The Cryptographic Protocol Shapes Analyzer (CPSA) attempts to enumerate all essentially different executions possibe for a cryptographic protocol. We call them the shapes of the protocol. Naturally occurring protocols have only finitely many, indeed very few shapes. Authentication and secrecy properties are easy to determine from them, as are attacks and anomalies.

For each input problem, the CPSA program is given some initial behavior, and it discovers what shapes are compatible with it. Normally, the initial behavior is from the point of view of one participant. The analysis reveals what the other participants must have done, given the participant's view. The search is based on a high-level algorithm that was claimed to be complete, i.e. every shape can in fact be found in a finite number of steps. Further theoretical work showed classes of executions that are not found by the algorithm, however it also showed that every omitted execution requires an unnatural interpretation of a protocol's roles. Hence the algorithm is complete relative to natural role semantics.

The package contains a set of programs used to perform and display the analysis. A standards complient browser, such as Firefox, Safari, or Chrome, is required to display the results. Program documentation is in the doc directory in the source distribution, and installed in the package's data directory. You can locate the package's data directory by typing "cpsa --help" to a command prompt. New users should start learning to use the tool from the manual, found at "cpsamanual.pdf" in the data directory. Examples referenced in the manual can be found in the data directory as well. It is suggested that users make an examples directory and copy "*.scm *.xhtml" to their local examples directory, both so that they may be modified and for ease of access.

Serious Windows users should install MSYS so as to allow the use of make and script execution.

The theory and algorithm used by CPSA was developed with the help of Joshua D. Guttman, John D. Ramsdell, Jon C. Herzog, Shaddin F. Doghmi, F. Javier Thayer, Paul D. Rowe, and Moses D. Liskov. John D. Ramsdell and Moses D. Liskov implemented the algorithm in Haskell. CPSA was designed and implemented at The MITRE Corporation.