Final Portfolio Project The Final Portfolio Project is a comprehensive assessment of whatyou have learned during this course. The Final Project has t

Final Portfolio Project
The Final Portfolio Project is a comprehensive assessment of whatyou have learned during this course.
The Final Project has two parts: Limitations ofBlockchainand EmergingConcepts.
Blockchaincontinues to be deployed into various businesses and industries.However,Blockchainis not without itsproblems. Several challengeshave already beenassociated with the use of thistechnology. Identify at least 5 key challenges toBlockchain. Additionally, discuss potential solutions to these challenges. Lastly, please discuss if we will see the limitations toblockchainbe reduced or mitigated in the future.
Thereare several emerging concepts that are usingBig Data andBlockchainTechnology.Please search theinternetand highlight 5 emerging concepts that are exploring the use ofBlockchainand Big Data and how they are being used.
Conclude your paper with a detailed conclusion section which discusses both limitations and emerging concepts.

The paper needs to be approximately 6-8 pages long, including both a title page and a references page (for a total of 8-10 pages). Be sure to use proper APA formatting and citations to avoid plagiarism.
Your paper should meet the following requirements:
Be approximately 6-8 pages in length, not including the required cover page and reference page.
Follow APA7 guidelines. Your paper should include an introduction, a body with fully developed content, and a conclusion.
Support your answers with the readings from the course, the course textbook, and at leastfour scholarly journal articles from the UC library to support your positions, claims, and observations, in addition to your textbook. The UC Library is a great place to find resources.
Be clearly and well-written, concise, and logical, using excellent grammar and style techniques. You are being graded in part on the quality of your writing.

978-1-5386-5651-8/18/$31.00 2018 IEEE

Blockchain Challenges and Security Schemes:
A Survey

Sirine SAYADI
MEDIATRON Laboratory

Higher School of
Communication of Tunis,

[emailprotected]

Sonia BEN REJEB
MEDIATRON Laboratory

Higher School of
Communication of Tunis,

[emailprotected]

Zid CHOUKAIR
MEDIATRON Laboratory

Higher School of
Communication of Tunis,

[emailprotected]

Abstract With the increasing number of connected devices
and the number of online transactions today, managing all
these transactions and devices and maintaining network
security is a research issue. Current solutions are mainly based
on cloud computing infrastructures, which require servers
high-end and broadband networks to provide data storage and
computing services. These solutions have a number of
significant disadvantages, such as high maintenance costs of
centralized servers, critical weakness of Internet Of Things
applications, security and trust issues, etc. The blockchain is
seen as a promising technique for addressing the mentioned
security issues and design new decentralization frameworks.
However, this new technology has a great potential in the most
diverse technological fields. In this paper, we focus on
presenting an overview of blockchain technology, highlighting
its advantages, limitations and areas of application.

The originality of this work resides in the comparison
between the different blockchain systems and their security
schemes and the perspective of integrating this technology into
secured systems models for our comfort and our private life.

Keywords Blockchain, Security, Technology, Smart
Contracts, Consensus

I. INTRODUCTION

The current network model connects multiple computing

devices and will continue to support small-scale Internet of
Things networks that will not be able to meet the growing
needs of tomorrow’s large ecosystems. Centralized cloud
servers will remain a bottleneck. throttling and a point of
failure that can disrupt the network.

In this context, Blockchain technology appeared in 2009
by Nakamoto [1] “Bitcoin Developers” as a storage
technology serving decentralized large registers and as a
security technique for authenticating, authorizing and
verifying data generated.

With blockchain technology the concept of consensus has
emerged as a mechanism that ensures trust in communication
between two entities without the intervention of an
intermediary. We can use blockchain in cryptocurrency,
smart contracts, digital identity management, internet of
things, access control applications, automated peer-to-peer
insurance, in banks and in many other applications [2].

Since its inception, from the initial cryptocurrency to the
current smart contract, blockchain technology has shown
promising prospects in many areas of application.

This proposed paper will be a state-of-the-art study on
blockchain technology. Section 2 will present an overview of
blockchain technology. Section 3 will describe a semantic
study of the potential of blockchain technology. We present
in Section 4 some cases of use of this technology. Then we
will examine the security threats, some real attacks for this
technology, and its security enhancement solutions in Section
5 and finally we will conclude our paper by suggesting future
directions.

II. OVERVIEW OF BLOCKCHAIN TECHNOLOGIES

This section presents a complete visualization of
blockchain technology, how it works, its structure and
existing types.

A. Blockchain Process

The Blockchain process is described as a transaction

between users on the network that are grouped into blocks.
The block is validated and saved on the network by a
minor according to cryptographic techniques that depend
on the rules of the type of blockchain used.

In the bitcoin blockchain this technique is called the
“Proof-of-Work”, (POW), and “proof-of-stake” (POS) in the
blockchain ethereum. If the block is validated, it is time
stamped and added to the block chain. The transaction is then
visible to the receiver as well as the entire network. This
process takes some time depending on the blockchain (about
10 minutes for bitcoin, 15 seconds for Ethereum) [8].

Each blockchain is identified by its cryptographic hash
and carries a list of transactions and a hash to the previous
block.

The exception to this is the first block in the chain, called
“genesis”, which is common to all clients in a blockchain
network and has no parent. This establishes a link between
the blocks, thus creating a chain of blocks, or blockchain.
Any node having access to this ordered and back-linked
block list can read it and understand what is the current
global state of the data exchange on the network.

Figure 1: Blockchain Process

B. Blockchain Structure

A block is composed of two main parts which are the

Block Header and the transactions (see Figure 1). The Block
header contains several fields, the most important among
them are the block version, the Merkle tree Root Hash, time
stamp, nBits, Nonce and parent block hash. Transactions are
the data saved in the block [46].

These fields will be detailed below (see figure 2):

Block Version: Specifies the set of block validation
rules to follow [46].

Merkle tree Root Hash : is a condensed digital
fingerprint of all transactions in the block. The slightest
modification of a transaction in the block modifies this root.
Its principle is to calculate the hash of a node from a hash of
his sons [3].

Timestamp: current time in seconds in universal
time since January 1, 1970 [46].

nBits: target threshold of a valid block hash.

Nonce: A 4-byte field, which usually starts with 0
and increases for each hash calculation. On receipt of the new
block, the complete nodes compute the header hash only
once, to see if the Nonce is valid [37].

Parent block hash: The nodes save the data of the
block’s. Thus, all the nodes have the hash of the block 31, if
the block 32 is received by a node, it will determine that the
block 32 is the child of 31 by checking this field [37].

Figure 2: Simplified Block Structure

C. Type of Blockchain

There are three types of Blockchain technologies
presented in the following table :

Public blockchain from which everyone can
participate in the process of reaching consensus and
verifying the transaction. Like Bitcoin [4] and Ethereum [5].

Consortium blockchains: In this type, the node
can be chosen in advance if the data in blockchain can be
public or private. They can be considered as partially
decentralized like Hyperledger [6].

Private blockchain has strict management
authority over access to data. Nodes are restricted, not all
nodes can participate in this blockchain like Ripple [7].

Table 1: Comparative table of blockchain types [46]

All types of blockchain have advantages. The choice of
blockchain type depends on our needs and our proposed
services.

III. POTENTIELS OF BLOCKCHAIN

Blockchain technology is not only a technique, but it is a

technological revolution with very important security
features, its operating model using consensus and its shared
ledger to solve the problems of traditional centralized
models.

A. Basic Security Techniques

We detail in this section the different basic security

principle by specifying how Blockchain technology can
perfectly guarantee them.

Integrity: it to ensure that the information has not
been changed, only by those authorized to make
changes. Blockchain uses cryptographic mechanisms
to guarantee that operations are immutable with the
purpose of verifying integrity.

Availability: it ensures the availability of data for
every need. the service is always active at the request
of a legitimate users. Blockchain allows users to
maintain blocks in a decentralized manner with
various copies on the blockchain.

Pivacy: is the guarantee that only authorized persons
can access to the information. The Blockchain uses a
pseudo-anonymization mechanism (hash functions) to
hide user identities to ensure confidentiality.

Authentication: a procedure by which a computer
system certifies the identity of a person or a computer
to allow that person to access certain secure resources.
The Blockchain technology provides this function by
providing private keys for users who are authorized to
carry out transactions.

Non-repudiation: Is the impossibility, for a person or
any other entity engaged in a communication, to deny
having received or sent a message, and this is ensured
by blockchain technology.

B. Shared Ledger

This is the basic feature of blockchain technology, it

means that blockchain does not have a centralized node, data
is processed, stored and updated in a decentralized way. This
avoids the problems of single deffain point and offers a peer
to peer communication such that all nodes are interconnected
and all participants in the network are equal without a central
node.

C. Smart Contract

The smart contract is autonomous computer programs

that once started, automatically execute pre-defined
conditions with conditional statements of the type if ….
Then …. Using the information available on the blockchain.

These contracts must be able to reduce audit costs,
execution, arbitration and fraud. They may have to manage
funds or authenticate external entities [8].

D. Consensus

A consensus is a secure fundamental trust mechanism. It

characterizes a general agreement of existence of the
members of a group. It allows you to make a decision
without the need of an intermediary or a trusted authority.

In the existing blockchain system, there are several
consensus mechanisms. We will quote the best known
below:

PoW (Proof of Work) :

Method used to validate Blockchain network blocks. This
method requires users to use their computing power to
validate a block. Minors compete against each other. As a
result, the higher the computational power (combining
several computers, to increase computing power), the more
likely they are to find the result of a “Hash” function and thus
validate the block. In the Bitcoin blockchain it is necessary to
count a validation every 10 minutes approximately [9].

PoS (Proof of Stake):

A chance to validate a block is based on how much of a
stake (or cryptocurrency) the miners have. For example, if
you had 5% of the cryptocurrency, you could extract 5% of
all its transactions. People with more currency are thought to
be less likely to attack the network. Its operating principle
based on the richest person has more power in the network is
unfair because the power here depends on the balance held in
the account [46]. The PoS save more energy (reduces the
amount of calculation) but increases the flow. Unfortunately,
if the operating cost is close to zero, attacks could result.

PBFT (Practical Byzantine Fault Tolerance) :

The problem of Byzantine generals is a metaphor that
deals with questioning the reliability of transmissions and the
integrity of the interlocutors. A Byzantine fault is therefore a
failure that consists of the presentation of erroneous or
inconsistent information. The consensus “Practical Bizantine
Fault Tolerance” (PBFT) is a state machine replication
protocol that tolerates arbitrary, or “Byzantine” faults. It is
fault-resistant, fast, long-lived and an attack does not impact
its performance too much. This protocol consists of three
phases: pre-preparation, preparation & validation, it requires
3f + 1 replicates to tolerate f simultaneous Byzantine faults.
When a message is sent on the platform, the nodes retransmit
the transaction to all peers. If at least 2/3 of the nodes confirm
the validity of the transaction it is confirmed. The platform
allows users to transfer peer-to-peer ownership regardless
[46].

Many other consensus mechanisms can be found , such as
DPoS (Delegated Proof of Stake), PoB (Proof of Bandwidth)
[10], PoEt (Proof of Elapsed Time) [11], PoA (Proof of
Authority) [12], Ripple [48], Tendermint[49] etc. that are
used in some blockchain systems.

A comparison between some of the most used consensus
algorithms is presented in table 2 [46].

With these advantages presented in this section from the
basic security techniques, smart contracts, shared ledger and
the consesus, blockchain technology has attracted attention in
several areas..

In the next section, we will introduce some areas of use of
blockchain technology as a solution concept.

Table 2: Comparison between some consensus algorithms

Property POW POS PBFT

Identity
management
of nodes

Without
permission

Without
permission

With
permission

Energy saving No partial yes

Power
tolerated

<25% computing power <51% stake <33,3% Defective replicas Example Bitcoin Ethereum Hyperledger IV. CASES USE OF BLOCKCHAIN AND APPLICATIONS In our days, Blockchain technology is used in many areas, not only in the financial application, but also in other areas such as supply chain traceability, identity certification, insurance, International payments, the Internet Of Things and the protection of privacy etc [25, 26, 31, 32, 33,34]. We detail in this section some uses of blockchain technology: 1) Digital Currency : Several transaction systems have been built recently by blockchain technology, which makes a revolution in digital currency and online payment system. With these digital currencies and the crypthography technique, transfers can be made without the need of the central bank. For example, we can send and receive bitcoins using public keys, with all anonymity we can record transactions. Several other cryptocurrency like ethereurm, ripple, litecoin and etc [27]. 2) Smart Contract: Smart Contract is a digital contract that runs automatically through a computer system. It controls the digital assets of the user, by formulating a set of rules containing the rights and obligations of the users. Smart Contract is like an automatic trusting authority among participants [28]. Ethereum is an open source blockchain platform offering a decentralized virtual machine based on the Smart Contract. To manage these contracts Ethereum uses its digital currency called ETH, users can create many applications, services or different contracts on this platform [29]. 3) Hyperledger : Hyperledger is an open source blockchain platform, launched by the Linux Foundation in December 2015 with the aim of improving reliability and performance. It aims to support global business transactions of large technology, financial and supply chain companies etc [30]. 4) Blockhcain To Ensure privacy, Access control and Integrity Protecting our personal information and our private life is a challenge in our day. [35][36] uses blockchain technology based POW in IOT applications to ensure integrity and confidentiality. Blockchain can also be used for access control. Just save the history daily in blockchain as a signed transaction specifying public keys with access rights. Only minors authetified with his private keys can include this transactions in their blocks [37]. Based on blockchain technology, Ouaddah and al. [36] presented the FaiAccess framework with its different parts to allow users to control their data. Zyskind et al. [34] exploited the access control option provided by the blockchain with storage in a distributed hash table of several selected nodes. The Blockchain is used here for data location management and their access. Ali and al. [33] used blockchain to build "Blockstack ID" which is an identity system and a decentralized PKI. This system consists of a control plane that is a name registration protocol and links and a data plan that is responsible for storing the data that must be signed by the name owner's key. 5) Blockchain For Eletronic Transactions The Blockchain can be used as a base that will support the shared economy, based on machine-to-machine (M2M) communication. Several propositions in the theme [38, 39, 40, 41, 42]. Blockchain technology allows agents to autonomously perform a variety of transactions and to store the history of each transaction with transaparance and no deffiliation. Sun et al. [41] specifies that Blockchain technology leads to the Internet of decentralized and autonomous objects. The blockchain supports all processing transactions between devices and each device can manage its behaviors and roles in an autonomous way. Using the Bitcoin network, [40] described a model of data exchange by electronic money, between a sensor and a client. [38] described a Bitcoin-based e-commerce model for IOT devices. This composite model consists of 4 layers (the technical layer for the management of the Blockchain module, the infrastructure layer containing the smart contract platforms and IoT services, the content layer containing the participants and the IOT products and the layer exchange that contains the P2P transaction system). We can find many other proposals that use Blockchain technology for economic transactions for IoT like ADEPT [43], Filament [39], Waston IoT platform [44], IOTA [42] etc. 6) Blockchain To Secure Smart Home : Dorri et al. [45, 50] proposed a lightweight blockchain solution adopted for IoT without cryptocurrency to illustrate a smart home containing a power computer that is responsible to control and audit communications and provide access control between devices. It maintains a private blockchain and is considered minor without the need for the proof of work concept because only this computer is responsible for managing the blockchain. Other devices receive a private key and a public key to perform transactions. For example, if a sensor wants to open the faucet, it will send a transaction to the faucet, which will check in Blockchain if that sensor is allowed to open it. A smart home is the best example for IoT Blockchain combination. The services offered by blockchain technology can be contribute to shared economies and to the smart cities where objects connect seamlessly and anonymously to exchange and share data. V. SECURITY ISSUES OF A BLOCKCHAIN TECHNOLOGIE We describe in this section some recently encountered limitations that can affect the good functioning of blockchain technology by presenting some models in the form of the proposed improvement solutions to limit these risks. A. Risks to Blockchain 1) 51% Vulnerability: The consensus mechanism has a vulnerability of 51%, which can be exploited by attackers to manipulate the blockchain. In PoW, if the hash power of a minor> 50% of the
blockchain’s total hash power, the 51% attack can be
initiated. As a result, mining resources concentrated in a few
mining pools can cause fears, as a single pool controls more
than half of all computing power [13].

In the PoS, if the number of cryptocurrencies owned by a
single by a single miner is greater than 50% of the total
blockchain. A 51% attack can occur which an attacker can
arbitrarily manipulate information from the blockchain [47].

An attacker can exploit this vulnerability to carry out
attacks; we will mention some of each after following [15]:

Run a double spending by modifying the
transaction data (same coins are spent multiples
times).
Change the order of transactions.
Prevent normal mining operations of other miners
(Denial of service attack).

2) Double Spending attack:

A customer provides a seller with a signed transaction;
the seller verifies the validity with a peer who confirms the
transaction. If the client is malicious, it can create a
conflicting transaction by generating a double spend (the
same crypto currency spent twice) and having it validated by
another peer before the first transaction has spread across the
network. Both transactions are therefore proposed for
mining. Depending on which will be treated first, it is this
truth that will be imposed on the entire network by
registration in one block and invalidate the other. In this
case, if the seller had delivered before validation by the
minor, he was robbed … resulting in a double spending [14]
[47].

3) Smart Contracts Risks

Dependency of the transaction order:

In order to update the blockchain, in each era, each miner

will propose his own block. Since a block can contain
multiple transactions, the state of the blockchain can change
several times during an epoch.

This attack can be triggered if two successive

transactions of the same block invoke the same smart

contract. The order of execution of these two successive
transactions affects the final state because the execution of
the smart contract is associated with a single state [47].

The time stamp dependency:

Each block in the blockchain contains a timestamp field.

Some conditions for triggering smart contracts depend on
the timestamp, which is defined by the minor according to
the time of his local system. Smart contracts depend on time
stamp fields are vulnerable, if they can be changed by
attackers [47].

Under-Optimized Smart Contract :

The gas value corresponds to the computing resources

exploited by the bandwidth operation, memory occupancy
and many other parameters used in Ethereum as a function
of time.

We can find some resource-intensive operations such as
dead code operations and the use of loops by exchanging the
gas value according to the cryptocurrency. [47].

4) Denial Of Service Attack

An attacker can launch a DoS (Denial of Service) attack
by exploiting a set of operations executed in a single
transaction. This is because some heavy operations require
too low gas values. This can cause a waste of resources [16].

5) Selfish Mining Attack:

This attack is conducted by mining in order to obtain

undue rewards or to waste the computing power of honest
minors [18]. The attacker holds the blocks discovered in
private and then tries to forge a private channel. The authors
in [19] proposed a Selfish-Mining attack, which attract other
honest miners to dispel their computing resources
unnecessarily to keep working on blocks that lead to a
stalemate instead of attaching them to the longest chain.

6) Reentrancy Attack:

It is the fact of exploiting a recursive sending for

example the biggest flight about 60 million US dollar of the
contract CAO by this attack just after its deployment of 20
days [17].

7) Liveness Attack

In [20] the authors proposed this attack to exploit the

dilation of the confirmation duration in order to obtain a
target transaction.

8) The Balance Attack

Christopher and al. [21] proposed this attack based on
PoW blockchain, which consists of identifying subgroups of
miners with similar mining power and delaying messages
passed between them in order to mine blocks before them.

B. Security Improvements

1) Smart Pool

L. Luu et al [22] proposed a new Smart Poll mining pool
system, implemented as a smart contract. It is a
decentralized mining protocol that replaces the centralized
pool operator.

It retrieves client transactions that contain information
about mining tasks. Then the miner performs a hash
calculation and returns the completed shares to the
smartpool. A threshold sets an amount, if the shadow of
actions made reaches this threshold, the miners will be
committed to a smartpool contract that verifies the actions
and delivers rewards to the customer [47].

2) Quantitative Framework

In [23] the authors proposed a quantitative framework is

used to analyze the performance and security provisions of
the blockchain. it is a blockchain simulator and a security
model that mimics its execution to evaluate basic security
and performance.

This model specifically focuses on the attacks of selfish
and double-spending mining by taking into consideration the
consensus protocol used and network parameters such as
block propagation delays, block sizes, delays network, block
rate and the mechanism of propagation of information etc.

3) Oyente

Loi and al. [24] proposed a new program called Oyente

that tracks errors in smart contracts. This tool can also detect
bugs and injection attacks in smart contracts.

Oyente analyzes the bytecode of smart contracts and
follows the EVM execution model [47].

VI. CONCLUSION AND PERSPECTIVES

In this paper, we presented an overview of Blokchain

technology. We have described its different security
potentials by specifying a comparison between some of the
most widely used consensus algorithms in different
blockchain systems. We have also clarified the fields of use
of this technology because in recent years, it has shown its
potential in several applications and this is due to the
advantages of this technology and its decentralized nature.
These applications permeate everyday life, business and
society as a whole, transforming the world into a more
efficient world. And finally, we indicated that many
maneuvers of this technology, then specifying the
improvement solutions proposed to defend them.

Blockchain then presents many promising opportunities
that open up many paths for the future and for a connected
world in complete security. However, the challenges remain
in the resources and consensus models used.

That’s why, we aims in future work to leverage the
benefits, limitations of blockcahin technology, and
enhancement solutions to produce a new secure system

model that integrates this technology with the Internet Of
Things technology for a connected and secure world.

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