Security Uses of Cryptography
1)Transmitting over insecure channels
2)Storage on insecure media (essentially the same ideas as 1) but applied to a different need)
3)Authentication of computers or people at end of a message transmission. This includes digital signatures and password hashing
4)Integrity check that message delivered was the one sent (this is different from ensuring that nobody read information which is 1)). This is called message integrity