trap
= T =
trash
trap door n.
(alt. `trapdoor') 1. Syn. back door
-- a Bad Thing. 2. [techspeak] A `trap-door function' is
one which is easy to compute but very difficult to compute the
inverse of. Such functions are Good Things with important
applications in cryptography, specifically in the construction of
public-key cryptosystems.
--Jargon File, autonoded by rescdsk