The cryptographic unit operates in {HEAD ~ response} to a specific authorized user giving permission to undertake a specific cryptographic operation on data input to the BCU only upon {TAIL ~ the specific authorized user} being determined as an authorized BCU user, whereby a specific private key corresponding to the specific authorized user is enabled for use in the specific cryptographic operation after which the specific private key is disabled 
The cryptographic unit operates in { HEAD ~ response } to a specific authorized user giving permission to undertake a specific cryptographic operation on data input to the BCU only upon { TAIL ~ the specific authorized user } being determined as an authorized BCU user , whereby a specific private key corresponding to the specific authorized user is enabled for use in the specific cryptographic operation after which the specific private key is disabled
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