Mastering Ethereum: Building Smart Contracts and DApps

The Core Framework

• Ethereum is a deterministic, Turing-complete "world computer" — a stored-program computer fused with a blockchain; one shared world state advanced by the EVM.
• Power is a liability. Generality (Turing-completeness, delegatecall, rich languages) is also attack surface; gas bounds execution and defensive programming keeps it safe.
• Determinism forbids on-chain randomness — which is why oracles, off-chain storage, and external entropy exist.
• Immutable code + irreversible value ⇒ you can't patch a deployed bug and lost keys/wrong addresses are permanent. Reuse audited code ("security by maturity").
• Spec over implementation: Ethereum is defined by the Yellow Paper, so many interoperable clients exist by design.

Quick Lookup

Situation	Do This	Avoid This
Sending value	Validate recipient; a wrong to burns ether	Trusting an unchecked address
External calls in a contract	Checks-Effects-Interactions + reentrancy guard	State update after the call (the DAO)
Arithmetic	Solidity ≥0.8 checks overflow (was SafeMath)	Assuming uint won't wrap
Need randomness	Commit-reveal / VRF / oracle	block.timestamp/blockhash entropy
Calling another contract	Hardcode/verify the address; new or known address	Casting an arbitrary address to a type
Backing up a wallet	Store the BIP-39 mnemonic offline	Relying on the password alone
Writing a contract	Reuse OpenZeppelin; minimize complexity	Rolling your own crypto/token

The Key Insight

Ethereum is a "single shared-state...world computer" — and because that computer is open, immutable, and adversarial, its power is inseparable from its risk. (Core thesis, Chapters 1 & 13)

Key Diagrams: Key→Address→Transaction→EVM flow · Reentrancy & Checks-Effects-Interactions