically impossible to copy SG-
Lock hardware.
The for that used functions are the functions of the SG-Lock API (appli-
cation programming interface). They are contained in the software library
SGLW32.DLL, that is delivered with the SG-Lock hardware. The SG-Lock API
provides varying types of functions, of which according to the type of protection
different are used. For an effective software protection not all of the functions
have to be used.
3.2 Protection Strategies
The most frequently applied type of protection of software against illegal use is
the simple ”run or run not“ copy protection, that avoids that the software runs
on more PCs than paid for. In this case the repeatedly test whether the copy
protection key is installed on the PC or not is the main task.
Other protection strategies shall allow the software to run only a limited num-
ber of starts. For that a counter, that logs the number of starts, is needed addition-
ally beside the existance of the copy protection key. SG-Lock provides counter
variables for purposes like that.
A similar limit to run software is the use of an application only up to a certain
date. In that case a date is stored in the SG-Lock memory to verify at program
start and during software use, that has not been reached.
Another alternative to control software use is ”pay per use“. The user pays
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