What are the four basic tasks in designing a particular security service?

1. Design an algorithm for performing the security-related transformation.                                            The algorithm should be such that an opponent cannot defeat its purpose.
2. Generate the secret information to be used with the algorithm.
3. Develop methods for the distribution and sharing of the secret information
4. Specify a protocol to be used by the two principals that makes use of   the    security algorithm and the secret information to achieve a particular security.