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 ?
Our priority is keeping our users safe, and back doors make them more vulnerable," said an employee of a public U.
Identifying and assessing back doors is only two-thirds of the process, however.
Let's look at the Front Door, the Back Door and how a Supply Chain Management (SCM) professional can help capture the monies being lost to the company's bottom line.
A muddy footprint was also visible on the back door and the apartment had been trashed, police said.
This back door led into the laundry room, which wasn't just a laundry room.
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 woman was at her home in Loughview Road on Friday when two men forced their way into the property by a back door.
Part of this I speak of from personal experience: (A) I don't deal with death very well, as most people don't, and (B) in any nursing home that I've been in throughout my career, as well as most hospitals, you walk in through the front door, but you leave by the back door.
Write to Rick Steves, Europe Through the Back Door, P.
Even when we walked in through your computer's back door, we still had to crack a few passwords to get your personal information to authorize credit card use.
The staffers say they were excluded from prayer meetings, told to enter through the back door and denied use of the lunchroom.
The officers ran to the back door and forced their way into the burning residence where they found a small unconscious child who Officer Rieson carried outside to safety.