Provably Secure Universal Steganographic Systems

TL;DR

This paper introduces a universal, distribution-free steganographic system that guarantees indistinguishability of covertexts, achieves near-Shannon entropy transmission rates, and operates effectively with increasing alphabet size and block length.

Contribution

It presents a simple, provably secure steganographic method applicable to any i.i.d. source with unknown distribution, achieving optimal information transmission rates.

Findings

Transmission rate approaches Shannon entropy as block size increases.

System maintains statistical indistinguishability of covertexts.

Performance improves with larger alphabet and block sizes.

Abstract

We propose a simple universal (that is, distribution--free) steganographic system in which covertexts with and without hidden texts are statistically indistinguishable. The stegosystem can be applied to any source generating i.i.d. covertexts with unknown distribution, and the hidden text is transmitted exactly, with zero probability of error. Moreover, the proposed steganographic system has two important properties. First, the rate of transmission of hidden information approaches the Shannon entropy of the covertext source as the size of blocks used for hidden text encoding tends to infinity. Second, if the size of the alphabet of the covertext source and its minentropy tend to infinity then the number of bits of hidden text per letter of covertext tends to $\log(n!)/n$ where $n$ is the (fixed) size of blocks used for hidden text encoding. The proposed stegosystem uses randomization.