BIP-85 child keys are an advanced convenience feature for deriving separate wallet recovery words from the wallet currently loaded on your BitBox02. The original wallet is the parent wallet, and each generated set of 12 or 24 BIP-39 recovery words is a child key. You can use those child recovery words to create a separate wallet in a compatible wallet app.
BIP-85 can make it easier to recreate several wallets from one well-protected BitBox02 backup. It does not add security, however. Anyone who can access the parent wallet can regenerate its child keys, so BIP-85 is most useful when you understand and accept that shared recovery relationship.
BIP-85 does not add another security layer
A BIP-85 child wallet is separate for everyday use, but it is not independent from the parent backup. Anyone with the parent recovery information can regenerate its child keys. If your goal is additional protection rather than simpler recovery, an optional passphrase or a deliberately designed multisignature setup addresses a different problem from BIP-85.
How BIP-85 child keys work
BIP-85 is a standard for deriving new, deterministic information from a wallet's root key. The BitBox02 uses the BIP-39 part of the standard to generate child recovery words.
When you choose a word count and an index, the BitBox02 always generates the same child key from the same parent wallet. A different word count or index generates a different child key. The BitBox02 displays the corresponding keypath so you can verify which parameters are being used.
The child recovery words look and work like any other compatible BIP-39 recovery words. They do not reveal that they came from BIP-85, and they cannot be used to calculate the parent recovery words or another child key.
For an illustrated explanation of derivation paths and more practical examples, read One backup, infinite possibilities: BIP-85 child keys explained on the BitBox blog.
The full standard supports several types of deterministic information. The BitBoxApp workflow described here is specifically for generating BIP-39 recovery words. For the technical details, see the official BIP-85 specification.
What controls access and recovery
BIP-85 changes the recovery relationship between wallets. The parent wallet can recreate every child key derived from it, while one child key cannot recreate the parent or its sibling child keys.
| Recovery information | Why it matters |
|---|---|
| Parent recovery words and the exact optional passphrase, if used | Someone with this information can access the parent wallet and regenerate its BIP-85 child keys. |
| One set of child recovery words | Someone can access that child wallet, but the child key cannot reveal the parent wallet or sibling child keys. |
| Word count and index | These parameters are not enough to access a wallet by themselves, but you need them to reliably recreate the intended child key. |
An optional passphrase changes the parent wallet
If you generate a BIP-85 child key while using an optional passphrase, that passphrase is part of the parent wallet from which the child key is derived. To regenerate the same child key later, you need the original BitBox02 recovery words, the exact passphrase, the same word count, and the same index.
A different or missing passphrase opens a different parent wallet and therefore produces different child keys. For the broader recovery implications, read how a passphrase works.
Protect every child key
A child key is a complete set of recovery words that controls its child wallet. Even if you intend to rely on the parent wallet for recovery, the child recovery words remain sensitive whenever they exist.
Keep child recovery words offline
Never enter a BIP-85 child key into a computer, smartphone, website, browser extension, password manager, cloud service, or AI chatbot unless you are deliberately restoring that child wallet in a trusted compatible wallet. Anyone who obtains the child recovery words can control the funds in that child wallet.
When BIP-85 can be useful
BIP-85 is most useful when you intentionally want several wallets and prefer one deterministic recovery source. Examples include:
- a limited-value mobile wallet for everyday payments;
- a separate wallet for testing compatible wallet software; or
- a wallet for a family member or another trusted person when everyone understands that the parent-wallet owner retains recovery access.
A child wallet created for someone else is not independent ownership. The person controlling the parent wallet can always regenerate the child key. Explain that clearly, and have the recipient move the funds to a wallet they generated independently when they should have sole control.
A child wallet imported into a smartphone remains a hot wallet. Its BIP-85 origin does not make the phone or wallet app more secure. Limit the funds according to the environment in which the child key will be used.
When BIP-85 is the wrong tool
Do not use BIP-85 because you expect it to protect child wallets from compromise of the parent backup. A passphrase can add a separate secret to a wallet, while multisignature setups can distribute control across multiple keys. These approaches solve different problems from BIP-85.
BIP-85 is also a poor fit when wallets require genuinely independent owners, separate organizational authority, or recovery that must not depend on one parent backup. For those cases, create independent wallets with independent recovery plans.
If you only need one wallet, or if tracking child keys and their parameters would make your setup harder to understand, there is no need to use BIP-85. A simpler setup is often easier to recover correctly years later.
Compatibility with other wallets
A wallet app only needs to support BIP-39 recovery words to restore the wallet represented by a BitBox02 child key. The target app does not need BIP-85 support when you already have the child recovery words.
Regenerating the child key from the parent is different. The wallet or device performing that derivation must support BIP-85 and use the same BIP-39 parameters. Compatibility claims should therefore distinguish between importing an existing child key and regenerating one from the parent wallet.
The BitBoxApp does not provide a way to switch the BitBox02 directly between the parent wallet and a child wallet. In normal use, you generate the child key with the BitBox02 and restore those child recovery words in a separate compatible wallet.
Before you use BIP-85
Before generating a child key:
- define what the child wallet is for and how much value it should hold;
- record its word count, index, and purpose in a way you can understand later;
- document whether the parent wallet depends on an optional passphrase, without storing that passphrase together with the parent recovery words; and
- plan how you will protect both the parent and child recovery words offline.
The word count and index do not replace the recovery words and are not additional security secrets. Recording them prevents you from having to search through possible child keys during recovery.
When you are comfortable with these responsibilities, follow the steps to generate a BIP-85 child key with your BitBox02.