Recover passphrase from BIP32 store

[shamatar]

Due to many requirements for such feature I should clarify:

• Existing BIP32Keystore does NOT save the initial entropy (passphrase), it only stores latest element in key tree derivation path (please refer to BIP32 spec) to be able to produce user's keys. That means that you are SAFE TO USE the same seed phrase for Bitcoin, Litecoin, Ethereum, etc, and compromising the wallet will not give the hacker information about anything by your Ethereum wallet only!
• I'll implement recoverable BIP32 keystore in the next release. Developers will be able to use it at their own risk!

Sincerely, Alex

[shamatar]

After evaluation of options we will not implement a recoverable BIP32 keystore due to huge amount of confusion that will be between normal and recoverable implementations. Developers should keep the passphrase somewhere before user fully writes it down and then delete it.