Paper 2026/2210 Original: eprint.iacr.org/2026/2210 ↗

Skyhook: Trustless Cross-Chain Value Transfer with a Fully Scriptless Pool

Abstract

Facilitating value transfers with a scriptless chain is a longstanding problem in cryptography. We present a cross-chain messaging and value transfer protocol that maintains game-theoretic atomicity even when one party is operating on a chain which is fully scriptless, such as shielded Zcash, which has no scripting capabilities at all and requires transactions to be virtually identical. The observation is that consensus protocols which utilise segregated witness schemes to ensure transaction ID unmalleability (such as ZIP 244 in Zcash, SegWit in Bitcoin) segregate transaction data from the transaction witness component (which is the part that is actually signed). The transaction identifier is, therefore, a virtually collision-resistant commitment to the effects intended by the transaction, computable before signing, and in many chains, even without the knowledge of the signer. A contract on another chain can therefore recompute a future transaction ID from the few fields it needs to see, such as the recipient, the value and the expiry, while every other part of the transaction arrives as an opaque digest. It learns that any transaction with this ID has the agreed effect, without learning anything about the sender and without the recipient signing anything. An optional zero-knowledge layer hides the recipient and value as well. Combined with a light client for the settlement chain on the Turing-complete chain, this yields fully trustless verification that a shielded payment occurred, with no validator consortium or multisig that can be hacked or stalled.