Wallet: enable seed phrase recovery from API

[pinheadmz]

The bcoin API does not have a method to return a wallet's seed phrase once the wallet has been encrypted. That means that if a user creates a wallet and encrypts in the same command (i.e. mkwallet --passphrase=...) they will not be able to back up their seed phrase!

One possible way to do this might be switching the JSON function by this.key instead of this.encrypted:

bcoin/lib/wallet/masterkey.js

Lines 658 to 677 in 0551096

	toJSON(network, unsafe) {
	if (this.encrypted) {
	return {
	encrypted: true,
	until: this.until,
	iv: this.iv.toString('hex'),
	ciphertext: unsafe ? this.ciphertext.toString('hex') : undefined,
	algorithm: MasterKey.algByVal[this.alg].toLowerCase(),
	n: this.n,
	r: this.r,
	p: this.p
	};
	}
	return {
	encrypted: false,
	key: unsafe ? this.key.toJSON(network) : undefined,
	mnemonic: unsafe && this.mnemonic ? this.mnemonic.toJSON() : undefined
	};
	}

this.encrypted is a property of the wallet that never changes once a passphrase has been set. this.key is null by default and only contains a value (the wallets unencrypted private key) when the wallet is unlocked.

I tried making this change locally and seems to work as expected:

--> bwallet-cli --network=regtest --id=two  master
{
  "encrypted": true,
  "until": 0,
  "iv": "349e254a48767ce61a24a15da179fc61",
  "ciphertext": "49e5335079c08e59bffe1946bab0f1d75f9cca39a98fe08e99990090a89e7eade58d46fe2f40d35988daa3922481bcabbf6209cc1dbe340ebdbfb9288bcdba10834117f39f62cff43ad9dd35e71596fa7bb7e6f894e6d2892b4c5b264a55f01f",
  "algorithm": "pbkdf2",
  "n": 50000,
  "r": 0,
  "p": 0
}

--> bwallet-cli --network=regtest --id=two  unlock wow123
Unlocked.

--> bwallet-cli --network=regtest --id=two  master
{
  "encrypted": false,
  "key": {
    "xprivkey": "tprv8ZgxMBicQKsPdUW9zaJrkwLy2gMMsVQLPqT47Y3fhXUqn3TGHCwiPEBjGxvxzEySL9YuBjgLYxU2vmQeJFJgaUde7UcqWvVFKpLpX11q8Je"
  },
  "mnemonic": {
    "bits": 128,
    "language": "english",
    "entropy": "e3e7496235b8fc43166a4dcc4b5b9986",
    "phrase": "token demise flat hidden more canoe fluid endless slush food toy artwork"
  }
}

--> bwallet-cli --network=regtest --id=two  lock
Locked.

--> bwallet-cli --network=regtest --id=two  master
{
  "encrypted": true,
  "until": 0,
  "iv": "349e254a48767ce61a24a15da179fc61",
  "ciphertext": "49e5335079c08e59bffe1946bab0f1d75f9cca39a98fe08e99990090a89e7eade58d46fe2f40d35988daa3922481bcabbf6209cc1dbe340ebdbfb9288bcdba10834117f39f62cff43ad9dd35e71596fa7bb7e6f894e6d2892b4c5b264a55f01f",
  "algorithm": "pbkdf2",
  "n": 50000,
  "r": 0,
  "p": 0
}

[pinheadmz]

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