Abstract
Two of the fastest types of cryptographic algorithms are the stream cipher and the almost-universal hash function. There are secure examples of each that process data in software using less than one CPU cycle per byte. Hashstream combines the two types of algorithms in a straightforward manner yielding a PRF that can both consume inputs of and produce pseudorandom outputs of any desired length. The result is an object useful in many contexts: authentication, encryption, authenticated encryption, random generation, mask generation, etc. The HS1-SIV authenticated-encryption algorithm—a CAESAR competition second round selection—was based on Hashstream and showed the promise of such an approach by having provable security and topping the speed charts in several test configurations.