What is double signing?
- Author
- CRYPTO PORT Editorial
- Published
- Updated
- Reading time
- 5 min
In short
Double signing is when a validator issues two contradictory signatures for the same height or the same vote. It is treated as abetting a chain split and carries the heaviest slashing penalty on most networks. In practice, the cause is rarely malice — it is usually the operational mistake of running two nodes on one key.
Key points
- Issuing two conflicting signatures for the same thing
- Punished hardest because it abets chain splits
- Usually caused by running two nodes on one key
- Detected when anyone submits the conflicting pair as evidence
Definition
Issuing mutually contradictory signatures with the same validator key for the same block height or vote. Also known as equivocation.
Proof-of-stake safety assumes each validator supports exactly one history. Signing two different blocks at the same height leaves the network unable to tell which one the validator backs, and the fork cannot resolve.
Anyone can submit the conflicting pair to the chain as evidence. Once submitted, a portion of the validator's stake is confiscated and the validator is normally ejected from the active set. Some designs scale the penalty up sharply when many validators offend at once.
The most common real cause is an operator starting a standby node while the primary was in fact still running. If both load the same signing key, each believes it is the legitimate one and signs. Restoring from a backup produces the same outcome.
The defences are a slashing-protection database that refuses to sign below an already-signed height, and an architecture where the key can only be used in one place. Achieving redundancy by naively running two instances is the single most dangerous design.
Watch out for
- · Accidental double signing is punished exactly like deliberate double signing
- · If you delegate, your validator's double signing can reduce your own principal
- · Migrating a server without carrying over the slashing-protection history risks an offence