-SECRECY ENSURED

TECHNOLOGYKEY DISTRIBUTUION CLASSICAL CRYPTOGRAPHY QUANTAM CRYPTOGRAPHY WORKING INTRODUCTION SECURITY CONCLUSION ADVANTAGESLIMITATIONS

 The recent application of the principles of quantum mechanics to cryptography has led to a remarkable new dimension in secret communication.  Quantum cryptography is an effort to allow two users of a common communication channel to create a body of shared and secret information.

 The whole point of cryptography is to keep information out of the hands of anyone but its intended recipient.  Even if the message gets intercepted, the meaning won’t be apparent to the intercepted – unless the interceptor is able to decipher it.

Principle of Cryptography.

 Alice wants to send a message to Bob, without an eavesdropper Eve intercepting the message.

CRYPTOGRAPHY Classical Quantum

 Encryption algorithm and related key are kept secret.  Breaking the system is hard due to large numbers of possible keys.  For example: for a key 128 bits long there are – keys to check.

 An important and unique property of quantum cryptography is the ability of the two communicating users to detect the presence of any third party trying to gain knowledge of the key.  Quantum technology promises to revolutionize secure communication at an even more fundamental level.

 Quantum Cryptography – ensuring the most secure transmission of the secret information – works on the principle of – “ Quantum Mechanics”.  Transmission is carried out at the bit level with the help of various types of alignment of the photons.  It also solves the problem of key distribution arising in the Classical Cryptography.

 A user can suggest a key by sending a series of photons with random polarizations. This sequence can then be used to generate a sequence of numbers. The process is known as quantum key distribution. Main Features:  Key distribution distance: up to 60 km  Key distribution rate: up to 1000 bits/s

 Photon Source.Photon Source.  Photon Detector. Photon Detector.  Communication channel. Communication channel.

 Photon Gun.  Light - emitting p-n junction.  Single ion.

 Avalanche photodiodes.  Germanium detectors.  Silicon.  Photo multiplier.

 Fiber optical communication link.  Free – space laser communication.

 Quantum cryptography obtains its fundamental security from the fact that each qubit of information is carried by a single photon, and that each photon will be altered as soon as it is read once.  This makes impossible to intercept message without being detected.

 The presence of noise can impact detecting attacks.  Eavesdropper and noise on the quantum channel are indistinguishable.  Detecting eavesdropper in the presence of noise is hard.

 messages.  Telephone calls.  Financial Transactions.

 The most important contribution of quantum cryptography is a mechanism for detecting eavesdropping.  Quantum key distribution enables “encrypted communications on demand,” because it allows key generation at transmission time over an unsecured optical communications link.

 We have to use pure fiber optic end-to- end network and boosters are needed at some distance, so it is expensive.  It will also be critical to authenticate the identity of the recipients.  It is also not clear how to modify the scheme in order to deal with noisy quantum transmissions.  It is hard to transmit a photon, entangled over great distances. Photon detectors aren't particularly reliable.

 Currently it works only over short distances, but there are situations in which even short-distance transmission is useful. Also, with sufficient technical improvements, it might be possible in the future to implement quantum cryptography over long distances.  The devices for implementing such methods exist and the performance of demonstration systems is being continuously improved. Within the next few years, such systems could start encrypting some of the most valuable secrets of government and industry.