In cryptography, scrypt is a password-based key derivation function created by Colin Percival, originally for the Tarsnap online backup service. The algorithm was specifically designed to make it costly to perform large scale custom hardware attacks by requiring large amounts of memory. In 2012, the scrypt algorithm was published by IETF as an Internet Draft, intended to become an informational RFC, which has since expired.[1] It is used as a proof-of-work scheme by the digital currency Litecoin.[2]