| Backdoor (computing) ： ウィキペディア英語版|
A backdoor in a computer system (or cryptosystem or algorithm) is a method of bypassing normal authentication, securing unauthorized remote access to a computer, or obtaining access to plaintext while attempting to remain undetected. The backdoor may take the form of a hidden part of a program, a separate program (e.g., Back Orifice) may subvert the system through a rootkit〔.(wired.com: "How a Crypto ‘Backdoor’ Pitted the Tech World Against the NSA" (Zetter) 24 Sep 2013 )〕
Default passwords can function as backdoors if they are not changed by the user. Some debugging features can also act as backdoors if they are not removed in the release version.〔http://blog.erratasec.com/2012/05/bogus-story-no-chinese-backdoor-in.html〕
The threat of backdoors surfaced when multiuser and networked operating systems became widely adopted. Petersen and Turn discussed computer subversion in a paper published in the proceedings of the 1967 AFIPS Conference.〔H.E. Petersen, R. Turn. "System Implications of Information Privacy". ''Proceedings of the AFIPS Spring Joint Computer Conference'', vol. 30, pages 291–300. AFIPS Press: 1967.〕 They noted a class of active infiltration attacks that use "trapdoor" entry points into the system to bypass security facilities and permit direct access to data. The use of the word ''trapdoor'' here clearly coincides with more recent definitions of a backdoor. However, since the advent of public key cryptography the term ''trapdoor'' has acquired a different meaning (see trapdoor function), and thus the term "backdoor" is now preferred. More generally, such security breaches were discussed at length in a RAND Corporation task force report published under ARPA sponsorship by J.P. Anderson and D.J. Edwards in 1970.〔''Security Controls for Computer Systems'', Technical Report R-609, WH Ware, ed, Feb 1970, RAND Corp.〕
A backdoor in a login system might take the form of a hard coded user and password combination which gives access to the system. A famous example of this sort of backdoor was used as a plot device in the 1983 film ''WarGames'', in which the architect of the "WOPR" computer system had inserted a hardcoded password (his dead son's name) which gave the user access to the system, and to undocumented parts of the system (in particular, a video game-like simulation mode and direct interaction with the artificial intelligence).
Although the number of backdoors in systems using proprietary software (software whose source code is not publicly available) is not widely credited, they are nevertheless frequently exposed. Programmers have even succeeded in secretly installing large amounts of benign code as Easter eggs in programs, although such cases may involve official forbearance, if not actual permission.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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