Cryptographic Schemes for Secret Long-Distance Underwater Communications

— Due to small packet sizes, classical data protection schemes are unsuitable for underwater communications. This article addresses this problem and contains two main results. As a first result, a new symmetric-key encryption protocol adaptable to small message sizes is introduced. The encryption scheme leverages the flexible Quantum Permutation Pad (QPP) symmetric key block cipher. It combines QPP with the block cipher counter mode and a random number generator seeded with a shared secret to adapt QPP to the short underwater protocol data units. Encryption and decryption algorithms are defined, building on QPP in counter mode. The algorithms are analyzed. The analysis demonstrates that the scheme does not achieve perfect indistinguishability. However, the analysis also demonstrates that the message collision probability can be very low. The scheme is generic and adaptable. As a second result, the new symmetric encryption scheme is adapted to the long-range underwater communication protocol (Pronounced you Whisper) UWSPR. The design is analyzed consistently with the theory. Related relevant issues are also addressed, such as key sizes and key generation with the challenges specific to the underwater environment.