As a fundamental building block, we construct a scheme to store a cryptographic secret such that it remains \emph{information theoretically} hidden, even given arbitrary continuous leakage from the storage. To this end, we use a randomized encoding and develop a method to securely \emph{refresh} these encodings even in the presence of leakage. We then show that our encoding scheme exhibits an efficient additive homomorphism which can be used to protect important cryptographic tasks such as identification, signing and encryption. More precisely, we propose \emph{efficient} implementations of the Okamoto identification scheme, and of an ElGamal-based cryptosystem with security against continuous leakage, as long as the leakage adheres the above mentioned restrictions. We prove security of the Okamoto scheme under the DL assumption and \emph{CCA2 security} of our encryption scheme under the DDH assumption.
Category / Keywords: foundations / Publication Info: extended version of a paper accepted to Asiacrypt 2011 Date: received 21 Sep 2011 Contact author: stefan at dziembowski net Available format(s): PDF | BibTeX Citation Version: 20110922:025118 (All versions of this report) Short URL: ia.cr/2011/519 Discussion forum: Show discussion | Start new discussion