CELS (Crystalline Encryption Layered Security): A Security Extension of Messaging Applications using Post-Quantum Cryptography

Privacy and security are vital for digital communications to protect sensitive information and enable free expression. In this paper we present CELS (Crystalline Encryption Layered Security), a security extension based on a hybrid cryptographic approach that layers post-quantum cryptography (PQC) on top of a messaging application, to provide end-to-end data security. We introduce two CELS protocols, one for shared key establishment and one for key retrieval. Our prototype implementation, Discord CELS is a Firefox sidebar extension that adds end-to-end message encryption to a Discord server channel with native webhooks. It uses CRYSTALS-Kyber-1024 compiled with Emscripten for key encapsulation along with AES-256 GCM and PBKDF2 from the Web Crypto API for data encryption. CELS is resistant to attacks by both classical and quantum computers. CELS enables users to protect their messages with end-to-end encryption from being viewed by the messaging application company when using their existing service such as Discord. It is adaptable to other messaging applications and has cross-device flexibility, subject to platform constraints. Extensive performance evaluations demonstrate that the prototype system achieves good efficiency with low overhead, making it a practical security enhancement.