| The traditional method for describing cryptographic hash algorithms is to offer two components: the compression function and an iteration scheme. This paper shows that describing cryptographic hash algorithms as being comprised of four components more easily and more accurately illustrates the operation of the algorithm and simplifies analysis. In the four-component framework, cryptographic hash algorithms are divided into preprocessing, iterative structure, combining function and finalization components. As part of the iterative structure, a global state is initialized, updated according to the preprocessed input, and finalized into the output of the algorithm: the hash value.;Each component lends itself to providing or preserving security properties in the overall algorithm. The four components are individually examined for the properties they provide and attacks they may prevent. Existing techniques for each component (that may not have been initially framed as such) are presented and analyzed and a few novel techniques are introduced. An extensive list of algorithms, including all published candidates for SHA-3, the forthcoming United States Advanced Hash Standard, are analyzed for their choices of each of their four components. |
