back door
back door
back′ door′
n.
Noun | 1. | ![]() |
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单词 | back door | |||||||||
释义 | back doorback doorback′ door′n.
back doorback doorback doorback doorback door(security)Historically, back doors have often lurked in systems longerthan anyone expected or planned, and a few have become widelyknown. The infamous RTM worm of late 1988, for example,used a back door in the BSD Unix "sendmail(8)" utility. Ken Thompson's 1983 Turing Award lecture to the ACMrevealed the existence of a back door in early Unix versionsthat may have qualified as the most fiendishly clever securityhack of all time. The C compiler contained code that wouldrecognise when the "login" command was being recompiled andinsert some code recognizing a password chosen by Thompson,giving him entry to the system whether or not an account hadbeen created for him. Normally such a back door could be removed by removing it fromthe source code for the compiler and recompiling the compiler.But to recompile the compiler, you have to *use* the compiler- so Thompson also arranged that the compiler would *recognisewhen it was compiling a version of itself*, and insert intothe recompiled compiler the code to insert into the recompiled"login" the code to allow Thompson entry - and, of course, thecode to recognise itself and do the whole thing again the nexttime around! And having done this once, he was then able torecompile the compiler from the original sources; the hackperpetuated itself invisibly, leaving the back door in placeand active but with no trace in the sources. The talk that revealed this truly moby hack was published as["Reflections on Trusting Trust", "Communications of the ACM27", 8 (August 1984), pp. 761--763]. back doorA secret way to take control of a computer. Also called "trap doors," back doors are built into software by the original programmer, who can gain access to the computer by entering a code locally or remotely. For example, a back door in an application would enable a person to activate either normal or hidden functions within the software. A back door in an operating system would provide access to all system functions in the computer. See Easter Egg and Back Orifice.back doorback dooradjective A slang term referring to the anus; anal.back doorBack Door2. Any way to access a computer system other than logging in or using "normal" channels. Programmers often put back doors into their programs, or a hacker may create one. 3. See: Back-Door Listing. back doorthe informal mechanism whereby the BANK OF ENGLAND buys back previously issued TREASURY BILLS in the DISCOUNT MARKET at their ruling market price in order to release money to help the DISCOUNT HOUSES overcome temporary liquidity shortages. This is done as a means of increasing the liquid funds available not only to the discount houses themselves but also to the COMMERCIAL BANKS at prevailing interest rates to enable them to maintain their lending. Compare FRONT DOOR.back door
Synonyms for back door
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