Slashing Protection

The security of Ethereum 2.0's proof of stake protocol depends on penalties for misbehaviour, known as slashings. Validators that sign conflicting messages (blocks or attestations), can be slashed by other validators through the inclusion of a ProposerSlashing or AttesterSlashing on chain.

The Lighthouse validator client includes a mechanism to protect its validators against accidental slashing, known as the slashing protection database. This database records every block and attestation signed by validators, and the validator client uses this information to avoid signing any slashable messages.

Lighthouse's slashing protection database is an SQLite database located at $datadir/validators/slashing_protection.sqlite which is locked exclusively when the validator client is running. In normal operation, this database will be automatically created and utilized, meaning that your validators are kept safe by default.

If you are seeing errors related to slashing protection, it's important that you act slowly and carefully to keep your validators safe. See the Troubleshooting section.


The database will be automatically created, and your validators registered with it when:

Avoiding Slashing

The slashing protection database is designed to protect against many common causes of slashing, but is unable to prevent against some others.

Examples of circumstances where the slashing protection database is effective are:

  • Accidentally running two validator clients on the same machine with the same datadir. The exclusive and transactional access to the database prevents the 2nd validator client from signing anything slashable (it won't even start).
  • Deep re-orgs that cause the shuffling to change, prompting validators to re-attest in an epoch where they have already attested. The slashing protection checks all messages against the slashing conditions and will refuse to attest on the new chain until it is safe to do so (usually after one epoch).
  • Importing keys and signing history from another client, where that history is complete. If you run another client and decide to switch to Lighthouse, you can export data from your client to be imported into Lighthouse's slashing protection database. See Import and Export.
  • Misplacing slashing_protection.sqlite during a datadir change or migration between machines. By default Lighthouse will refuse to start if it finds validator keys that are not registered in the slashing protection database.

Examples where it is ineffective are:

  • Running two validator client instances simultaneously. This could be two different clients (e.g. Lighthouse and Prysm) running on the same machine, two Lighthouse instances using different datadirs, or two clients on completely different machines (e.g. one on a cloud server and one running locally). You are responsible for ensuring that your validator keys are never running simultanously – the slashing protection DB cannot protect you in this case.
  • Importing keys from another client without also importing voting history.
  • If you use --init-slashing-protection to recreate a missing slashing protection database.

Import and Export

Lighthouse supports v4 of the slashing protection interchange format described here. An interchange file is a record of all blocks and attestations signing by a set of validator keys – basically a portable slashing protection database!

You can import a .json interchange file from another client using this command:

lighthouse account validator slashing-protection import <my_interchange.json>

Instructions for exporting your existing client's database are out of scope for this document, please check the other client's documentation for instructions.

When importing an interchange file, you still need to import the validator keystores themselves separately, using the instructions about importing keystores into Lighthouse.

You can export Lighthouse's database for use with another client with this command:

lighthouse account validator slashing-protection export <lighthouse_interchange.json>


Misplaced Slashing Database

If the slashing protection database cannot be found, it will manifest in an error like this:

Oct 12 14:41:26.415 CRIT Failed to start validator client        reason: Failed to open slashing protection database: SQLError("Unable to open database: Error(Some(\"unable to open database file: /home/karlm/.lighthouse/medalla/validators/slashing_protection.sqlite\"))").
Ensure that `slashing_protection.sqlite` is in "/home/karlm/.lighthouse/medalla/validators" folder

Usually this indicates that during some manual intervention the slashing database has been misplaced. This error can also occur if you have upgraded from Lighthouse v0.2.x to v0.3.x without moving the slashing protection database. If you have imported your keys into a new node, you should never see this error (see Initialization).

The safest way to remedy this error is to find your old slashing protection database and move it to the correct location. In our example that would be ~/.lighthouse/medalla/validators/slashing_protection.sqlite. You can search for your old database using a tool like find, fd, or your file manager's GUI. Ask on the Lighthouse Discord if you're not sure.

If you are absolutely 100% sure that you need to recreate the missing database, you can start the Lighthouse validator client with the --init-slashing-protection flag. This flag is incredibly dangerous and should not be used lightly, and we strongly recommend you try finding your old slashing protection database before using it. If you do decide to use it, you should wait at least 1 epoch (~7 minutes) from when your validator client was last actively signing messages. If you suspect your node experienced a clock drift issue you should wait longer. Remember that the inactivity penalty for being offline for even a day or so is approximately equal to the rewards earned in a day. You will get slashed if you use --init-slashing-protection incorrectly.

Slashable Attestations and Re-orgs

Sometimes a re-org can cause the validator client to attempt to sign something slashable, in which case it will be blocked by slashing protection, resulting in a log like this:

Sep 29 15:15:05.303 CRIT Not signing slashable attestation       error: InvalidAttestation(DoubleVote(SignedAttestation { source_epoch: Epoch(0), target_epoch: Epoch(30), signing_root: 0x0c17be1f233b20341837ff183d21908cce73f22f86d5298c09401c6f37225f8a })), attestation: AttestationData { slot: Slot(974), index: 0, beacon_block_root: 0xa86a93ed808f96eb81a0cd7f46e3b3612cafe4bd0367aaf74e0563d82729e2dc, source: Checkpoint { epoch: Epoch(0), root: 0x0000000000000000000000000000000000000000000000000000000000000000 }, target: Checkpoint { epoch: Epoch(30), root: 0xcbe6901c0701a89e4cf508cfe1da2bb02805acfdfe4c39047a66052e2f1bb614 } }

This log is still marked as CRIT because in general it should occur only very rarely, and could indicate a serious error or misconfiguration (see Avoiding Slashing).

Limitation of Liability

The Lighthouse developers do not guarantee the perfect functioning of this software, or accept liability for any losses suffered. For more information see the Lighthouse license.