Secret Message Transmission by HARQ with Multiple Encoding
This work addresses secure communication between agents like Alice and Bob in wireless networks, offering a novel approach that is not a trivial extension of existing schemes.
The paper tackles secure message transmission over block fading channels by proposing a new HARQ-based scheme using multiple codewords with independent randomness, ensuring decodability and secrecy for characterized channel classes, and derives the average achievable secrecy throughput to account for outages.
Secure transmission between two agents, Alice and Bob, over block fading channels can be achieved similarly to conventional hybrid automatic repeat request (HARQ) by letting Alice transmit multiple blocks, each containing an encoded version of the secret message, until Bob informs Alice about successful decoding by a public error-free return channel. In existing literature each block is a differently punctured version of a single codeword generated with a Wyner code that uses a common randomness for all blocks. In this paper instead we propose a more general approach where multiple codewords are generated from independent randomnesses. The class of channels for which decodability and secrecy is ensured is characterized, with derivations for the existence of secret codes. We show in particular that the classes are not a trivial subset (or superset) of those of existing schemes, thus highlighting the novelty of the proposed solution. The result is further confirmed by deriving the average achievable secrecy throughput, thus taking into account both decoding and secrecy outage.