# Confidential Smart Contracts and Blockchain to Implement a Watermarking Protocol
## 9 Related Work  
The evolution of watermarking protocols has led to \"buyer-seller\" solutions that leverage public key infrastructures, asymmetric fingerprinting, and \"privacy homomorphic\" encryption for watermark insertion. Such solutions effectively address classic issues documented in the literature, such as the \"unbinding problem\" and the \"customer's right problem\" [4]. In these solutions, the seller inserts a watermark encrypted with the buyer's public key directly into the content, which is also encrypted using the same public key. Consequently, the buyer can access the content with personalized protection by decrypting it with his/her private key. However, many existing protocols rely on TTPs as \"watermark certification authorities\" or agents essential for ensuring the correctness and security of the protection transactions executed. Such a situation has prompted researchers to seek new solutions that eliminate TTPs from the developed protocols, all while avoiding complex actions for buyers during the content purchase transactions from sellers. According to such an approach, watermarking protocols that utilize blockchain technology and smart contracts to bypass TTPs represent one of the most advanced and promising solutions in the literature. Y-DWMS [44] adopts the aforementioned approach and leverages blockchain technology and smart contracts to deliver traditional services such as watermark verification for disclosed copies, authentication of informers' reports, and traceability of infringements. In addition to these classic services, Y-DWMS introduces specific functionalities to reward informers, penalize infringers, and mitigate losses incurred by copyright holders. Despite these innovative services, Y-DWMS is affected by specific problems, particularly concerning privacy, and its security level has not been validated. SBBC (Secret Block-Based Blockchain) [45] exploits blockchain technology and smart contracts to create a digital content trading system. It comprises both off-chain and on-chain components. The off-chain components implement an initial authentication phase, enabling users to engage in digital content transactions. Digital fingerprints are embedded in the traded content to monitor any illegal leaks. Additionally, the content is encrypted, ensuring that only authorized users can access it, thereby safeguarding the income of legitimate content creators. The on-chain components provide licensing services. Specifically, authorized users run smart contracts to initiate the licensing process, generating secret blocks representing their transactions and recording them on the blockchain. Following verification and agreement from all blockchain nodes, public blocks are added to the blockchain to finalize purchase licenses. SBBC also addresses performance issues that typically affect blockchain-based systems by proposing an efficient consensus algorithm. However, it lacks a thorough security analysis and has yet to demonstrate resilience against the traditional challenges faced by watermarking protocols [4; 46]. FingerChain [47] is a multi-owner media-sharing system focused on digital copyright protection, built on a consortium blockchain network. It employs smart contracts and asymmetric fingerprinting to allow authorized owners to share their media for a fee. This system benefits from the absence of a TTP to implement the protection protocol and a high efficiency level on the owner's side due to the \"client-side embedding\" technique for watermark insertion [48]. However, the watermarking scheme used requires clients to eliminate noise sequences from the purchased content and generate secret fingerprints. These security measures can be complex for ordinary web users [4]. While the systems discussed above present innovative approaches to watermarking protocols, they exhibit certain limitations that the protocol outlined in this article aims to address.