Three types of cryptography: secret-key, public key, and hash function.
Secret-key: uses the same key for both encryption as well as decryption.
Public key: Public key encryption, in which a message is encrypted with a recipient's public key. The message cannot be decrypted by Digital signatures.
Hash function:A cryptographic hash function is a hash function which takes an input (or 'message') and returns a fixed-size alphanumeric string.