1. Cryptographic Protocols
Reference: , Charles P., Security in Computing, 2nd Edition, Prentice Hall, 1996.
4/22/2019
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.
4/22/2019
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.
4/22/2019
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.
4/22/2019
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.
4/22/2019
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.
4/22/2019
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.
4/22/2019
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.
4/22/2019
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.
4/22/2019
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
4/22/2019
Ref: Pfleeger96, Ch.4