# Blockchain and Smart Contracts for Digital Copyright Protection
## 2 Related Work
DRMChain proposes innovative ideas, but it cannot be considered a proof-of-concept. Its security is not proven for the whole system but only for single services. As a result, the ability to solve the classic problems of watermarking protocols is not guaranteed. BMCProtector [26] uses a public blockchain, smart contracts, and the IPFS to protect music copyright. In particular, the smart contracts automatically implement the payment of royalties to copyright owners. However, BMCProtector adopts a Key Protection Center, in the form of TTP, to manage the keys that music owners and buyers use to encrypt/decrypt the distributed audio files. Furthermore, its security is not proven. Another example of a complex copyright management system is described in [27]. It exploits different technologies to manage purchase transactions among buyers and sellers. Moreover, it does not employ WCAs. In particular, an improved ElGamal encryption algorithm is used to protect the buyers' and sellers' keys. A public blockchain is employed to record copyright and transaction data securely. The IPFS keeps watermarked contents, whereas smart contracts manage the purchase transactions and copyright information. The overall outcome is a system that can protect digital content. However, its internal structure is complex. So it is practically impossible to prove the security of the whole system, mainly with respect to the \"unbinding problem\" or \"customer's rights problem\". Y-DWMS [28] is a DRM system that exploits blockchain and smart contracts to protect digital copyrights. In particular, smart contracts are exploited because they cannot be repudiated, whereas blockchain is employed because it cannot be tampered with. This way, Y-DWMS can implement the classic services of a DRM, such as watermark verification in the disclosed copies, authentication of the informers' reports, and traceability of infringements. In addition, Y-DWMS also implements specific services to reward informers, punish infringers, and recover losses suffered by copyright holders. However, Y-DWMS has not been proven secure since it is affected by some problems, mainly concerning account management and privacy. SBBC (Secret Block-Based Blockchain) [29] is a system expressly developed to employ blockchain in the digital content trading environment. It consists of off-chain and on-chain network components. The off-chain components implement a preliminary authentication phase, after which users can trade digital content. Digital fingerprints are embedded into the traded contents to track illegal leaks. Furthermore, the traded contents are encrypted, and only the rightful users can access them, thus ensuring income for the legitimate content authors. The on-chain components implement the DRM services. The licensed users create secret blocks of their transactions and record them in the blockchain: through the verification and agreement of all blockchain participants, public blocks are added to the blockchain to finalize the transactions. SBBC represents a complete system for digital content trading based on blockchain. It specifically addresses the performance problems that affect systems based on blockchain. However, SBBC lacks a security analysis. So, it has yet to be proven secure against the classic problems of watermarking protocols [1; 30]. FingerChain [31] is a copyrighted multi-owner media-sharing system based on a consortium blockchain network and asymmetric fingerprinting. The system enables authorized owners to share their media for a fee. It uses smart contracts and the \"client-side embedding\" watermarking protocol proposed in [7] to protect shared media. Its strengths are the absence of TTP to implement the protection protocol and the high owner-side efficiency due to client-side embedding. However, as reported above, the adopted watermarking scheme requires clients to remove noise sequences from the purchased contents and to generate secret fingerprints. These are security actions that are difficult for ordinary web users [1].