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Bitcoin Core 0.21 Tor v3 Onion Services: Migration Guide
Bitcoin Core 0.21 Tor v3 guide covering BIP 155 address relay, listenonion migration, key files, permissions, reachability, rollback and privacy tests.
This guide explains Bitcoin Core Tor v3 onion services in plain English. It summarises the important changes, who they affect and what should be checked before an upgrade.
TL;DR
- What it is: Bitcoin Core 0.21 added Tor v3 hidden-service support and BIP 155 address relay. When automatic onion listening was enabled, Core created a v3 service by default and stored its key in onion_v3_private_key, leaving an existing Tor v2 key untouched.
- Why it matters: Tor v3 support modernised Core’s onion reachability in 0.21. Operators still needed to protect the new identity key, validate proxy and inbound paths independently and plan the privacy effects of continuity, rotation and downgrade.
- 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.
What this means in simple English
Bitcoin Core is widely used software for running a Bitcoin node. A release can change networking, wallet tools, transaction policy or operator settings without changing every rule of Bitcoin itself.
Beginners can focus on what changed and why it matters. Node operators should also read the official release notes and test their own configuration before upgrading.
Simple example
Think of the transaction as a form passed between several authorised signers. Each person or device checks the same payment details before adding approval. Passing the form around does not make the payment safe unless every signer checks what it contains.
Key terms in plain English
- BIP
- Bitcoin Improvement Proposal: a document describing a proposed rule, standard or process. Its status must be checked separately.
- Bitcoin Core
- Widely used software that validates Bitcoin and can provide wallet, network and operator tools.
- Node
- A computer running Bitcoin software that checks data and communicates with other peers.
Version boundary
Core 0.21 supported Tor v2 and v3 but default automatic creation moved to v3. Pin Tor and Core versions and distinguish local proxy use from advertising an inbound onion service.
Address relay
BIP 155 addrv2 enables peers to gossip Tor v3 and other longer network addresses. Receiving an address does not establish reachability, identity or trust.
Key files
The old onion_private_key remained untouched, while the v3 private key was stored as onion_v3_private_key. Protect ownership and mode, back up only under an explicit identity-retention policy and never expose either key.
Migration
Create and verify the v3 service, test inbound reachability through independent Tor paths, update authorised peer and monitoring records, then retire old references deliberately.
Rollback
Older Core releases cannot understand every new peers.dat address record and may start with an empty peer database. Keep versioned backups and expect peer discovery to rebuild after downgrade.
Privacy
A stable onion key is a persistent network identity. Decide whether continuity or rotation best fits the threat model, keep clearnet and onion correlations out of public logs and review DNS and proxy fallbacks.
How specialists test it
Node operators test the release on a representative non-production system. They check startup, normal operation, failure handling and restart before changing a live node. Connected wallets, monitoring and mining services should also be checked.
Frequently asked questions
What is Bitcoin Core 0.21 Tor v3 Onion Services?
Bitcoin Core 0.21 added Tor v3 hidden-service support and BIP 155 address relay. When automatic onion listening was enabled, Core created a v3 service by default and stored its key in onion_v3_private_key, leaving an existing Tor v2 key untouched.
Is Bitcoin Core 0.21 Tor v3 Onion Services active or supported today?
Require a second reviewer and explicit rollback or expiry, and pause payments, signing or network-dependent services until post-change evidence is complete.
Why does Bitcoin Core 0.21 Tor v3 Onion Services matter?
Tor v3 support modernised Core’s onion reachability in 0.21. Operators still needed to protect the new identity key, validate proxy and inbound paths independently and plan the privacy effects of continuity, rotation and downgrade.
Do beginners need to use the technical details?
Only if you run a Bitcoin Core node or maintain software that connects to one. Ordinary Bitcoin users can read the summary without changing any software.
Conclusion
Tor v3 support modernised Core’s onion reachability in 0.21. Operators still needed to protect the new identity key, validate proxy and inbound paths independently and plan the privacy effects of continuity, rotation and downgrade.
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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