Security

https://www.ietf.org/rfc/rfc2828.txt

5 services
1 Confidentiality : Protects data against unauthorized disclosure. Use encryption.
2 Integrity: Ensures data has not been changed, destroyed, or lost in an unauthorized or accidental manner. Use a hash function.
3 Accountability: Accountability directly supports non-reputation and provides protection against false denial of involvement in a communication. Use a digital signature.
4 Authentication: Confirm identity of a system entity. Use a Message Authentication Code (MAC)
5 Availability: Services are accessible and available to authorized users or processes in an information infrastructure. Difficult to protect. ex. Denial of Service attack.

Of the five services, four can be achieved by using encryption. That is why cryptography and network security go hand in hand.