Sealminer DL1 Hydro
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This guide explains BIP 89 Chain Code Delegation in plain English. It covers the problem behind the BIP, why it matters and whether the proposal is part of Bitcoin today.
TL;DR
- What it is: BIP 89 specifies deployed Chain Code Delegation for multisignature wallets. A privileged delegatee keeps the BIP32 chain code associated with a delegator’s base public key and supplies only the scalar tweaks needed for particular signing contexts.
- Why it matters: Chain Code Delegation can reduce balance and activity visibility in collaborative custody without giving away a signing key. Its safety depends on strict role separation, authenticated tweak data, complete verification and uncompromising blind-nonce lifecycle controls.
- Current position: Require a second reviewer and explicit rollback or expiry, and pause payments, signing or network-dependent services until post-change evidence is complete.
BIP 89 Chain Code Delegation in simple English
BIP 89 Chain Code Delegation: The delegator retains a non-extended keypair but no chain code. The delegatee holds the corresponding chain code, computes child tweaks and may share its xpub with other delegatees, limiting what the delegator can scan.
Simple example
A node operator is checking BIP 89 Chain Code Delegation. Its plain protocol is not concurrently secure: sessions must not overlap and every blind nonce must be single-use and erased after signing.
Key terms in plain English
- BIP:
- Bitcoin Improvement Proposal: a document describing a proposed rule, standard or process. Its status must be checked separately.
- Node:
- A computer running Bitcoin software that checks data and communicates with other peers.
Roles and objective
The delegator retains a non-extended keypair but no chain code. The delegatee holds the corresponding chain code, computes child tweaks and may share its xpub with other delegatees, limiting what the delegator can scan.
Derivation boundary
All derivation from the delegated public extended key is non-hardened because the delegatee has no private key. Hardened indices must fail rather than be silently transformed.
Tweak bundle
For each signing context the authenticated bundle maps participant base public keys to 32-byte big-endian aggregate scalar tweaks. Transport is outside the BIP, so deployments must specify authentication, replay protection and versioning.
Non-blinded mode
The delegator receives the child-key tweak and message, can reconstruct the relevant script, verify inputs and optional change, and produce a BIP340 signature while learning only that signing context.
Blinded mode
The alternative reveals only a blinded challenge and parity information. Its plain protocol is not concurrently secure: sessions must not overlap and every blind nonce must be single-use and erased after signing.
Policy limits
Input and change verification can confirm the supplied tweaks reproduce the expected script and help calculate outflow. Recipient, amount and organisational approval checks remain application responsibilities.
How specialists test it
Developers test the proposal with made-up data on an isolated test network. They check normal cases and deliberately invalid cases. Different implementations should reach the same result before anyone relies on the proposal.
Frequently asked questions
What is the main point of BIP 89 Chain Code Delegation?
BIP 89 Chain Code Delegation: The delegator retains a non-extended keypair but no chain code.
For BIP 89 Chain Code Delegation, what should a beginner know about roles and objective?
The delegator retains a non-extended keypair but no chain code. The delegatee holds the corresponding chain code, computes child tweaks and may share its xpub with other delegatees, limiting what the delegator can scan.
For BIP 89 Chain Code Delegation, what should a beginner know about derivation boundary?
All derivation from the delegated public extended key is non-hardened because the delegatee has no private key.
For BIP 89 Chain Code Delegation, what should a beginner know about tweak bundle?
For each signing context the authenticated bundle maps participant base public keys to 32-byte big-endian aggregate scalar tweaks.
Conclusion
Chain Code Delegation can reduce balance and activity visibility in collaborative custody without giving away a signing key. Its safety depends on strict role separation, authenticated tweak data, complete verification and uncompromising blind-nonce lifecycle controls.
Primary sources
Check the current specification status and the documentation for the exact implementation you operate before moving production funds or changing a mining node.
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