About Me!

Blockchain | System and Operations | AI

• Software Developer with 7+ Years of Experience
• Blockchain, AI & Programming
• Studying AI at Kathmandu University
• Ruby, Python, JavaScript, Go, Solidity

Things we will cover today

• Blockchain Basics
• Bitcoin and Ethereum Overview
• Smart Contracts and EVM
• Wallets and Transactions

Before Bitcoin! The Trust Problem

• Online transactions rely on middlemen (banks, companies)
• Central points can be hacked, corrupted, censored
• "What happens if your bank decides to freeze your account?"
• "Can you send money to someone in another country without a bank?"

@neymarsabin

Then Came Bitcoin, 2008...

• Niche, Geeky idea in 2008
• Cryptocurrency that solved the double spending problem
• Peer-to-Peer electronic cash system
• Super Secure, Decentralized, and Transparent
• Whitepaper: Bitcoin: A Peer-to-Peer Electronic Cash System by Satoshi Nakamoto
• Genesis Block: January 3, 2009 - first block mined by Satoshi

10,000 BTC for 2 Pizzas, 2010

@neymarsabin

Vitalik Buterin and Ethereum, 2013

• Launched Ethereum in 2015
• Turning the blockchain into a global World Computer
• Major flood of Smart Contracts, DeFi, NFTs, MetaVerse etc.

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Why Blockchain?

• Decentralization: No single point of control or failure
• Transparency: All transactions are visible to everyone
• Security: Cryptographic techniques ensure data integrity
• Immutability: Once data is added, it cannot be changed or deleted
• Trustless: No need to trust a third party; trust the code and math
• Permissionless: Anyone can join and participate in the network

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Blocks-Chain

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Consensus Mechanisms

• Proof of Work (PoW) -> miners solve complex puzzles to validate transactions (Bitcoin, Ethereum (pre-Merge))
• Proof of Stake (PoS) -> validators stake tokens to propose and validate blocks (Ethereum (post-Merge), Cardano)
• Proof of Authority (PoA) -> trusted validators validate transactions (VeChain, POA Network)
• Others -> Proof of History (Solana)

Proof of Work(PoW)

• A consensus mechanism where a random node (miner) creates the next block solving a computational puzzle

H( No \\ p_hash || T1 || T2 || ... || Tn ) < Target

• No = nonce (a random value that miners change to find a valid hash) with brute force method
• p_hash = previous block's hash
• Tx = transactions in the block
• Target = a value that the hash must be less than to be considered valid

Anatomy of a Block

Then, What is Blockchain?

@neymarsabin

Where is Blockchain used?

• Supply Chain Transparency -> track products from origin to consumers
• Digital Identity -> secure, verifiable IDs for individuals without centralized databases
• HealthCare Records -> Share patient data across hospitals
• Cross-Border Payments -> Fast, low-fee cross border payments
• Intellectual Property and Royalities, Energy Trading

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Blockchain Networks

• Each Chain = a different universe with its own rules
• Think like linux distros, but for blockchains
• Think like different countries with their own laws and currencies

Popular chains: Ethereum, Polygon, BSC, Solana, Avalanche

Some popular public blockchains

• Bitcoin, Ethereum -> Blockchain OGs
• BSC, Fantom -> EVM-compatible chains with low fees
• Polygon -> Layer 2 scaling solution for Ethereum
• Solana -> High-speed blockchain for decentralized applications
• Avalanche -> Highly scalable and customizable blockchain platform
• Cosmos, Polkadot, Near -> Interoperable blockchains ecosystem
• Arbitrum, Optimism -> Layer 2 rollups for Ethereum scaling

Popular Blockchains

Accounts and Wallets

has a unique public address, derived from a public key, which can be shared with others to receive funds, similar to a bank account number.

• Account -> Send and receive transactions on the blockchain
• Wallet -> Tool that manages your private and public keys
• Hold Keys -> Control over your crypto assets by holding private keys
• Address -> Public identifier for sending/receiving funds, derived from public key

Public/Private Keys & Hash Functions

• Unique fingerprints of data, called hashes
• Minor changes in input produce vastly different outputs (Avalanche effect)
• Ideally changing one input bit should flip ~50% of output bits
• Bitcoin uses SHA-256, Ethereum uses Keccak-256

openssl genpkey -algorithm RSA -out private_key.pem -pkeyopt rsa_keygen_bits:2048
openssl rsa -pubout -in private_key.pem -out public_key.pem
openssl rsa -text -in private_key.pem

How Wallet Address is Generated?

• A bitcoin address is created by hashing public key using SHA-256 and then RIPEMD-160
• Ethereum address is created by taking the last 20 bytes of the Keccak-256 hash of the public key

address = RIPEMD160(SHA256(public_key))  # Bitcoin
address = last_20_bytes(Keccak256(public_key))  # Ethereum

• Bitcoin address: 1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa
• Ethereum address: 0x742d35Cc6634C0532925a3b844Bc454e4438f44e

What's a MetaMask?

• browser extension and mobile app that serves as a wallet and gateway to blockchain apps
• Install Metamask from -> metamask.io
• Supports Ethereum and other EVM-compatible blockchains
• Allows users to manage their accounts, sign transactions and interact with dApps

MetaMask Workflow

Transactions

• A transaction is a signed instruction sent from one account to another.
• It tells the Ethereum network to do something — transfer ETH, deploy a contract, or call a function.
• changes the blockchain's state.

Transaction Flow

{
  "jsonrpc": "2.0",
  "method": "eth_sendTransaction",
  "params": [
    {
      "from": "0x5ac5b8D9Efb99b49176eBfcB1A78f8F85FcB0967",
      "to": "0xFb30D953a3fE1298df870C390Cf75A506091C607",
      "gas": "0x5208" (21000 in decimal),
      "gasPrice": "0x9502f900" (25000000000 wei in decimal),
      "value": "0xde0b6b3a7640000" (1 ETH in wei in decimal),
      "nonce": "0x1" (1 in decimal)
    }
  ],
  "id": 1
}

Etherscan Tx Details

{
"lock_time":0,
"size":226,
"inputs":[
  {
    "prev_out":{
      "index":139,
      "hash":"40120e43f00ff96e098a9173f14f1371655b3478bc0a558d6dc17a4ab176387d"
    },
    "script":"483045022100de6fd8120d9f142a82d5da9389e271caa3a757b01757c8e4fa7afbf92e74257c02202a78d4fbd52ae9f3a0083760d76f84643cf8ab80f5
  }
],
"version":1,
"vin_sz":1,
"hash":"d28ca5a59b2239864eac1c96d3fd1c23b747f0ded8f5af0161bae8a616b56a1d",
"vout_sz":2,
"out":[
    {
      "script_string":"OP_DUP OP_HASH160 c568ffeb46c6a9362e44a5a49deaa6eab05a619a OP_EQUALVERIFY OP_CHECKSIG",
      "address":"1JzouJCVmMQBmTcd8K4Y5BP36gEFNn1ZJ3",
      "value":33324,
      "script":"76a914c568ffeb46c6a9362e44a5a49deaa6eab05a619a88ac"
      255
    },
    {
      "script_string":"OP_DUP OP_HASH160 9386c8c880488e80a6ce8f186f788f3585f74aee OP_EQUALVERIFY OP_CHECKSIG",
      "address":"1ET3oBGf8JpunjytE7owyVtmBjmvcDycQe",
      "value":93376,
      "script":"76a9149386c8c880488e80a6ce8f186f788f3585f74aee88ac"
    }
  ]
}

Explore Here: blockchain explorer

Transaction Fees = Instructions Runtime Measurement

• Gas = unit measuring computational work in Ethereum
• Every operation costs gas — prevents infinite loops and spam.
• Gas price × Gas used = Transaction fee
• Unused gas is refunded; out-of-gas halts execution.
• All nodes simulate the same contract execution → ensures consensus and security.

EVM Opcodes with Gas Costs

learn more about opcodes here: https://ethereum.org/developers/docs/evm/opcodes/

What is a Smart Contract?

• A program stored on the blockchain
• Executes automatically when conditions are met
• Cannot be changed once deployed
• Lives forever… even if you regret writing it!!

Think of it as:

• A vending machine
  → You put coins, it gives you snacks.
  → No cashier, no trust issues.

Understanding EVM! -> Heart of Ethereum

• EVM = Ethereum Virtual Machine, runtime environment for smart contracts.
• Global decentralized computer, every node executes the same code to ensure consensus.
• Executes bytecode compiled from high-level languages (e.g., Solidity, Vyper).
• Deterministic → same input, same output on every node.
• Each opcode consumes gas (computational cost).

Anatomy of a Smart Contract

• State Variables, Functions → rules of interaction
• Events → logs that tell the outside world what happened
• Modifiers → extra checks on functions (like “onlyOwner”)

uint public count;
function increment() public onlyOwner {
    count++;
}

modifier onlyOwner() {
    require(msg.sender == owner, "Not owner");
    _;
}

What are ERC20 Tokens?

• ERC-20: The Standard for Fungible Tokens
• ERC-20 is a smart contract standard for creating fungible tokens on Ethereum.
• Defines how tokens behave and interact with wallets, exchanges, and other contracts.
• “Fungible” = every token unit is identical (like ETH or USD).
• Used for stablecoins, governance tokens, utility tokens, etc.

ERC20 standard: https://eips.ethereum.org/EIPS/eip-20

How do ERC20 Tokens Work?

• smart contract storing a mapping of balances.
• When you transfer tokens, it updates the balances in the contract - no phyiscal tokens move.
• Tokens live as numbers in contract storage, not as separate assets.
• Compatible with any wallet of dApp that follows the ERC-20 standard.

USDC token: Etherscan USDC

Web3 Application

Applications: Payments

• Stablecoin (USDC/USDT): fast, global, low-cost settlement
• Cross-border transfers: no banks, no friction
• Micropayments: pay-per-use APIs, streaming payments
• Merchant adoption: crypto checkout (Stripe, Coinbase Commerce)
• Programmable payments: automated subscriptions & escrow logic

Applications: Rewards, Utility

• Rewards & Incentives: staking yields, loyalty points, on-chain badges
• Utility Tokens: access to features, governance, voting power
• Brand adoption: ticketing, memberships, digital merch
• Interoperability: assets usable across many apps/games

Applications: NFTs and Digital Collectibles

• NFTs
• Collectibles
• Digital Art
• In-Game Assets
• Royalities
• Metaverse Land
• Domain Names

Applications: DAOs and Governance

• Taxation
• Voting Systems
• Decentralized Organizations
• Digitized Ids
• On-chain Governance
• Welfare Distribution

Future of Blockchain

• Scalability -> multiple Layer 2 solutions (rollups, sidechains)
• Interoperability -> cross-chain bridges and protocols, e.g., Polkadot, Cosmos
• Privacy -> zero-knowledge proofs, confidential transactions, e.g. Zcash, Tornado Cash
• Sustainability -> energy-efficient consensus mechanisms, e.g., Proof of Stake

Recap

• Blockchain, Bitcoin, Ethereum
• Smart Contracts = self-executing code on blockchain
• Wallets = manage keys and interact with blockchain
• Web3 = decentralized apps powered by blockchain
• Future = scalability, interoperability, privacy, sustainability

Thank You!

• Slides available at: https://everestwalk.neymarsabin.dev/slide
• telegram: https://telegram.me/neymarsabin

Tools to get started!!!

• Remix IDE -> remix.ethereum.org
• Hardhat -> Ethereum DE -> hardhat.org
• Foundry -> Ethereum Framework -> foundry.paradigm.xyz
• Slither -> Solidity static analysis tool -> github.com/crytic/slither
• Truffle Site -> trufflesuite.com
• OpenZeppelin -> Smart contract library -> openzeppelin.com
• Consensys -> Developer ecosystem -> consensys.net
• Tenderly -> Smart contract monitoring -> tenderly.co

Resources

• Bitcoin Whitepaper
• Ethereum Whitepaper
• Solidity Documentation
• Crypto Zombies
• Wagmi
• https://101blockchains.com/ebooks/
• https://www.coindesk.com/consensus-magazine