amountof the traded assets (synthetic and collateral), as well as
expirationTimestampof the order and a
nonce(to prevent replay attacks).
assetIdof the two orders matches (i.e. bought
assetIdof one is the sold
assetIdof the other)
assetIdis the collateral.
starkKeythat corresponds to the order's
expirationTimestampof the order refers to the future.