# CRYPTOGRAPHY - Entropy and randomness

## Contents

## Introduction

In information theory, the entropy of a random variable is the average level of "information", "surprise", or "uncertainty" inherent to the variable's possible outcomes.
## Concepts

## Pseudorandomness

### Pseudorandomness

### Oblivious pseudorandomness

Cloudflare (Privacy Pass context): an oblivious PRF (OPRF) is a protocol between a server S and a client C. In the protocol, S holds a key K for some PRF F and C holds an input x. The security goal is that C receives the output y = F(K,x) without learning the key K and S does not learn the value x.
- Efficient Batched Oblivious PRF with Applications to Private Set Intersection - https://eprint.iacr.org/2016/799
- Highly-Efficient and Composable Password-Protected Secret Sharing (Or: How to Protect Your Bitcoin Wallet Online) - https://eprint.iacr.org/2016/144