What Is A Trapdoor Function?
In cryptography, a trapdoor function is one that can easily be computed in one direction but the inverse is very difficult to perform. These functions can use a secret to efficiently perform the inverse calculation. Trapdoor functions are one-way functions widely used in public-key cryptography.
Trapdoor functions and one-way functions are used interchangeably, all trapdoor functions are one-way functions, but not all one-way functions are trapdoor functions. They differ from one-way functions because of the secret they can use to inverse the computation. In our case, this is the private key that is linked with a public key.
The name trapdoor function is an analogy as falling through a trapdoor into a pit is easy, although climbing out can prove challenging – unless you have a ladder.