I. INTRODUCTIONII. Cryptographic SymbologyIII. Conceptual ModelA. ArchitectureB. ExecutionC. Output-only processesD. Register processesIV. Graphical User InterfaceV. Process ImplementationVI. Test ModelsA. A simple LFSRB. Effect of noise on stream ciphersVII. Further DevelopmentVIII. ConclusionA. Screen capture images from the second model testECE-746-04B-001-PR-LYONSAbstract—An interactive graphical environment is presentedas an educational tool for teaching applications of cryptographicalgorithms and other software systems. A design concept isshown, based on research into the efficacy of experientiallearning in graphical environments. The implementation of thedesign allows for many different types of software components tobe integrated with the system without rebuilding the system.The results of two test exercises are shown, validating theusefulness of the developed system as an educational aid.Index Terms—Cryptography, algorithms, models, education.I. INTRODUCTIONEACHING cryptography, particularly at the undergraduatelevel, is difficult if (as is typical) the students have littleor no experience with cryptographic technology. Examiningalgorithms in theory, using abstract representations, is muchless effective than allowing students to experimentthemselves, but cryptographic software is usually embeddedin specific applications and amenable to low-level inspection.TNumerous studies (especially [1]) have indicated thatexperiential learning is much more effective than reviewingabstract concepts or theoretical implementations.Unfortunately, it is difficult to provide an appropriateeducational experience when teaching cryptography: thealgorithms themselves tend to be overwhelmingly complex inimplementation, and in practice they are typically embeddeddeeply in specific applications.For example, the application known as PGP (from itsorigins as Pretty Good Privacy) includes five symmetricencryption algorithms, three hash algorithms and threepublic-key algorithms, but it is designed to be integrated withother applications (e.g. email clients) [5]. It is not possible toaccess individual algorithms in isolation for analytical orexperimental purposes.Existing cryptographic analysis tools typically focus onperformance of specific algorithms, which are usuallyembedded in the tools. An example is the KRYPTOS package[6], which includes nine symmetric encryption algorithms,the RSA asymmetric encryption algorithm and severalsignature, hash and Message Authentication Code (MAC)algorithms, but is specifically designed to provide timinganalysis of operation performed on data obtained from files.The author presents a novel solution to the problem, in theform of software package named CAMERA (for "ACryptographic Application Modeling Environment forResearch and Analysis"). The package is intended to allowusers to experiment with software components, specificallyManuscript received May 9, 2004. This work was produced as a requirementof ECE 746 Secure Telecommunication Systems, Spring 2004 semester, GeorgeMason University (Instructor: Kris Gaj).M. X. Lyons is an Instructor of Information Technology in the School ofInformation Technology and Engineering at George Mason University, Fairfax,VA 22030 USA (email: [email protected]).(but not limited to) cryptographic algorithms and relatedcomponents. The scope of application of the package is broad,from low-level primitive operators (such as 1-bit registers andexclusive OR (XOR) functions, as used in linear feedbackshift registers (LFSRs) [7], to complex systems incorporatingmultiple algorithms (see §VI.B below for an example).In contrast to existing applications which embed specificalgorithms into the software, CAMERA uses sophisticatedsoftware techniques to allow run-time discovery of compatiblesoftware modules, which can be incorporated into systemmodels created and edited by the user. The package includes anumber of basic modules and samples of cryptographicalgorithms encapsulated in the modular format, but theprimary advantage of the design is the ability of the user toeasily add any software component that meets the modularrequirements.The design also allows for detailed examination of amodeled system as it is executed. The state of individualmodular components can be inspected between modelexecution cycles, and even changed (e.g. to simulate the effectof noise or tampering).To enhance the learning experience and ease of use, thesystem uses a graphical user interface (GUI). The user is ableto manipulate icons representing software modules and createlinks between them to model data flows. The GUI uses aplatform-independent graphical implementation which ismapped to the native "look and feel" of the platform on whichit is executed.II.CRYPTOGRAPHIC SYMBOLOGYCertain domains in the information processing field havewell defined formal symbologies or notation schemes forrepresenting data, hardware, software and related entities. Forexample, the symbols used for data processing flowchartshave been standardized for more than three decades [9], [10].Unfortunately, a survey of available literature revealed nosuch standardization for symbols used in cryptographicdiagrams. Significant differences are observed betweensources (e.g. [11] and [14]) and even for different diagramswithin a single source (e.g. [12] and [13]; [14], [15] and[16]). The author of the textbook used for this courseconfirmed in [18] that no formal symbology has been definedfor cryptography.To accommodate existing variations in symbols used inpotential user communities, CAMERA supports the use ofcustom icons for each component module. In modularizing acomponent for use with CAMERA, one of the requiredelements is the name of an image file in GraphicsInterchange Format (GIF), Joint Photographic Experts Group(JPEG) or Portable Network Graphics (PNG) format (see [19]for a comparison of these three