Domain extender for collision resistant hash functions: Improving upon Merkle-Damgård iteration

We study the problem of securely extending the domain of a collision resistant compression function. A new construction based on directed acyclic graphs is described. This generalizes the usual iterated hashing constructions. Our main contribution is to introduce a new technique for hashing arbitrary length strings. Combined with DAG based hashing, this technique gives a new hashing algorithm. The amount of padding and the number of invocations of the compression function required by the new algorithm is smaller than the general Merkle-Damg̊ard algorithm. Lastly, we describe the design of a new parallel hash algorithm.