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No—if the compromised key is a Tor v3 onion service’s master identity key. A v3 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. Only some auxiliary keys can be replaced while the address remains the same, and that depends on exactly which key was exposed.
The short answer depends on which key leaked
Tor v3 services use several kinds of keys. The long-term master identity key establishes the service’s cryptographic name. Other keys support descriptor signing and operational functions but do not directly encode the onion address.
| Compromised material | Can it be replaced without changing the address? | Immediate implication |
|---|---|---|
Master identity private key, stored by Tor as private_key_ed25519 |
No | The attacker may impersonate the service under the existing address. A replacement identity necessarily has a new address. |
| Blinded signing key or another descriptor-signing key | Potentially, depending on the key and deployment | Remediate the affected signing function, then verify that the master private key and its host were not exposed. |
| OnionBalance shared secret or related operational credential | Potentially, for that function | Change the exposed secret and review manager, instance and host access. This does not replace the aggregate service’s identity key. |
| Host credentials or service-directory access | Not a key-rotation question by itself | Assume the master key may also be compromised until the host and files have been investigated. |
The first task in an incident is therefore identification: determine whether the leaked bytes are the master identity private key or an auxiliary credential. Treating every key as interchangeable can either force an unnecessary address change or leave an impersonation-capable identity key in an attacker’s hands.
Why a v3 address cannot survive master-key replacement
The Tor address specification defines the encoded address as base32(PUBKEY | CHECKSUM | VERSION). The PUBKEY component is the service’s 32-byte Ed25519 master identity public key. The checksum helps detect transcription errors, and the version byte identifies the address format, but neither one gives an operator a way to substitute a different public key.
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Changing the private identity key changes its corresponding public key. Once that public key changes, the base32 value changes as well, so the resulting service has a different 56-character v3 address. Restarting Tor, rebuilding descriptors or changing a configuration path cannot alter this protocol binding.
This is why “rotate the key but keep the name” is not an available recovery operation for a v3 identity compromise. The name is not an account label stored separately from the key; it is an encoding of the public identity itself.
Master identity keys and auxiliary keys have different jobs
Master identity key
The master identity key is long-term. Its public half is the identity component embedded in the onion address, while its private half proves control of that identity. Tor’s documented service-directory layout places the private half in private_key_ed25519. The same directory contains a hostname file holding the service’s onion address.
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Blinded signing keys
Tor derives blinded signing keys from the identity key for descriptor-related operations. These keys have a separate role and are rotated on a schedule. Their rotation is not rotation of the address identity: the address continues to encode the same long-term master public key.
A descriptor-signing-key incident can therefore have a narrower remedy than a master-key incident, but only after you confirm that the derivation source, service host and backups did not expose the master private key as well.
OnionBalance material
OnionBalance adds a manager-and-instance architecture for an aggregate onion service. Its v3 design discusses distributing or deriving descriptor-signing material and includes a shared secret whose compromise can let an attacker impersonate the service until the secret is changed. That secret and those descriptor mechanisms are operational controls; they do not replace the aggregate service’s long-term identity key.
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What to do when the master private key is exposed
- Stop assuming the current address is exclusive. Record the time and circumstances of exposure, but do not describe the old address as safely recovered merely because the legitimate server is still online.
- Scope the breach. Check whether the exposed item is the service directory’s
private_key_ed25519, a blinded or descriptor-signing key, an OnionBalance shared secret, a host credential or a backup containing any of them. Investigate the machine, backups, logs and administrative accounts that could have revealed the master key. - Contain the compromised environment. Restrict access to the old service and preserve evidence according to your incident process. Do not copy the compromised master key into a new deployment as a supposed rotation; that would reproduce the same identity.
- Generate a new v3 identity. Tor’s control-port
ADD_ONIONcommand can generate a new v3 Ed25519 keypair. When Tor generates the pair, it returns the private key unless the request includesDiscardPK. Preserve the returned private key securely because it is the credential for the new address. - Deploy the replacement service. Configure the new identity in a clean, controlled environment and verify that Tor reports a new ServiceID. The new ServiceID is derived from the new public key, so it will not match the compromised address.
- Re-establish trusted distribution. Publish the replacement address through channels whose integrity does not depend on the compromised onion service. Examples include an independently controlled website, a separately protected signing key, an established mailing list or direct communication with known users. The Tor specifications do not define one universal migration channel or a guaranteed client cutover period.
- Retire the old identity deliberately. Explain that the old address must no longer be trusted for authenticity, and remove the compromised private key from active systems after preserving whatever forensic records your incident process requires.
Generating another keypair while leaving the old service advertised does not make both names equivalent. Users need an explicit authenticity signal that distinguishes the replacement address from an attacker’s copy of the old service.
When an address-preserving response may be possible
If investigation proves that only an auxiliary key was exposed, rotate or revoke that key according to the function it serves. For example, a descriptor-signing key may be replaced without changing the master public key encoded in the address. The exact action depends on the key type and the deployment, so first map the credential to its role rather than applying the master-key procedure automatically.
- Confirm that the master private key was never readable by the attacker.
- Check whether the auxiliary key was derived from, stored beside or backed up with the master key.
- Review host access, process memory, administrator accounts and copies of the service directory.
- Rotate the affected auxiliary secret and validate that descriptors or instance authentication use the new material.
- Monitor for continued impersonation or unauthorized publication after the change.
Scheduled blinded-key rotation is normal protocol operation, not evidence that the onion address itself has changed. Clients should continue to use the same address only when the master identity remains trustworthy.
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Single onion service
For a conventional service, the critical artifacts are easy to identify: hostname records the address and private_key_ed25519 holds the master private key. Losing control of the latter means creating a new identity and communicating a new address.
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OnionBalance aggregate service
OnionBalance separates an aggregate service from its backend instances and gives operators additional descriptor-signing and secret-management choices. Those choices can change how an operational compromise is contained, but they do not change the address formula. The aggregate name still depends on its long-term master public key.
When an OnionBalance secret is exposed, change that secret and assess the manager and instances. When the aggregate master key is exposed, follow the new-identity procedure instead; changing only the shared secret cannot restore exclusive control of the aggregate address.
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Calling a new key a “rotation” of the old address
A new keypair is a new identity. Use language such as “replacement service” or “new onion address” so users do not infer that the old name remains cryptographically safe.
Deleting only the hostname file
The hostname file is a record of the address, not the credential that defines it. Removing or editing that file does not invalidate a copied master private key.
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Rotating descriptors while ignoring the host
Auxiliary-key remediation is insufficient if an attacker had filesystem or administrator access that could also reveal the master key. Scope the host compromise before declaring the address identity safe.
Announcing the replacement through the compromised channel alone
An attacker controlling the old identity can repeat or alter an announcement made only through that service. Use at least one independently trusted channel and state clearly which address is replacement and which is no longer trusted.
Assuming client migration is automatic
The specifications establish the key-to-address binding, not a universal migration timetable or a guaranteed percentage of users who will find the new address. Plan outreach for the actual audience and retain the old address only as an incident reference, not as an authenticity anchor.
Quick Recap
Decision checklist
- Was
private_key_ed25519exposed? Create a new v3 identity and address. - Was only a blinded or descriptor-signing key exposed? Investigate scope, rotate that key and verify the master key remains confidential.
- Was an OnionBalance shared secret exposed? Change the secret and review manager and instance access; this alone does not change the aggregate address.
- Is the key type unknown? Treat the incident as unresolved until the artifact is identified and the host and backups are checked.
- How should the new address be announced? Use channels independently protected from the compromised service and do not promise a protocol-defined cutover period.
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