Hash Preimage

A hash preimage is the original input data that, when processed through a cryptographic hash function, produces a specific hash output. In the context of Hashed Time-Lock Contracts, the preimage is the secret value that the recipient must disclose to unlock the funds held in the contract.

Because cryptographic hash functions are one-way, it is computationally infeasible to determine the preimage from the hash output alone. The security of the atomic swap depends entirely on the secrecy of this preimage until the moment of settlement.

If the preimage is leaked prematurely, the security of the transaction is compromised. The recipient is incentivized to keep the preimage secret until they are certain they will receive the expected assets.

Once the preimage is revealed to claim the funds, it becomes visible on the blockchain, allowing the other party to use it to complete their side of the swap. This mathematical relationship is the core of the trustless guarantee.

It acts as the digital key that authorizes the release of locked value.