TUTORIAL: Using BIP85 To Back Up Your Seeds

BIP39 seed phrases generate an incredible amount of data. Did you know, your seed phrase can generate more seed phrases?

BIP85 uses your seed as a parent seed to generate more seeds, which are referred to as child seeds. And any child seed can be used as a parent seed to generate more child seeds. It's all just math. Amazing, amazing math.

Just as your seed phrase always generates the same keys and addresses for a wallet, with BIP85, your seed phrase will always generate the same child seed phrases using an index number. I should also mention that it's impossible for anyone with a child seed and its index number to calculate the parent seed that generated it.

Let's say you're a parent and you want to create a Bitcoin wallet for each of your kids to inherit someday. Take your Bitcoin seed and assign each kid an index number for their child seed. Perhaps use the year each was born. Or, let's say you manage a business where employees get expense accounts and you want those to be in Bitcoin. Use each employee number as their BIP85 index number. If anyone loses their seed words, you can generate them again using your parent seed plus their index number.

Here's how to use BIP85:

Create a seed (any BIP39 seed will do), but don't use it as your wallet. Instead, use that seed as a parent seed with a BIP85 index number to generate child seeds. Use the child seeds as your wallets. A BIP85 index is any whole number (in other words, no decimals).

You can see how this works by using Ian Coleman's excellent Mnemonic Code Converter website (scroll down to click "Show BIP85"). Side note: only use that site for testing. Never with your real seed.

https://iancoleman.io/bip39/

Here's an example. Let's use this 24 word seed phrase as a parent seed:

chicken pet almost magic size across mushroom group creek hub aware wonder stairs save few toddler midnight woman maximum fitness during order hip nice

Hey, that's a nice seed. We'll call it "Nice" through the rest of this tutorial.

Let's use 42 as the BIP85 index number to generate a 24 word child seed:

length ensure west try neglect novel sand vibrant head evidence banana addict bachelor invest play shrug egg allow comic winter envelope evoke left lawsuit

The same child seed will always be generated by this "Nice" parent seed using BIP85 index number 42.

Here's the 12 word child seed that will always be generated by the "Nice" parent seed using BIP85 index number 42:

door clay stove fury hill protect deny curtain add win ice immune

I name my seeds, for the sake of keeping track of them. So, if I named my parent seed "Nice," I'd name the child seed for index #42 "Nice 42."

Since these child seeds will be the seeds you use to store your coins, follow best practices. Write the child seed on paper. Make a metal backup.

Here's the beauty of starting with a parent seed: If you lose the child seed you're using as your wallet, no worries. You can easily generate it again by using your parent seed and the BIP85 index number.

BIP85 is an amazing tool. It can be used to create the ultimate backup of your backups. It's especially good for multisig backups.

Let's say you're setting up a 2 of 3 multisig wallet. Again, using the "Nice" parent seed, let's choose BIP85 index numbers 6, 7 and 42 for a 2 of 3 multisig. We could choose any index numbers. I just like these numbers since 6 times 7 equals 42 (and 42 is the answer to Life, The Universe And Everything).

These are our three 12 word child seeds for multisig:

Index #6: round zero jazz engage amused order fitness section move oblige raccoon artefact

Index #7: razor actress core enact paper convince leader dinosaur slim mobile rent banner

Index #42: door clay stove fury hill protect deny curtain add win ice immune

There you go. If you lose any of your multisig seeds, all you need to get them back is your parent seed and the index number. If you want to keep things simple, you could use index numbers 1, 2, and 3 for your three multisig seeds.

Let's try it! Here's our "Nice" parent seed with BIP85 index numbers 1, 2, and 3.

Index #1: update target agree drive beef kiwi twist crystal damage emerge proof obey

Index #2: enforce mixture good observe erosion omit leg inflict educate region nasty nest

Index #3: flag jeans caution taxi obey hungry crater crater day auction before average

Another great use for BIP85 is generating a 24 word child seed to use as your seed and a 12 word child seed to use as your passphrase. This eliminates the possibility of having a typo in your passphrase, and any hardware wallet that can scan passphrases using QR can scan it, which means you'll never have to type it. Krux is excellent open source firmware for using a Maix Amigo as a hardware wallet, and Krux does Passphrase QR. Krux also does encrypted SeedQR, which means your QR codes are safe to keep anywhere as long as your encryption key is strong. Here's an example. I have to assume other hardware wallets will add this feature soon, because it's fantastic.

Here's my advice for how to use BIP85:

Use a hardware wallet that can generate BIP85 child seeds, such as Blockstream Jade or ColdCard.

Write your parent seed on paper. Make a metal backup.

Write your child seed on paper along with its name and index number, so you'll always know how you created it. Make a metal backup.

I use a Blockstream Jade to generate BIP85 child seeds, and I use Krux as my hardware wallet. I realize owning two hardware wallets seems like overkill, but Jade costs $65 and the hardware to run Krux (a Maix Amigo) costs $50. So, that's $115 total.

Only use BIP85 if you understand it. And test your setup before using it to store coins. I'm a big believer in setting up a new wallet, writing down the first address, and then wiping it out & setting it up again from scratch to prove I get the same first address... to prove I didn't make a mistake.

Owning Bitcoin means being your own bank. BIP85 can be a powerful tool, as a Master Backup of your backups for recovering your seeds if anything is lost. I highly recommend it.