Slashing

TL;DR

Slashing is the mechanism that makes proof-of-stake economically secure. Validators who attack the chain have evidence of the attack posted on-chain and are tombstoned, which removes them from the active validator set. On the testnet today slashing is tombstone-only: no stake is burned. Burning part of the stake is planned, not live. All slashing is keyed on objectively verifiable evidence. There is no human jury.

Slashable offenses

Today, only one behaviour is slashable, with a second planned:

• Double-signing. Casting two conflicting finality votes for the same round, or producing two different blocks for the same slot. This is what a validator would do to attack GRANDPA finality. Always a bug or an attack - never an accident.
• Prolonged downtime (planned, not live). A downtime penalty for missing more than a threshold fraction of blocks is planned. Today an offline validator simply misses the rewards it would have earned.

Being offline briefly, being slow, running old software, disagreeing with governance - none of these are slashable. Slashing is only for protocol-breaking behaviour.

Evidence & detection

For double-signing: anyone who sees two conflicting signed votes from the same validator can post them as evidence in a slashing transaction. The chain verifies the signatures mathematically - no judgement call required. If both signatures verify against the same validator pubkey at the same height and round but sign different hashes, the slashing contract fires.

For downtime: there is no automatic downtime slash on the testnet today. A downtime penalty is planned.

The tombstone

A slashed validator's state gets a tombstone marker set to true and the validator is removed from the active set. Tombstone is permanent and irreversible. The validator's pubkey is banned from rejoining the candidate set, even if they unbond and try again with the same key.

Permanence is on purpose. A validator who double-signs has demonstrated either a catastrophic operational failure or active malice. Either way, they don't get another chance with that key.

Stake impact

No stake is burned today. On the testnet, a slash tombstones the validator and removes it from the active set; its bonded ASE is not reduced. Burning a fraction of the stake on top of the tombstone is planned, and the fractions will be published before it goes live.

Losing the seat still costs a tombstoned validator every future reward from that key, which is the penalty that matters today.

Recovery

After a slash, the validator can still unbond its stake (1,296,000 blocks, about 30 days at 2-second blocks; longer when blocks are slower). But the tombstoned key is dead forever. To rejoin the validator set, the operator must register a new validator with a new Dilithium3 key, and any reputation they had is reset.

For operators, the practical implication is that your validator key is your identity. Protect it; back it up; do not run it on two machines at once. For that story, see Slashing Risks and Validator Key Backup.

Delegators (future)

Delegation is not live on the testnet; it is coming in a future update. Validators bond only their own ASE today, so a slash affects only the validator itself. How penalties will apply to delegated stake will be defined when delegation ships. See Delegation.