Software cracking

 Software cracking

Software cracking is the process of
bypassing the registration and
payment options on a software
product to remove copy protection
safeguards or to turn a demo
version of software into a fully
functional version without paying
for it.
Cracking software generally requires
loading the executable into a
hexadecimal code editor and
directly modifying it. The executable
is then run in place of the original.
Software cracking is considered
illegal and cracked software is often
called pirated software. Cracked
software generally has had the
executable modified and can cause
undesirable behaviour.
The most common software crack is
the modification of an application's
binary to cause or prevent a specific
key branch in the program's
execution. This is accomplished by
reverse engineering the compiled
program code using a debugger
until the software cracker reaches
the subroutine that contains the
primary method of protecting the
software (or by disassembling an
executable file with a program such
as IDA). The IDA (Interactive
Disassembler), as a disassembler
commonly used for reverse
engineering, performs the process
of automatic code analysis thereby
leveraging cross-references between
code sections and interactively
identifying the parameters of API
calls. Normally, the software
cracker using an IDA begins with
tracking an automatically generated
disassembly listing and then
renames and annotates the
information to the listing, until the
algorithm of the software is traced
to be effectively reverse-engineered.
The binary is then modified using
the debugger or a hex editor in a
manner that replaces a prior
branching opcode with its
complement or a NOP opcode so
the key branch will either always
execute a specific subroutine or skip
over it. Almost all common software
cracks are a variation of this type.
A good example of this technique is
a crack that removes the expiration
period from a time-limited trial of
an application. These cracks are
usually programs that patch the
program executable and sometimes
the .dll or so linked to the
application.
Similar cracks are available for
software that requires a hardware
dongle. A company can also break
the copy preventions of programs
that they have legally purchased but
that are licensed to particular
hardware, so that there is no risk of
downtime due to hardware failure
(and, of course, no need to restrict
oneself to running the software on
bought hardware only).
In other cases, it might be possible
to decompile a program in order to
get access to the original source
code or code on a level higher than
machine code. This is often possible
with scripting languages. An
example is cracking (or debugging)
on the .NET platform.