Unformatted text preview: described. (2) Add all assumptions about the initial state of the protocol. (3) Attach logical formulas to the statements: assertions about the state of the system after each statement. (4) Apply the logical postulates to the assertions and assumptions to discover the beliefs held by the parties in the protocol. The authors of BAN logic “view the idealized protocols as clearer and more complete specifications than traditional descriptions found in the literature....” [283,284]. Others are not so impressed and criticize this step because it may not accurately reflect the real protocol [1161,1612]. Further debate is in [221,1557]. Other critics try to show that BAN logic can deduce characteristics about protocols that are obviously false —see [285,1509] for a rebuttal—and that BAN logic deals only with trust and not security . More debate is in [1488,706,1002]. Despite these criticisms, BAN logic has been a success. It has found flaws in several protocols, including Needham-Schroeder and an early draft of a CCITT X.509 protocol . It has uncovered redundancies in many protocols, including Yahalom, Needham-Schroeder, and Kerberos. Many published papers use BAN logic to make claims about their protocol’s security [40,1162,73]. Other logic systems have been published, some designed as extensions to BAN logic [645,586,1556,828] and others based on BAN to correct perceived weaknesses [1488,1002]. The most successful of these is GNY , although it has some shortcomings . Probabalistic beliefs were added to BAN logic, with mixed success, by [292,474]. Other formal logics are [156,798,288];  attempts to combine the features of several logics. And [1124,1511] present logics where beliefs can change over time. The fourth approach to the analysis of cryptographic protocols models the protocol as an algebraic system, expresses the state of the participants’ knowledge about the protocol, and then analyzes the attainability of certain states. This approach has not received a...
View Full Document
- Fall '10
- Cryptography, Bruce Schneier, Applied Cryptography, EarthWeb, Search Search Tips