The invention provides a computer-implemented method and corresponding system which is implemented using an electronic ledger such as a blockchain. This may or may not be the Bitcoin blockchain. The invention can be used to implement, execute and/or control the performance of a task or process. A method according to the invention comprises the steps of generating a blockchain Transaction which comprises: at least one signed input which comprises a value; and at least one modifiable output. It further comprises the step of extracting the value from the signed input and providing it to a portion of logic to obtain a result; and using the result to modify the output of the Transaction. The transaction provides a record and/or representation of the execution of the portion of logic and/or the result. The signed input is provided to the Transaction using an unlocking script. The at least one input is signed using a signature hash type which renders the input as non-modifiable. This may be the signature hash type SIGHASH_NONE. The Transaction may further comprise at least one unsigned input. The unsigned input may be signed after the output has been modified. The unsigned input can be signed using a signature hash type which prevents modification of the whole Transaction, and may be the signature hash type is SIGHASH_ALL. Further the value can be embedded in a public key associated with the signed input; and extracted from the public key so as to provide it to the portion of logic. The portion of logic can be arranged to implement the functionality of a logic gate or combination of gates, such as an AND, NOT, OR, NOR, XOR, IMPLY, NAND, NONIMPLY or XNOR gate. Thus, the invention provides a highly versatile and useful technical approach for implementing tasks using a blockchain.