This document provides an overview of blockchain and Ethereum. It defines blockchain as a decentralized, distributed database or ledger of records that maintains information in immutable blocks. Each block contains a collection of transactions and points to the previous block. Blockchain applications include cryptocurrencies, smart contracts, supply chain management, and more. The document then discusses Ethereum, describing its peer-to-peer network and how transactions are executed and added to the blockchain via miners and validators. It provides details on Ethereum smart contracts and includes an example ballot smart contract written in Solidity to illustrate how voting would work.

1. Blockchain
Presented by:
Sathya Peri
Associate Professor
CSE Department,
Indian Institute of Technology
Hyderabad, India
1 of 39

2. Outline of the Talk
Introduction to Blockchain
Ethereum
Hands-on Ethereum
2 of 39

3. Introduction
• Blockchain
2 of 39

4. Introduction
Why Blockchain?
Centralized vs Distributed Platformsa
• Centralized Platforms:
◦ Information going through
a single point.
◦ Lack of transparency.
◦ Needs to pay transaction fees.
• Blockchain Technology:
◦ Decentralized Distributed System.
◦ No centralized control.
◦ Stores information on
a peer-to-peer network.
Clearing
House
Centralized Ledger
Distributed Ledger
a
Source: https://www.rathbones.com/knowledge-and-insight/blockchain-internet-value
3 of 39

5. Introduction
Blockchain
• Blockchain is a decentralized, distributed database or ledger of
records.
b
https://bitcoin.org/en/
c
https://www.ethereum.org/
d
https://www.hyperledger.org/
4 of 39

6. Introduction
Blockchain
• Blockchain is a decentralized, distributed database or ledger of
records.
• It maintains information in the form of blocks.
b
https://bitcoin.org/en/
c
https://www.ethereum.org/
d
https://www.hyperledger.org/
4 of 39

7. Introduction
Blockchain
• Blockchain is a decentralized, distributed database or ledger of
records.
• It maintains information in the form of blocks.
• Each block is a collection of transactions and has a pointer to its
previous block.
b
https://bitcoin.org/en/
c
https://www.ethereum.org/
d
https://www.hyperledger.org/
4 of 39

8. Introduction
Blockchain
• Blockchain is a decentralized, distributed database or ledger of
records.
• It maintains information in the form of blocks.
• Each block is a collection of transactions and has a pointer to its
previous block.
• By design these blocks are immutable but publicly readable.
b
https://bitcoin.org/en/
c
https://www.ethereum.org/
d
https://www.hyperledger.org/
4 of 39

9. Introduction
Blockchain
• Blockchain is a decentralized, distributed database or ledger of
records.
• It maintains information in the form of blocks.
• Each block is a collection of transactions and has a pointer to its
previous block.
• By design these blocks are immutable but publicly readable.
• Example: Bitcoinb, Ethereumc, and Hyperledgerd etc.
b
https://bitcoin.org/en/
c
https://www.ethereum.org/
d
https://www.hyperledger.org/
4 of 39

10. Introduction
Transaction Flow in Blockchain
A wants to
send money
to B.
A
The transaction is
broadcasted to every
peer in the network.
21
? ?
?
??
?
3
Miners execute the
transactions and
form a block. Then
block is
broadcasted to
every peer in the
network.
4
Validator validate
the transactions in
the block.
The block then can be added
to the chain, which provides
an indelible and transparent
record of transactions.
5
The money moves
from A to B.
B
6
Figure: High-level Overview of Transaction Flow in Blockchain
5 of 39

11. Introduction
Blockchain Applications
Figure: Blockchain applicationse
e
https://medium.com/practical-blockchain/use-cases-of-blockchain-tech-application-13a940edf6fb
6 of 39

12. Introduction
Blockchain Classification
Three Different types of Blockchain depending on their applications.
• Public Blockchain
• Private Blockchain
7 of 39

13. Introduction
Blockchain Classification
Three Different types of Blockchain depending on their applications.
• Public Blockchain
• Private Blockchain
Properties Public Private
Consensus
Participants
All nodes (permission less) Organization (permissioned node)
Access
Permission
Public Restricted
Efficiency Low High
Data
Security
Very High Data Breach Possible
Example Bitcoin, Ethereum Hyperledger Fabric
7 of 39

14. Ethereum
7 of 39

15. Ethereum
High Level Design
• Ethereum nodes form a peer-to-peer system.
8 of 39

16. Ethereum
High Level Design
• Ethereum nodes form a peer-to-peer system.
• Clients (external to the system) wishing to execute smart
contracts, contact a peer of the system.
8 of 39

17. Ethereum
High Level Design
• Ethereum nodes form a peer-to-peer system.
• Clients (external to the system) wishing to execute smart
contracts, contact a peer of the system.
Peer1
Peer2
Peer3
Peer4
Client1
Client2
Client3
T1
T2
T3
B1 B2 B3
B1 B2 B3
B1 B2 B3
B1 B2 B3
Figure: Clients send Transaction T1, T2 and T3 to Miner (Peer4)
8 of 39

18. Ethereum
High Level Design
Peer4 T1 T2 T3 FS
Hash of the
Previous
Block
B1 B2 B3 B4
Figure: Miner forms a block B4 and compute final state (FS)
8 of 39

19. Ethereum
High Level Design
Peer1
Peer2
Peer3
Peer4
B1 B2 B3
B1 B2 B3
B1 B2 B3
B1 B2 B3 B4
B4
B4B4
Figure: Miner broadcasts the block B4
8 of 39

20. Ethereum
High Level Design
Peer1
Peer2
Peer3
B1 B2 B3
B1 B2 B3
B1 B2 B3
B4
B4
B4
T1 T2 T3 FS
Hash of the
Previous
Block
T1 T2 T3 FS
Hash of the
Previous
Block
T1 T2 T3 FS
Hash of the
Previous
Block
Compute CS
Compute CS Compute CS
Figure: Validators (Peer 1, 2 and 3) compute current state (CS)
8 of 39

21. Ethereum
High Level Design
Peer1
Peer2
Peer3
B1 B2 B3
B1 B2 B3
B1 B2 B3
B4
B4
B4
T1 T2 T3 FS
Hash of the
Previous
Block
T1 T2 T3 FS
Hash of the
Previous
Block
T1 T2 T3 FS
Hash of the
Previous
Block
CS = FS
Reject Block B4
No Yes Agree on
Block B4
CS = FS
Reject Block B4
No Agree on
Block B4
Yes
CS = FS
Agree on
Block B4
No
Reject Block B4
Yes
Figure: Validators verify the FS and reach the consensus protocol (PoW)
8 of 39

22. Ethereum
High Level Design
Peer1
Peer2
Peer3
Peer4
B1 B2 B3
B1 B2 B3
B1 B2 B3
B1 B2 B3 B4
B4
B4
B4
Figure: Block B4 successfully added to the blockchain
8 of 39

23. Ethereum
Smart Contracts
• Modern Blockchain systems interpose an additional software layer
between clients and the blockchain.
9 of 39

24. Ethereum
Smart Contracts
• Modern Blockchain systems interpose an additional software layer
between clients and the blockchain.
• Client requests are directed to scripts, called smart contracts.
Examples: Ballot, Coin, Simple Auction etc.
9 of 39

25. Ethereum
Smart Contracts
• Modern Blockchain systems interpose an additional software layer
between clients and the blockchain.
• Client requests are directed to scripts, called smart contracts.
Examples: Ballot, Coin, Simple Auction etc.
• Smart contracts are similar to a legal contract in which terms are
recorded in a legal language.
9 of 39

26. Ethereum
Smart Contracts
• Modern Blockchain systems interpose an additional software layer
between clients and the blockchain.
• Client requests are directed to scripts, called smart contracts.
Examples: Ballot, Coin, Simple Auction etc.
• Smart contracts are similar to a legal contract in which terms are
recorded in a legal language.
• Advantages:
1. No need for a trusted third party
to validate the contract.
2. Low contracting enforcement.
3. Compliance costs.
9 of 39

27. Ethereum
Ballot Smart Contract
Initializes
contract
with a list
of
proposals
Create
Contract
Deploy
struct Proposal {
bytes32 name;
uint voteCount
};
struct Voter {
uint weight;
bool voted;
address delegate;
uint vote;
};
Proposal[ ] public proposals;
mapping(address=>Voter) public voters;
constructor ( proposalNames [ ]) { }
function giveRightToVote ( address voter ) { }
function delegate ( address to ) { }
function vote (uint proposal) { }
function winningProposal ( uint winningProposal ) { }
function winnerName (bytes32 winnerName) { }
State
Methods
vote (proposal Id)
or
delegate (address to)
throw
Voter.votedTrue
Increment voteCount
for proposal Id
or
add weight to
address "to"
False
Chairperson Voter
Figure: Execution of Ballot Smart Contract
10 of 39

28. Ethereum Ballot Smart Contract
1 pragma solidity >=0.4.22 <0.7.0;
2 contract Ballot {
3 struct Voter {
4 uint weight; //weight is accumulated by delegation
5 bool voted; //if true, that person already voted
6 address delegate; //person delegated to
7 uint vote; //index of the voted proposal
8 }
9 struct Proposal {
10 bytes32 name; // short name (up to 32 bytes)
11 uint voteCount; // number of accumulated votes
12 }
13 address public chairperson; //chairperson of ballot
14 Proposal[] public proposals; //state variable
15 mapping(address => Voter) public voters; //state variable
16 //methods
17 constructor(bytes32[] memory proposalNames) public {};
18 function giveRightToVote(address voter) public {};
19 function delegate(address to) public {};
20 function vote(uint proposal) public {};
21 function winningProposal() public view returns (uint winningProposal_){};
22 function winnerName() public view returns (bytes32 winnerName_){};
23 }
11 of 39

29. Ethereum
Ballot Smart Contract
1 constructor(bytes32[] proposalNames) public {
2 chairperson = msg.sender;
3 voters[chairperson].weight = 1;
4 for (uint i = 0; i < proposalNames.length; i++) {
5 // Proposal({..}) creates a Proposal object
6 // proposals.push(..) appends it to the end of `proposals`.
7 proposals.push(Proposal({name:proposalNames[i],voteCount:0}));
8 }
• Constructor is called only once during contract deployment.
12 of 39

30. Ethereum
Ballot Smart Contract
1 constructor(bytes32[] proposalNames) public {
2 chairperson = msg.sender;
3 voters[chairperson].weight = 1;
4 for (uint i = 0; i < proposalNames.length; i++) {
5 // Proposal({..}) creates a Proposal object
6 // proposals.push(..) appends it to the end of `proposals`.
7 proposals.push(Proposal({name:proposalNames[i],voteCount:0}));
8 }
• Constructor is called only once during contract deployment.
• Chairperson deploys the contract.
12 of 39

31. Ethereum
Ballot Smart Contract
1 constructor(bytes32[] proposalNames) public {
2 chairperson = msg.sender;
3 voters[chairperson].weight = 1;
4 for (uint i = 0; i < proposalNames.length; i++) {
5 // Proposal({..}) creates a Proposal object
6 // proposals.push(..) appends it to the end of `proposals`.
7 proposals.push(Proposal({name:proposalNames[i],voteCount:0}));
8 }
• Constructor is called only once during contract deployment.
• Chairperson deploys the contract.
• Given ‘proposalNames’ it create proposal objects and add to ‘Proposal[]’.
12 of 39

32. Ethereum
Ballot Smart Contract
1 function giveRightToVote(address voter) public {
2 require( msg.sender == chairperson,
3 "Only chairperson can give right to vote.");
4 require( !voters[voter].voted, "The voter already voted.");
5 require(voters[voter].weight == 0);
6
7 voters[voter].weight = 1;
8 }
• Chairperson gives right to voter to cast the vote on the ballot contract.
13 of 39

33. Ethereum
Ballot Smart Contract
1 function delegate(address to) public {
2 Voter storage sender = voters[msg.sender];
3 require(!sender.voted, "You already voted.");
4 require(to != msg.sender, "Self-delegation is disallowed.");
5
6 while (voters[to].delegate != address(0)) {
7 to = voters[to].delegate;
8 require(to != msg.sender, "Found loop in delegation.");
9 }
10 sender.voted = true;
11 sender.delegate = to;
12 Voter storage delegate_ = voters[to];
13 if (delegate_.voted) {
14 proposals[delegate_.vote].voteCount += sender.weight;
15 } else {
16 delegate_.weight += sender.weight;
17 }
18 }
• If the delegate already voted, directly add to voted proposal.
• If the delegate did not voted yet, add to his/her weight to respective voter.
14 of 39

34. Ethereum
Ballot Smart Contract
1 function vote(uint proposal) public {
2 Voter storage sender = voters[msg.sender];
3 require(sender.weight != 0, "Has no right to vote");
4 require(!sender.voted, "Already voted.");
5
6 sender.voted = true;
7 sender.vote = proposal;
8 proposals[proposal].voteCount += sender.weight;
9 }
• Voter casts their vote (including votes delegated to you) to proposal
‘proposals[proposal]’.
15 of 39

35. Ethereum
Ballot Smart Contract
1 function winningProposal() public view returns (uint winningProposal_){
2 uint winningVoteCount = 0;
3 for (uint p = 0; p < proposals.length; p++) {
4 if (proposals[p].voteCount > winningVoteCount) {
5 winningVoteCount = proposals[p].voteCount;
6 winningProposal_ = p;
7 }
8 }
9 }
• Computes the winning proposal while considering all votes into account.
16 of 39

36. Ethereum
Ballot Smart Contract
1 function winnerName() public view returns (bytes32 winnerName_) {
2 winnerName_ = proposals[winningProposal()].name;
3 }
• Calls winningProposal() function to get the index of the winner contained in the
proposals array.
• Returns the name of the respective winner.
17 of 39

37. Ethereum
Solidity
• High-level Object-Oriented language for smart contracts.
18 of 39

38. Ethereum
Solidity
• High-level Object-Oriented language for smart contracts.
• A Contract programming language that has similarities to
Javascript and C.
18 of 39

39. Ethereum
Solidity
• High-level Object-Oriented language for smart contracts.
• A Contract programming language that has similarities to
Javascript and C.
• Solidity is compiled to bytecode that is executable on the
Ethereum Virtual Machine (EVM).
18 of 39

40. Ethereum
Solidity
• High-level Object-Oriented language for smart contracts.
• A Contract programming language that has similarities to
Javascript and C.
• Solidity is compiled to bytecode that is executable on the
Ethereum Virtual Machine (EVM).
18 of 39

41. Ethereum
Solidity
• High-level Object-Oriented language for smart contracts.
• A Contract programming language that has similarities to
Javascript and C.
• Solidity is compiled to bytecode that is executable on the
Ethereum Virtual Machine (EVM).
Figure: Solidity Execution
18 of 39

42. Hands-on Ethereum
18 of 39

43. Hands-on
Goal of this session
How to write the smart contracts and deploy it on Ethereum
network?
19 of 39

44. Hands-on
Introduction to Remix
• Remix is IDE to create, deploy, track and test the smart contracts.
20 of 39

45. Hands-on
Introduction to Remix
• Remix is IDE to create, deploy, track and test the smart contracts.
• Remix provides three kinds of environments.
20 of 39

46. Hands-on
Introduction to Remix
• Remix is IDE to create, deploy, track and test the smart contracts.
• Remix provides three kinds of environments.
1. Javascript VM: It provides five accounts each with 100 ethers to work
with smart contracts.
20 of 39

47. Hands-on
Introduction to Remix
• Remix is IDE to create, deploy, track and test the smart contracts.
• Remix provides three kinds of environments.
1. Javascript VM: It provides five accounts each with 100 ethers to work
with smart contracts.
2. Injected Web3: It injects network from extensions like Metamask. Any
number of accounts present in Metamask included network are
provided to work with smart contracts.
20 of 39

48. Hands-on
Introduction to Remix
• Remix is IDE to create, deploy, track and test the smart contracts.
• Remix provides three kinds of environments.
1. Javascript VM: It provides five accounts each with 100 ethers to work
with smart contracts.
2. Injected Web3: It injects network from extensions like Metamask. Any
number of accounts present in Metamask included network are
provided to work with smart contracts.
3. Web3 Provider: It injects network which is running in local system.
Probably it injects local networks provided by Truffle, Ganache-cli etc.,
and whatever accounts present in local network are provided to work
with smart contracts.
20 of 39

49. Hands-on
Introduction to Remix
Figure: Remix Ethereum Browser
21 of 39

50. Hands-on
Introduction to Remix
Figure: GUI – Provides to import/create files
22 of 39

51. Hands-on
Introduction to Remix
Figure: GUI tools to import/create files
23 of 39

52. Hands-on
Introduction to Remix
Figure: IDE - provides to create/edit smart contracts
24 of 39

53. Hands-on
Introduction to Remix
Figure: Terminal – to view the transaction details
25 of 39

54. Hands-on
Introduction to Remix
Figure: Compile Tab – to compile/configure the Solidity version
26 of 39

55. Hands-on
Introduction to Remix
Figure: Run tab – to deploy and interact with contract
27 of 39

56. Hands-on
Introduction to Remix
Figure: Run tab – to deploy and interact with contract
28 of 39

57. Hands-on
Introduction to Remix
Figure: Run tab – to deploy and interact with contract
29 of 39

58. Hands-on
Metamask
• MetaMask is a bridge that allows you to visit the distributed web
of tomorrow in your browser today.
30 of 39

59. Hands-on
Metamask
• MetaMask is a bridge that allows you to visit the distributed web
of tomorrow in your browser today.
• It allows you to run Ethereum Decentralize Application right in
your browser without running a full Ethereum node.
30 of 39

60. Hands-on
Metamask
• MetaMask is a bridge that allows you to visit the distributed web
of tomorrow in your browser today.
• It allows you to run Ethereum Decentralize Application right in
your browser without running a full Ethereum node.
30 of 39

61. Hands-on
Metamask
31 of 39

62. Hands-on
Metamask
32 of 39

63. Hands-on
Metamask
33 of 39

64. Hands-on
Metamask
34 of 39

65. Hands-on
Metamask
35 of 39

66. Hands-on
Metamask
36 of 39

67. Conclusion
• Blockchain like Ethereum is a decentralized, distributed database
or ledger of records.
37 of 39

68. Conclusion
• Blockchain like Ethereum is a decentralized, distributed database
or ledger of records.
• Ethereum can make wonderful Dapps using smart contract which
can solve real life issues.
37 of 39

69. Conclusion
• Blockchain like Ethereum is a decentralized, distributed database
or ledger of records.
• Ethereum can make wonderful Dapps using smart contract which
can solve real life issues.
• Smart contracts achieve trust between peers or organizations
without the help of third party.
37 of 39

70. Conclusion
• Blockchain like Ethereum is a decentralized, distributed database
or ledger of records.
• Ethereum can make wonderful Dapps using smart contract which
can solve real life issues.
• Smart contracts achieve trust between peers or organizations
without the help of third party.
• With the help of Solidity, Remix, Metamask, Truffle and other
tools, we can build good smart contracts and Dapps.
37 of 39

71. Conclusion
• Blockchain like Ethereum is a decentralized, distributed database
or ledger of records.
• Ethereum can make wonderful Dapps using smart contract which
can solve real life issues.
• Smart contracts achieve trust between peers or organizations
without the help of third party.
• With the help of Solidity, Remix, Metamask, Truffle and other
tools, we can build good smart contracts and Dapps.
• Finally, we can achieve beyond cryptocurrencies by using Ethereum
Blockchain.
37 of 39

72. Assignment
Write your first smart contract in Solidity
Develop a Money transfer contract with following functions:
• Create 5 unique accounts.
• transferMoney(): To transfer the money from an account to
another account.
• getbalance(): To view the balance of account.
38 of 39

73. Thanks &
Questions Please!!
39 of 39