BIP-85

Jul 29, 2025

1. Understanding the BIP-85

1.1 What is BIP-85?

BIP-85 is an advanced function that lets you create several seed secondary phrases from one seed main phrase.

Each seed secondary sentence can be used to create a completely independent Bitcoin wallet. These wallets can be used for a variety of purposes: a Hot Wallet on mobile, a wallet for a relative, a separate savings wallet, etc.

All seed sub-phrases are mathematically derived, but it is impossible to trace back to the seed main phrase from a sub-phrase. This ensures complete separation between each wallet.

As long as you have access to your seed main phrase (and the associated passphrase if you're using one), you can regenerate any seed secondary phrase identically, without having to save it separately.

1.2 Why use BIP-85?

BIP-85 is useful if you want to :

Create several independent Bitcoin wallets without multiple backups
Manage your funds according to different uses (savings, expenses, family, projects)
Guaranteeing safeguards for relatives ("Uncle Jim" function)
Delete a wallet without losing access to your funds
Simplify your security: just one seed key phrase to protect

1.3 Advantages over BIP-32

With BIP-32, a single seed sentence can be used to generate a complete hierarchy of Bitcoin accounts and addresses, using derivation paths (for example: m/44'/0'/0'/0/0). Each path can represent a separate account, but all remain linked to the same seed sentence. So, if this seed phrase is compromised, all derived accounts become accessible.

With BIP-85, a seed main sentence can be used to generate several totally independent seed secondary sentences: if one of these secondary seeds is compromised, the attacker will never be able to go back to the main seed or access the other wallets.

This makes it possible to compartmentalize risks:

You can use a secondary seed for Hot Wallet or temporary use, accepting a higher exposure.
Even if this Hot Wallet is compromised, your other funds, protected by other secondary seeds or kept offline, remain safe.

On the other hand, for both BIP-32 and BIP-85, if the main seed is compromised, all funds are vulnerable. It is therefore crucial to protect it with the highest level of security.

2. Practical use cases for BIP-85

BIP-85 allows you to create multiple Bitcoin wallets from a single seed core phrase, each with its own seed secondary phrase. Here are five practical use cases for organizing and securing your Bitcoin funds. Each case explains why using BIP-85 is more practical than managing multiple accounts with a single seed phrase via BIP-32.

2.1 Limiting the risk of a less-secure wallet

Scenario: You use a "Hot Wallet" wallet (installed on an Internet-connected device), for daily transactions.
Solution BIP-85: You create a seed secondary phrase dedicated to this wallet.
Advantage over BIP-32: You don't need to import the seed primary phrase onto your phone, reducing the risk of hacking. Only the seed secondary phrase is compromised, protecting your other wallets. With BIP-32, you need to use the seed main phrase and a bypass path, exposing all your funds.

2.2 Create a wallet for a family member

Scenario: You set up a Bitcoin wallet for someone close to you (e.g. your mother), while being able to recover it if they lose it.
Solution BIP-85: You create a dedicated seed secondary sentence and share only this one.
Advantage over BIP-32: With BIP-32, creating an account for a loved one requires either sharing your main seed phrase, risking all your funds and complicating management for your loved one (managing branching paths), or creating a new seed phrase to save in addition to your main seed phrase.

2.3 Facilitating the management of separate wallets

Scenario: You separate your bitcoins for different purposes (e.g. long-term savings, non-KYC funds).
Solution BIP-85: You create seed secondary phrases dedicated to each objective.
Advantage over BIP-32: With BIP-32, all accounts share the same seed phrase, which complicates management in third-party wallets by requiring derivation paths such as m/44'/0'/0' to be managed. In addition, it is not possible to assign a separate account per device (e.g. "savings on Coldcard", "daily on mobile", "vacations on Trezor"). BIP-85 assigns a unique seed secondary phrase per objective, which is easy to identify and import separately on each device.

2.4 Using a temporary wallet for transactions

Scenario: You need a temporary wallet for a one-off transaction or to preserve confidentiality (e.g.: mixing of funds, interaction with a Exchange KYC, etc.).
Solution BIP-85: You create a seed secondary sentence, use it for the transaction, then destroy it if necessary, knowing that it can be regenerated.
Advantage over BIP-32: With BIP-32, a temporary account depends on the seed main sentence, exposing all your funds if compromised.

3. Before you start

Hardware (optional)
Coldcard Mk4 or Q1
MicroSD card
Basic knowledge
Understanding mnemonic phrases (BIP-39): a list of 12 to 24 words to save a wallet.
Know what a Bitcoin wallet is: software or device to manage your bitcoins, and how to restore it with a mnemonic phrase.
More resources in Annexes.
Compatible software
Sparrow wallet (computer, for watch-only or advanced management)
Nunchuck (mobile, for multi-signatures)
BlueWallet (mobile)
...
3.4 Coldcard configuration
Initialize a seed sentence of 24 words on the Coldcard.
Optional: Add a passphrase to secure access to BIP-85 branches.
Activate useful options: NFC (for export), disable USB on battery (security).

4. Step-by-step tutorial

Follow these steps to create, use and retrieve a secondary mnemonic with BIP-85 on your Coldcard.

4.1 Generate a seed secondary sentence

You will create a seed secondary phrase from your seed main phrase.

Switch on your Coldcard, enter your PIN code.

1. If you have applied a passphrase to your main seed:
From the Home screen, go to passphrase.
- Choose Add Word and enter your password.
- Press Apply.
- Check the wallet's identity: Go to Advanced > View Identity to note the wallet's fingerprint.
1. Go to BIP-85 menu
From the Home screen, go to Advanced > Derive seed B85
Read the warning and confirm.

The ColdCard informs you that the seeds generated are mathematically derived from your main seed, but cryptographically totally independent.

1. Choose a format

Select the seed phrase format: 12, 18 or 24 words. Check the number of words accepted by the Wallet into which you want to import your seed phrase.

1. Select index
Enter an index between 0 and 9999.
This index is crucial for regenerating the secondary seed at a later date. Keep it carefully with a label such as: "Index 1 = Wallet mobile", "Index 2 = family project", "Index 4 = test mix", ...
If you lose it, you won't lose access to your funds, but you'll have to test combinations from 0 to 9999 to find them.

1. Note or export seed secondary sentence

ColdCard now displays a new seed secondary sentence. You can :

The note manually.
Press :
- 1` to save it on the SD card
- 2 to enter "use this seed" mode on the ColdCard (useful for exporting or signing a transaction)
- 3` to display a QR code (to be scanned with a mobile application such as BlueWallet or Nunchuck)
- 4` to send it by NFC

💡 At this point, you have an independent seed phrase, usable in any Wallet BIP39 (Trezor, Ledger, BlueWallet, Nunchuck...).

4.2 Using the secondary seed

You can now use this derived seed to create a new wallet in :

a mobile app
another Hardware Wallet
a Multisig wallet

4.3 Recovering a lost seed secondary phrase

To retrieve a secondary seed at any time, repeat the process:

Restart your ColdCard
Enter your PIN
Enter your passphrase, if defined
Go to Advanced > Derive seed B85
Choose format (12/18/24 words)
Enter the same index (e.g. 1)
You'll get exactly the same secondary seed

5. Limits, risks and best practices

5.1 Dependence on seed main sentence + passphrase

The use of BIP85 relies entirely on the 24-word seed main sentence, as well as on passphrase if you've applied one.

From these two elements, all seed secondary phrases can be regenerated.
Without one of these 2 elements, you lose access to all derivative wallets.

5.2 Risks in multi-signature configuration

We strongly advise against using secondary seed phrases generated from the same primary seed phrase in a multi-sig configuration: if the device or the primary seed phrase is compromised, all the multi-sig keys could be regenerated by an attacker.

5.3 Software compatibility

Not all applications directly support BIP85 derivation. However, seeds generated via BIP85 are standard BIP39 seeds (12, 18 or 24 words), and can therefore be used in any BIP39-compatible wallet.

5.4 BIP85 account register

It is recommended to keep an up-to-date personal register of seed secondary phrases.

It allows you to find out quickly which BIP85 index corresponds to which wallet, without having to keep seed secondary phrases.
This register should remain minimalist, with no explicit mention of Bitcoin, and should be stored separately from the main seed. Remember to mention it in your inheritance plan.

The register can contain :

bIP85 index used (number from 0 to 9999)
a usage or reference name (e.g. Hot Wallet, personal savings, Wallet from Mom)
if necessary, the wallet fingerprint for verification in ColdCard

5.5 Backup

Backups must include :

the main seed
gW-76 (if used)

Never store together:

the main seed and passphrase
the main seed and the BIP85 account register

More resources in Annexes.

APPENDICES

A.1 Glossary

BEEP
BIP-32
BIP-39
BIP-85
seed phrase
passphrase
Multisig

Dive into the cryptographic principles that power Bitcoin wallets.

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Bitcoin Wallet Architecture

Dive into the cryptographic principles that power Bitcoin wallets.

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Author

This tutorial has been written by Manuel Proquin

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Manuel Proquin

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Discovering Bitcoin hasn't fundamentally changed who I am, but it has considerably amplified my power to act, both on my own scale and for society as a whole. Owning Bitcoin embodies clear vision, critical thinking and strength of character. By safeguarding their finances from inflation and censorship, Bitcoiners strengthen their autonomy and influence, shaping the future according to their values. Despite the challenges, Bitcoin inspires a determined optimism to build a freer, more resilient world of tomorrow. Also a Bitcoin consultant and coach, founder of orangepeel.fr, administrator of the Bitcoin Meetup in Nantes (France) and an avid board sports enthusiast.

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