(Zohar, a) On the basis of hardware mining,

(Zohar, 2017)In this paper they have discussed bit coin as
decentralized crypto currencies and its emergence as a new application domain
for computer sciences .Bit Coin is decentralized currency and it allows
everyone to be part of it.

Digital money is not new, but bit coin has few
fascinating features which make it different from both computational and economic

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In Bit Coin
money perception is set according to predefined schedule. crypto graphic rules
for locking its operation. In this paper they have basically discussed what
research topics and challenges research are there to work on in recent trends
of decentralized   currencies. It includes scalability that means
as bit coin blocks are generate slowly, once every ten minutes. As the no of
transactions grow the protocols have been introduced and are still in research.
Secondly they have discussed about incentives, that the bit coin system is very
secure but several problems are identified to overcome this, the work has to be
done and network security is also important as P2P(Peer to Peer Network) is
essential to its  security.                                             

(July, 2005)As Crypto currencies are fascinating recent concept
whose popularity exploded in the past few years .In this paper a research oriented
introduction related to crypto currencies .Some of its weaknesses have been
discussed and how people are dealing with them and Bitcoin is compared with
other coins like red coin, zero coin etc. They have discussed Bitcoin
main design principles which includes the transaction ledger (the block chain),
as a technique that can be used to prevent double-spending of electronic cash.
We will point out that the Sybil attacks should be taken into account when
designing a protocol that emulates such a ledge. In security weaknesses of Bit coin
the quality of the Bit coin design have been discussed. We will mention some
incidents when programming errors lead to forks that needed to be resolved manually
and we will explain the transaction malleability problem. On the basis of these
three properties they have distinguished bit coin from other coins a) On the
basis of hardware mining, is that one of the problems of Bit coin is that mining
in hardware is much more efficient than mining in software, and hence it is completely
infeasible now a days to be a miner without investing in specialized hardware.
We will describe the Lit coin, which is a currency that was supposed to have
the property that it is not economical to mine in hardware. b) Less wasteful
crypto currencies. Another problem with the Proofs of Work is that they require
the miners to spend significant amounts of electricity on mining. There are
essentially two approaches to create less wasteful crypto currencies. The one
is to create a crypto currency where the work is spent on some useful task. We
will give an overview of the currencies belonging to this class the Perm coin,
and the Prime coin. The second approach is to replace work by some other type
of resource. This includes the Proofs of Stake, and the Proofs of Space, which
is used in the recent Space coin proposal. They will give a short over view of
these approaches. c) More anonymity. Since the Bit coin’s transaction ledger is
public, the only anonymity in this system comes from the fact that the users
are using pseudonyms, instead if their real names. Hence concludes with an
overview of the open research problems in this area, like the need for better
understanding of the Bitcoin security model, and improvement of the block chain

(Farell, 2015)This paper seeks
to provide a brief yet complete analysis of the crypto currency industry with
particular exploration of Bitcoin, the first decentralized crypto currency. Particular
attention will be given to examining theoretical economic differences between Existing

  This paper provides an overview of the
industry. A brief history of digital currencies, which shifts into a discussion
of Bitcoin. It provides detailed analysis of coin economics, dividing the major
currencies by their network security protocol mechanisms, and discussing the
long term theoretical implications that these classes entail. Here they have
discussed network security protocol. The mechanisms are discussed in the order
that follows. Also discussion on the proof of work mechanism used in the
Bitcoin protocol and various all coins, their proof of stake  protocol scheme first introduced by Peer coin
in 2011, which relies on a less energy intensive security mechanism than Power
of Work. They have discussed a hybrid Power of work or power of stake
mechanism. They presents the results of a systematic review of twenty one crypto
currencies. They provides summary of aspects affecting industry growth,
focusing heavily on the monitoring environment in public perception and
acceptance of crypto currency as a payment system in the current trade
environment. It also concludes the analysis note on sources because the crypto
currency industry is still young and factors that impact it are changing on a
daily basis, few complete or fully updated academic sources exist on the topic.
While academic work was of course consulted for this project, the majority of
the information that informs this paper was derived from White Papers or combined
using raw data. A note on terminology: When used in its theoretical or generous
sense, “Bitcoin” will be capitalized, but when used in its unit sense, it will not
be that is “Bitcoin protocol versus 2,000 bitcoin”. The abbreviation “BTC” will
also be used to refer to Bitcoin units. All other coins will be referenced by
their capitalized names.

The crypto currency industry is rapidly
moving forward. Further, the industry has expanded dramatically in the number
of coins currently in circulation. Here a survey has been conduct for
monitoring transaction of Bitcoin, per day its rate in how many countries
people have purchased it etc.

(Nakamoto, 2008) Now a day’s online trading on the Internet is
becoming popular and financial institutions are helping as third parties for
electronic payments. Completely non-reversible transactions are not really
possible, since financial institutions cannot avoid these problems. The cost
of facilitation will definitely increase cost of transaction. A certain
percentage of fraud is accepted as unavoidable but payment doubts can be
avoided only by using physical currency, but no mechanism exists to make
payments over a transport network system not involving trusted party. The
need of an automated expense system created on cryptographic evidence instead
of trust that allows two agreeable parties to deal direct excluding trusted
third party. Transactions that are computationally unrealistic to inverse protects
vender from frauds, while routine procedure could

Be easily applied for protecting
purchasers. In this paper, a proposed solution has been presented for double spending
problem using a P2P distributed timestamp server for creating computational resilient
of the sequential order of transactions. The system will remain secure till nodes
are mutually control large power of Central Processing Unit than any group of
attacker nodes.


A P2P type of automated economic
system which allow online payments to be sent directly to one another without
using any financial organization. Here the problem of double spending has been
discussed even instead of using Digital signatures. The network itself requires
least arrangement and messages are broadcasted, by accommodating the longest proof
of work chain the nodes can leave and come back with the network.

(T. Courtois, Emirdag, & A. Nagy,
2014) At
this time bitcoin is facing a lot of   practical issues like approval of slow
transactions to be done, huge amount of transactions storing at web nodes, reducing
 level of secrecy , great changeability
accepted, few of cyber-attacks  accepted.
Fast transaction acceptance of bitcoin and other crypto currencies are also
explained.  Presently users have time lag
minimum ten minutes even more for larger transactions for avoiding  double spending attack.
Some essential questions in this paper. a) Can a decentralized network centralized
power will indicate and command slow transactions? b) How much times a Bitcoin trades
be made faster? c) Could bitcoin be fixed at a lowest price?

a crypto currency, that is distributed peer to peer economic system. It is an
electronic system which manages the ownership of a severely stable resource of intangible
transferable units which really works as a distributed belongings record or digital
signatory facility. This is quite different than handling the possession of
shares in old-fashioned economic markets. Modern financial institutes
increasingly just do not trust each other, they build co-operative vigorous and
distributed and increasingly opaque, electronic systems which are and able to
both serve the different objectives of participants (e.g. traders) and uphold certain
security policies. Is Bitcoin actually so brilliant to be called the Internet
of money as it is sometimes claimed? Not just the speed, tremendous least
latency trades are a rule in
the economic industry even normal people have admittance to fast bank transfers
and actual credit card transactions. Bitcoin leftovers somewhat the horse gait
of money. Fast transaction acceptance in bitcoin and other crypto currencies
has been discussed in this paper. Bitcoin needs some changes in order to fulfil
the most needs of modern customers.


comparison to traditional financial marketplaces such as stock marketplaces.
There is a number of similarities with bitcoin. Trading is gradually becoming decentralized,
especially in the United States. Resources are exchangeable and in limited supply.
Financial institutions gradually more just do not trust each other, but want to
build cooperative automated systems which can role in presence of mischievous supporters.
Markets are becoming transparent, at least for inspection, although it’s
difficult to attain in today’s markets. Bitcoin is as computer-generated. Possessions in economic
markets. Ownership requires some type of proof.


(Porru, Pinna, Marchesi, & Tonelli, 2017) In this paper,
we recognize the need for software engineers to devise specialized tools and
techniques for Block chain-oriented software development. Certifying effective testing
activities, improving association in large teams, and allowing the development
of smart contracts as key factors in the upcoming of block chain-oriented
software improvement.


issues and new guidelines for block chain-oriented software engineering, and new
studies the essential for new precise software engineering practices for the block
chain section. To this purpose, we identified the most related
challenges for the state-of practice Block chain-oriented software engineering,
emphasized uniqueness of some of the most popular Block chain-oriented software
projects going on in the world, proposed new research directions for block
chain oriented software engineering, based on the results obtained from the
previous steps.

the present work, we stressed the most plain questions of state-of-art block
chain-oriented software development, by promoting the need for new skilled roles,
enhanced security and reliability, new modeling languages, and specific metrics.

proposed new directions for block chain-oriented software engineering, focusing
on teamwork among large groups, testing activities, and specific tools for the
creation of smart contracts.