An architecture for robust pseudo-random generation and applications to /dev/random

We present a formal model and a simple architecture for robust pseudorandom generation that ensures resilience in the face of an observer with partial knowledge (or even partial control) of the generator’s entropy source. Our model and architecture ensure the following properties: • Resilience. The generator’s output looks random to an observer with no knowledges of the internal state. This holds even if that observer has complete control over data that is used to refresh the internal state. • Forward security. Past output of the generator looks random to an observer with no knowledges of the past internal state, even if it was later able to learn the internal state. • Backward security/Break-in recovery. Future output of the generator looks random, even to an observer with knowledge of the current state, provided that the generator is refreshed with data of sufficient entropy. Architectures such as above were suggested before. This work differs from previous attempts in that we present a formal model for robust pseudo-random generation, and provide a formal proof within this model for the security of our architecture. To our knowledge, this is the first attempt at a rigorous model for this problem. Our formal modeling advocates the separation of the entropy extraction phase from the output generation phase. We argue that the former is information-theoretic in nature, and should therefore rely on combinatorial and statistical tools and not on cryptography. On the other hand, we show that the latter phase can be implemented using any standard (non-robust) cryptographic PRG (which is turn can theoretically be built from any one-way function). We also discuss the applicability of our architecture as a replacement for the current implementation of /dev/(u)random in Linux, and also examine using it as an architecture for pseudorandom generation on smartcards.