Do you have multiple mnemonics written down on paper and you are afraid to mix or lose them in some catastrophic event? There exists a solution for that. BIP85 is a standard that allows you to deterministically derive new mnemonics or entropies from a single mnemonic phrase.

In this blog post, we will delve into the practicality and usefulness of BIP85, exploring how it simplifies key management and enhances security for crypto enthusiasts.

BIP85

Mnemonic words became quite standard for storing private keys. They are easy to write down and remember. Different wallets might use different standards to generate mnemonic words but all start with some “initial entropy” and then process the mnemonic into a BIP32 key, or private key. Derived BIP85 entropy is very similar to other standard tree derivation paths except that it uses deterministic random number to point to the specific node in the tree. The only thing you will need to know is the index of derived mnemonic. This can be safely stored in your password manager and even if you lose it, you can still brute force first 1000 indexes in quite reasonable time.

Securely storing mnemonic words is a great challenge on its own. Having multiple of them is even more. Luckily there is no need for one person to store more than one mnemonic phrase because you can generate them as many as you want.

Let’s say you have a cold storage wallet, hot wallet on mobile phone and lightning node. If you are not using BIP85 you would probably have 3 different mnemonic phrases to manage?

Tools and Best Practices

There are multiple tools online with which you can generate and test BIP85 by yourself. One of them is iancoleman.io or Seed Tool. You can generate BIP85 mnemonic phrase by checking “Show BIP85” checkbox. Of course don’t you dare to enter your real mnemonic phrase into some online tool.

There are also several secure options to derive BIP85 mnemonic phrase. The easiest is to use hardware wallet but most of the wallets don’t have support for BIP85 yet (and looks like they never will). I know you can use Coldcard, Jade or Seedsigner to directly derive BIP85 mnemonic phrase offline. But what if you don’t have any of these devices?

People will usually recommend you to boot into tails Linux, load the needed tool and go offline. This still feels quite risky and if you are paranoid you will have to destroy computer afterwards. Not very practical IMO…

I have solved my problem by using old, half working raspberrypi (RPI) which doesn’t have any wireless connectivity. My RPI cannot not load web browser but only terminal, so I wrote short python script and I will never ever connect RPI to internet again, but I can still use it to derive BIP85 mnemonic phrase whenever I need to.

Core lightning and LND derivation

When generating wallet for core lighting you can use command lightning-hsmtool generatehsm hsm_secret which will offer you to write derived mnemonic before generating hsm_secret.

However, for LND you will find out that plain derived mnemonic is not good enough because it requires aezeed format. Aezeed incorporates more data, like birthday and version into the mnemonic itself. For this kind of wallets, you can still use BIP85 to derive new entropy (pick WIF from derived mnemonic), but you will have to convert it to aezeed format later.

If you are running LND node in umbrel, you can use the following commands to generate aezeed mnemonic phrase and then use “recovery option” on the first run.

sudo docker exec -it lightning_app_1 bash
cd /app/apps/backend/utils && node

.load deterministic-aezeed.js
deterministicAezeed("<write your WIF here>")

Source

Conclusion:

In the world of cryptocurrency, securely managing private keys is paramount. BIP85 offers a revolutionary approach to key management, simplifying the process while enhancing security. By utilizing a single mnemonic phrase, users can derive multiple keys across different wallets and cryptocurrencies, streamlining wallet management and reducing the risk of key loss. As we’ve discovered, BIP85 is a powerful tool that empowers crypto enthusiasts to take control of their digital assets securely.

Resources

• BIP85 specification
• SLP368 BITCOINQNA – BITCOIN SEED TOOL podcast
• Mastering Bitcoin by Andreas M. Antonopoulos