14-05-2012, 12:52 PM
Quantum Cryptography
Introduction to quantum cryptography.ppt (Size: 682 KB / Downloads: 217)
Cryptography.
Transmitting information with access restricted to the intended recipient even if the message is intercepted by others.
Cryptography is of increasing importance
in our technological age using broadcast, network communications, Internet ,e-mail,
cell phones which may transmit sensitive information related to finances, politics,
business and private confidential matters.
PKC :the modern cryptography
In 1970s the Public Key Cryptography emerged.
Each user has two mutually inverse keys,
The encryption key is published;
The decryption key is kept secret.
Anybody can send a message to Bob
but only Bob can read it.
Elements of the Quantum Theory
Light waves are propagated as discrete quanta called photons.
They are massless and have energy, momentum and angular momentum called spin.
Spin carries the polarization.
If on its way we put a polarization filter
a photon may pass through it or may not.
We can use a detector to check of a photon has passed through a filter.
Heisenberg Uncertainty Principle
Certain pairs of physical properties are related in such a way that measuring one property prevents the observer from knowing the value of the other.
When measuring the polarization of a photon, the choice of what direction to measure affects all subsequent measurements.
If a photon passes through a vertical filter
it will have the vertical orientation regardless of its initial direction of polarization.