Anamorphic Encryption with CCA Security: A Standard Model Construction
2026-04-09 • Cryptography and Security
Cryptography and Security
AI summaryⓘ
The authors explore a way to keep secret messages safe even if someone forces you to give up your secret keys. They introduce a new kind of encryption system called Anamorphic Key Encapsulation Mechanism (AKEM), which works with both public and private keys. Their design improves security by making it hard for attackers to break the code, even with strong access to decryption tools. The authors prove their method is secure using solid math foundations, and it can be used in existing encryption systems to better protect hidden messages.
Anamorphic encryptionKey Encapsulation Mechanism (KEM)Public-Key EncryptionSymmetric-Key EncryptionCCA-securityRandomness recoveryIND-CCA securityCiphertextInjective functionKEM-DEM paradigm
Authors
Shujun Wang, Jianting Ning, Qinyi Li, Leo Yu Zhang
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.