Cryptanalysis on deniable encryption

Abstract

The notion of Deniable Encryption is a cryptographic primitive, which enables legitimate users to face coercion by dynamic adversaries without revealing true secret internals of the cryptosystem. Deniable Encryption provides a way to generate fake internals that correctly explain the cipher text. When considering existing deniable schemes, two major variations can be found; schemes based on the concept of Deniable crypto-systems introduced by R. Canetti et al. and plausible deniable schemes. The schemes based on plausible deniability are not always depending on cryptographic systems, but rather use different approaches such as steganography or hardware level hidden volumes. With the objective of cryptanalysis, this research has been focused on deniable crypto-systems. The existing deniable encryption schemes proposed provide different levels and types of deniability, which makes it difficult to find a common model for the cryptanalysis. Therefore, This research has narrowed down the cryptanalysis to full-sender-deniable encryption, which is the strongest notion in sender deniability. In order to evaluate the real world implementation of full-sender-deniable encryption, this research has implemented a crypto-system using sparse-set. This research has also introduced a new type of sparse-set generation, which provides better performance compared to the two sparse-set generation methods proposed by Canetti et al. Based on the common model of full-sender-deniable encryption, our cryptanalysis has been focused on three main areas; deniability limitation already given by Canetti et al., statistical cryptanalysis and cryptanalysis based on faking algorithm. Since the encryption function of full-sender-deniable encryption is a public parameter, the adversary can coerce the sender to generate randomness by further faking and have additional data to detect the original faking. This is a new scenario that has been considered in this research, where it can be applicable in situation like rubber hose cryptanalysis.