Slide 1: Introduction

R3zk0n · October 2, 2025

API   Cloud   Evasion   Exploitation   Network   Security
Contents
    • Title: Solidity Contracts and Blockchain Vulnerabilities
    • Overview:
      • Understanding blockchain, cryptocurrency, and smart contracts.
      • Exploring Solidity and common vulnerabilities in smart contracts.
      • Practical setup and examples.

    Slide 2: Agenda

    • What is Blockchain?
    • What is Cryptocurrency?
    • What are Smart Contracts?
    • What is Solidity?
    • Setting up DefiLabs
    • Reentrancy Attacks

    Slide 3: What is Blockchain?

    • Definition and Basic Concepts
      • A blockchain is a decentralized, distributed ledger technology.
      • It records transactions in a secure, verifiable, and immutable manner.
    • Decentralization and Distributed Ledgers
      • No central authority; consensus is maintained across a network of nodes.
      • Each node has a copy of the entire ledger, ensuring transparency and security.

    Slide 4: What is Cryptocurrency?

    • Definition and Examples
      • Cryptocurrencies are digital or virtual currencies that use cryptography for security.
      • Examples: Bitcoin (BTC), Ethereum (ETH).
    • How Cryptocurrencies Use Blockchain Technology
      • Transactions are recorded on a blockchain to ensure transparency and security.
      • Decentralized nature eliminates the need for intermediaries.

    Slide 5: What are Smart Contracts?

    • Definition and Purpose
      • Smart contracts are self-executing contracts with the terms directly written into code.
      • They automatically enforce and execute contract terms.
    • Automation and Trustless Transactions
      • Eliminate the need for intermediaries by automating contract execution.
      • Provide trustless transactions, reducing the risk of fraud.

    Slide 6: What is Solidity?

    • Brief Introduction to Solidity Programming Language
      • Solidity is a high-level programming language designed for writing smart contracts on Ethereum.
      • Syntax similar to JavaScript, designed to run on the Ethereum Virtual Machine (EVM).
    • Role of Solidity in Developing Smart Contracts on Ethereum
      • Enables developers to create and deploy decentralized applications (dApps).
      • Facilitates the implementation of complex logic and automated processes.
    • Ethereum Virtual Machine (EVM)
      • The EVM is the runtime environment for smart contracts in Ethereum.
      • Ensures that code executes exactly as intended.

    Slide 7: Setting up DefiLabs

    • Foundry
      • Install from: Foundry GitHub
      • Foundry is a fast, portable and modular toolkit for Ethereum application development.
    • Truffle + Ganache-CLI
      • Truffle: A development framework for Ethereum.
      • Ganache-CLI: A personal blockchain for Ethereum development.
    • Remix IDE
      • Online editor for writing, compiling, and deploying smart contracts.
      • Accessible at: Remix IDE

    Slide 8: Reentrancy Attacks

    • Explanation of Reentrancy
      • A reentrancy attack occurs when a contract repeatedly calls back into itself before the initial execution is complete.
      • The call function sends Ether to msg.sender before updating the balance.
      • If msg.sender is a contract, it can exploit this by re-entering the contract in a fallback function.
    • Example and Impact
      • Example: A malicious contract withdraws funds multiple times in one transaction.
      • Impact: Drains the contract’s balance, leading to significant financial loss.
    • Pragma 0.8.0 and Later
      • Solidity versions 0.8.0 and later include built-in checks for arithmetic underflow and overflow.
      • These checks prevent the reentrancy attack by causing the transaction to revert if an underflow/overflow is detected.

    Slide 9: Overflow Attacks

    • Explanation of Overflow Attacks
      • An overflow attack occurs when an arithmetic operation exceeds the maximum limit of the data type.
      • This causes the value to wrap around to a much lower value, allowing manipulation.
    • Example and Impact
      • Example: Increasing a lock time value beyond its maximum causes it to wrap around to a low value.
      • Impact: Allows an attacker to bypass time-based restrictions.
    • Solidity 0.8.0 and Later
      • Solidity versions 0.8.0 and later include built-in checks for overflow and underflow.
      • Disabling these checks using unchecked can reintroduce the vulnerability for demonstration purposes.

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