back door

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back door

(security)
(Or "trap door", "wormhole"). A hole in the security of a system deliberately left in place by designers or maintainers. The motivation for such holes is not always sinister; some operating systems, for example, come out of the box with privileged accounts intended for use by field service technicians or the vendor's maintenance programmers. See also iron box, cracker, worm, logic bomb.

Historically, back doors have often lurked in systems longer than anyone expected or planned, and a few have become widely known. 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 ACM revealed the existence of a back door in early Unix versions that may have qualified as the most fiendishly clever security hack of all time. The C compiler contained code that would recognise when the "login" command was being recompiled and insert some code recognizing a password chosen by Thompson, giving him entry to the system whether or not an account had been created for him.

Normally such a back door could be removed by removing it from the 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 *recognise when it was compiling a version of itself*, and insert into the recompiled compiler the code to insert into the recompiled "login" the code to allow Thompson entry - and, of course, the code to recognise itself and do the whole thing again the next time around! And having done this once, he was then able to recompile the compiler from the original sources; the hack perpetuated itself invisibly, leaving the back door in place and 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 ACM 27", 8 (August 1984), pp. 761--763].

back door

A 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.
References in periodicals archive ?
A spokesman for Cleveland Police said the back door on that occasion was closed but unlocked.
Air India ( AI) operates some of its flights with only one entry- exit point ; Many AI flights are operating with the back door shown as inoperative due to shortage of cabin crew ; In an emergency like crash- landing, there would be a near stampede with only one exit door ; AI also facing a heavy rate of attrition with 33 pilots having quit this year alone ; Some of the pilots joined other airlines without even resigning ; Many pilots have resigned citing inefficiency and weak administration, which they allege has caused the mess at the carrier
After all, isn't this how he got into government - by sneaking in the back door on the tails of his Tory masters?
There is no getting away from the benefits of the back door diplomacy, The back door diplomacy with India will once again be initiated, if it suits Pakistan's interests," The News quoted Qureshi, as saying.
But then you leave the back door unlocked and someone enters and walks out with your jewelry.
WORCESTER - A city man allegedly kicked down the back door of a Payson Street apartment Saturday afternoon and stole antique coins and cash from inside before a neighbor chased and caught him.
And once the back door is locked, it should stay that way.
I stood at the back door, rang the bell, then entered their home with an immediate sense of peace as I passed over the threshold.
The back door distance is one measure of the existence and strength of the communication channel between board members that can be used to influence decisions by the full board.
He would have frequently noticed Negro passengers getting on at the front door and paying their fares, and then being forced to get off and go to the back doors to board the bus, and often he would have noticed that before the Negro passenger could get to the back door, the bus drove off with the fare in the box.
The burglars made off through the back door with a sum of cash.