Bip39 algorithm https://squareblogs.net/edelinepge/using-python-to-produce-a-bip39-mnemonic-a-developers-point-of-view Although it takes advantage of BIP32 strategy you can continue to import BIP39 seeds into Electrum wallet. Also other than BIp32 There's BIP44 version which some wallet use for that era of seeds. Exactly how much stability does a passphrase increase? A BIP39 passphras... https://bookmark-share.com/story20057959/bip39-docs-5-simple-statements-about-bip39-converter-explained-https-t-me-bip39-chat