# A Survey on Blockchain-Based Search Engines
###### Abstract  
With the increasing growth of different types of data, search engines have become an essential tool on the Internet. Every day, billions of queries are run through few search engines with several privacy violations and monopoly problems. The blockchain, as a trending technology applied in various fields, including banking, IoT, education, etc., can be a beneficial alternative. Blockchain-based search engines, unlike monopolyic ones, do not have centralized controls. With a blockchain-based search system, no company can lay claims to user's data or access search history and other related information. All these data will be encrypted and stored on a blockchain. Valuing users' searches and paying them in return is another advantage of a blockchain-based search engine. Additionally, in smart environments, as a trending research field, blockchain-based search engines can provide context-aware and privacy-preserved search results. According to our research, few efforts have been made to develop blockchain use, which include studies generally in the early stages and few white papers. To the best of our knowledge, no research article has been published in this regard thus far. In this paper, a survey on blockchain-based search engines is provided. Additionally, we state that the blockchain is an essential paradigm for the search ecosystem by describing the advantages. search engine; monopoly; decentralization; blockchain; security; privacy +
Footnote †: journal: Medical  
search system, no company can lay claims to users' data or access search history and other related information. All these data will be encrypted and stored on a blockchain. Therefore, instead of a monopolist company controlling data, they will be in total control of their owners. Blockchain-based search engines can further provide users with a private key to protect their data. Valuing users' searches and paying them in return for use is another advantage of a blockchain-based search system. Today, the blockchain has grown to be a trending technology, finding applications in various fields, including banking [1], IoT [2], healthcare [3], media [4], education [5], etc. On the other hand, blockchain technology improves several aspects in various applications such as file sharing [6], video streaming [7], cloud [8], fog and edge computing [9], smart grid [10], message passing [11], and database [12]. Therefore, considering the potential of the blockchain, using it in developing search systems will result in a new generation of search engines with new capabilities which solve the problems of the conventional ones. Conventional search engines and their monopolized market, user's concerns, and the popularity of blockchain to solve problems indicate the need to establish a blockchain-based search system. The monopolized market includes ranking and advertising, and the users' concerns, include privacy and security. In this regard, few efforts have been made to provide blockchain-based search engines, which are Nebulas [13], Bit Clave [14], Presearch [15], and DeSearch [16]. These systems are generally in early stages, and their structures have been reported only as a few white papers. In this paper, first, the blockchain applications are reviewed to show the popularity of this technology and its potential to provide new solutions. Then, a survey on blockchain applications in developing search systems is provided. Describing the advantages of the blockchain-based search system, we elucidate that blockchain technology is an essential paradigm for search ecosystems. To the best of our knowledge, no research article has been published in this regard thus far. To show the motivations, the innovations of this research are expressed.