“…where x, x, and b maintain the signification reported above, while f (x) and ∆(x) denote a function of the original signal features and a signal-dependent quantization step, respectively [1,42]. Therefore, by directly operating in the encrypted domain, the watermark insertion can be obtained by applying the following expression [37,46,47]: In the first implementations documented in [16,17], the adopted blockchain is classified as "public", with a fully decentralized architecture, and is based on the "proof of work" (PoW) consensus algorithm [10][11][12]. Its nodes are implemented in Ethereum [49], whereas the smart contracts are coded in Solidity [50].…”