Information-leakage in hybrid randomized protocols

In light of the vast number of existing cryptographic protocols, performance tradeoffs become a major obstacle when selecting one for practical usage. For instance, protocols known to be secure but inefficient compete with others being efficient but offering less security. We tackle such tradeoffs by investigating sequences of random protocol instances (randomized protocols) and analyzing the rate at which information leaks from such a sequence. Remarkably, it can be demonstrated that the mutual information between an eavesdropped ciphertext and the plain text decays exponentially fast with the length of the protocol sequence. Using simple tools from game-theory, we devise a generic technique to assemble several protocols of different performance into a single protocol, unifying the advantages of its ingredients. We call this a hybrid randomized protocol. We illustrate our technique by using simplified multipath transmission as an example, while observing that our general construction is in no way restricted to this scenario.