# Function - One way

> Code - (Programming|Computer) Language > (Function | Operator | Map | Mapping | Transformation | Method | Rule | Task | Subroutine)

### Table of Contents

## 1 - About

With a one way function, it should be hard to determine the original input when only the output is known.

They are fundamental tools for:

- cryptography,
- and other data security applications

A function f is one-way if and only if f can be computed by a polynomial time algorithm,

For instance, a cryptographic hashing function is designed to always produce the same result from the same password input, and to minimize collisions where two different passwords can produce the same result. This hash is always the same length and cannot be directly decrypted to reveal the plaintext password.

## 2 - Articles Related

## 3 - Relationship

The relationship of one-way functions to cryptography

Can the reader say what two numbers multiplied together will produce the number 8616460799?

I think it unlikely that anyone but myself will ever know. William Stanley Jevons (The 'Principles of Science' book 1874)

## 4 - Easy / Hard

In applied contexts, the terms “easy” and “hard” are usually interpreted relative to some specific computing entity; typically “cheap enough for the legitimate users” and “prohibitively expensive for any malicious agents”.