Feign East, Strike West! Constructing Covert Channel on TLS 1.3

Summary

Researchers propose CCCC, a covert communication scheme that stays fully compliant with standard TLS 1.3 and so evades auditors who hold the session key and inspect traffic. It uses collision ciphertexts that let one AES ciphertext-tag pair decrypt successfully, and embeds a hidden vector in a standard EdDSA signature during the handshake. The authors formally define the collision ciphertext security properties, give an AES-GCM and EdDSA instantiation, and report a full prototype with only moderate overhead versus standard TLS 1.3.