Oracles & bridges
Blockchains can't see the outside world or each other on their own — oracles and bridges are the plumbing that connects them, and the biggest attack surface in crypto.
> What oracles do
A smart contract can't natively fetch a price, a sports score, or a weather report. Oracles (Chainlink, Pyth, RedStone) are networks of nodes that fetch off-chain data, aggregate it, and push it on-chain. DeFi lending, derivatives, and stablecoins all depend on them.
> Bridges connect chains
A bridge locks tokens on chain A and mints an equivalent representation on chain B. When you move ETH from Ethereum to Arbitrum, that's a bridge. Native bridges (built by the chain team) are safer than third-party bridges.
> Why they get hacked
Bridges concentrate huge amounts of value in a single contract or multisig — over $2 billion has been stolen from bridge exploits alone. Rule of thumb: minimize how much you keep bridged and prefer canonical, well-audited bridges only.