BIP39 Passphrase
security · wallet
An optional string combined with a BIP39 mnemonic to derive a different seed and wallet.
- Also known as
- 25th word
A BIP39 passphrase is combined with the mnemonic during seed derivation. The same words with no passphrase, a different passphrase, or even a capitalization change produce unrelated seeds and addresses. Every passphrase is syntactically valid, so a typo usually opens a different, empty wallet rather than showing an error.
"25th word" is a common but misleading nickname: the passphrase can be any supported string and is not another checksum-protected mnemonic word. If it cannot be recovered, the intended wallet may be inaccessible; if it is weak, an attacker who has the mnemonic may be able to guess it offline.
- Verify the wallet's BIP39 passphrase support and character handling before funding it.
- Back up the passphrase separately from the mnemonic under a deliberate recovery plan.
- Test restoration and expected addresses with a small amount before relying on the setup.
Related terms
Seed Phrase
→A human-readable backup that can recreate a wallet’s private keys, addresses, and spend authority.
wallet · security
Deterministic Wallet
→A wallet that derives all keys and addresses from a single seed phrase, enabling easy backup and recovery.
wallet · security
Extended Public Key (xpub)
→A BIP32 extended public key that derives many child public keys and addresses without revealing private keys.
wallet · hd-wallet