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No—if the compromised key is the v3 onion service’s master identity key. A v3 onion address is derived from that key’s 32-byte Ed25519 public key, plus a checksum and version byte. Replacing the identity key therefore produces a different 56-character address. Rotating descriptor-signing, blinded-signing, or other auxiliary keys can be possible without changing the address, but those are different keys with different jobs.
The first incident-response question is consequently not “How do I restart Tor?” but “Which key was exposed?” The answer determines whether you can remediate one function or must migrate every user to a new address.
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Why a v3 onion address cannot survive master-key replacement
Tor v3 names are not arbitrary labels stored in a configuration file. The address specification defines an onion address as a base32 encoding of three fields: the service’s public identity key, a checksum, and a version byte. The public-key field is the 32-byte Ed25519 master public key, commonly identified as KP_hs_id.
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That construction creates a permanent cryptographic binding. Anyone who decodes the address can recover the public identity key that the address represents. If you generate a replacement private key, its public half is different, so the encoded address is different as well. Editing a text file, restarting the daemon, changing a hostname, or replacing a descriptor key cannot alter that mathematical relationship.
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What the 56-character address represents
- Identity: the 32-byte Ed25519 master public key.
- Integrity: a checksum that helps detect malformed addresses.
- Version: the v3 format indicator.
The result is the familiar 56-character v3 onion name. The address is therefore an identifier for a keypair, not a movable pointer that can be reassigned to another keypair.
Why a restart does not help
A service restart may reload keys or publish fresh descriptors, but it does not replace the public key encoded in the address. Keeping the old address requires keeping the same master identity key. If that private key has been copied by an attacker, retaining the address also means retaining an identity that is no longer under your exclusive control.
Identify the compromised key before deciding whether to migrate
A v3 service uses several kinds of key material. They are not interchangeable, and compromise of one does not automatically prove compromise of the others. Verify the exact file, process, control-port response, backup, or host credential involved.
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| Material | Primary role | Address impact | Immediate question |
|---|---|---|---|
Master Ed25519 identity private key, documented as private_key_ed25519 |
Defines the long-term service identity and the public key encoded in the v3 address | Compromise requires a new identity and a new address | Could an unauthorized party copy or use this private key? |
| Blinded signing keys | Derived operational keys used for descriptor-related signing and privacy-preserving operation | Rotating them does not rotate the address | Was exposure limited to a current blinded key or its storage? |
| Other descriptor-signing material | Signs service information during publication | Usually a narrower remediation, subject to the exact design and exposure | Can you revoke or replace this signing material without exposing the master key? |
| OnionBalance shared secret or instance credentials | Coordinates an aggregate service and its instances | Changing the secret does not replace the aggregate identity encoded in the address | Was the aggregate identity key also accessible? |
| Host or account credentials | May grant access to the machine, service directory, backups, or control port | Impact depends on what those credentials allowed an attacker to read or invoke | Could the attacker reach the master key indirectly? |
Tor’s documented service-directory layout places the address in hostname and the private master key in private_key_ed25519. Seeing a compromised host, account, backup, or deployment pipeline is therefore not proof that only an auxiliary key was exposed; investigate whether those paths could also read the master key.
What to do when the master identity private key is exposed
Treat the existing address as an identity that an attacker may be able to impersonate. The objective is containment and a controlled migration, not an attempt to preserve the old name.
- Contain the exposure. Isolate the affected host, account, backup, CI job, control-port client, or administrator workstation. Preserve logs and copies needed for incident analysis, but do not continue distributing the suspected key.
- Confirm the key’s role. Establish whether the leaked material is the service’s
private_key_ed25519or a different operational key. Also check whether the attacker had filesystem, backup, or control-port access that could have exposed the master key even if the original alert named another secret. - Assume the old address is no longer exclusive. A person holding the master private key can create valid identity signatures for that address. Clients cannot distinguish your legitimate use from an attacker’s use merely because you restart your own service.
- Generate a new Ed25519 v3 identity. Tor’s control protocol supports
ADD_ONIONwith either a supplied private key or a newly generated v3 keypair. When Tor generates the pair, it returns the private key unlessDiscardPKis requested. Capture and protect the returned key through a controlled secret-management process; suppressing the return is appropriate only when you already have a reliable way to preserve the private key. - Build the replacement service around the new key. Use a new service identity and verify that Tor reports a new ServiceID and address. Keep the old service and its evidence separate while you validate the replacement; do not overwrite the only copy of incident data.
- Move content and administration carefully. Recreate the service configuration, application data, access controls, monitoring, and backups without copying the compromised identity key into the replacement. Review every automation step that previously handled the old service directory.
- Publish the new address through independent channels. Use channels whose integrity does not depend solely on the compromised onion service: an already authenticated operator account, a separately protected website or repository, a signed release process, or direct communication with known users. State clearly that the former address must no longer be trusted for identity.
- Retire the old identity according to your threat model. Stop serving the old instance when the new address is available and users have a credible way to learn it. Continue monitoring the old name for impersonation reports, but never treat continued availability of the old service as proof that it is authentic.
- Rotate adjacent secrets. Change host credentials, control-port authentication, deployment tokens, backups, and application secrets that may have been reachable during the incident. A new onion key does not repair a compromised operating environment.
What users need to know
Tell users exactly which address is being retired, which new address replaces it, when the change takes effect, and how the announcement was authenticated. Do not imply that the old address has been “updated” or “rekeyed.” It is a different identity and must be validated through the independent channel you chose.
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When an auxiliary key is the only thing exposed
If investigation shows that the master private key remained protected, the address may not need to change. Remediation should match the exposed key’s function and lifetime.
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Tor derives blinded signing keys from the long-term identity key and rotates them on a schedule. They support descriptor signing and related protocol operations; they are not the public key encoded in the address. Replacing a blinded key therefore addresses its own exposure without creating a new onion name, provided the master key and the surrounding host remain trustworthy.
Descriptor-signing keys
Descriptor material can have a narrower validity period and role than the master identity. Determine which descriptors could have been forged, replace the affected signing material using the mechanism appropriate to your deployment, and inspect whether the attacker could also read the master key. Do not infer address safety solely from the label “descriptor key.”
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OnionBalance secrets and instance credentials
OnionBalance deployments separate an aggregate service from backend instances and provide designs for distributing or deriving descriptor-signing material. A compromised shared secret can let an attacker impersonate the service within that architecture until the secret is changed. Rotate the secret and review every instance, manager, and transport that used it. This is still not a method for replacing the aggregate service’s master identity key while retaining its encoded address.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.OnionBalance does not create an address-preserving rekey
OnionBalance changes how an aggregate service is operated, not how a v3 name is formed. The aggregate address remains bound to its long-term public identity key. Managers and instances may have additional keys, secrets, and descriptor-signing arrangements, so an incident can require several targeted rotations. None of those mechanisms permits a replacement aggregate identity key to claim the old address.
Keep the scopes separate during response: rotate the exposed OnionBalance secret or instance material where appropriate, while treating any exposure of the aggregate master private key as a full identity compromise.
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Common mistakes that prolong an onion-key incident
- Replacing only
hostname: a hostname file records the address; changing text there cannot make a different key authenticate as that address. - Rotating a blinded key and declaring victory: scheduled operational-key rotation does not repair exposure of the master identity key.
- Reusing the old private key for convenience: this preserves the very identity that may be controlled by an attacker.
- Announcing the replacement solely on the old onion site: users have no independent way to know that announcement was not forged.
- Deleting evidence before scoping access: removal can destroy logs needed to determine whether backups, control-port clients, or other hosts were also exposed.
- Assuming a new backend fixes an old address: changing servers or applications does not change the cryptographic identity represented by the address.
A practical decision checklist
Use this sequence to make the rotation decision:
- Locate the exact secret or credential reported as compromised.
- Map it to the Tor key role: master identity, blinded signing, descriptor signing, OnionBalance secret, or host access.
- Determine whether the attacker could read or use
private_key_ed25519, including through backups and automation. - If yes, generate a new Ed25519 v3 identity and plan a new address; do not promise address preservation.
- If no, rotate only the affected auxiliary material, validate its replacement, and keep the existing address under observation.
- Communicate any address change through an independently trusted channel and document the authentication method.
- Review the entire environment for secondary compromise before declaring the incident closed.
What the specifications do not promise
Tor’s specifications establish the address-to-public-key binding and describe the relevant key roles and control-port behavior. They do not set a universal migration deadline, guarantee that every client will recover a replacement address, or provide a single communication channel that is trusted for every audience. Those outcomes depend on how users obtained the original address and which independent channels the operator can authenticate.
The protocol-level conclusion is firm even when the operational timeline is not: a compromised master identity cannot be swapped out under the same v3 name. Only a new identity and a new address restore exclusive control.
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