Bip39 Rules. The sole purpose All those letters are listed is to make it a lot easier for our human brains to browse them and possibly memorize our recovery phrase. Passphrase values are stored during the /.tmp.tmp file over the MicroSD card. The values are encrypted with AES-256 (CTR manner) https://financebank92581.wikimeglio.com/9466714/the_anatomy_of_the_bip39_phrase_entropy_text_and_safety