**Key Encapsulation Mechanism**, also known as KEM, is a triple of algorithms and a corresponding key space , a ciphertext space with

- The algorithm takes a public parameter as an input and returns a public and secret-key pair ().
- The probabilistic (
*encapsulation*) algorithms takes as an input and returns a ciphertext and a key . - The deterministic (
*decapsulation*) algorithm takes as inputs and returns a key , with denoting as a failure.