Figure 1.4 The figure states the internal working paradigm of a blockchain.

      The final element within the block is the hash which is from a previous block (refer to Figure 1.4). This creates a chain of blocks and is the main element behind blockchain architecture’s security [4]. As an example, assume a bock range from 1 till 46; block 45 points to block 46. The very first block in a chain is a bit special—all confirmed and validated blocks are derived from the genesis/creator block.

      Any corrupt attempt provokes/results the blocks to change [4, 5]. All the assumed block’s hashes get changed resulting to the mismatch of hashes which then carry incorrect or invalid information and render the whole blockchain system invalid.

      On the other hand, in theory, it could be possible enough to adjust or alter all the blocks with the help of strong computer processors (processors here means highly configured computers). However, there is a solution that eliminates this possibility called proof-of-work [1]. This allows a user to slow down the process of creation of new blocks. In the architecture of Bitcoin blockchain, it majorly takes around 10 min to determine or collects the necessary information of proof-of-work and adds a new block to the chain, but as it was discussed the block can only be added by the person which have the best computational system, here logical ability works rare rather than the system power, hence this work is done by miners—special nodes within the Bitcoin blockchain structure. The miners who win in the race get to keep the transaction fees from the block that they verified as a reward [1, 4].

      Each new user (node) joining the peer-to-peer network (a network which have internet connection to share files and folders) of blockchain receives a full copy of the system. Once a new block is created, the detail of it is sent to each node within the blockchain system [4]. Then, each node verifies the information of the block and checks whether the information/data stated there in the block is correct. If everything is alright, the block is added to the local blockchain in each node.

      All the nodes inside blockchain architecture create a consensus protocol. A consensus system is a set of network rules, and if everyone abides by them, they become self-enforced inside the blockchain.

To manage and protect the term privacy under blockchain technology, one must satisfy the subsequent requirements:

      The private or open blockchain must have an entrance control strategy or approval plan to fulfil the security prerequisites of blockchain, which fulfils the total straightforwardness of the blockchain information. Be that as it may, if the case is of an open setting, everybody can have an access to the blockchain with no limitations, the protection issues must be handled on the following factors:

      As it is referenced over, a transaction or a block of a blockchain contains the identity of the previous transaction, the addresses of its members or participants, values (trade), timestamp and unique mark of its sender. Due to its natural behavior or characteristic, it is possible to trace back and follow the flow of transactions to extract and collect the users’ physical identities or other common and additional private information through the tools techniques and also of data mining. In this section, it is referred towards the Bitcoin system as a typical instance to analyze the privacy threats for the blockchain network.

1.3 De-Anonymization

Users majorly/always create an alias when they hook up with the Bitcoin system. However, thanks to the general public and openness of blockchain, it’s possible to run a static analysis of the blockchain which allow us to track and unhide the masked users, that’s what de-anonymization is. Here, we have list out many attacks which will work under to de-anonymize the users’ real identities.

      1.3.1 Analysis of Network

      The blockchain majorly performs its work on the P2P network, which suggests that a node will share public its IP address when broadcasting the transactions. Researchers and scientist have identified three abnormal relay patterns for analyzing the network which could be mapped to Bitcoin addresses to IP addresses (i.e., multi-relayer & non-rerelayed transaction, single-relayer transactions and multi-relayer & rerelayed transactions).

      1.3.2 Transaction Fingerprinting

      Another major issue or threat that can cause problem to the data of transaction and for which the anonymity becomes problem is a transaction’s user-related features. Androulaki et al. have explained six characteristics that may portray a few highlights of transaction conduct, i.e., Random time-interval (RTI), hour of day (HOD), time of hour (TOH), time of day (TOD), coin flow (CF) and input and output balance (IOB). Abundance consideration on these characteristics may expand the odds to de-anonymize an individual client [1].

      1.3.3 DoS Attacks

      A denial-of-service assault might be a cyber assault and the most known and basic issue, where the noxious assailant attempts to look for or hack a machine or system asset being inaccessible to its customers by disturbing or ending web/network services of the host associated with the web or neighborhood server. The most well-known way or method to deal and handle with, be covered up by IP addresses or to hide the IP in P2P network is utilizing anonymity network systems (e.g., TOR).

      1.3.4 Sybil Attacks

      A Sybil attack is another digital attack where the pernicious attacker and programmers destabilize the stature or notoriety system of a P2P network by making an outsized number of nom de plume or phony characters, utilizing them to understand a disadvantageous impact. Concerning the de-anonymization inside the blockchain, Bissias et al. broke down and judge that Sybil attacks could stop and break the decentralized anonymity protocol and can expand the likelihood to search out the clients’ genuine identities.

1.4 Transaction Pattern Exposure

      Except some personal information, majorly all transactional information goes to the public network which can be used to get the statistical distribution, which may help to get some guidelines and regulations for the blockchain applications.

      1.4.1 Transaction Graph Analysis

      Under this the major focus is on discovering and analyzing some overall transaction features (e.g., daily turnover, exchange rate or transaction pattern) over time.

      1.4.2 AS-Level Deployment Analysis

      This technique aims to get the bitcoin network by recursively connecting to clients, requesting and collecting their lists of other connected or peer IP addresses. In this flow,