BitcoinExtKey encrypt with password implementation is missing

[nopara73]

One can easily from BitcoinExtKey a BitcoinSecret, but not the other way around.
Although I am not sure why, but I take it as the expected behaviour. In this case the need arises for encryption and decryption of BitcoinExtKey.

[NicolasDorier]

There is no standard for encrypting a BitcoinExtKey. If encryption with password is needed for an ExtKey then the best is to use BIP39 with the Mnemonic class.

[nopara73]

That is a transparent box design: Designing the system in terms of how it will look from the inside.
Should I implement it into NBitcoin, or you would like to keep it this way and close the issue?

[nopara73]

After playing with Mnemonic I think I understand what the design should be, please correct me if I'm wrong:
Mnemonic AND password gives us the ExtKey.
A user has to know the password and (if not lazy) the mnemonic.
But the mnemonic should be stored by the wallet, too in encrypted form, and this encryption happens with the password.
This way the user don't have to type the mnemonic every time it logs into its wallet, only if it loses the encrypted file, in order to recover its wallet.

If I am finally on the right track here, I see how it would be a bad idea to implement encryption directly to the BitcoinExtKey, what I recommended in my previous comment (however it will still cost a lot of developer time for others until they finally figure this out, if they don't start out with Mnemonic right away.)

Is the mnemonic encryption supported somehow by NBitoin? (Currently I am using this StringCipher: http://stackoverflow.com/a/10177020/2061103)

[NicolasDorier]

Correct, I explain the Mnemonic it very well in my book http://n.bitcoin.ninja/ takes a look.