back door

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back door

(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].
This article is provided by FOLDOC - Free Online Dictionary of Computing (

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 encryption backdoor, Easter Egg and Back Orifice.
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References in periodicals archive ?
So far, no one has tried the back door. If they do, I'll know about it.
Remexi is a basic back door Trojan that allows attackers to open a remote shell on the computer and execute commands.
In May, Mozilla along with a number of other tech industry leaders, including Apple, Google, Facebook, Twitter, Yahoo and Microsoft, ( signed a letter to President Barack Obama urging him to reject any proposals that would requireAaAaAeAeAaAeAeA decryption keys or back doors. A weeks later, a group of the world's top cybersecurity experts ( released a paper saying that the creation of back-door technologies would put sensitive data at risk of being compromised by hackers, terrorists or even just rogue federal agents or company employees.
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
Second, assess the risk inherent in each back door. Is any back door located in a target industry, such as financial institutions or government agencies?
Once the additional back doors are installed, they fetch a larger back door that carries out the cyber espionage activities.
The burglar made off with two wallets, containing cards, PS100 and a car key fob, after entering through an unlocked back door at about 7.40pm on Wednesday.
He opened the back door, and grabbed at the intruder.
However, delegates clearly felt any suspension was the thin end of the wedge and an attempt by the Tory-led coalition to deregulate Sunday trading by the back door.
ISLAMABAD, March 24, 2012 (Balochistan Times): The veteran Hurriyet leader Syed Ali Geelani has warned Pakistan to restrain from back door diplomacy on Kashmir issue with India.