Unformatted text preview: tography. The parties can be friends and trust each other implicitly or they can be adversaries and not trust one another to give the correct time of day. A cryptographic protocol involves some cryptographic algorithm, but generally the goal of the protocol is something beyond simple secrecy. The parties participating in the protocol might want to share parts of their secrets to compute a value, jointly generate a random sequence, convince one another of their identity, or simultaneously sign a contract. The whole point of using cryptography in a protocol is to prevent or detect eavesdropping and cheating. If you have never seen these protocols before, they will radically change your ideas of what mutually distrustful parties can accomplish over a computer network. In general, this can be stated as: — It should not be possible to do more or learn more than what is specified in the protocol. This is a lot harder than it looks. In the next few chapters I discuss a lot of protocols. In some of them it is possible for one of the participants to cheat the other. In others, it is possible for an eavesdropper to subvert the protocol or learn secret information. Some protocols fail because the designers weren’t thorough enough in their requirements definitions. Others fail because their designers weren’t thorough enough in their analysis. Like algorithms, it is much easier to prove insecurity than it is to prove security. The Purpose of Protocols
In daily life, there are informal protocols for almost everything: ordering goods over the telephone, playing poker, voting in an election. No one thinks much about these protocols; they have evolved over time, everyone knows how to use them, and they work reasonably well. These days, more and more human interaction takes place over computer networks instead of face-to-face. Computers need formal protocols to do the same things that people do without thinking. If you moved from one state to another and found a voting booth that looked com...
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- Fall '10
- Cryptography, Bruce Schneier, Applied Cryptography, EarthWeb, Search Search Tips