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Software cracking (known as "breaking" in the 1980s) is the modification of software to remove or disable features which are considered undesirable by the person cracking the software, especially copy protection features (including protection against the manipulation of software, serial number, hardware key, date checks and disc check) or software annoyances like nag screens and adware. A crack refers to the mean of achieving software cracking, for example a stolen serial number or a tool that performs that act of cracking. Some of these tools are called keygen, patch or loader. A keygen is a handmade product license generator that often offers the ability to generate legitimate licenses in your own name. A patch is a small computer program that modifies the machine code of another program. This has the advantage for a cracker to not include a large executable in a release when only a few bytes are changed. A loader modifies the startup flow of a program and does not remove the protection but circumvents it.〔〔 〕 A well known example of a loader is a trainer used to cheat in games.〔 〕 Fairlight pointed out in one of their .nfo files that these type of cracks are not allowed for warez scene game releases.〔 〕〔 〕〔 〕 A nukewar has shown that the protection may not kick in at any point for it to be a valid crack.〔 〕 The distribution of cracked copies is illegal in most countries. There have been lawsuits over cracking software. It might be legal to use cracked software in certain circumstances.〔(【引用サイトリンク】title=Is reverse engineering legal? )〕 ==History== The first software copy protection was applied to software for Apple II, Atari 800 and Commodore 64 computers. Software publishers have implemented increasingly complex methods to try to stop unauthorized copying of software. On the Apple II, unlike modern computers that use standardized device drivers to manage device communications, the operating system directly controlled the step motor that moves the floppy drive head, and also directly interpreted the raw data, called ''nibbles'', read from each track to identify the data sectors. This allowed complex disk-based software copy protection, by storing data on half tracks (0, 1, 2.5, 3.5, 5, 6...), quarter tracks (0, 1, 2.25, 3.75, 5, 6...), and any combination thereof. In addition, tracks did not need to be perfect rings, but could be sectioned so that sectors could be staggered across overlapping offset tracks, the most extreme version being known as spiral tracking. It was also discovered that many floppy drives did not have a fixed upper limit to head movement, and it was sometimes possible to write an additional 36th track above the normal 35 tracks. The standard Apple II copy programs could not read such protected floppy disks, since the standard DOS assumed that all disks had a uniform 35-track, 13- or 16-sector layout. Special nibble-copy programs such as Locksmith and Copy II Plus could sometimes duplicate these disks by using a reference library of known protection methods; when protected programs were cracked they would be completely stripped of the copy protection system, and transferred onto a standard format disk that any normal Apple II copy program could read. One of the primary routes to hacking these early copy protections was to run a program that simulates the normal CPU operation. The CPU simulator provides a number of extra features to the hacker, such as the ability to single-step through each processor instruction and to examine the CPU registers and modified memory spaces as the simulation runs (any modern disassembler/debugger can do this). The Apple II provided a built-in opcode disassembler, allowing raw memory to be decoded into CPU opcodes, and this would be utilized to examine what the copy-protection was about to do next. Generally there was little to no defense available to the copy protection system, since all its secrets are made visible through the simulation. However, because the simulation itself must run on the original CPU, in addition to the software being hacked, the simulation would often run extremely slowly even at maximum speed. On Atari 8-bit computers, the most common protection method was via "bad sectors". These were sectors on the disk that were intentionally unreadable by the disk drive. The software would look for these sectors when the program was loading and would stop loading if an error code was not returned when accessing these sectors. Special copy programs were available that would copy the disk and remember any bad sectors. The user could then use an application to spin the drive by constantly reading a single sector and display the drive RPM. With the disk drive top removed a small screwdriver could be used to slow the drive RPM below a certain point. Once the drive was slowed down the application could then go and write "bad sectors" where needed. When done the drive RPM was sped up back to normal and an uncracked copy was made. Of course cracking the software to expect good sectors made for readily copied disks without the need to meddle with the disk drive. As time went on more sophisticated methods were developed, but almost all involved some form of malformed disk data, such as a sector that might return different data on separate accesses due to bad data alignment. Products became available (from companies such as Happy Computers) which replaced the controller BIOS in Atari's "smart" drives. These upgraded drives allowed the user to make exact copies of the original program with copy protections in place on the new disk. On the Commodore 64, several methods were used to protect software. For software distributed on ROM cartridges, subroutines were included which attempted to write over the program code. If the software was on ROM, nothing would happen, but if the software had been moved to RAM, the software would be disabled. Because of the operation of Commodore floppy drives, one write protection scheme would cause the floppy drive head to bang against the end of its rail, which could cause the drive head to become misaligned. In some cases, cracked versions of software were desirable to avoid this result. A misaligned drive head was rare usually fixing itself by smashing against the rail stops. Another brutal protection scheme was grinding from track 1 to 40 and back a few times. Most of the early software crackers were computer hobbyists who often formed groups that competed against each other in the cracking and spreading of software. Breaking a new copy protection scheme as quickly as possible was often regarded as an opportunity to demonstrate one's technical superiority rather than a possibility of money-making. Some low skilled hobbyists would take already cracked software and edit various unencrypted strings of text in it to change messages a game would tell a game player, often something not suitable for children. Then pass the altered copy along in the pirate networks, mainly for laughs among adult users. The cracker groups of the 1980s started to advertise themselves and their skills by attaching animated screens known as crack intros in the software programs they cracked and released. Once the technical competition had expanded from the challenges of cracking to the challenges of creating visually stunning intros, the foundations for a new subculture known as demoscene were established. Demoscene started to separate itself from the illegal "warez scene" during the 1990s and is now regarded as a completely different subculture. Many software crackers have later grown into extremely capable software reverse engineers; the deep knowledge of assembly required in order to crack protections enables them to reverse engineer drivers in order to port them from binary-only drivers for Windows to drivers with source code for Linux and other free operating systems. Also because music and game intro was such an integral part of gaming the music format and graphics became very popular when hardware became affordable for the home user. With the rise of the Internet, software crackers developed secretive online organizations. In the latter half of the nineties, one of the most respected sources of information about "software protection reversing" was Fravia's website. Most of the well-known or "elite" cracking groups make software cracks entirely for respect in the "The Scene", not profit. From there, the cracks are eventually leaked onto public Internet sites by people/crackers who use well-protected/secure FTP release archives, which are made into pirated copies and sometimes sold illegally by other parties. The Scene today is formed of small groups of skilled people, who informally compete to have the best crackers, methods of cracking, and reverse engineering. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「software cracking」の詳細全文を読む スポンサード リンク
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