Cryptography – Cryptanalysis
Patent
1992-05-01
1993-09-07
Buczinski, Stephen C.
Cryptography
Cryptanalysis
361 56, 361 58, 361111, 455 1, H04K 102, H04K 300, H02H 900
Patent
active
052436489
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a protective device for computers and the like, adapted to prevent the pick up, the recording and the unauthorized use of data from the computers during the working thereof, and to protect them against high energy transient disturbances taking place on the main A.C. power line.
It is known that normally operating electronic devices can behave both as sources and receivers of electromagnetic waves. More particularly the computers, when considered as receivers can be disturbed or in case damaged by sudden high energy transients (natural lightnings, voltage switchings, switching noises due to transitions in low and medium voltage substations by the supplying company, radiowaves generated by industrial installments, sporadic disturbances caused by house appliances or motorcars, etc.) that can take place on the A.C. power line to which they are connected; when considered as sources, computers can radiate information carrying electromagnetic waves that can nullify the data privacy when properly picked up.
The electromagnetic waves generated from computers and their peripheral equipments (video terminals, printers peripheral disk drivers, tape drivers, etc.) can be either directly radiated through air or guided through the power supply cables and hence along the power distribution network, thus turning this latter in a sort of radiating antenna having quite extended size and easy to be reached by people aiming to unauthorized data gathering.
More precisely, the signals within a data processing system can produce undesired emission through the following mechanisms:
A)--The information can be found recovered as an amplitude or phase modulation of the current adsorbed from the electric main.
This may happens since the power supply has to feed also the current for the signal processing circuit and the interface circuits preparing for and adapting the same to the different periheral devices.
When using a switching power supply, the information signal can be present in form of a modulation of carriers at a rather high frequency.
Indeed, any change of the current drawn from the switching power supply by the load causes a change in the duty cycle of the device acting as a switch (chopper), this latter in turn has switching times quite short and consequentely generates high frequency spectrum components.
It is evident that such signals generated in the feeder circuit propagate more easily as signals guided through the power network.
B)--The radiated emission that is more easily reduced to the information caused by the data processing can originate either from sources within the system or actuated by phoenomena in the outer environment but anyhow strictly related to the electronic circuits controlling the generation of the image for a video terminal and the interfacing circuits, circuitry and wirings connected thereto (graphic boards, color boards, etc.).
Namely, these circuits besides forming the baseband video signals (more than 5 MHz wide), are a source of spurious signals that contains the video signal in form of amplitude modulation, and therefore the confidential information that is the result of the processing system at the precise moment.
The drive for these undesired emission can take place by means of a "beating" with electromagnetic fields present in the environment (circular video channel carriers or AM or FM radio stations carriers), or with electromagnetic fields purposely generated and transmitted by people interested to pick up the confidential information.
EP 0 240 328 in the name of Datasafe Ltd. provides a computer security device, with a view to preventing access to data stored in a computer installation by remote sensing of stray electromagnetic radiation emitted by the installation. This invention, however, can only protect a single computer, to which is directly connected by means of an antenna, at a time, because its type of antenna, being a flexible wire to be wound around the computer connection cables, can be connected to one computer only, and is composed of an e
REFERENCES:
patent: 3806882 (1974-04-01), Clarke
patent: 4802055 (1989-01-01), Beckerman
patent: 4932057 (1990-06-01), Kolbert
patent: 5165098 (1992-11-01), Hoivik
Gilardi Giovanni
Scarazini Severino
Buczinski Stephen C.
Data Protection S.R.L.
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