1. A method of dynamic key cryptography, the method comprising: selecting a subset from a set of minutia types; for a particular device, sending a challenge to the device, wherein: the challenge includes information from which the device can collect actual values of minutia corresponding to the selected subset of minutia types in order to form a cryptographic key; the cryptographic key is never transmitted from the device across any communication channel; and the cryptographic key is used to encrypt an actual response to the challenge; pre-processing a set of responses to the challenge based on tracking updates of minutia from which the selected subset of minutia types is selected, wherein: the set of pre-processed responses covers a range of all actual responses possible to be received from the particular device if the combination of the particular device with collected actual values of minutia is valid; comparing the actual response from the particular device to the set of pre-processed responses; and validating the combination of the particular device with the collected actual values if the actual response is included in the set of pre-processed responses for the particular device,