Cryptography as practised for 3500 years before the mid-1970s used one secret, known by both the enciphering and deciphering parties. Anyone possessing that secret (called the key) was able to do either operation. In public key cryptography there are two different keys, one used to encipher data and the other used to decipher it. While one of these keys is kept private, the other is made public, and the system is designed so that knowledge of the public key does not allow the private key value to be determined. Normally it is assumed that the private key is controlled by just one person who will be referred to here as the keyholder.