Libcrypt is a copy protection

Copy protection

Copy protection, also known as content protection, copy obstruction, copy prevention and copy restriction, refer to techniques used for preventing the reproduction of software, films, music, and other media, usually for copyright reasons.- Terminology :Media corporations have always used the term...

 mechanism developed by Sony

Sony

, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....

 for use in their PlayStation systems. The protection consists of a two-stage verification algorithm: the first stage attempts to validate the game disc as an original PlayStation disc; following that, a checksum

Checksum

A checksum or hash sum is a fixed-size datum computed from an arbitrary block of digital data for the purpose of detecting accidental errors that may have been introduced during its transmission or storage. The integrity of the data can be checked at any later time by recomputing the checksum and...

 is then calculated from the data on disc and is passed as a magic number

Magic number (programming)

In computer programming, the term magic number has multiple meanings. It could refer to one or more of the following:* A constant numerical or text value used to identify a file format or protocol; for files, see List of file signatures...

 to subroutines.

The protection code is written in the PlayStation's native assembly language

Assembly language

An assembly language is a low-level programming language for computers, microprocessors, microcontrollers, and other programmable devices. It implements a symbolic representation of the machine codes and other constants needed to program a given CPU architecture...

, which is enough to thwart some older modchip

Modchip

A modchip is a small electronic device used to modify or disable built-in restrictions and limitations of computers, specifically videogame consoles...

s and Action Replay

Action Replay

Action Replay is the brand name of a series of video game cheating devices created by Datel. As of 2010, Action Replays are currently available for some of the current major gaming platforms which include the Nintendo DS, Nintendo DSi, PlayStation 2, and the PlayStation Portable, and many older...

-like devices, as they work by intercepting library calls rather than tracing CPU registers. However, newer circumvention devices can emulate the response codes. The protection scanning software ClonyXXL rates Libcrypt as 2/5 skulls in terms of difficulty, implying that it is relatively easy to circumvent.

Only some PlayStation titles actually use Libcrypt -- most are simply unprotected.