1. A method for producing a secure key, the method comprising: receiving a plurality of input keys comprising a first input key, a second input key and a third input key; generating a first output key based on said plurality of input keys comprising said first input key, said second input key and said third input key; and continuing said generating of said first output key via a modified at least one of said plurality of input keys, until said first output key differs from at least one of said plurality of input keys, wherein said first output key is unique and differs from said at least one of said plurality of input keys, and said at least one of said plurality of input keys is a key variation comprising a device identity.