Trapdoor

A trapdoor is a sliding or hinged door, flush with the surface of a floor, roof, or ceiling, or in the stage of a theatre. A hatch, an opening which may also be in a wall and need not be flush with the surface, is similar; in some cases either name is applicable. A small door in a wall, floor or ceiling used to gain access to equipment is called an access hatch or access door.

History

Originally, trapdoors were sack traps in mills, and allowed the sacks to pass up through the mill while naturally falling back to a closed position.

Many buildings with flat roofs have hatches that provide access to the roof; on ships, hatches—usually not flush, and never called trapdoors—provide access to the deck. Cargo ships, including bulk carriers, have large hatches for access to the holds.

Gallows

Most 19th- and 20th-century gallows featured a trapdoor, usually with two flaps. The victim was placed at the join. The edge of a trapdoor farthest from the hinge accelerates faster than gravity, so that the prisoner does not hit the flaps but falls freely.

Trap Door (magazine)

Trap Door is a science-fiction fanzine published by Robert Lichtman, with the first issue appearing in October 1983.

History

It received nominations for the Hugo Award for Best Fanzine in 1987 and 1992.

The magazine is published irregularly and (especially in more recent years) infrequently. As of December 2014, a total of 31 issues had been published. Although it has never won a Hugo Award – most likely due to its limited circulation not reaching enough Hugo Award voters – the magazine is highly regarded and has won (or placed high) on various polls within the science-fiction fanzine subculture (such as the Fan Activity Achievement Award, which it won in 2000, 2004, 2010, 2011, 2013 and 2014).

A wide range of science-fiction fans and professionals have contributed to the magazine over the years. This list is in the order of their first appearance:

Trapdoor function

A trapdoor function is a function that is easy to compute in one direction, yet difficult to compute in the opposite direction (finding its inverse) without special information, called the "trapdoor". Trapdoor functions are widely used in cryptography.

In mathematical terms, if f is a trapdoor function, then there exists some secret information y, such that given f(x) and y, it is easy to compute x. Consider a padlock and its key. It is trivial to change the padlock from open to closed without using the key, by pushing the shackle into the lock mechanism. Opening the padlock easily, however, requires the key to be used. Here the key is the trapdoor.

An example of a simple mathematical trapdoor is "6895601 is the product of two prime numbers. What are those numbers?" A typical solution would be to try dividing 6895601 by several prime numbers until finding the answer. However, if one is told that 1931 is one of the numbers, one can find the answer by entering "6895601 ÷ 1931" into any calculator. This example is not a sturdy trapdoor function – modern computers can guess all of the possible answers within a second – but this sample problem could be improved by using the product of two much larger primes.