JASC: Journal of Applied Science and Computations ISSN NO: 1076-5131 BLOCKCHAIN TECHNOLOGY B.Mona, Shaik Yasmeen, Nada Faiz, Ms.PR .Anisha, Dr.BV Ramana Murthy, Mr.C.Kishor Kumar Reddy Stanley college of Engineering and Technology for Women Chapel road, bids, Hyderabad -500001 [email protected]@gmail.com,[email protected] [email protected] ,[email protected] Abstract Blochchain serves as an immutable edger which allows transactions take place in d - decentralize manner.Blockcahin based-applications are rapidly increasing, covering numerous fields. However there are challenges of blockchain technology .We provide an overview on the history of blockchain and its architechture.Technical challenges and recent advances are listed.Possible future of blockchain in is research is also discussed. We also lay various applications of blockchain. 1. Introduction Nowadays crytocurrency has become a buzzword in both industry and academia .As one of the most successful cryotocurrency ,Bitcoin has enjoyed a huge success with its capital market searching 10 billion dollars in 2016 with a specially designed data storage structure ,transactions in Bitcoin network could happen without any third party and the core technology to build bitcoin is blockchain ,which was first propose in 2008 and implemented in 2004.A blockchain is a decentralized ,disturbed database that is used to maintain a continuously growing list of records, called blocks. Each block contains a timestamp and a link to previous block.Blockchin is named that way because it is basically and endless chain of blocks.The order o this chain defines the order in which the transaction in the blocks took place. The blockchain is created with a very specific problem to solve the double spacing problem. 2. Blockchain A Specially Designed Data Storage Structure, Transactions in Bitcoin Network could happen without any third party and the Core Technology to Build Bitcoin is Blockchain.It is a decentralized, distributed database that is used to maintain a continuously growing list of records called blocks. It could be regarded as a public ledger and all committed transactions are stored in a list of blocks. This chain grows as new blocks are appended to it continuously. Each block contains a timestamp and a link to a previous block. As it is endless chain of blocks, it is called as blockchain.The order of this chain defines the order in which transaction in the blocks took place. 3. History of Blockchain Technology Blockchain seemingly came up out together nowhere together with Bitcoin in 2013.Importance of blockchain has been increasing day by day .Dubain is powered by government in the world by 2020.Blockchain and Bitcoin are created by “SATOSHI NAKHAMOTO”.He was born On 5th April 1975 as with most inventions he used and combined many already present techniques.Example Encryption Methods where already present .Blockchain solved a very specific problem in mind to solve :the double spending problem.Blockchain solves many problems because the database is very disturbed, very transparent Volume VI, Issue I, January/2019 Page No:526 JASC: Journal of Applied Science and Computations ISSN NO: 1076-5131 4. Literature Survey I. Eyal and E. G. Sirer[10] describes the phase as the literature search. In this phase we explain the methodological framework for conducting the literature search. According to us the search can be conducted in different ways. We suggest starting the search for relevant literature in leading journals. However, the literature search in this paper was divided into four phases. First, we establish a common ground by searching generally for the concepts across various platforms to identify a knowledgebase as the foundation for the literature review. As established above, the primary focus has been on the keyword Blockchain, due to the fact that extensive literature exists on both ecosystems and platforms. Second, when the common ground has been established, we identify the primary drivers within the IS research field We take foundation in the senior scholars basket of journals, in which we identify the basket of eight, consisting of the essential journals within IS research. However, there exist various ways of identifying literature with high quality. Additionally, we also identify other relevant journals that are included. In our database search. In step three, we conduct a forward- and backwards each to ensure that we have exhausted the concepts within the area of interest. The literature found in step three is mapped into customized version of M. Sharples and J. Domingue[8] backward/forward matrix. After we conclude that we have reached an exhaustive point of our re-search, we add the literature found in the forward/backward search to our original concept matrix to ensure a full overview of the topic. How-ever, we note that due to the exclusion of technical papers, we cannot claim to be exhaustive, but note that we reach a point of theoretical saturation with the selected articles. Theoretical saturation is reached.When no new categories and properties emerge from the data .During our general search, we start out by searching for literature on Google Scholar to create a quick overview of the research topic. During this phase, we use a concept matrix approach where the concepts are identified and mapped in the matrix. This allows us to get a full overview of the research landscape within our topic of interest. 5. Analysis 5.1 Blockchain Architechtutre Volume VI, Issue I, January/2019 Page No:527 JASC: Journal of Applied Science and Computations ISSN NO: 1076-5131 As ,we know that the blocks, holds a complete list of transaction records like conventional public Ledger. FIGURE 1 illustrates an example of blockchain which has continuous sequence Of block. The first block of a blockchain is called genes is block which has no parent block 5.2 Internals of Blockchain A. Block: A Block consists of the block header and the block body as shown in FIGURE 2. Block version: Indicates which set of block validation riles to follow. Merkle tree root hash: The hash value of all the transactions in the block. Timestamp: Current time as seconds in universal time since January 1st 1970. n Bits: Target threshold of a valid blockhash. Parent Blockhash: A 256 bit hash value that points to the previous block B. Digital Signature: The typical digital signature is involved with two phases: signing phase and verification phase. This digital signature algorithm used in blockchains is the elliptic digital signature algorithm (EDSA). C. Key characteristics of Blockchain: Decentralization: Here, third party is no longer needed in blockchain.It is used to maintain data consistency in distributed network. Persistency: Here, blocks that contain invalid transactions could be discovered immediately. Volume VI, Issue I, January/2019 Page No:528 JASC: Journal of Applied Science and Computations ISSN NO: 1076-5131 Anonymility: Each user can interact with the blockchain with a generated address, which does not reveal the real identity of the user D.Taxonomy of Blockchain Systems: Current block chain systems are categorised roughly into three types: public block chain, private blockchain and consortium blockchain .A private blockchain is regarded as an untralized network since it is fully controlled by one organisation. In public blockchain all records are visible to the public and everyone could take part in the consensus process. In a consortium blockchain, only a group of pre-selected nodes would participate in the consensus process. 5.3 Changes and recent Advances Even though blockchain has great potential, it faces many challenges which limit the wide usage of blockchain.Some major challenges and recent advantages are ● Scalability: Because of the amount of transactions increasing day by day blockchain becomes bulky. The job of the node is to store all transactions to validate them on the block chain because they have to check if the source of the current transaction is unspent or not as the original restriction of the block size and the interval is used to generate a new block, the Bitcoin blockchain can only process nearly 7 transactions per second .Which cannot fulfil the requirement and needs of processing millions of transactions in real-time fashion. In order to address the scalability problem of blockchain, it is classified onto two types, here a database named account tree is used to hold the balance of all non –empty addresses .Light weight client could also help fix this problem. Where some, a novel scheme allowed light weight clients to outsource expensive computations. ● Redesigning Blockchain:Bitcoin next generated is proposed and it main idea is to decouple conventional block into two part .Key block for leader election and microblock to store trabsactions.Bitcoin-NG is the heaviest chain strategy in which microblock carries no weight. In the above way, blockchain is redesigned and the trade-off between block size and network security has been addressed. ● Privacy leakage: Blockchain preserve privacy through the public and private keys. Many methods have been proposed to develop anonymity of blockchain,which is divided into two types ● Mixing: Here, in blockchain users addresses are psuedoymous.But we can still link addresses to user identity as users make transactions with the same addresses frequently. Mixing is a service which provides anonymity by transferring funds from multiple input addresses to multiple outputs. ● Anonymous: In zero coin. Zero knowledge proof is used. Minors don’t have proper transaction with digital signature but to validate coins belong to a list of valid coins. It reveals payments destination and amounts.So; inorder to prevent this zero cash was proposed to addresses this problem. In that, zero knowledge sufficient non-interactive arguments of knowledge are leveraged. ● Selfish Minning: Blockchain gets easily attacked by colliding selfish minor’s .EYAL and SIRER proved that the network is vulnerable even if only a small portion of the Volume VI, Issue I, January/2019 Page No:529 JASC: Journal of Applied Science and Computations ISSN NO: 1076-5131 Hashing power is to cheat.