certification authority is a trusted third party that certifies public keys.
digital signature: used to prove the integrity of a message. To create a digital signature, a private key is needed. With the public key (and the right algorithm), the integrity can then be checked. RSA is the most common used digital signature algorithm.
hash function: A good cryptographic hash algorithm converts arbitrary data into a seemingly-random number.
private key: A secret (randomly generated) number that should only be known to the person who generated it. It's used to create a digital signature and encrypt messages.
public key: A number that can be calculated from a private key. It needs not be kept private. The private key cannot be calculated from the public key.
salt: a random string that is either added to the data to be encrypted or the password in order to make dictionary attacks more difficult.