# Empirical Evaluation of Privacy Efficiency in Blockchain Networks: Review and Open Challenges
###### Abstract
Besides that, it is also envisioned that in the era of quantum computing, it will be easier to decrypt the codes and break the hashes [16] of blockchain networks. Blockchain privacy can be achieved by strengthening the vulnerabilities of the blockchain architectural design. The fundamental building blocks of a blockchain system include hashing [17], cryptography [18], consensus [19] and smart contracts [20]. Each of these building blocks tend to either strengthen or weaken the privacy of the system. In this paper, we present a detailed description of these building blocks and their role in achieving privacy. This will help the blockchain enthusiasts to comprehend the issue in hand at deeper levels. Realizing the potential hazard of blockchain's privacy issue, numerous blockchain researchers and enthusiasts are working towards the issue. Some are digging deeper into the causes and factors resulting in privacy breach [14; 16; 21; 22] while others are trying to provide a viable and universally accepted solution to the problem [23; 24; 25]. Despite the extensive research the issue persists. We argue that the reason behind the problem persistence is a result of the following:  
1. Lack of literary resources for understandability of various blockchain components and features with respect to their effect on privacy. 2. Unavailability of a proper evaluation criteria that judges the efficiency privacy of a solution. 3. Absence of a concrete quantifiable value to empirically assess the degree of privacy offered by a solution. Hence a comprehensive awareness of the role of each blockchain component towards privacy protection is much needed for ability to create better privacy preserving solutions. Moreover, proper analysis mechanism of these solutions is required to accurately evaluate the potential of each solution. Therefore, in this study, we bridge the said gap in literature by presenting a comprehensive review and solutions to the aforementioned existing issues. To accomplish the task, we first discuss the issue of privacy in detail. Further, we present a survey and classification of the privacy preserving solutions based on blockchain component/feature exploited for privacy provision. To the best of our knowledge, no manuscript has presented such classification so far. Next, we discuss the criteria and parameters adopted by several research works to evaluate these classified privacy solutions in blockchains. Most of the evaluations are performance based which is not sufficient with respect to privacy. This is because a solution might be utilizing lesser computational resources and consequently resulting in weaker privacy protection. Therefore, it is hard to judge the strength of a solution merely based on computing resources used. Hence, we introduce more parameters that affect the degree of privacy protection. These parameters include various features that make privacy protection stronger, and several features that can breach the privacy. Subsequently, we formulate a validation framework that considers these introduced parameters to empirically analyze the potential of the privacy technique under study. Calculation carried out based on the values of these parameters results in a singular value ranging between 0 and 1 (with 0 being no privacy preserved and 1 being maximum privacy preservation). We term this value as privacy precision in the formulated framework. To essentially evaluate any solution, considering both, pros and cons is significant. Our aspirations with this research are that it will be used as a benchmark when assessing blockchain based privacy solutions.