BlockchainBasics :

Certificate

Course

This repo. contains my assignment and notes of the Blockchain Basics course offered by Buffalo University on Coursera.

Core topics :

Blockhain - for decentralised, peer to peer connection

Developing Trust:

• Validation
• Verification
• Consensus Protocol
• Immutable Recording

use of immutable distributed ledger

Unspent Transaction Output (UTXO)

• Unique Identifier
• index
• amt
• optional : condition

Transaction (Tx)

• Refernce no. to the current transaction
• Reference to one or more input UTXOs
• Reference to one or more output UTXOs (newly generated by the current transaction)
• Total input and output

Genesis Block (Block0) :

The zeroth or first block of the block chain

Summary

• No. of transactions
• Output total
• Estimated Transaction
• Transaction fees
• Height
• Time stamp
• Received Time
• Relayed by
• Difficulty
• Bits
• Size
• Weight
• Version
• Nonce
• Block Reward

Hash

• Previous Block
• Next Block
• Merkle Root

Work of miners

• verify transactions
• Broadcast transactions
• compete to create a block
• Reacg consensus by validating blocks
• Broadcast new bolck
• confirm transactions

Miners perform operations designed by bolckchain proetocal

Transaction 0

• for paying minor fees
• does not have an input UTXO
• is called coin based transaction

Smart Contract

Ethereum bolckchain used the optional scripting feature to develop a full blown code execution framework called smart contract

Execution of smart contract is initiated by a message embedded in the tracnsaction

Types of Blockchain

• only cryptocurrency - Bitcoin
• currency + Bussiness logic - Etherium
• Only Bussiness logic - Linux foundation's Hyperledger

Categories:

• Public
• Private
• Permissioned / consortium

Solidity for Smart Contract

Basic Syntax

pragma solidity ^0.40; contract SimpleStorage { uint storedData; function set (uint x){ storedData =x; }

function get() constant returns (uint){ return storedData; } }

The code is rum in EVM or ethereum virtual machine

Reference no.

input UTXOs --> output UTXOs

TYpes of Accounts

• Externaly owned acc
• Contract Acc

Externally owned acc can transfer ethers or messages

Contract accs are used to hold ethres while acting as an intermediary.

Eg - Caution money will be stored in the contract acc and transferred in the respective acc as per the situations and norms.

Accounts need to pay fees for transaction.

These are paid in wei, a lower denominationof ether.

1 ether = 10^18 wei

Transaction involves :

• Signature of sneder authorizing transfer
• Amount of wei
• Message to a contract
• Start gas (max no. of steps)
• gas price (fee for computation)

Header --> Transactions --> Runneruo headers

Ethereum Node

An ethereum node is a computational system representing a business entity or an individual participant.

An ethereum full node hosts the software needed for transaction initiation, validation, mining, block creation, smart contract evaluation and EVM.

A blockchain maintains both a state hash and a receipt hash

Incentive Model

Gas limit

Amount of gas available

Gas spent

Amount of gas spent on block creation

Proof of work puzzle winner gets the transaction amount, others who solve it are know as Ommers who get a small bit of it.

Securing Block chain - Verification and Validation

Hashing and assymetric key encryption

Public key cryptography algorithm

Caesar Algo.

encryption is done by shifting the alphabets by a particular distance.

issue - requires transfer of key and is easy to get and hence more prone to hacking

public key cryptography with two keys are used.

A tracnsaction or a contract locked by one's private key can be opened by a public key only and vice versa.

sender locks it with his private key and receiver's public key while the receiver unlocks it with his private key and sender's public key.

Algorithm used for genrating key pair

ECC - Elliptic Curve Cryptography

whereas RSA (Rivet-Shamir-Adelman) is used in various other applications such as amazon cloud.

Hashing

transforms an arbitrary length input data to a unique fixed length value (256 bits)

Algorithm is a one way function and hence collision free

secure hash agorithm which has 2^256 possible combinations.

Hashing is used to generate

• Account Address
• Digital Signatures
• Transition hash
• State Hash
• Receipt hash
• Block header hash

Smart Contracts