Clear DefinitionsExtended Public Key
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Pronunciation
[ek-sten-did puh-blic key]
Analogy
An xpub is like giving someone a map of safe deposit box locations without giving them the keys.
Definition
An xpub: a Base58Check‑encoded representation of an HD wallet’s public key and chain code, enabling derivation of child public keys without private keys.
Key Points Intro
xpubs facilitate watch‑only and multisig via:
Key Points
Public derivation: Derive child pubs non‑hardened.
Chain code: Ensures secure child key generation.
Base58Check: Encodes version, depth, fingerprint, index.
Wallet interoperability: Import across HD wallets.
Example
Importing an xpub into a watch‑only Electrum wallet lets you see all addresses and balances without spending capability.
Technical Deep Dive
xpub structure: 4‑byte version, 1‑byte depth, 4‑byte parent fingerprint, 4‑byte child index, 32‑byte chain code, 33‑byte public key, 4‑byte checksum. Derived via HMAC‑SHA512 CKDpub function.
Security Warning
xpub leak allows address generation and tracking, compromising privacy.
Caveat
Cannot derive hardened children; xprv needed for full derivation.
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