Custody: wallets, keys and seed phrases

Owning crypto really means controlling the private keys that authorise spending it. Custody is the question of who holds those keys — and it is the single most important security topic in this entire track.

Keys, not coins

Your coins are records on the blockchain. What you actually hold is a private key — a secret that proves you can move the coins at a given address. Whoever knows the key controls the coins. This is why key management is security.

Self-custody vs custodial

• Custodial: a third party (such as a centralized exchange) holds the keys for you. Convenient, but you are trusting them — and they can be hacked, freeze access, or fail.
• Self-custody: you hold your own keys in your own wallet. Full control, full responsibility. There is no password reset and no helpdesk.

Hot, cold and hardware wallets

• A hot wallet is connected to the internet (a phone or browser app). Convenient for small amounts and active use, but more exposed to malware and phishing.
• A cold wallet is kept offline, dramatically reducing remote attack risk.
• A hardware wallet is a dedicated offline device that keeps your keys isolated and signs transactions without exposing the key to your computer. It is the practical standard for securing meaningful amounts.

The seed phrase

When you create a self-custody wallet you receive a seed phrase (recovery phrase) — usually 12 or 24 words that can regenerate all your keys. Treat it as the master key to everything:

• Never type it into a website or share it with anyone — no legitimate service will ask for it. Almost every crypto theft from individuals comes from a leaked or phished seed phrase.
• Store it offline, ideally on paper or metal, in more than one secure place. Never store it as a screenshot, in cloud notes, or in email.
• If you lose it, the funds are gone forever. With self-custody, the responsibility is entirely yours — which is both the freedom and the burden of holding your own keys.