Session: ASME Undergraduate Student Design Expo

Paper Number: 176176

Minimal Chua Circuit as a Keystream for Lightweight Image Encryption 

Secure communication relies on encryption keys known only to the communicating parties. Such keys must be random or, at minimum, indistinguishable from random to an adversary. Nonlinear dynamical circuits offer a compact hardware route to pseudo-randomness because their trajectories exhibit sensitive dependence on initial conditions. Among these, Chua’s circuit produces broadband chaotic signals with rich structure using a very small component count. This work investigates whether a minimalist implementation of Chua’s circuit can serve as a hardware keystream generator for a lightweight stream cipher. The goal is to balance hardware simplicity with strong statistical unpredictability and ease of integration in embedded systems.

Using a simple construction of Chua’s circuit, we extract a digital pseudo-random sequence from an analog state variable. The signal is conditioned through amplification and band limiting, sampled at an appropriate rate, and passed through a bias removal and decorrelation stage to reduce autocorrelation and enforce symbol balance. The resulting bitstream drives a conventional stream cipher in which encryption is performed by an XOR operation between the plaintext and the keystream. To visualize diffusion and confusion, we encrypt black and white test images. Decryption repeats the XOR operation using the identical keystream derived from the same initial conditions and parameters, yielding exact reconstruction under the correct key.

We develop a modeling and evaluation protocol to quantify encryption quality and guide design choices. Key parameters include resistance ratios and nonlinearity slopes in the Chua element, supply voltage, sampling rate, and the seeding of initial conditions. We evaluate histogram flattening, horizontal and vertical pixel correlation, diagonal correlation, and Shannon entropy. We also plan to quantify sensitivity to plaintext changes, and we will run tests to benchmark pseudo-randomness. Key space size is reported in terms of discretized initial conditions and parameter tolerances. Key sensitivity is characterized by single-bit perturbations in the seed that propagate to large Hamming distance changes in the keystream. Throughput and estimated energy per encrypted pixel are measured to assess viability for resource‑constrained platforms.

Practical considerations are addressed to support deployment. A lightweight synchronization protocol shares the initial conditions and parameter set as the secret key and uses a short preamble for keystream alignment. Component tolerances and thermal drift are handled by one‑time calibration of the return map and periodic alignment checks. The analog front end and digital post‑processing are intentionally simple to control cost and power. We discuss security hygiene, including prevention of keystream reuse, randomized rekeying schedules, and constant‑time implementation of digital steps to reduce side‑channel leakage.

A proof‑of‑concept prototype is being built and tested on a suite of images. The study will compare the chaotic hardware keystream against software pseudo‑random generators of similar complexity, chart safe operating regions that preserve chaos, and document failure modes such as windowing into periodic behavior. The results are expected to clarify when a minimalist Chua‑based keystream is appropriate for fast, low‑power, and low‑cost secure links. Overall, the work positions simple chaotic circuits as credible mixed‑signal entropy sources for stream ciphers in embedded sensing, edge robotics, and low‑latency control where conventional heavyweight cryptography may be impractical.

 

 

Presenting Author: Thomas Holloway University of Memphis

Presenting Author Biography: I am a Junior at the University of Memphis currently pursuing my BS in Mechanical Engineering. Currently I am working independent research, and I am exploring nonlinear circuits.

Authors:

Thomas Holloway University of Memphis
Ayush Gupta University of Memphis
Vipin Agarwal University of Memphis