jellyfish-wallet-mnemonic to support encrypt and decrypt

[fuxingloh]

What would you like to be added:

1. jellyfish-wallet-mnemonic with encrypt and decrypt function extended above 24 word.
2. 24 word must unlock the wallet, this just encrypt the 24 words on rest.

Why is this needed:

The 24 words mnemonic seed should serve as a cold storage of your HD seed.
However the 24 words should not sit in your device (phone/browser/desktop) unencrypted as rest.
Encryption can be done with biometric authentication provided by device, jellyfish-wallet-mnemonic just need to provide the interface to do it.

Reference example: https://github.com/bitcoin/bips/blob/master/bip-0038.mediawiki

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[ivan-zynesis]

@fuxingloh Not very certain about the requirement, this is allow user store an the encrypted mnemonic during first time create or import? The encrypted is protected with a "simpler" (than the ori mnemonic seed) user selected passphrase?

interface EncryptionOptions {
  passphrase: string // caller known passphrase
  encryptedSetter: () => void // caller provide storage
  encryptedGetter: () => string
}

static fromSeed (seed: Buffer, options: Bip32Options, encOpt?: EncryptionOptions): MnemonicHdNodeProvider { /* add encryption process here */ }

static from (encrypted: string, passphrase): MnemonicHdNodeProvider // allow user to unlock wallet with simple passphrase within a device with encrypted mnemonic stored

[fuxingloh]

1. Generate mnemonic seed for cold storage
2. Generated mnemonic seed must be the actual seed used for signing transaction
3. Mnemonic seed stored at rest is dangerous
4. Encrypt mnemonic seed while it's at rest
5. When the user wants to perform a transaction, decrypt encrypted mnemonic seed

So yeah, the encryption protects the original mnemonic seed at rest. It is only loaded into memory when it's required for a brief period.

[fuxingloh]

There is also some flow/complications to this, as the wallet should only encrypt private key. The pubKey should be accessible at rest.