Final Report and Presentation- Value: 40%

Full Name Muhammad Hassam Khalid

Student ID 11669134

Subject ITC571 – Emerging Technology and Innovations

Assignment No Assessment 04 - Capstone Project Report

Due Date 29-May-2020

Lecturer’s Name Malka N. Halgamuge

Table of Contents

1. Introduction: ......................................................................................................................................................... 4

2. Materials and methods: ......................................................................................................................................... 8

2.1. Data Collection .......................................................................................................................... 9

2.3. Analysing and filtering: .............................................................................................................. 9

2.4. Data Derivation: ........................................................................................................................ 9

2.5. Derived data as benchmark for proposition: ............................................................................ 10

3. Consensus algorithms for permission-less blockchain: ...................................................................................... 10

3.1. Proof-of-Work: ........................................................................................................................ 10

3.1.1. Advantages: ............................................................................................................................. 10

3.1.2. Disadvantages: ......................................................................................................................... 10

3.2. Proof-of-Stake: ......................................................................................................................... 11

3.2.1. Advantages: ............................................................................................................................. 11

3.2.2. Disadvantages: ....................................................................................................................... 11

4. Consensus algorithms for permissioned blockchain: .......................................................................................... 11

4.1. Byzantine Fault Tolerance algorithm and variants: .................................................................. 11

4.1.1. Advantages: ............................................................................................................................. 12

4.1.2. Disadvantages: ......................................................................................................................... 12

4.2. Raft: ........................................................................................................................................ 12

4.2.1. Advantages: ............................................................................................................................. 12

4.2.2. Disadvantages: ......................................................................................................................... 12

5. Proposition based on 2-tier architecture containing permissioned and permission-less blockchain: .................. 13

5.1. 1st-Tier of the architecture: ...................................................................................................... 13

5.1.1. Voting based consensus Algorithm (VBCA): ............................................................................ 13

5.2. 2nd-Tier of the architecture: ...................................................................................................... 15

5.2.1. Practical Byzantine Fault Tolarent Consensus Algorithm: ....................................................... 15

6. Advantages of the proposed 2-tier architecture: ................................................................................................. 16

6.1. Enhanced security and privacy: ............................................................................................... 16

6.2. Scalability: ............................................................................................................................... 16

6.3. Reliability: ............................................................................................................................... 16

7. Results: ............................................................................................................................................................... 17

7.1. Modes: ..................................................................................................................................... 17

7.2. Platform: ................................................................................................................................. 17

7.3. Consensus Algorithms: ............................................................................................................. 17

7.4. Throughput: ............................................................................................................................ 17

7.5. Energy Use: ............................................................................................................................. 17

7.6. Scalability: ............................................................................................................................... 17

7.7. Transaction: ............................................................................................................................. 18

7.8. Nodes: ...................................................................................................................................... 18

7.9. Technology used: ..................................................................................................................... 18

8. Discussion: .......................................................................................................................................................... 18

9. Future Direction: ................................................................................................................................................. 18

Bibliography ................................................................................................................................................................ 19

Permission-ed Blockchain and Permission-less Blockchain: Studying Consensus

Algorithms and Proposing 2-tier architecture based on Voting System.

Abstract-- With the rapid use of internet technology, its security and performance are at risk.

The data on the internet can be compromised and the performance can be bottlenecked. The

solution to this problem is the blockchain technology. Reason of choosing this field is because

blockchain is a new technology whose demand is rapidly increasing and now is one of the

most demanding field in the IT sector. Permissioned and permission-less blockchain, each

having its own properties and limitations and can be used in different scenarios. Blockchain

is based on peer-to-peer topology containing connected nodes. Each node has cryptographic

hash of the previous node (no malicious or unauthorized node can enter the linked nodes),

timestamp and relevant data. Blockchain provides resistant to the interference and

modification of the data and each node has separate processing power thus enhancing

security and performance of the host network. In permission-less blockchain the nodes can

be public, anyone can add nodes to increase the performance (Bitcoin), while permissioned

blockchain is used within enterprise or between enterprises where the nodes are private and

new nodes need authorization to be added in link nodes. The aim of this paper is to study the

permissioned and permission-less blockchain, their similarities and differences, some of the

consensus algorithms they use. Outcome of the paper being understanding of each algorithm

on which their whole functioning is based with description and further explanation of each

algorithm and proposing a two-tier architecture which will contain voting based algorithm

for enhanced performance.

Key words – Permission-less blockchain, Permissioned blockchain, consensus algorithm,

architecture, blockchain

1. Introduction: As the field of IT is expanding, Computer networking sector is also implementing new

technologies which are getting more popular. Blockchain being one of them. Blockchain

technology is one of those technologies which is being used in a faster rate (Bambrough, 2020).

The main reason that the blockchain is getting more and more popular is based on the principle of

distributed peer-to-peer networking. P2P allows blockchain to distribute the work and resource

among multiple computers in the network called nodes (Belotti, Božić, Pujolle, & Secci, 2019).

This provides blockchain security from DDOS and other attacks which allows blockchain to be

used in different sectors like finance and healthcare where the security of private data is critical.

The data among the nodes is shared and its record is stored in a distributed ledger in the form of

transactions. The ledger is not controlled by a single entity rather the nodes in the network make

up the distributed ledger combined which develops an environment which is not controlled by a

single entity (Wüst & Gervais, 2018). The ledger is expanded in the form of blocks containing

timestamps and each block contains hash value of the previous block thus making a chain.

Blockchain technology provides the properties to data like data privacy, data redundancy, data

availability and data privacy which makes it suitable to be used in critical sectors (Wüst & Gervais,

2018) (Ge, Sun, & Szalachowski, 2019).

Blockchain has two modes, permission-less blockchain and permissioned blockchain. Permission-

less blockchain is an open blockchain network where the nodes are public. Anyone can add nodes

in the permission-less blockchain network. As the name defines, the nodes do not need any special

permission to be added in the network. Bitcoin is based on the permission-less blockchain type.

Bitcoin is an open platform/cryptocurrency where people can add nodes in the network by lending

their computation power and get reward in return (Belotti, Božić, Pujolle, & Secci, 2019).

Permission-less blockchain requires constant source of computation power and energy because of

encryption and decryption of data (Ge, Sun, & Szalachowski, 2019). Permissioned blockchain, as

the name implies is blockchain in which the nodes require permission of certificate of authority in

order to be added in the network, the nodes are private and known (Cash & Bassiouni, 2018). The

permissioned blockchain is used in an organization or between organizations and the nodes are in

the organization. This blockchain is more secure and robust as it provides more security,

Hyperledger is based on permissioned blockchain (Belotti, Božić, Pujolle, & Secci, 2019).

The whole blockchain technology works based on consensus algorithm. Consensus algorithm is a

process of agreement between the nodes or group of nodes to perform certain task (Pahlajani,

Kshirsagar, & Pachghare, 2019). Permission-less and permissioned blockchain uses consensus

algorithms based on the use case and resources available. Permission-less blockchain has

algorithms like proof based (PoW, PoS, PoX) (Chaudhry & Yousaf, 2018). Whereas, Permissioned

blockchain mostly use voting based consensus algorithms (Wang, Zhang, Xu, & Zhou, 2019) and

Byzantine fault Tolerance algorithm and its variations. Permissioned blockchain also use smart

contracts which script or software that resides in the network and provides agreement (Lasisi &

Hsu, 2019). (use summary table to add more algorithm names)

Proof-of-work (PoW) is the most commonly used consensus algorithm which includes solving

complex work in order to gain consensus. In proof-of-Stake (PoS) (Kim, Ullah, & Kim, 2019),

consensus is provided to the nodes which have more stake in the network (Pahlajani, Kshirsagar,

& Pachghare, 2019). But these algorithms use large amount of computation power. In

Permissioned blockchain the Byzantine fault Tolerance algorithm and its variations are used to

achieve agreement between the nodes even if there are faults, like one node cannot communicate

with the server while others can. BFT algorithm has variations each with its own feature (Bach,

Mihaljevic, & Zagar, 2018). While the voting-based algorithms like Raft choose a node based on

voting who controls the consensus among the nodes (Panda, et al., 2019).

Permission-less blockchain can be an ideal solution for most use cases, but it suffers with some

limitations like high energy use, malicious nodes, and no control over the public nodes (Lopez,

Montresor, & Datta, 2019). Meanwhile private blockchain covers those limitations but is complex.

Table 1: Data about modes of blockchain and its consensus algorithm collected from 12 published papers.

The solution that this report provides is based on implementing 2-tiers of blockchain network in

order to increase security, high throughput, high scalability and reliability. The permission-less

tier will handle all the transactions using a voting-based consensus algorithm in which a node is

chosen which is responsible of the consensus and provides every node work to perform according

to each node’s specification (Dataset). Permissioned blockchain tier will contain the distributed

ledger and uses byzantine fault tolerant algorithm in order to ignore errors to a certain threshold

and provide data redundancy. Both tiers will have one-way communication, 1st tier will send data

to 2nd tier for storage but cannot read, alter or delete the data in the 2nd tier.

The motivation of this paper comes from the idea in which one mode of blockchain can cover the

limitation of other mode of blockchain and vice versa, building a system which will have the main

features of both permission-less and permissioned blockchain. This type of architecture can be

implemented in many scenarios specially in IOT where the devices are constraint and do not

perform very well with blockchain (Singh, Singh, & Kim, 2018). The contributions that this paper

provides are as follows:

• Discussing consensus algorithms of permission-less blockchain and permissioned

blockchain.

• Features and limitations of both blockchains.

• Proposing a 2-tier architecture which will provide enhances scalability, reliability, security

and throughput.

• Clear a pathway for the proposed architecture for future work.

2. Materials and methods: The research required for this report was based on a hybrid approach which is based on:

• problem-oriented method.

• Quantitative method.

Problem-oriented method is understanding and describing the problem domain in depth including

the background the background in order to fully understand the nature and the scope of the problem

which is to be solved (Deakin, 2019). While quantitative method includes collection and derivation

of relevant data from different sources and developing conclusion based on propositions (UNA,

2019).

Permissioned and permission-less blockchain are used in different scenarios. One’s weakness is

covered by the other but are not implemented together. This paper will propose an architecture

which will use both the blockchains to achieve the features of both.

Figure 1: Features of each tier in the proposed architecture.

The steps taken to perform the hybrid methodology are as follows:

2.1.Data Collection: Collecting relevant data from the chosen papers is included in this step.

The data collected is in raw format. According to the this report the data will be collected

relevant to the consensus algorithm and the performance of the blockchain using the

consensus algorithm. Table 1 shows the data collected of the blockchain and performance.

2.2.

Figure 2: Data about modes of blockchain obtained from the 12 chosen papers.

2.3.Analysing and filtering: The data gathered is filtered, categorized and analyzed in depth

in order to understand the background and the nature of the problem scope. The data

relevant to the proposition is given high priority in analyzing.

2.4.Data Derivation: Data is derived from the raw data gathered in the step A in the form of

dataset. This data will be used for the discussion phase and in explanation of why the

proposition is done. The data is derived relevant to the consensus algorithms which is the

backbone of the blockchain and proposition.

Figure 3: Data about the algorithms obtained from 12 papers and also data highlighted in (Panda, et al., 2019)

2.5.Derived data as benchmark for proposition: The dataset derived in the previous step is

used as the benchmark for the proposition. To compare what the proposed architecture

covers. This will help in pointing out the features of the proposed architecture which will

require more work and focus in the future.

3. Consensus algorithms for permission-less blockchain: Permission-less blockchain has several consensus algorithms which can be implemented, one of

the main advantages of the algorithms in this mode of blockchain is that they support scalability,

permission-less blockchain are highly scalable and the nodes are public as well. Most common

algorithms used are as follows:

3.1. Proof-of-Work:

PoW is the most used algorithm in the blockchain, it is also one of the first developed. In this

algorithm the nodes are given consensus after they perform certain work and proof the work done.

PoW gives same level of priority to all the nodes available in the network. The nodes are given a

value to hash and nonce value (noise/work) is added according to difficulty, Once the output hash

value contains zero-bit numbers at the start which is required, that node/miner is granted the

consensus to add block of transaction in the network (Chaudhry & Yousaf, 2018).

3.1.1. Advantages:

• PoW is highly scalable.

• Gives same consensus priority to all the nodes in the network

3.1.2. Disadvantages:

• Uses large amount of energy and computation power.

• Doesn’t punish malicious nodes.

• If an attacker introduces malicious nodes in the network and controls 51% of the network,

he can control the whole PoW system and network. E.g. sybil and DOS attacks.

3.2. Proof-of-Stake:

PoS is a hybrid algorithm which was developed to cover the limitations of PoW like high energy

and computation use. This system uses features of PoW and uses PoS for security. Unlike PoW,

the work doesn’t depend on the specs of the node to perform work, instead the miner/node must

buy stake in the blockchain network in order to get validated to add a block in the chain. Higher

the stake of a miner, more the chance of him to get the validation (Belotti, Božić, Pujolle, & Secci,

2019).

3.2.1. Advantages:

• PoS uses less energy and computation power compared to PoW.

• Transaction speed in PoS is faster compared to PoW.

3.2.2. Disadvantages:

• The minder/node with the most wealth gets the consensus while other have to buy stake in

order to get validation.

• Attacker still have chance to get inside the PoS blockchain network by buying enough

stake.

4. Consensus algorithms for permissioned blockchain: The nature of consensus in permissioned blockchain is different as compared to permission-less

blockchain as permissioned blockchain is private and the nodes are known (nodes also know each

other). The consensus algorithm in permissioned blockchain depends on many attributes like

scalability, throughput speed and reliability (Nadir, 2019). Permissioned blockchain also uses

smart contracts to achieve consensus among the nodes. Moreover, not all nodes are involved in

the consensus process.

4.1. Byzantine Fault Tolerance algorithm and variants:

This algorithm is used in the permissioned blockchain to achieve consensus even if there are

problems in the network like malicious nodes or if one node cannot communicate with the server

while others can. This is achieved by the process of replication and implementing a tolerant

threshold, BFT has three phases pre-prepare, prepare and commit. Primary nodes assign sequence

number to the request message, the request message which contains digital signature and message

body is forwarded to the nodes which are participating in the consensus. The nodes receive the

message and verify it by the digital signature and the message gets forwarded to the other nodes

and again verification is done. Even if one of the nodes is failed others will pass the message

through the phases and reply will be sent back because of the tight relation between the nodes.

BFT can be configured to fulfill the needs BFT has several variants (Bach, Mihaljevic, & Zagar,

2018).

4.1.1. Advantages:

• Fast throughput speed.

• Uses less energy.

• Enhanced privacy and reliability.

• High responsive time because of low latency.

4.1.2. Disadvantages:

• As the message is multi-casted to the nodes in stages, the scalability of network using BFT

is highly limited.

• Sybil attack can hinder the network.

4.2. Raft:

Raft is a voting-based algorithm used in permissioned blockchain. Candidate nodes are chosen

which have better relationship with other nodes. A leader node is chosen from the candidates

through voting. Remaining nodes and candidates become followers of the leader node. The data

flows from the leader to the followers. The leader is chosen per round called term. Once a term is

finished a new leader is chosen. Leader proposes a specific value to the followers, if the value is

accepted by the followers then consensus is achieved (Panda, et al., 2019).

4.2.1. Advantages:

• Raft works even if 50% nodes of the network are failed.

• Less complexity compared to BFT.

4.2.2. Disadvantages: • Slow speed if the leader elected has low specifications.

• Does not support Byzantine nodes.

5. Proposition based on 2-tier architecture containing permissioned

and permission-less blockchain: The proposition that this report proposes is an architecture based on 2- tiers. The architecture

contains the properties of both permission-less and permissioned blockchain. The architecture

once implemented will result in enhanced reliability, high scalability, high throughput and

improved security. The figure below gives the idea of the proposition.

Figure 4: Proposed 2-tier architecture.

5.1. 1st-Tier of the architecture:

The 1st tier of the blockchain is based on permission-less blockchain which contains public nodes.

Permission-less blockchain supports high scalability compared to permissioned blockchain. Public

nodes can be added to improve the performance of the blockchain network. In the proposed

architecture the 1st tier will be responsible to perform all the work given. The nodes in the 1st tier

will perform the work and will send the data to 2nd tier for storage. 1st tier can only send data to

2nd tier for storage but cannot read or modify the data in the 2nd tier.

5.1.1. Voting based consensus Algorithm (VBCA):

Consensus algorithm is the backbone of the blockchain. The proposed consensus algorithm for 1st

tier permission-less blockchain is a voting-based algorithm which includes voting a node to

become a delegator which will control the consensus in the network without any problem. The

proposed algorithm works in steps:

• The nodes with better relations with other nodes are selected as candidates.

• Voting is done by the non-candidate nodes, the candidate node with the most nodes is

selected as the leader/delegator.

• The remaining candidate nodes and all non-candidate nodes become follower nodes.

• The follower nodes send their specifications (ram, processing power etc.) in the form of

datasets to the delegator.

• The delegator node is only responsible to provide consensus among the nodes by providing

them work to perform according to datasets and to update the datasets after fixed time.

• Delegator stores the datasets and provides each node with work according to their datasets

by sending value, once the follower acknowledges the value the follower node receives the

work and consensus is achieved.

• The datasets are updated after fixed time, delegator sends request to follower nodes to

update the datasets. If the dataset contains unusual change compared to the previous dataset

then the delegator flags that follower node as malicious node. As a result, all the progress

of the malicious node is confiscated and is flagged.

Figure 5: Proposed voting based algorithm which detected a malicious node.

This consensus algorithm will help in improve the processing time of the network as the delegator

is responsible for the consensus, saving time and energy of other nodes by not involving in the

consensus algorithm. The algorithm will also enhance security and the delegator keeps an eye on

the nodes through their datasets. Unlike PoW, this algorithm punishes the malicious nodes by

taking over their progress and flagging them. Proof-of-Work algorithm is the most used consensus

procedure, but it does not include any process of punishing the malicious nodes.

5.2. 2nd-Tier of the architecture:

2nd tier of the architecture is based on permissioned blockchain. Unlike 1st tier, this tier is private

and contains private nodes. The distributed ledger is stored in the 2nd tier. This tier gets the data

from the 1st tier for storage, only the nodes in this part of the architecture are able to read or modify

the ledger or data stored, whereas the nodes in the 1st tier cannot due to enhanced privacy. Since

this network is also blockchain, it will require consensus algorithm in order to work, which will

be practical Byzantine Fault Tolerant algorithm.

5.2.1. Practical Byzantine Fault Tolarent Consensus Algorithm:

PBFT is a variant of Byzantine Fault Tolerant algorithm which was designed to cover the

limitations of the BFT. BFT specially PBFT provides consensus among the nodes even if some of

the nodes are faulty or respond with faulty data. PBFT works in five phases which are request, pre-

prepare, prepare, commit and reply. PBFT achieves this with following steps.

• A primary node is chosen, other nodes become secondary.

• Primary node receives the request message. Which is the first phase.

• Primary node checks the validity of the request message by verifying its digital signature,

during the pre-prepare phase.Once the validity of the request message is approved, primary

nodes multicasts the message to the secondary node.

• In prepare phase, secondary nodes receive the message again check digital signature and

communicate with eachother to compare the results. Once at least two-third nodes of the

network should be able to perform work. Threshold of maximum one-third of nodes can

fail.

• Once verified, secondary nodes commit to the message, consensus is achieved and nodes

perform the work.

• Once the consensus is achieved and work performed, nodes sends reply in reply phase.

Figure 6: Phases of the PBFT where one secondary node failed (Panda, et al., 2019).

PBFT defines a tolerant threshold in order to gain consensus by the feature of replication. Even if

there are faulty or malicious nodes in the network the honest nodes will be able to perform the

required task until they are in majority. This property will allow the permissioned blockchain

network to perform work even if it has a few problems thus increasing availability and reliability.

6. Advantages of the proposed 2-tier architecture: 6.1. Enhanced security and privacy:

Delegator/leader in the 1st tier architecture will be able to flag the malicious nodes in the network

by looking for the unusual changes in their datasets. PBFT in 2nd tier will provide consensus even

if there are faulty or malicious nodes in the network. Public nodes in 1st tier cannot read or modify

data/ledger which is stored in the 2nd tier due to one way communication from 1st tier to 2nd tier.

6.2. Scalability:

1st tier which is public is highly scalabale, 2nd tier is scalabale to an extent.

6.3. Reliability:

PBFT in 2nd tier works even if there are faulty or malicious nodes in the network which have to

be equal or less than one-third in number of nodes in the network.

7. Results: The discussion on the result will be based on the discussion on the Table 1 which is the summary

table of all the papers chosen and comparing with the proposed architecture.

7.1. Modes:

Modes highlighted in the Table 1 are Permission-less and Permissioned modes of the blockchain.

Permission-less is the public blockchain while Permissioned is the private blockchain. These two

modes are also included in the proposed architecture, in which the 1st tier is the Permission-less

mode while 2nd tier is the Permissioned mode of the blockchain.

7.2. Platform:

The identified platforms in the Table 1 are Bitcoin, Ethereum and Ripple which are the

Permission-less (public) platforms while Hyperledger is the Permissioned (Private) platform.

7.3. Consensus Algorithms:

The algorithms in the Table 1 for Permission-less are Proof-based (PoW, PoS, PoX), while

algorithms for Permissioned blockchain pointed in the Table 1 are (BFT and its varients, SCP,

Paxos and Raft). These shows that the voting based algorithms are best for fast and reliable

consensus which proves the performance of the newly proposed voting based algorithm in the 1st

tier of the proposed architecture.

7.4. Throughput:

The algorithms which are highly scalable like Proof-based (PoW,PoS and PoX) have less

throughput speed. Whereas, the algorithms which support limited scalability like (BFT and

varients, Raft, Paxos ) have very high throughput speeds. This shows that the Practial Byzantine

Fault Tolarent Algorithm in the 2nd tier have high throughput speeds.

7.5. Energy Use:

Proof based algorithms uses high amount of energy and computation power compared to the

Voting based and BFT and its varient algorithms and it can be seen in Table 1.

7.6. Scalability:

Algorithms with high throughput speeds like Byzantine Fault Tolerant and its varients, SCP, Paxos

and Raft are very limited in scalability whereas in Permission-less the proof-based algorithms are

highly scalable. In the proposed architecture the 1st tier is more scalable as compared to the 2nd

tier.

7.7. Transaction:

In the Table 1 a trend can be seen that the mode of blockchain which is highly scalable has slow

transaction speeds. In the proposed architecture the transcation throughput is scalable because of

the algorithms implemented.

7.8. Nodes:

Table 1 shows that not all nodes in Permissioned blockchain are involved in consensus, whereas

in voting based algorithms the leader node manages consensus. Whereas, in Permission-less

blockhain all the nodes receive same consensus priority.

7.9. Technology used:

In some papers chosen, it is pointed out that Permissioned blockchain can use sharding algorithms

to perform complex tasks in less time, and it can be used for asset management in financial

instititions. The proposed architecture supports such protocols.

8. Discussion: Even though it is pointed out that Permission-less blockchain mainly uses proof-based consensus

algorithms, it also supports voting based consensus algorithms. In some cases, the voting based

algorithms have more performance than the typical proof-based algorithms. The discussion in

result shows that even if proof-based algorithms are more scalable, but have less throughput speeds

compared to other algorithms. On the other hand, the voting based algorithms have higher

throughput speed and also support high scalability which is comparable to proof-based algorithms.

Byzantine Fault Tolerant algorithms use moderate amount of energy, it lies in between the proof-

based algorithms and voting based algorithms, hence BFT and its varients are suitable for most

Permissioned blockchain use cases with an added bonus of improving the reliability of the network

as BFT and its varients provide consensus even if equal or less than one-third of the nodes in the

networks have failed or are malicious.

9. Future Direction: The proposed 2-tier architecture enhances the performance overall due to its unique nature, but

there are some key areas which can be improved and can be focused in the future. The key areas

which can be focused are:

Support for constraint devices in 1st tier: Since the 1st tier in the proposed architecture is

public, public nodes can be added which will send their specifications like ram and processing

power as datasets to the leader node in the network. Improvement is required so that constraint

devices with limited resources can be added in the 1st tier and can be better utilized.

Communication between the two tiers: The communication between the 1st and 2nd tier

can be made reliable, and according to observations LoRa (Long Range) gateway can also be used

for the purpose. Research on the aspect of improving communication between two blockchain

networks using LoRa gateway can be done.

Proposed architecture for IOT: The proposed architecture can be implemented in the field

of IOT. For example, the IOT devices like security cameras can be added in the 1st Permission-

less tier which is public. The recordings of the cameras go to 2nd Permissioned tier which exists

inside the company which sells the cameras for storage. This will enhance the security and improve

the privacy of the customers.

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