HD wallets derive a key tree
BIP32 defines extended keys: a key plus chain code that can derive many child keys. An extended private key can derive private and public descendants; an extended public key can derive only non-hardened public descendants.
This structure lets one backup recover many addresses, but it also creates powerful secrets. Sharing an extended public key can expose a branch's addresses and transaction history even though it cannot normally sign spends.
Derivation paths describe location
A derivation path records where a key sits in the hierarchy. Hardened steps prevent public derivation across that boundary and are commonly marked with an apostrophe or h.
Wallet standards use purpose, coin type, account, change and address indexes to improve interoperability. A seed alone may be insufficient for straightforward recovery if the wallet's derivation and script type are unknown.
Descriptors describe outputs
An output script descriptor states how a wallet's scripts and keys are constructed. It can describe single-key, multisignature and Taproot policies, key origins and derivation ranges in a compact, checksummed form.
A descriptor backup can preserve wallet policy and address generation without necessarily containing private keys. Whether it can spend depends on the key material included.
Watch-only is useful but not private
A watch-only wallet can derive addresses and track outputs without holding signing keys. It is useful for monitoring, accounting and keeping private keys on a separate signing device.
The watch-only system learns the addresses and activity it tracks. Protect descriptors and extended public keys as privacy-sensitive information even when they cannot directly spend funds.
Test recovery as a complete system
A robust backup records the seed or keys, passphrase requirements, derivation information, descriptor or multisig policy, key fingerprints and recovery instructions. Store copies so one incident cannot destroy everything.
Test recovery with a disposable wallet or small balance before relying on the design. Never type a real seed into a website, chat, lesson or untrusted recovery tool.
Visual recap
From root material to a spendable wallet
Recovery needs both authority and enough structural information to reconstruct the intended outputs.
Seed material
Master key
Derivation path
Descriptor policy
Addresses and UTXOs
Signing device
Key takeaways
- BIP32 extended keys derive a hierarchy of child keys.
- Extended public keys cannot normally spend but can expose wallet history.
- Derivation paths identify branches and script conventions.
- Descriptors preserve output policy, not just individual addresses.
- A recovery test must reproduce the wallet structure as well as its secret material.
Lesson recap
Check what you learned
Reveal each model answer, then honestly mark whether you understood it or need another review.
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Recall
Why can an extended public key be sensitive even though it cannot normally sign?
References
