Programs that generate valid CD keys or serial/registration numbers for a piece of software are also commonly called keygens. These are made available by software cracking groups for free download on various websites dedicated to software piracy. The use of Keygens to activate software without purchasing a genuine code is illegal.
Legal issues aside, there are two major issues in using keygens: Product activation and online key verification.
Keys generated with a key generator may not work with software that is used online, including downloading software updates. This is because the user must confirm their serial number every time the software connects to the server, and the key may be invalid for various reasons.
One reason is that the cracker may have misinterpreted the original algorithm, creating a key that was "good enough" to let the software be installed, but not letting all possible future generated keys be valid.
Another reason may be that the software developers only accept keys that they know were distributed with the media during production, or had been issued with an online registration, causing a cryptographically correct key to still be denied.
A third reason could be a secondary unpublished algorithm that is used by the vendor, e.g., to extend the previous example, the characters 0, 7, 9, C, and K are never allowed. The software that confirms the key on the user's machine does not know these numbers and characters are not allowed, and will accept the keygen output, but the online confirmation fails.
Keys for massively multiplayer online games are different; usually each key is uniquely generated by the producer and included with the product, usually in a tamper-proof medium such as a scratch card or tamper-proof envelope. These keys will usually become uniquely linked to a certain game account upon usage and are rendered "useless" by this process. Therefore, MMOGs are not usually subject to piracy.
Keygens may also contain viruses (depending on whom they are downloaded from). When the program is opened, instead of providing a valid key, the program may install harmful software on the computer on which it was installed.
Software developers have tried to prevent piracy by using 'Product Activation', which requires the user to connect to the internet or call a number in order to make a program usable. Newer keygens also contain a method to bypass the product activation. Some software manufacturers like Adobe include telephone activation which requires you to give a special code when you call. A method used by some keygens allows one to type the number given by the product to generate the (telephone) activation code which is then typed into the software. Some software developers, such as Norton, have worked around this by not including this feature or making it harder to locate in the program's code. This makes it harder for cracking groups to write an activation code.
Keygens are widely available but the legality of their use differs internationally.
US Patent Issued to VIA Technologies on Nov. 15 for "Apparatus and Method for Providing User-Generated Key Schedule in a Microprocessor Cryptographic Engine" (Texas Inventors)
Nov 19, 2011; ALEXANDRIA, Va., Nov. 19 -- United States Patent no. 8,060,755, issued on Nov. 15, was assigned to VIA Technologies Inc. (New...
Publication No. WO/2009/094939 Published on Aug. 6, Assigned to Huawei Technologies for Mobile Internet Protocol Route Optimization Signaling Protection Method, System, Node, Home Agent (Chinese Inventors)
Aug 13, 2009; GENEVA, Aug. 13 -- Chunqiang Li and Zhigang Huang, both of China, have developed a method for protecting mobile internet protocol...