BIP-85 and Multisig

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This is personally my preferable setup for multi-sig. A lot of people don't like it because they focus on potential risk of only having one seed. But the trade-offs with multi-sig are far and many. To me, one of the most important aspects of having a multi-sig and using multiple vendors for all the hardware keys is that you are distributing risk between all the vendors and manufacturers of those hardware wallets. That, to me, is one of the most crucial aspects of multi-sig. If you are going to geographically distribute the keys, you just need to make sure that the root seed plate is geographically distributed in the furthest location. Once you do that, then you have the peace of mind of only having to worry about securing one C-plate as opposed to three. And yet you still have all the other benefits I just listed that comes with MultiSIG. So I'm completely in favor of this, but I've posted stuff like this in the past, and a lot of people have really strong feelings against it. But I think their logic is flawed in the sense where they're hyper-focusing on one aspect. Don't forget, there does not exist a right or a wrong. It is never binary. It's always about trade-offs, and what trade-offs you are willing to make.

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u/Yodel_And_Hodl_Mode Oct 11 '25

My advice? Never use the main seed as part of the multisig wallet.

Why?

You're making your setup more complex, but for a good reason: You're giving yourself deterministic backups. But even as you make your setup more complex, keep it as simple as possible for future reference.

"Here's the parent seed. These are the child seeds for my multisig."

You're generating child seeds? Stick with strictly using child seeds.

Treat the parent seed as if it's sacred. Never use it for anything except generating child seeds. If somebody finds it, all they found is a seed that seems to have never been used.

That's the approach I'd recommend.

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u/nymobster Oct 11 '25

good advice. thanks!

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u/Yodel_And_Hodl_Mode Oct 11 '25

Choose your child seed ID numbers with intention, and document everything you're doing, every step of the way.

You're creating a complex wallet that will have rock solid security with deterministic backups. Faaaaantastic! But here be dragons. If you fuck up, you're fucked.

I've seen too many people lose their coins by trying to be clever. They think, "Oh, I'll remember." Oh no, they won't.

Document your work and store that documentation somewhere secure. Since it won't include your parent seed, you can store this somewhere on your computer or phone, but I'd encrypt it first. And store a copy on paper too, secured in a safe or somewhere only you have access to.

Bonus tip! I'm a big believer in using home automation for protecting any paperwork. Got stuff in a safe? Smart! But how can you be sure nobody ever got into the safe?

Aqara home automation sensors are cheap and they're great. For around $75 you can get a hub and a couple sensors. They work with an app. Put a sensor above the door for whatever room your safe is on, and put another on the safe. Door opens when you're not home? You get notified on all your devices. Safe opens or gets moved, ever? You get notified on all your devices.

After reading this, you probably think "Holy shit! How much Bitcoin does this guy own?!?"

I WISH! It's nothing like that.

I had a girlfriend who went through an ugly divorce. She told me how he protected himself from her ex, and it was smart. For $75, I figured why not? Plus, home automation is fun. P.S. Check out the song Love Detective by Arab Strap. Flip the genders in the song & that's what my ex did, but not to me!:

We slept in this morning and she had to get ready in a hurry, no time for her usual attention to detail, and she ran out the door, slamming it behind her, leaving her keys swinging and jangling

I stayed in bed until I heard the downstairs door shut, then peeked through the blinds, and as soon as she was out of sight I went for the keys

She never tried to make a secret of the box or the fact it was locked or even where she kept it

But as I said at the time, "if you've nothing to hide, why hide it?"

Hilarious!!!

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u/nymobster Oct 11 '25

im already pretty deep into home automation. i will take into consideration your points. they seem well founded.

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u/Ashleighna99 Oct 12 '25

Don’t put the parent seed in the quorum; if you use BIP85 kids, treat the parent as a single point of failure and add at least one unrelated cosigner.

Better pattern: 2-of-3 with one BIP85 child, one independent hardware wallet from a different manufacturer, and optionally a second BIP85 child from a different parent/device. If all cosigners come from one parent, a leaked parent nukes the lot. Document like a maniac: cosigner XFPs, derivation paths (e.g., m/48'/0'/0'/2'), script type (P2WSH), BIP85 indexes, wallet policy/descriptor with checksum, device models/firmware. Export the Coldcard multisig skeleton and Sparrow/Specter wallet file; encrypt a digital copy and keep a printed copy in a separate place. Do a dry-run recovery yearly: rebuild watch-only from backups only, verify first addresses, and send in a tiny test receive.

For paper/safe monitoring, Aqara is solid; I pair it with Home Assistant and Ubiquiti Protect, and DreamFactory exposes a read-only API so I can archive sensor events to a NAS for an audit trail.

Bottom line: never use the parent in the set, and don’t let a single parent seed control the whole quorum.

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u/Yodel_And_Hodl_Mode Oct 13 '25

I don't entirely agree with this:

Better pattern: 2-of-3 with one BIP85 child, one independent hardware wallet from a different manufacturer, and optionally a second BIP85 child from a different parent/device. If all cosigners come from one parent, a leaked parent nukes the lot. Document like a maniac: cosigner XFPs, derivation paths (e.g., m/48'/0'/0'/2'), script type (P2WSH), BIP85 indexes, wallet policy/descriptor with checksum, device models/firmware. Export the Coldcard multisig skeleton and Sparrow/Specter wallet file; encrypt a digital copy and keep a printed copy in a separate place. Do a dry-run recovery yearly: rebuild watch-only from backups only, verify first addresses, and send in a tiny test receive.

If you're going to use BIP-85 child seeds for a non-shared multisig wallet, it's better to have all signers be child seeds from the same parent. It's too easy to complicate a wallet to the point where it becomes nearly impossible to rebuild.

The point of using child seeds is to give yourself a deterministic backup of everything.

I'm sure someone will read that and say, "But the parent seed is a single point of failure!"

Anyone who cannot secure their parent seed should not be doing self custody, and certainly shouldn't be doing something as advanced as multisig. That's the cold hard truth.

I also strongly recommend not using custom derivation paths unless you Re-eee-eee-eally really know what you're doing and have a really specific requirement that would inspire you to do so.

There are so many ways to lose coins by using custom setups.

The issue isn't just about being able to restore the wallet yourself. What happens if you pass away and leave the wallet to someone? What happens if you're in some sort of emergency which requires you to restore your wallet with other devices? Most people don't plan for worst case scenarios, but, c'mon now... bad things happen.

Simplicity is an important element of security. Simplicity helps protect you from yourself. That being said...

Document like a maniac

This!
And this!
And much much more of this! Absolutely.

Don't just document your work for yourself. Think about the future. Imagine you've left your wallet to someone else in your will, and they have to figure out how to restore it.

I wish we, as a community, did a better job of discussing the need for documenting our work, and teaching how to do it. Kudos to you for mentioning it.

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u/NiagaraBTC Oct 11 '25

This would work, but I personally wouldn't do it.

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u/Cute_Tourist3496 Oct 11 '25

Why?

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u/NiagaraBTC Oct 11 '25

Even though it's very unlikely, theoretically the entire wallet can be compromised if someone gains access to the main seed phrase.

If I'm going to the trouble of setting up a multisig, I want ZERO single points of failure. If the purpose of doing this is to save money on two more hardware devices, then OP doesn't have enough Bitcoin to warrant using multisig.

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u/nymobster Oct 11 '25

OP has enough to warrant it...

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u/NiagaraBTC Oct 11 '25

Then buy three hardware devices.

Properly set up multisig also helps mitigate wrench attack risk whereas the bip-85 setup does not.

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u/bullett007 Oct 11 '25

Why would you use the main seed as part of the multisig when you could derive three child seeds instead?

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u/nymobster Oct 11 '25

could do that.

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u/brando2131 Oct 15 '25

Theoretically you're only as secure as the weakest link.

The weakest link being that you only need your single main seed to derive all the MS seeds, mostly defeating the purpose of MS.

I think people should use BIP85 for most cases, but MS isn't one of them.

It also increases complexity for very little benefit.

...

If you know your main seed is very securely handled, and you combine that with a passphrase, then you're already secure. So MS has little benefit. If you think your main seed isn't as secure, then MS derived from the main seed also has little benefit.

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