Does specifying the optional passphrase after regenerating a wallet with the same BIP39 word list as earlier create a new, different and empty wallet?

Question

A core-lightning user generated years ago a wallet with a BIP39 word list and lightning-hsmtool generatehsm hsm_secret without specifying an optional passphrase, then moved their Bitcoin there, funded a channel, and have been using their node every couple of weeks when shopping - regenerating when needed with lightning-hsmtool generatehsm hsm_secret and accessing from my backups lightningd.sqlite3 , always running their node and shopping without an optional passphrase.

Now, the same user started to become concerned with the security of their setup and wishes to use the optional passphrase. Does specifying the optional passphrase after regenerating a wallet with the same BIP39 word list as earlier create a new, different and empty wallet? Or does the wallet stay the same? Can they just start using the passphrase with their old wallet (without running the risk of their channels being closed as a penalty)?

Answer 1

The optional passphrase is included in the generation of the root secret, and adding one after the fact will therefore change the generated secret:

Using a passphrase comes with a significant amount of added personal responsibility. You may choose to avoid using a passphrase because:

• if you forget or lose your passphrase, you will permanently lose access to your funds - even if you have your recovery phrase.

[from the Jade help]

If you use a BIP39 passphrase of "abc", a wallet will be generated using both your recovery phrase and passphrase of "abc". However if you log in again and enter a different passphrase, for example "abcd", an entirely different wallet will be logged in to than before.

There is no way to derive a recovery phrase + passphrase from an existing secret either (since BIP39 hashes the phrase to derive the secret), so there is no way to add the passphrase after the fact, independently of where it is used.