BIP85

BIP85 is a Bitcoin Improvement Proposal for generating child seeds from a master seed, providing deterministic entropy for use in secure key derivation and backup processes.

Blockchain

Updated: Mar 20, 2026

Also known as: deterministic entropy child seed derivation BIP-85

What Is a BIP85?

A BIP85 is a Bitcoin Improvement Proposal that defines a method for generating child seeds from a master seed in a deterministic manner. It provides a secure way to derive multiple cryptographic keys for various purposes while maintaining the integrity and security of the original seed. BIP85 is specifically designed for use in secure key derivation processes, such as wallet backup and recovery.

The process works by using a master seed, typically derived from a BIP39 mnemonic, as the root of a tree-like structure of child seeds. Each child seed can then be used to generate additional keys or entropy, making it possible to create separate, independently usable key sets from the same initial seed. The derivation path follows a standardized format that allows for predictable and repeatable results.

BIP85 is particularly relevant for cryptographic security and backup systems. It allows users to create additional keys or entropy without compromising the security of their original seed. This is critical for use cases like multi-signature wallets or creating backups in different locations. By enabling deterministic entropy generation, BIP85 ensures that users can generate new keys in a secure and verifiable manner without requiring new sources of randomness.

The key characteristics of BIP85 include its reliance on the master seed as the root, the deterministic nature of child seed generation, and its applicability in both key derivation and secure backup scenarios. Its primary advantage is in generating entropy from an existing source, which reduces the need for additional randomization steps, thus improving security and ease of use.

Real-World Examples

Example 1: When setting up a Ledger hardware wallet, BIP85 can be used to generate multiple child seeds from a master seed. This allows the user to create separate keys for different wallets, such as one for long-term storage and another for day-to-day transactions, without compromising the security of the original seed.

Using BIP85, a user can derive different child seeds for each wallet type, making the backup process easier and more secure.
The child seeds can be generated in a deterministic way, meaning they can be rederived anytime using the master seed, ensuring predictable results during wallet recovery.

Example 2: In a multi-signature wallet setup, BIP85 is used to generate child seeds for each cosigner. Each participant's keys are derived from the same master seed, ensuring secure and verifiable key generation while maintaining independence for each cosigner's wallet.

In this setup, BIP85 ensures that each cosigner's key is independently generated but traceable back to the same root seed, enhancing security.
The use of deterministic child seeds reduces the need for additional sources of entropy, making the key generation process simpler and more reliable.

Example 3: A user who needs to store backup keys in multiple locations might use BIP85 to generate child seeds for each backup, all derived from the same master seed. This ensures that if one backup is lost, the others can still be used for recovery.

With BIP85, the user can generate multiple child seeds for backups in different geographic locations while still maintaining the security of the original seed.
The deterministic nature of BIP85 guarantees that the child seeds are exactly the same each time, facilitating easy recovery.