Patent ID: 8164419

Claim:
An electronic lock box apparatus, comprising: an electrical power source, a controller circuit, a memory circuit, a precise time counter, a secure compartment having an actuatable access member, a manual data entry apparatus, and a device read/write port; and a separate portable memory device that exchanges data with said device read/write port, said portable memory device containing a plurality of alterable memory elements that store a data value P; wherein, said controller circuit is configured: (a) to read said data value P that is stored on said portable memory device; (b) to calculate, using a predetermined message digest function, an encryption key value K, wherein said predetermined message digest function is seeded with an initial value J that is based on a current value T of said precise time counter, and wherein said encryption key value K changes as said value T of said precise time counter changes; (c) to receive a user-determined code C that is entered at said manual entry apparatus; (d) to process, said predetermined message digest function, said user-determined code C, and said encryption key value K, to generate a message digest result Q; (e) to compare said data value P to said message digest result Q, and if P=Q, then to grant access to said secure compartment by actuating said access member; (f) said message digest result P changes state when said current value T of said precise time counter reaches a predetermined value U 2 that is sufficiently different in numeric units from an earlier value U 1 of said current value T of said precise time counter; and (g) said user enters a user-selected value C 2 at a central computer apparatus during a first epoch time interval to be processed and to generate a message digest result P 1 that is stored on said portable memory device as said data value P, and then presents said portable memory device to said electronic lock box apparatus during a second epoch time interval and enter said user-determined code C at said manual entry apparatus, and if C=C 2 , then: (i) if said portable memory device was most previously updated by said central computer apparatus with said data value P during said second epoch time interval, then said data value P will be equal to said message digest result Q and said access to said secure compartment will be granted by said electronic lock box apparatus; and (ii) if said portable memory device was most previously updated by said central computer apparatus with said data value P during a moment other than said second epoch time interval, then said data value P will not be equal to said message digest result Q and said access to said secure compartment will not be granted by said electronic lock box apparatus.