OneWay Functions for PublicKey Cryptography
Learn about the functions of publickey cryptography.
Having stated the blueprint for a publickey cryptosystem, we now need to consider how such a publickey cryptosystem can be designed. The first step in this direction is to precisely state the properties we need publickey encryption to satisfy.
Trapdoor oneway functions
Publickey encryption can be thought of as a function that anyone should be able to compute since the encryption key is public. This function has these two obvious properties:

The function should be ‘easy’ to compute: In other words, it should be computable in polynomial time. If this is not the case, it will be impractical to encrypt anything.

The function should be ‘hard’ to reverse: In other words, an algorithm for finding the input from a given output should run in exponential time. If this is not the case, then an attacker might efficiently determine a plaintext from their knowledge of the ciphertext and the public encryption key.
A function having the properties above is often referred to as a oneway function.
Get handson with 1200+ tech skills courses.