Bonds, challenges and slashing

Bonds

A bond is money locked behind a bonded atom. It is what an attacker forfeits when a claim resting on that atom is proven false.

• Posting. PostBond { class, label, amount } draws USD from the sender’s coins and posts it behind the atom bond:<sender>:<label> (class Economic, Institutional or Adjudicator). Posting again tops the bond up. Only the sender can bond its own atoms.
• Locking. When a claim is issued, every bond it rests on (directly, through the claims it references, or as its adjudicator) is locked until the end of the claim’s challenge period. A claim’s cost of corruption therefore cannot quietly fall after someone relies on it.
• Withdrawing. After the lock, WithdrawBond { atom } returns the part that is neither slashed nor reserved. There is no CLI command for it yet.

A bond’s state is visible in sion claim show:

"bond": {
  "amount": 50000000,
  "atom": "05ab20b32354fee47b00f925cbe55bee5f3c5d80f248e7f9d7f159ac9168b90b",
  "locked_until": 5147,
  "owner": "51af757f7b8c05fb893f2aa8ea2282edc04e13af93b41d672515563df2cf6d8f",
  "pool": 0,
  "reserved": 0,
  "slashed": 0
}

Challenges

Anyone can challenge a claim until its challenge period ends.

Challenge { claim, target, evidence, deposit }:

• target must be a bonded atom the claim rests on directly. To dispute an atom that a referenced claim rests on, challenge that claim, under its own adjudicator. (The claim’s adjudicator was chosen by the party that put that atom at stake.)
• The claim must name an adjudicator. A claim without one cannot be challenged in this implementation.
• evidence is a digest of the counter-evidence; the evidence itself lives elsewhere.
• deposit is drawn from the challenger’s coins, against frivolous challenges.

The challenge’s identifier hashes the claim, the target, the evidence and the challenger. It appears in the ChallengeOpened event; sion events prints it.

Rulings

Rule { challenge, upheld } must be sent by the owner of the adjudicator atom’s bond. The adjudicator must not itself be broken, and a challenge is decided once.

• Rejected. The challenger’s deposit goes to the owner of the challenged bond.
• Upheld. The deposit returns to the challenger, and the target atom is broken:
  1. Slash. The bond’s entire unslashed amount moves to a pool held for compensation.
  2. Falsify. Every active claim is re-evaluated in issue order; a claim whose formula is now false is falsified, and so is everything resting on it.
  3. Compensate. Every live reservation on a falsified claim is paid from the pools of its broken atoms: its allocation divided by κ, up to its value at risk. Reservations on claims that still hold but lost an atom become degraded.
  4. Release. Pool funds beyond every outstanding liability are released: a share to the challenger (challenger_share_permille, 500 on the devnet, that is half) and the rest to the treasury.

Victims are paid first: compensation comes out of the pool before the challenger’s share.

On the devnet

Dana’s claim rests on her 50 USD bond deliveries; the judge’s 200 USD adjudicator bond settles disputes; Erin relied on the claim for 10 USD (reserving 20 USD). Frank challenges:

$ sion challenge frank b677314a931e86fee2403fe437822ec7d087f0df37dbd9452735b16177c41634 05ab20b32354fee47b00f925cbe55bee5f3c5d80f248e7f9d7f159ac9168b90b 1 --evidence "the dock log shows no delivery"
frank signs: Challenge assumption 05ab20b3 of claim b677314a, depositing 1 USD. Fee 0.0012 USD; valid until Pulse 71.
Pulse 53: Done: challenge opened against assumption 05ab20b3 of claim b677314a; fee 0.0012 USD.
  digest f30a2fcab05141770b82dd8949581829b3fad5886e7904b143ba13283bb14792

$ sion events --from 53 --limit 10
Pulse    53  {"ChallengeOpened":{"challenge":"7b4e969a2f903a5b35b0f661d8908eff35fb3c6607036316d55752593a1dce07","claim":"b677314a931e86fee2403fe437822ec7d087f0df37dbd9452735b16177c41634","target":"05ab20b32354fee47b00f925cbe55bee5f3c5d80f248e7f9d7f159ac9168b90b"}}

$ sion rule judge 7b4e969a2f903a5b35b0f661d8908eff35fb3c6607036316d55752593a1dce07 --upheld
judge signs: As adjudicator, uphold challenge 7b4e969a. Fee 0.0011 USD; valid until Pulse 73.
Pulse 56: Done: 50 USD slashed from assumption 05ab20b3; claim b677314a falsified; account f9b79999 compensated 10 USD; challenge upheld; fee 0.0011 USD.
  digest 60734219cf31f2903e3c2af0c10d5cce4c869ea90bf56f32b94eefc9466b8451

Erin (f9b79999) went from 99.9988 to 109.9988 USD. Frank got his 1 USD deposit back plus half of the 40 USD left in the pool after compensation, ending at 119.9988 USD. The claim’s status became Falsified { at: Pulse(56), causes: [AtomId(05ab20b3)] } and its cost of corruption 0.

In this implementation

• Built: bonds, locks, withdrawal, challenges with deposits, rulings, slashing, falsification propagation, compensation, release to the challenger and the treasury.
• Not built: automatic slashing when a contradiction is cryptographically checkable (every challenge needs an adjudicator).
• Separate: validators’ stake is slashed for equivocation by its own transaction, outside the Assurance Algebra; see Slashing for equivocation.