1. A machine comprising: a processor system with at least one processor; and a memory system with one or more machine readable media, the machine readable media storing thereon one or more instructions, which when executed cause the processor system to implement a method including at least acquiring two sets of user identifying data, via different acquisitions; transforming, by the processor system, the user identifying data, the transforming including at least a mapping of one of the two sets of user identifying data onto another of the two sets of user identifying data, calculating, by the processor system, an invariant from one or more transformations of the user identifying data, the transforming of the user identifying data being a result of the one or more transformations, the invariant being a relationship between two objects that, within a tolerance determined prior to authentication, does not change under the one or more of the transformations between the two objects, and generating by the processor system, an authentication key based on the invariant.