BTA CBDE flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

EOA vs contract account

An EOA is controlled by a private key, has no code, and originates transactions. A contract account has code and storage, cannot initiate transactions, and acts only when called.

Effective gas price

After EIP-1559 the price paid per gas equals the block baseFee plus the priority fee the sender offers, and the total fee is gasUsed multiplied by that sum.

Base fee mechanism

Each block's baseFee is burned and adjusts up or down based on how full the previous block was relative to the 50 percent gas target, damping congestion spikes.

Account nonce

For an EOA, the nonce counts sent transactions and enforces ordering; for a contract, it counts contracts created and starts at one under EIP-161.

Event topics and data

Indexed event parameters become topics usable for log filtering, while non-indexed parameters are ABI-encoded into the log data field. Contracts cannot read logs.

EVM gas and memory

Every opcode charges gas, memory expansion costs grow quadratically with size, and a revert rolls back state while still consuming gas already spent.

Storage vs memory vs calldata

Storage persists between calls, memory is a temporary per-call copy, and calldata is read-only input data. External function reference parameters default to calldata.

Function visibility keywords

Public is callable internally and externally, external only externally, internal from this contract and derived ones, and private only from the declaring contract, though all code is on-chain.

receive and fallback

receive() handles calls with empty calldata, typically plain ETH transfers. fallback() handles unmatched calldata. Both must be payable to accept ETH.

Modifier execution order

Modifiers wrap the function body at the underscore placeholder. Multiple modifiers nest in declaration order, so the first listed runs its pre-body code first.

Custom errors versus require

Declaring error X and reverting with it encodes a four-byte selector plus arguments, cheaper than require strings, and is surfaced by tooling as a named revert.

Storage slot packing

Adjacent state variables smaller than 32 bytes can share one slot to save gas, but structs and arrays always begin a new slot and cannot pack across boundaries.

ecrecover zero-address pitfall

ecrecover returns address(0) when the signature is invalid rather than reverting, so callers must check the recovered address is nonzero and matches the expected signer.

Checked arithmetic default

Since Solidity 0.8.0, overflow and underflow revert automatically. An unchecked block disables these checks to save gas where overflow is provably impossible.

Hardhat Network features

Hardhat's in-process EVM provides Solidity console.log, readable stack traces, instant mining, and mainnet forking configured through forking.url in hardhat.config.

Foundry toolchain

forge builds and tests, cast queries and sends transactions, and anvil runs a local node. Tests are Solidity contracts using cheatcodes such as vm.prank and vm.deal.

Optimizer runs setting

The Solidity optimizer runs value trades deployment size against runtime cost: lower values favor smaller bytecode, higher values favor cheaper repeated execution.

Ethers.js provider vs signer

A provider performs read-only calls and queries chain state, while a signer holds an account and authorizes state-changing transactions. Contracts need a signer to write.

OpenZeppelin Contracts

An audited library of reusable Solidity primitives such as ERC20, ERC721, Ownable, AccessControl, and ReentrancyGuard, installed via npm and imported by path.

Secret key management

Private keys and RPC URLs are stored in a .env file excluded from version control, loaded via dotenv, and referenced in config as process.env values.

eth_call versus eth_sendTransaction

eth_call simulates execution against current state, costs no gas, and returns data immediately. eth_sendTransaction broadcasts a signed transaction and returns only a hash.

Injected wallet provider

Wallets inject window.ethereum, exposing eth_requestAccounts to connect, eth_chainId to identify the network, and accountsChanged and chainChanged events the UI must handle.

Transaction receipt polling

A sent transaction yields a hash before mining. Clients poll eth_getTransactionReceipt until status is 1 for success or 0 for revert, then decode emitted logs.

Token decimals conversion

ERC-20 balances are integers scaled by ten to the power of decimals. Use parseUnits before sending amounts and formatUnits when displaying them to users.

EIP-712 typed signing

Structured data signing presents named fields to users and hashes them with a domain separator, which the contract verifies via ecrecover to prevent cross-chain replay.

Event backfill with queryFilter

Live updates arrive through contract.on subscriptions, but history requires queryFilter over bounded block ranges because RPC providers cap the number of blocks scanned.

Reentrancy defense

Follow checks-effects-interactions by updating balances before external calls, and add a ReentrancyGuard mutex so a reentrant call reverts before reaching sensitive logic.

CREATE2 address derivation

The address is the last 20 bytes of keccak256 of 0xff, the deployer address, a chosen salt, and keccak256 of the init code, enabling deterministic deployment.

Proxy storage collision risk

Upgradeable proxies share storage with implementations, so layouts must be append-only and slot conflicts checked with tooling before any upgrade is deployed.

Initializer protection

Upgradeable contracts use initializers instead of constructors, so implementations must call _disableInitializers in the constructor to prevent anyone initializing the logic contract directly.

Oracle manipulation risk

Spot reserves from a single AMM can be moved within one transaction, so price feeds should use time-weighted averages or decentralized oracles with staleness checks.

Contract test layers

Unit tests isolate functions, fork tests replay real mainnet state, fuzz and invariant tests probe accounting edge cases, and gas snapshots catch regressions across changes.