Protocol Failures in CryptosystemsThis chapter first appeared in the Proceedings of the IEEE, vol. 76, no. 5, May 1988.

When a cryptoalgorithm is used to solve data security or authentication problems, it is implemented within the context of a protocol that specifies the appropriate procedures for data handling. The purpose of the protocol is to ensure that when the cryptosystem is applied, the level of security or authentication required by the system is actually attained. In this chapter, we survey a collection of protocols in which this goal has not been met, not because of a failure of the cryptoalgorithm used, but rather because of shortcomings in the design of the protocol. Guidelines for the development of sound protocols will also be extracted from the analysis of these failures.