The invention provides a computer-implemented control method and corresponding system. The method may control or influence a device, system or other resource such as a technical process. The invention can provide a mechanism for emulating or otherwise executing the functionality of a logic gate via a computer-based distributed ledger (blockchain). This may be the Bitcoin blockchain or an alternative network/protocol. The invention provides logic embedded within a redeem script such that it determines which particular private keys have been used to sign an unlocking script, and then interprets the provision of those keys in accordance with a predetermined function. In a preferred embodiment, the method may comprise the steps of providing a blockchain Transaction comprising a redeem script for an output, wherein the redeem script: i) specifies a plurality of public keys, each associated with a corresponding private key; and wherein each public key is uniquely associated with a potential state of at least one data source; and ii) comprises logic arranged to provide a result based on which of the plurality of associated private key(s) is used to sign the unlocking script; wherein a minimum number of said private keys must be used to sign an unlocking script of a further blockchain Transaction in order to spend the output. Preferably, the logic is arranged to implement the functionality of a logic gate such as a NOT, AND, OR, NOR, XOR, IMPLY, NAND, NONIMPLY or XNOR gate.