bitcoin-s/docs/key-manager/key-manager.md

---
id: key-manager
title: Key Manager
---


### Key Manager

The key manager module's goal is to encapusulate all private key interactions with the [wallet](../applications/wallet.md) project.

As of this writing, there is only one type of `KeyManager` - [`BIP39KeyManager`](../../key-manager/src/main/scala/org/bitcoins/keymanager/bip39/BIP39KeyManager.scala). 

The [`BIP39KeyManager`](../../key-manager/src/main/scala/org/bitcoins/keymanager/bip39/BIP39KeyManager.scala) stores a [`MnemonicCode`](../../core/src/main/scala/org/bitcoins/core/crypto/MnemonicCode.scala) on disk which can be decrypted and used as a hot wallet.
 
Over the long run, we want to make it so that the wallet project needs to communicate with the key-manager to access private keys.

This means that ALL SIGNING should be done inside of the key-manager, and private keys should not leave the key manager.

This makes it easier to reason about the security characteristics of our private keys, and a way to provide a uniform interface for alternative key storage systems (hsm, cloud based key storage, etc) to be plugged into the bitcoin-s library.

#### Creating a key manager

The first thing you need create a key manager is some entropy.

A popular way for bitcoin wallet's to represent entropy is [BIP39](https://github.com/bitcoin/bips/blob/master/bip-0039.mediawiki) which you [can use in bitcoin-s](../../core/src/main/scala/org/bitcoins/core/crypto/BIP39Seed.scala)

You can generate a `MnemonicCode` in bitcoin-s with the following code

```scala mdoc
import org.bitcoins.core.crypto._

//get 256 bits of random entropy
val entropy = MnemonicCode.getEntropy256Bits

val mnemonic = MnemonicCode.fromEntropy(entropy)

//you can print that mnemonic seed with this
println(mnemonic.words)
```

Now that we have a `MnemonicCode` that was securely generated, we need to now create `KeyManagerParams` which tells us how to generate
generate specific kinds of addresses for wallets.

`KeyManagerParams` takes 3 parameters:

1. `seedPath` there is where we store the `MnemonicCode` on your file system
2. [`purpose`](../../core/src/main/scala/org/bitcoins/core/hd/HDPurpose.scala) which represents what type of utxo this `KeyManager` is associated with. The specification for this is in [BIP43](https://github.com/bitcoin/bips/blob/master/bip-0043.mediawiki)
3. [`network`](../../core/src/main/scala/org/bitcoins/core/config/NetworkParameters.scala) what cryptocurrency network this key manager is associated with


This controls how the root key is defined. The combination of `purpose` and `network` determine how the root `ExtKey` is serialized. For more information on how this works please see [hd-keys](hd-keys.md)

Now we can construct a native segwit key manager for the regtest network!

```scala mdoc

import org.bitcoins.core.crypto._

import org.bitcoins.core.config._

import org.bitcoins.core.hd._

import org.bitcoins.keymanager._

import org.bitcoins.keymanager.bip39._

import java.nio.file._

//this will create a temp directory with the prefix 'key-manager-example` that will
//have a file in it called "encrypted-bitcoin-s-seed.json"
val seedPath = Files.createTempDirectory("key-manager-example").resolve(WalletStorage.ENCRYPTED_SEED_FILE_NAME)

//let's create a native segwit key manager
val purpose = HDPurposes.SegWit

//let's choose regtest as our network
val network = RegTest

val kmParams = KeyManagerParams(seedPath, purpose, network)

val km = BIP39KeyManager.initializeWithMnemonic(mnemonic, kmParams)

val rootXPub = km.right.get.getRootXPub

println(rootXPub)
```

Which should print something that looks like this

`vpub5SLqN2bLY4WeXxMqwJHJFBEwxSscGB2uDUnsTS3edVjZEwTrQDFDNqoR2xLqARQPabGaXsHSTenTRcqm2EnB9MpuC4vSk3LqSgNmGGZtuq7`

which is a native segwit `ExtPubKey` for the regtest network!

You can always change the `network` or `purpose` to support different things. You do _not_ need to initialize the key manager
again after initializing it once. You can use the same `mnemonic` for different networks, which you control `KeyManagerParams`.

```scala

//let's create a nested segwit key manager for mainnet
val mainnetKmParams = KeyManagerParams(seedPath, HDPurposes.SegWit, MainNet)

//we do not need to all `initializeWithMnemonic()` again as we have saved the seed to dis
val mainnetKeyManager = KeyManager(mnemonic, mainnetKmParams)

val mainnetXpub = mainnetKeyManager.getRootXPub

println(mainnetXpub)
```

Which gives us something that looks like this

`zpub6jftahH18ngZw98KGjRo5XcxeKTQ2eztsvskb1dC9XF5TLimQquTs6Ry7nBBA425D9joXmfgJJCexmJ1u2SELJZJfRi95gcnXadLpZzYb5c`

which is a p2sh wrapped segwit `ExtPubKey` for the bitcoin main network!

#### Creating a key manager from existing mnemonic

To create a `KeyManager` from existing mnemonic you need to specify the `seedPath` and then construct the `KeyManagerParams` that you would like.

Finally you call `KeyManager.fromParams()` that reads the mnemonic from disk and create's the key manager