As the cryptographic community transitions toward Post-Quantum Cryptography (PQC), the structural complexity and size of public keys and verification keys have increased significantly. This paper introduces the theoretical construct of a "Parasitic Verification Key"—a cryptographically valid public key that conceals auxiliary data within its bit structure. We analyze the feasibility of embedding malicious payloads or covert channels within the redundancy or format flexibility of verification keys in code-based and lattice-based cryptosystems. We demonstrate that the large key sizes inherent in PQC schemes provide a fertile ground for data exfiltration and trust-chain subversion, proposing a new class of Key-Hiding attacks.
If an attacker wishes to embed a payload $P$ into $\textbfA$: parasite inside verification key
In peer-to-peer PQC systems, users exchange verification keys directly. If an attacker presents a parasitic key, the victim accepts it. The parasite might contain metadata identifying the attacker's shadow identity or malicious routing instructions, hidden within the key structure itself, extracted later by a colluding party. We demonstrate that the large key sizes inherent
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