Cryptography Reference
In-Depth Information
ALICE
LEO Satellite
ST RV/Other
BOB
Albuquerque
New Mexico
BOB
O. Teide,
Cananes
8500km
Figure 9.9
Global key exchange using quantum cryptography.
9.4.2 Global Key Distribution via LEO Satellite
It should be noted that a cryptographic terminal mounted on a satellite is
just one side of a much larger experiment, resulting in a prototype global key
exchange system. Since space vehicles in polar orbits can access the majority
of the surface of the Earth, it makes sense to provide more than one ground
receiving station. Keys exchanged on one continent can be used to secure
those exchanged on another (Figure 9.9). The result is a truly strategic secure
communications system.
9.4.3 Satellite-to-Ground Quantum Key
Distribution Utilizing Entangled Photon Pairs
Using entangled (EPR) photons, it is possible to transmit secure keys to two
places at once (Figure 9.10). The technology required for this system is still im-
mature but could easily be integrated with that developed for the experiments
described above. One key limitation may be the losses associated with the
two optical paths from space to ground. Typically, optical losses due mainly
to diffraction will be (at best) around 15 dB (see Section 9.6). The system will
thus have to be able to cope with about 28-32 dB losses in the pair photon rate.
9.4.4 Other Quantum Key Exchange Scenarios
Further applications include satellite-to-satellite key exchange, particularly
LEO to MEO and GEO satellites. Here the ranges are 1000 to 35,000 km. How-
ever the hardware will be similar to that developed for ground-to-satellite
key exchange, albeit with higher losses. An attractive proposition is to have a
satellite in GEO exchanging keys with a ground station or with LEO satellites
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