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Settlement is authorized by two BLS signatures, one from each party, over one fixed message: the SettlementAuth.

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What gets signed

Eight fields, byte-identical for both parties: The message is tagged so a settlement signature can’t be mistaken for anything else. Because it commits to the order, both roots, the Maker’s key and both nullifiers, a signature authorizes exactly one settlement of exactly one trade, against exactly the deposits that existed. At payout, each chain refuses the signature if:
  • it was made over a different order
  • the chain, root or nullifier doesn’t match this payout
  • on the ad chain, the Maker’s key isn’t the one pinned when the order was locked
  • either party’s key isn’t live in the registry
Before signing, each party’s app checks the nullifier against its own half of the trade secret, and the Bridger’s app checks the Maker’s named key on the ad chain.

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Who signs

The trade’s two parties: the Maker’s settlement signer (named on the ad) and the Bridger. Each signs with the key registered for that wallet. The relayer doesn’t sign. Signing happens in the app, with no on-chain transaction. Parties sign independently, in any order.

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After both have signed

As soon as both signatures are in, either party can fetch the pair and keep it, so neither depends on the relayer to settle. The first signer’s signature is never shown before the second has signed. If the Maker’s pinned key ends before the trade settles, the relayer drops the pair and asks both parties to sign again.

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The status ladder

The status also shows whether the Maker has halted settlement, and any reason a payout can’t go through (for example, a nullifier mismatch, in which case the trade is refunded at its deadline). Everything after Signed (2/2) is automatic. The relayer combines, proves and submits; it can’t forge either signature and can’t settle without both.