Bitcoin does not store balances under names. It stores outputs locked to conditions, usually 'whoever can produce a signature from this key'. Producing that signature requires the private key, so control of the key is control of the coins.
Modern wallets generate keys deterministically from a single seed (BIP-32), backed up as a 12- or 24-word mnemonic (BIP-39). One backup restores every address the wallet will ever generate.
Custody is therefore a spectrum. On an exchange, the exchange holds the keys and you hold a claim; that is convenient and adds counterparty risk. In self-custody you hold the keys and carry the responsibility for backups, physical security and inheritance.
There is no support desk in the protocol. No one can reverse a transaction, restore a lost seed phrase, or freeze a thief's coins.
Explain more simply
A private key is a secret number. Whoever knows it can spend the coins. A public address is derived from it and is safe to share.
A seed phrase is a human-readable backup of that secret. Anyone who reads your seed phrase can take everything, instantly and irreversibly.
Real-world analogy
A public address is your letterbox slot; the private key is the only key to the box. A seed phrase is the master blueprint for cutting that key again.
Key facts
- Public addresses are safe to share; private keys and seed phrases never are.
- BIP-39 mnemonics are typically 12 or 24 words.
- Nobody, not this platform, not a wallet maker, not a miner, can restore a lost key.
Common misconception
“Support staff sometimes need your seed phrase to fix a problem.”
No legitimate service ever needs it. Every request for a seed phrase or private key, by email, chat, phone, video call or 'wallet validation' website, is theft in progress.[7]
Go deeper
A BIP-39 mnemonic can be combined with an optional passphrase, producing an entirely different wallet from the same words. Lose the passphrase and the funds are unreachable even with the correct 24 words.
Multisignature setups (for example 2-of-3) remove single points of failure by requiring several independent keys, at the cost of a more complex backup and recovery plan that must be documented and tested.
Quick check
Answer every question correctly (100%) to complete this lesson.
1.Which of these is safe to share publicly?
2.What does 'self-custody' mean?
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Extra exam questions
Every question here counts towards your accuracy, XP and rank. No guessing: every answer is explained.
Quick check
Answer every question correctly (100%) to complete this lesson.
1.What is a seed phrase (recovery phrase)?
2.Who legitimately needs to see your seed phrase?
3.What does "custody" mean in Bitcoin?
4.Why should a seed phrase never be stored as a photo or cloud note?
5.What is the safest material for a long-term seed phrase backup?
6.What does the phrase "not your keys, not your coins" mean?
7.What should you do if you receive an unexpected message asking you to 'verify' your seed phrase?
8.What is a private key used for?
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Sources
- BIP-39: Mnemonic code for generating deterministic keys, bitcoin/bips
- BIP-32: Hierarchical Deterministic Wallets, bitcoin/bips
- Bitcoin developer documentation, bitcoin.org / Bitcoin Optech glossary