Chaos-Based Hardware Trojan Covert Channel for Synchronized Chaotic Cryptosystems

Synchronized chaotic cryptosystems (SCCs) are increasingly adopted to secure communications in resourceconstrained edge devices. In this work, we reveal a critical vulnerability by introducing the first chaos-based hardware Trojan covert channel (HT-CC). The HT exploits the synchronization process of chaotic oscillators to generate a chaos-based spreading code that embeds the secret key below the noise floor of the legitimate transmission. We demonstrate the HT-CC in a secure image transmission scenario, showing that the covert channel operates in real time, incurs negligible overhead, does not degrade legitimate communication, and allows a rogue receiver to reliably recover the key. Existing HT-CC defenses fail against the proposed attack due to its chaos-based, time-varying spreading sequence.