# Blockchain and Cloud to Overcome the Problems of Buyer and Seller Watermarking Protocols
## 3 Goals of the Protocol and How to Achieve Them  
The considerations reported above and the experiences conducted in the last few years suggest that watermarking protocols should meet the following requirements. First of all, protocols should enable buyers to easily participate in the purchase transactions of contents [5]. In fact, buyers are to be considered common web users not provided with specific security competence. Therefore, they cannot usually generate watermarks, fingerprints, or security tokens, and can perform the only actions that can be executed by common web browsers. Protocols should enable content providers with different abilities and resources to easily take part in the protection scheme of distributed contents. In fact, content providers may be represented by very different web entities in the current web context. More precisely, a content provider can be a specialized entity provided with both competence and resources to apply an on-the-fly protection to the distributed contents. However, it can be also a common web user who only wants to protect his/her contents published on social platforms. Such a user, differently from specialized content providers, lacks both security competence and resources to protect his/her contents. As a consequence, protocols should enable content providers to eventually exploit \"security delegates\" to embed personalized watermarks in the distributed or published contents [11]. Protocols should not involve TTPs in the protection scheme, since TTPs could give rise to collusion problems with the other parties involved in the protocols. However, such a goal should be achieved without complicating the interaction schemes or forcing buyers to carry out complex security actions to complete the purchase transactions, thus making protocols impractical for the current Internet. A starting point to achieve the goals reported above can be represented by watermarking protocols able to combine a \"buyer friendly\" approach with the capacity to employ means and technologies to respectively: (1) support content providers in embedding personalized watermarks in the distributed contents; (2) simplify the protection scheme by restricting the role played by TTPs without forcing buyers to carry out complex security actions. In this regard, a possible solution can be found in enabling content providers to exploit cloud computing platforms to outsource the burdensome activity represented by the on-the-fly insertion of personalized watermarks. In fact, content providers can opt to pay cloud platforms as a function of their needs without having to defray the costs of adequate, private computing and storage resources. In addition, even ordinary web users can easily become content providers, since they can take advantage of cloud computing platforms to protect their contents without having resources and specific expertise. Moreover, such a solution can adopt the blockchain technology to limit the key role played by TTPs, thus supporting a decentralized approach for the protocol. In fact, a blockchain is a distributed ledger that can save data identifying the transactions among the entities involved in the protocol in cryptographic, hashed and signed blocks which are then timestamped and linked in a chain by means of a distributed consensus mechanism. The process makes the blocks resilient to modifications. Thus, they can be considered trusted for the transactions managed by the protocol, and can be also verified in a decentralized way by employing a consensus algorithm run by multiple web nodes to establish whether a transaction is valid or not. In addition, a blockchain also supports \"smart contracts\", which can be used to replace TTPs in performing the centralized actions needed to enable the protocol. More precisely, the smart contracts define preset rules, in the form of code, which are automatically executed when the terms of an agreement are reached between distinct web entities.