Secure coherent optical communication via QKD-based parallel SHA-256 stream cipher with dual-randomized affine construction.

Although quantum key distribution (QKD) provides information-theoretically secure keys, a significant gap exists between its relatively low key generation rate and the high-speed demands of classical optical communication. To address this challenge, this paper proposes a stream cipher encryption scheme based on QKD and Secure Hash Algorithm 256 (SHA-256). Core to the scheme is an innovative group-wise dual-randomized affine construction. Integrated with configurable grouping and parallel processing, this mechanism applies a linear mapping defined by dynamic initial vectors (IV) and variable full-domain strides to each data group. This approach achieves deep orthogonalization of the hash input space while preserving architectural parallelism. Simulation results demonstrate that the scheme achieves high-strength security protection while ensuring real-time performance of the communication link. Specifically, statistical analysis confirms that the ciphertext exhibits high entropy and negligible autocorrelation, alongside high key sensitivity. The scheme expands the computational search space beyond the conventional 2 bound, effectively countering pre-computation attacks.