A Formal Treatment of Remotely

Remotely keyed encryption schemes (RKESs), introduced by Blaze 6], support high-bandwidth cryptographic applications (such as encrypted video conferences) in which long-lived secrets (such as users' private keys) never leave lower-bandwidth environments such as secure smart-cards. We provide a formal framework in which to study the security of RKESs and give an RKES that satisses our formal security requirements. Our RKES is eecient in that the amount of communication and computation required of the smart-card is independent of the input size. Our proof of security uses the pseudorandom permutation framework of Naor and Reingold 14] in an essential way.