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Cryptographic Protocols

Cryptographic Protocols. Reference: , Charles P., Security in Computing, 2nd Edition, Prentice Hall, 1996. Definition of Protocols. A protocol is an orderly sequence of steps two ore more parties take to accomplish some task. Characteristics of a Good Protocol. Established in Advance

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Cryptographic Protocols

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  1. Cryptographic Protocols Reference: , Charles P., Security in Computing, 2nd Edition, Prentice Hall, 1996. Ref: Pfleeger96, Ch.4

  2. Definition of Protocols • A protocol is an orderly sequence of steps two ore more parties take to accomplish some task. Ref: Pfleeger96, Ch.4

  3. Characteristics of a Good Protocol • Established in Advance • Completely designed before it is used. • Mutually Subscribed • All parties agree to follow protocol steps, in order. • Unambiguous • Steps cannot be misunderstood. • Complete • For every situation that can occur there is a prescribed action to be taken. Ref: Pfleeger96, Ch.4

  4. Design and Implementation • A protocol sets the rules of behavior, as well as separates the process of accomplishing the task from the mechanism by which it is done. • Design assures that the protocol is correct. • Implementation simply requires a mechanism, which can change without affecting the design. Ref: Pfleeger96, Ch.4

  5. Arbitrated Protocols • An arbiter is a disinterested third party trusted to complete a transaction between two distrusting parties. • In a computer protocol, an arbiter is a trustworthy third party who ensures fairness. • The arbiter could be a person, program, or a machine. Ref: Pfleeger96, Ch.4

  6. Problems with Arbitrated Protocols • Trustworthy neutral third party is hard to find. • Maintaining availability of arbiter is costly. • Arbitration causes communications delay. • Arbitration service is a network bottleneck. • Secrecy is vulnerable, since arbiter has access to so much sensitive information. Ref: Pfleeger96, Ch.4

  7. Adjudicated Protocols • An adjudicator is a third party who can judge whether a transaction was performed fairly--for example, a notary public. • With adjudicated computer protocols, enough data is available for a third party to determine if two parties acted fairly. • However, failure is detected only after it has occurred. Ref: Pfleeger96, Ch.4

  8. Self-Enforcing Protocols • A self-enforcing protocol guarantees fairness. • If either party cheats, it is obvious to the other party. Ref: Pfleeger96, Ch.4

  9. Comparing the Protocols • The self-enforcing protocols are preferred, but not always possible. • Adjudicated protocols are preferred over arbitrated protocols. Ref: Pfleeger96, Ch.4

  10. Cryptographic Protocols • There are a number of problems that can be solved using secure protocols. • Key Distribution • Authentication of Keys • Authentication of Transactions • Contract Signing • Certified Mail Ref: Pfleeger96, Ch.4

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