Anamorphic Encryption with CCA Security: A Standard Model Construction

2026-04-08

AI Summary

This work addresses the lack of generic, CCA-secure steganographic encryption schemes in the standard model, a gap that undermines the security of covert channels under key exposure. The authors formally define an adaptive key encapsulation mechanism (AKEM) and propose a generic construction based on recoverable randomness and injective KEMs, seamlessly integrating steganography into the KEM-DEM paradigm. Their scheme is the first to achieve sIND-CCA security for general-purpose steganographic encryption in the standard model, supporting both public-key and symmetric-key variants. Notably, it remains secure even against a “dictator” adversary who possesses the decapsulation key, thereby significantly enhancing the practicality and robustness of covert communication within real-world cryptographic infrastructures.

Abstract

Anamorphic encryption serves as a vital tool for covert communication, maintaining secrecy even during post-compromise scenarios. Particularly in the receiver-anamorphic setting, a user can shield hidden messages even when coerced into surrendering their secret keys. However, a major bottleneck in existing research is the reliance on CPA-security, leaving the construction of a generic, CCA-secure anamorphic scheme in the standard model as a persistent open challenge. To bridge this gap, we formalize the Anamorphic Key Encapsulation Mechanism (AKEM), encompassing both Public-Key (PKAKEM) and Symmetric-Key (SKAKEM) variants. We propose generic constructions for these primitives, which can be instantiated using any KEM that facilitates randomness recovery. Notably, our framework achieves strong IND-CCA (sIND-CCA) security for the covert channel. We provide a rigorous formal proof in the standard model, demonstrating resilience against a "dictator" who controls the decapsulation key. The security of our approach is anchored in the injective property of the base KEM, which ensures a unique mapping between ciphertexts and randomness. By integrating anamorphism into the KEM-DEM paradigm, our work significantly enhances the practical utility of covert channels within modern cryptographic infrastructures.

Problem

• anamorphic encryption
• CCA security
• standard model
• covert communication
• key encapsulation mechanism

Innovation

• Anamorphic Encryption
• CCA Security
• Key Encapsulation Mechanism (KEM)
• Standard Model
• Covert Communication