Bip39 Passphrase. Now, at the next stage we use these receiving and change key bunch to make person non-public keys. Use the above make non-public keys and chain code and move them to the above mentioned talked about purpose kchild = kpar + hash(Kpar, cpar, i) to generate unique keys. https://ilovebookmark.com/story18582100/bip39-passphrase-https-linktr-ee-bip39-what-does-ian-coleman-bip39-mean