METHODICAL USE OF CRYPTOGRAPHIC TRANSFORMATIONS IN AUTHENTICATION PROTOCOLS

Design of cryptographic protocols for authentication and key managemen t is known to be a difficult problem. Although much research has been devoted to analysis techniques there remains a lack of basic design pr inciples. In the paper a common method of protocol design is identifie d which contributes to protocol problems in a number of ways. This is the practice of encrypting all relevant fields using a reversible cryp tographic transformation. A new design principle and a complementary n otation are introduced which help protocol designers to identify what form of encryption is really required. Several examples are used to il lustrate the problems and to show how the design principle and notatio n may be used in practice.