The emergence of quantum computing poses a fundamental threat to current public key cryptographic systems. This threat is necessitating a transition to quantum resistant cryptographic alternatives in all the applications. In this work, we present the implementation of a practical hybrid end-to-end encryption system that combines classical and post-quantum cryptographic primitives to achieve both security and efficiency. Our system employs CRYSTALS-Kyber, a NIST-standardized lattice-based key encapsulation mechanism, for quantum-safe key exchange, coupled with AES-256-GCM for efficient authenticated symmetric encryption and SHA-256 for deterministic key derivation. The architecture follows a zero-trust model where a relay server facilitates communication without accessing plaintext messages or cryptographic keys. All encryption and decryption operations occur exclusively at client endpoints. The system demonstrates that NIST standardized post-quantum cryptography can be effectively integrated into practical messaging systems with acceptable performance characteristics, offering protection against both classical and quantum adversaries. As our focus is on implementation rather than on novelty, we also provide an open-source implementation to facilitate reproducibility and further research in post quantum secure communication systems.

翻译：量子计算的出现对当前公钥密码系统构成了根本性威胁。这一威胁正迫使所有应用领域向抗量子密码替代方案过渡。本文提出了一种实用混合端到端加密系统的实现方案，该系统结合经典密码学与后量子密码学原语，兼顾安全性与效率。我们的系统采用NIST标准化的基于格的密钥封装机制CRYSTALS-Kyber实现量子安全的密钥交换，配合AES-256-GCM实现高效认证对称加密，并采用SHA-256进行确定性密钥派生。该架构遵循零信任模型，中继服务器仅协助通信传输而无法访问明文消息或密码密钥。所有加密与解密操作均仅发生在客户端端点。本系统证明，NIST标准化的后量子密码学能够以可接受的性能特征有效集成到实用消息系统中，为抵御经典与量子攻击提供双重保护。由于本研究侧重于工程实现而非理论创新，我们还提供了开源实现方案，以促进后量子安全通信系统的可复现性与进一步研究。