On Real-Time and Causal Secure Source Coding

TL;DR

This paper explores secure source coding under real-time and causal constraints, demonstrating optimal key rates for secure transmission and effective encryption strategies when eavesdroppers have degraded side information.

Contribution

It introduces new methods for secure source coding in real-time and causal settings, including optimal key rate bounds and encryption strategies based on side information quality.

Findings

Key rate can match average Huffman codeword length for real-time secure transmission.

Causal rate distortion coding combined with encryption is optimal when eavesdropper has degraded side information.

Secure coding strategies depend on the nature of side information and timing constraints.

Abstract

We investigate two source coding problems with secrecy constraints. In the first problem we consider real--time fully secure transmission of a memoryless source. We show that although classical variable--rate coding is not an option since the lengths of the codewords leak information on the source, the key rate can be as low as the average Huffman codeword length of the source. In the second problem we consider causal source coding with a fidelity criterion and side information at the decoder and the eavesdropper. We show that when the eavesdropper has degraded side information, it is optimal to first use a causal rate distortion code and then encrypt its output with a key.