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# 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 ](#troubleshooting ) section.
## Initialization
The database will be automatically created, and your validators registered with it when:
* Importing keys from another source (e.g. Launchpad, Teku, Prysm, `ethdo` ).
See [the docs on importing keys ](./validator-import-launchpad.md ).
* Creating keys using Lighthouse itself (`lighthouse account validator create`)
* Creating keys via the [validator client API ](./api-vc.md ).
## 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 ](#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 – **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
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Lighthouse supports the slashing protection interchange format described in [EIP-3076][]. An
interchange file is a record of blocks and attestations signed by a set of validator keys –
basically a portable slashing protection database!
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With your validator client stopped, you can import a `.json` interchange file from another client
using this command:
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```bash
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](./validator-import-launchpad.md).
---
You can export Lighthouse's database for use with another client with this command:
```
lighthouse account validator slashing-protection export < lighthouse_interchange.json >
```
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The validator client needs to be stopped in order to export, to guarantee that the data exported is
up to date.
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[EIP-3076]: https://eips.ethereum.org/EIPS/eip-3076
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### Minification
Since version 1.5.0 Lighthouse automatically _minifies_ slashing protection data upon import.
Minification safely shrinks the input file, making it faster to import.
If an import file contains slashable data, then its minification is still safe to import _even
though_ the non-minified file would fail to be imported. This means that leaving minification
enabled is recommended if the input could contain slashable data. Conversely, if you would like to
double-check that the input file is not slashable with respect to itself, then you should disable
minification.
Minification can be disabled for imports by adding `--minify=false` to the command:
```
lighthouse account validator slashing-protection import --minify=false < my_interchange.json >
```
It can also be enabled for exports (disabled by default):
```
lighthouse account validator slashing-protection export --minify=true < lighthouse_interchange.json >
```
Minifying the export file should make it faster to import, and may allow it to be imported into an
implementation that is rejecting the non-minified equivalent due to slashable data.
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## Troubleshooting
### Misplaced Slashing Database
If the slashing protection database cannot be found, it will manifest in an error like this:
```
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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/mainnet/validators/slashing_protection.sqlite\"))").
Ensure that `slashing_protection.sqlite` is in "/home/karlm/.lighthouse/mainnet/validators" folder
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```
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 ](#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
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`~/.lighthouse/mainnet/validators/slashing_protection.sqlite` . You can search for your old database
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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 ](#avoiding-slashing )).
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### Slashable Data in Import
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During import of an [interchange file ](#import-and-export ) if you receive an error about
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the file containing slashable data, then you must carefully consider whether you want to continue.
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There are several potential causes for this error, each of which require a different reaction. If
the error output lists multiple validator keys, the cause could be different for each of them.
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1. Your validator has actually signed slashable data. If this is the case, you should assess
whether your validator has been slashed (or is likely to be slashed). It's up to you
whether you'd like to continue.
2. You have exported data from Lighthouse to another client, and then back to Lighthouse,
_in a way that didn't preserve the signing roots_ . A message with no signing roots
is considered slashable with respect to _any_ other message at the same slot/epoch,
so even if it was signed by Lighthouse originally, Lighthouse has no way of knowing this.
If you're sure you haven't run Lighthouse and the other client simultaneously, you
can [drop Lighthouse's DB in favour of the interchange file ](#drop-and-re-import ).
3. You have imported the same interchange file (which lacks signing roots) twice, e.g. from Teku.
It might be safe to continue as-is, or you could consider a [Drop and
Re-import](#drop-and-re-import).
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If you are running the import command with `--minify=false` , you should consider enabling
[minification ](#minification ).
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#### Drop and Re-import
If you'd like to prioritize an interchange file over any existing database stored by Lighthouse
then you can _move_ (not delete) Lighthouse's database and replace it like so:
```bash
mv $datadir/validators/slashing_protection.sqlite ~/slashing_protection_backup.sqlite
```
```
lighthouse account validator slashing-protection import < my_interchange.json >
```
If your interchange file doesn't cover all of your validators, you shouldn't do this. Please reach
out on Discord if you need help.
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## 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][license].
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[license]: https://github.com/sigp/lighthouse/blob/stable/LICENSE
