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.

翻译：变形加密是隐蔽通信的重要工具，即使在事后妥协场景下也能保持消息的机密性。特别是在接收方变形设置中，即使用户被迫交出密钥，仍能隐藏秘密信息。然而，现有研究的主要瓶颈在于依赖CPA安全性，在标准模型中构造通用CCA安全的变形方案始终是一个未解决的开放挑战。为弥补这一空白，我们形式化定义了变形密钥封装机制（AKEM），涵盖公钥变形KEM（PKAKEM）和对称密钥变形KEM（SKAKEM）两种变体。我们提出了这些原语的通用构造方法，可通过任何支持随机数恢复的KEM进行实例化。值得注意的是，我们的框架为隐蔽信道实现了强IND-CCA（sIND-CCA）安全性。我们在标准模型中给出了严格的形式化证明，展示了该方案在对抗控制解封装密钥的"独裁者"时的鲁棒性。方案的安全根基建立在基础KEM的单射性质上，该性质确保了密文与随机数之间的唯一映射。通过将变形机制融入KEM-DEM范式，我们的工作显著增强了现代密码基础设施中隐蔽信道的实际可用性。