EVM Smart ContractsVerified Reference • August 2026
ERC-20 Token Standard Architecture
ERC-20 is the official technical standard used for implementing fungible token smart contracts on Ethereum and EVM-compatible blockchains.
Core Architectural Highlights:
Defines 6 mandatory functions: totalSupply, balanceOf, transfer, transferFrom, approve, allowance.
Defines 2 mandatory events: Transfer(address,address,uint256) and Approval(address,address,uint256).
Tether USDT uses 6 decimals of precision, unlike the 18-decimal default for Ether.
1. Standard Interface & Function Selectors
EVM smart contracts identify functions using 4-byte Keccak-256 function selectors. The transfer(address,uint256) function produces the signature 0xa9059cbb.
// Essential ERC-20 Interface (Solidity 0.8+)
interface IERC20 {
function totalSupply() external view returns (uint256);
function balanceOf(address account) external view returns (uint256);
function transfer(address recipient, uint256 amount) external returns (bool);
function allowance(address owner, address spender) external view returns (uint256);
function approve(address spender, uint256 amount) external returns (bool);
function transferFrom(address sender, address recipient, uint256 amount) external returns (bool);
}2. Allowance & Approval Risk Models
When interacting with decentralized applications, users call approve() to grant smart contracts permission to spend tokens via transferFrom(). Unlimited approvals (MaxUint256) create vulnerability vectors if the spender contract is exploited.