Paper 2021/406

Disappearing Cryptography in the Bounded Storage Model

Jiaxin Guan and Mark Zhandry

Abstract

In this work, we study disappearing cryptography in the bounded storage model. Here, a component of the transmission, say a ciphertext, a digital signature, or even a program, is streamed bit by bit. The stream is so large for anyone to store in its entirety, meaning the transmission effectively disappears once the stream stops. We first propose the notion of online obfuscation, capturing the goal of disappearing programs in the bounded storage model. We give a negative result for VBB security in this model, but propose candidate constructions for a weaker security goal, namely VGB security. We then demonstrate the utility of VGB online obfuscation, showing that it can be used to generate disappearing ciphertexts and signatures. All of our applications are NOT possible in the standard model of cryptography, regardless of computational assumptions used.