In some examples, a system includes a first processor, a second processor, and a storage medium to store first information comprising machine-readable instructions executable by the second processor. The first processor is to validate the machine-readable instructions using an iterative validation process involving a plurality of iterations at different times, where each respective iteration of the plurality of iterations includes issuing a respective indication to the second processor to compute a value based on a respective subset of the first information, wherein the respective indication includes respective subset information identifying the respective subset, wherein the respective subset information differs from different subset information included in another indication issued in another iteration of the plurality of iterations, the different subset information identifies a different subset of the first information. Each iteration further includes determining a validity of the machine-readable instructions based on the value returned to the first processor by the second processor.