Abstract: A first unit collects and stores data (bar codes 12) and reports to a second unit. The first unit keeps and communicates a first unit current record, for storage, of its (random and unpredictable) activities since last connection and a first unit past record for comparison, of its (random and unpredictable) activities up to last connection. Matching between its previously stored first unit current record and the received first unit past record makes the second unit grant access to the first unit and store the received first unit current record. The same can be done for the second unit by the first unit. Non-coupling invokes provision of extra identification, renewed coupling involving a common default set of records. Records can generate encryption keys. Random data and encryption prevent illegal access.

Abstract: A first unit collects and stores data (bar codes 12) and reports to a second unit. The first unit keeps and communicates a first unit current record, for storage, of its (random and unpredictable) activities since last connection and a first unit past record for comparison, of its (random and unpredictable) activities up to last connection. Matching between its previously stored first unit current record and the received first unit past record makes the second unit grant access to the first unit and store the received first unit current record. The same can be done for the second unit by the first unit. Non-coupling invokes provision of extra identification, renewed coupling involving a common default set of records. Records can generate encryption keys. Random data and encryption prevent illegal access.