Each row represents what principals can access a resource, essentially an access control list. Access Matrices are a way of modeling the access rights, but it is not usually done this way due to its sparseness. Secrecy Secrecy means restricting who can view a message, preventing others from seeing any meaningful data. Encryption is one mechanism used for secrecy. Data can be encrypted and decrypted using keys.
Symmetric algorithms use secret keys shared by two different users.
Ideally, we want functions that are easy to compute but hard to undo without a certain piece of knowledge, in this case, the key. By hard, we mean it would take millions of years to compute without the key. Integrity and Nonrepudiation Integrity deals with making data tamper-proof. Suppose an eavesdropper is observing an encrypted stream of information passing from one user to another. Even though the intruder cannot understand what the messages are, it is still possible to modify the data stream arbitrarily.