a cryptographic key, enabling Alice to scramble her messages in a way only Bob, knowing the same key, could unscramble. Privacy thus appeared to be generally unavailable to users lacking the means and foresight by which diplomats and spies share secret keys with their intended correspondents. Classical cryptography offered no purely mathematical solution to this "key distribution problem ". Meanwhile the only solution to the discreet communications problem appeared to be for Alice and Bob to confide their secrets in a trusted intermediary, who might later choose to blackmail them. All this was changed by PKC. The idea of PKC is for each user (eg Alice) to randomly choose a pair of mutually inverse transformations---a scrambling transformation and an unscrambling transformation---and to publish the directions for performing the former but not the latter. Anyone, including Bob, can then use Alice's public scrambling algorithm to prepare a message that only she can unscramble. Si
a cryptographic key, enabling Alice to scramble her messages in a way only Bob, knowing the same key, could unscramble. Privacy thus appeared to be generally unavailable to users lacking the means and foresight by which diplomats and spies share secret keys with their intended correspondents. Classical cryptography offered no purely mathematical solution to this "key distribution problem ". Meanwhile the only solution to the discreet communications problem appeared to be for Alice and Bob to confide their secrets in a trusted intermediary, who might later choose to blackmail them. All this was changed by PKC. The idea of PKC is for each user (eg Alice) to randomly choose a pair of mutually inverse transformations---a scrambling transformation and an unscrambling transformation---and to publish the directions for performing the former but not the latter. Anyone, including Bob, can then use Alice's public scrambling algorithm to prepare a message that only she can unscramble. Si
When elementary quantum systems, such as polarized photons, are used to transmit digital information, the uncertainty principle gives rise to novel cryptographic phenomena unachievable with traditional transmission media, e.g. a communications channel on which it is impossible in principle to eavesdrop without a high probability of disturbing the transmission in such a way as to be detected. Such a quantum channel can be used in conjunction with ordinary insecure classical channels to distribute random key information between two users with the assurance that it remains unknown to anyone else, even when the users share no secret information initially. We also present a protocol for coin-tossing by exchange of quantum messages, which is secure against traditional kinds of cheating, even by an opponent with unlimited computing power, but ironically can be subverted by use of a still subtler quantum phenomenon, the Einstein-Podolsky-Rosen paradox.
Cryptographic protocols can be classified by the type of security against eavesdropping which they provide. There exist mathematically secure schemes whose security relies on mathematical proofs (like the Vernam cipher discussed below) or conjectures (like public key RSA encryption) about the complexity of deciphering the message without possessing the correct key. The majority of current secure public Internet connections rely on such schemes. Alternatively, a cryptographic setup may provide a physically secure method for communicating. In these setups the security is provided by the physical laws governing the communication protocol. Here we first discuss a provably secure classical communication protocol and then quantum methods for distributing the necessary keys. The BB84 protocol relies on the impossibility of perfectly distinguishing non-orthogonal quantum states from one copy of the quantum system. The scheme was invented in 1984 and is the first of its kind. In contrast, the Ekert91 protocol makes use of Bell correlations between entangled pairs of photons. These correlations are destroyed when Eve attempts to make a measurement on one of the particles but also when imperfections, such as decoherence processes, affect the scheme. As long as no such “elements of reality” are introduced, and Bell correlations violating local realism can be generated by Alice and Bob, no eavesdropper can be present. One-time pads and the Vernam cipher The Vernam cipher is a cryptographic protocol which allows the encryption and decryption protocol to be publicly known. The security of the protocol relies entirely on the key which is private and not publicly known. Alice and Bob share identical n -bit secret key strings (one-time pad).
Quantum cryptography uses physics to develop a cryptosystem completely secure against being compromised, without the sender or the receiver of messages being known. The word quantum itself refers to the most fundamental behavior of the smallest particles of matter and energy. Quantum cryptography is different from traditional cryptographic systems in that it relies more on physics, rather than mathematics, as a key aspect of its security model. Essentially, quantum cryptography is based on the usage of individual particles/waves of light (photon) and their intrinsic quantum properties to develop an unbreakable cryptosystem (because it is impossible to measure the quantum state of any system without disturbing that system). Regular, non-quantum encryption can work in a variety of ways but generally a message is scrambled and can only be unscrambled using a secret key. The trick is to make sure that whomever you’re trying to hide your communication from doesn’t get their hands on your secret key.
Cryptography literally means "The art & science of secret writing & sending a message between two parties in such a way that its contents cannot be understood by someone other than the intended recipient."and Quantum word is related with "Light".Thus, Quantum Cryptography is a way of descripting any information in the form of quantum particles.There are no classical cryptographic systems which are perfectly secure.In contrast to Classical cryptography which depends upon Mathematics, Quantum Cryptography utilizes the concepts of Quantum Physics which provides us the security against the cleverest marauders of the present age.In the view of increasing need of Network and Information Security, we do require methods to overcome the Molecular Computing technologies (A future technology) and other techniques of the various codebrakers.Both the parts i.e.Quantum Key distribution and Information transference from Sender to Receiver are much efficient and secure.It is based upon BB84 protocol.It can be of great use for Govt.agencies such as Banks, Insurance, Brokerages firms, financial institutions, e-commerce and most important is the Defense & security of any country.It is a Cryptographic communication system in which the original users can detect unauthorized eavesdropper and in addition it gives a guarantee of no eavesdropping.It proves to be the ultra secure mode of communication b/w two intended parties.
This final chapter concerns cryptography , the principle of securing information against access or tampering by third parties. Classical cryptography refers to the manipulation of classical bits for this purpose, while quantum cryptography can be viewed as doing the same with qubits . I describe these two approaches in the same chapter, as in my view the field of cryptography should be understood as a whole and appreciated within such a broader framework, as opposed to focusing on the specific applications offered by the quantum approach. I, thus, begin by introducing the notions of message encryption , message decryption , and code breaking , the action of retrieving the message information contents without knowledge of the code's secret algorithm or secret key . I then consider the basic algorithms to achieve encryption and decryption with binary numbers, which leads to the early IBM concept of the Lucifer cryptosystem , which is the ancestor of the first data encryption standard (DES). The principle of double-key encryption , which alleviates the problem of key exchange , is first considered as an elegant solution but it is unsafe against code-breaking. Then the revolutionary principles of cryptography without key exchange and public-key cryptography (PKC) are considered, the latter also being known as RSA . The PKC–RSA cryptosystem is based on the extreme difficulty of factorizing large numbers . This is the reason for the description made earlier in Chapter 20 concerning Shor's factorization algorithm .
Cryptography literally means “The art & science of secret writing & sending a message between two parties in such a way that its contents cannot be understood by someone other than the intended recipient. ” and Quantum word is related with “Light”. Thus, Quantum Cryptography is a way of descripting any information in the form of quantum particles. There are no classical cryptographic systems which are perfectly secure. In contrast to Classical cryptography which depends upon Mathematics, Quantum Cryptography utilizes the concepts of Quantum Physics which provides us the security against the cleverest marauders of the present age. In the view of increasing need of Network and Information Security, we do require methods to overcome the Molecular Computing technologies (A future technology) and other techniques of the various codebrakers. Both the parts i.e. Quantum Key distribution and Information transference from Sender to Receiver are much efficient and secure. It is based upon BB84 protocol. It can be of great use for Govt. agencies such as Banks, Insurance, Brokerages firms, financial institutions, e-commerce and most important is the Defense & security of any country. It is a Cryptographic communication system in which the original users can detect unauthorized eavesdropper and in addition it gives a guarantee of no eavesdropping. It proves to be the ultra secure mode of communication b/w two intended parties.