* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Cryptography.ppt - 123SeminarsOnly.com
Quantum decoherence wikipedia , lookup
Spin (physics) wikipedia , lookup
Particle in a box wikipedia , lookup
Path integral formulation wikipedia , lookup
Measurement in quantum mechanics wikipedia , lookup
Relativistic quantum mechanics wikipedia , lookup
Probability amplitude wikipedia , lookup
Renormalization wikipedia , lookup
Bell test experiments wikipedia , lookup
Wave–particle duality wikipedia , lookup
Hydrogen atom wikipedia , lookup
Quantum field theory wikipedia , lookup
Copenhagen interpretation wikipedia , lookup
Quantum dot wikipedia , lookup
Double-slit experiment wikipedia , lookup
X-ray fluorescence wikipedia , lookup
Coherent states wikipedia , lookup
Density matrix wikipedia , lookup
Orchestrated objective reduction wikipedia , lookup
Quantum fiction wikipedia , lookup
Many-worlds interpretation wikipedia , lookup
Interpretations of quantum mechanics wikipedia , lookup
Symmetry in quantum mechanics wikipedia , lookup
Quantum computing wikipedia , lookup
Quantum entanglement wikipedia , lookup
Bohr–Einstein debates wikipedia , lookup
Quantum group wikipedia , lookup
Wheeler's delayed choice experiment wikipedia , lookup
Quantum electrodynamics wikipedia , lookup
Quantum machine learning wikipedia , lookup
Theoretical and experimental justification for the Schrödinger equation wikipedia , lookup
History of quantum field theory wikipedia , lookup
Canonical quantization wikipedia , lookup
Bell's theorem wikipedia , lookup
Quantum state wikipedia , lookup
Hidden variable theory wikipedia , lookup
EPR paradox wikipedia , lookup
Quantum teleportation wikipedia , lookup
QUANTUM CRYPTOGRAPHY AND ITS ADVANCES QUANTUM CRYPTOLOGY AND ITS ADVANCES Hridya Ramesh Mrs.Malini Thomas Asst.Professor Ms.Sreekala V Lecturer Department of Electronics & Communication Engineering Sahrdaya College of Engineering & Technology, Kodakara, P.B.No.17, Thrissur, 680684. ABSTRACT INTRODUCTION In this era, the need for security has attained In our contemporary world,security has paramount importance. As more of our sensitive information attained paramount importance. The necessity for security is stored in computers the need of data security becomes has increased beyond everything. And that is why ways of increasingly important. Protecting this information against staying secure has to developed and implemented. unauthorized usage is therefore a major concern for both operating systems and users alike. Cryptography is one such The concept of cryptology dates back to B.C. method of safeguarding sensitive data from being stolen or It’s a method used to encrypt our data securely. Though intercepted by unwanted third parties. Traditional cryptology present day security systems offer a good level of is certainly clever, but as with all encoding methods in code- protection, they are incapable of providing a "trust worthy" breaking history, it's being phased out. environment and are vulnerable to unexpected attacks. Many organizations posses valuable information they Quantum Cryptology is based on physics and not guard closely. As more of this information is stored in mathematics, unlike the present ones. By harnessing the computers the need of data security becomes increasingly unpredictable nature of matter at the quantum level, physicists important. have figured out a way to exchange information on secret keys. unauthorized usage is therefore a major concern for both Attaching information to the photons spin is the essence of operating systems and users alike. Cryptography is one Quantum Cryptology.In brief, the processes of encoding such method of safeguarding sensitive data from being (cryptography) and decoding (crypto analysis) information or stolen or intercepted by unwanted third parties. Traditional messages (called plaintext) into an otherwise meaningless data cryptology is certainly clever, but as with all encoding (cipher text) combined are cryptology.and when the keys used methods in code-breaking history, it's being phased out. Protecting this information against for this process are photons, it’s called Quantum Cryptology. Quantum Cryptology is based on physics and not mathematics, unlike the present ones. By harnessing the unpredictable nature of matter at the quantum level, physicists have figured out a way to exchange information on secret keys. Sahrdaya College Of Engineering and Technology 1 QUANTUM CRYPTOGRAPHY AND ITS ADVANCES The foundation of quantum physics is the unpredictability factor. This unpredictability is pretty much defined by Heisenberg's Uncertainty Principle. This principle says, essentially, that it's impossible to know both an object's position and velocity -at the same time. But when dealing with photons for encryption, Heisenberg's principle can be used to our advantage. To create a photon, quantum cryptographers use LEDs , a source of unpolarized light, capable of creating just one photon at a time, which is how a string of photons can be created, rather than a wild burst. SECURITY NEED FOR SECURITY Through the use of polarization filters, we can force the photon to take one state or another -- or polarize it. The thing about photons is that once they're polarized, they can't be accurately measured again, except by a filter like the one that From a security perspective computer systems have 3 general goals with corresponding threats to them as listed below: initially produced their current spin. So if a photon with a vertical spin is measured through a diagonal filter, either the photon won't pass through the filter or the filter will affect the photon's behavior, causing it to take a diagonal spin. In this sense, the information on the photon's original polarization is lost, and so, too, is any information attached to the photon's spin. Attaching information to the photons spin is the The first one data confidentiality is concerned with secret data remaining secret. More specifically if the owner of some data has decided that the data should be available only to certain people and no others, then the system should guarantee that release of data to unauthorized people does not occur. Another aspect of this is individual privacy. essence of Quantum Cryptology. Quantum cryptography uses photons to transmit a key. Once the key is transmitted, coding and encoding using the normal secret-key method can take place. The second goal, data integrity, means that unauthorized users should not be able to modify any data without the owner's permission. Data modification in this context includes not only changing the data, but also In brief, the processes of encoding (cryptography) and decoding (crypto analysis) information or messages (called plaintext) into an otherwise meaningless data (cipher text) combined are cryptology.and when the keys used for this removing data and adding false data as well. Thus it is very important that a system should guarantee that data deposited in it remains unchanged until the owner decides to do so. process are photons, it’s called Quantum Cryptology. The third goal, system availability, means that nobody can disturb the system to make unstable. It must be LITERATURE REVIEW Sahrdaya College Of Engineering and Technology 2 QUANTUM CRYPTOGRAPHY AND ITS ADVANCES able to ensure that authorized persons have access to the data and do not suffer form denial of service. Basically a virus is a piece of code that replicates itself and usually does some damage. In a sense the writer of a virus is also an intruder, often with Types of Data Threats high technical skills. In the same breath it must be said that a virus need not always be intentional and can Intruders: simply be a code with disastrous run time errors. The In security literature people who are nosing around places difference between a conventional intruder and a virus where they have no business being are called intruders or is that the former refers to person who is personally sometimes adversaries. Intruders can be broadly divided as trying to break into a system to cause damage whereas passive and active. Passive intruders just want to read the files the latter is a program written by such a person and they are not authorized to. Active intruders are more malicious then released into the world hoping it causes damage. and intend to make unauthorized changes to data. Some of the The most common types of viruses are: executable common program viruses, memory resident viruses, boot sector activities indulged by intruders are: viruses, device driver viruses, macro viruses, source Casual Prying: non-technical users who wish to read other people's e-mail and private files mostly do code viruses, Trojan horses etc. this. Snooping: This term refers to the breaking of the security of AN OVERVIEW OF SOME OF THE PRESENT a shared computer system or a server. Snooping is generally DAY DATA SECURITY SYSTEMS: done as a challenge and is not aimed at stealing or tampering of confidential data. User authentication: Commercial Espionage: This refers to the determined It is a method employed by the operating attempts to make money using secret data. For example an system or a program of a computer to determine the employee in an organization can secure sensitive data and identity of a user. Types of user authentication are: sell it away to rival companies for monetary gains. Authentication using passwords, authentication using physical objects (like smart cards, ATM cards etc.), It is very important that potential intruders (and their authentication using biometrics (like Finger prints, corresponding activities) are taken into consideration before retinal devising a security system. This is essential as the level of recognition threat and intended damage differ from one to another. authentication are password cracking, duplication of pattern scan, etc.). signature Inherent analysis, problems of voice user physical objects and simulation of biometrics by artificial objects. Virus: Sahrdaya College Of Engineering and Technology Anti-virus software: 3 QUANTUM CRYPTOGRAPHY AND ITS ADVANCES An antivirus software scans every executable file on a QUANTUM CRYPTOGRAPHY computer's disk looking for viruses known in its database. It then repairs, quarantines or deletes an infected files. CRYPTOLOGY However a clever virus can infect the anti-virus software Cryptography is the method in which a message itself. Some of the popular anti-virus soft wares are K7, or file, called plain text,is taken and encrypted into PCcillin, MCcafee,Eset Nod32 etc. cipher text in such a way that only authorized people know how to convert it back to plain text. There are Firewalls: limitless possibilities for keys used in cryptology. But It is a method of preventing unauthorized access to a there are only two widely used methods of employing computer system often found in network computes. A keys: public-key cryptology and secret-key cryptology. firewall is designed to provide normal service to authorized In both of these methods (and in all cryptology), the users while at the same time preventing unauthorized users sender (point A) is referred to as Alice. Point B is from gaining access to the system. In reality they add a known as Bob. level of inconvenience to legal users and their ability to control illegal access may be questionable. They also stop In the public-key cryptology (PKC) method, a ones computer from sending malicious software to another user chooses two interrelated keys. He lets anyone who computer. wants to send him a message know how to encode it using one key. He makes this key public. The other key he keeps Cryptography: to himself. In this manner, anyone can send the user an Cryptography is the method in which a message or file, encoded message, but only the recipient of the encoded called plain text, is taken and encrypted into cipher text in message knows how to decode it. Even the person sending such a way that only authorized people know how to the message doesn't know what code the user employs to convert it back to plane text. This is done commonly in four decode it. ways: The other usual method of traditional Secret key cryptography, public key cryptography, one way cryptology is secret-key cryptology (SKC). In this method, function cryptography and digital signatures. only one key is used by both Bob and Alice. The same key is used to both encode and decode the plaintext. Even the algorithm used in the encoding and decoding process can be announced over an unsecured channel. The code will remain uncracked as long as the key used remains secret. Sahrdaya College Of Engineering and Technology 4 QUANTUM CRYPTOGRAPHY AND ITS ADVANCES Traditional cryptology is certainly clever, but as listen in and gain information the users don't want that with all encoding methods in code-breaking history, it's being person to have. This is known in cryptology as the key phased out. distribution problem. It's one of the great challenges of cryptology: To Traditional Cryptology Problems The keys used to encode messages are so long that it keep unwanted parties - from learning of sensitive information. would take a trillion years to crack one using conventional Quantum physics has provided a way around this problem. computers. The problem with public-key cryptology is that it's By harnessing the unpredictable nature of matter at the based on the staggering size of the numbers created by the quantum level, physicists have figured out a way to combination of the key and the algorithm used to encode the exchange information on secret keys. message. These numbers can reach unbelievable proportions. What's more, they can be made so that in order to understand Quantum physics each bit of output data, you have to also understand every other Photons are some pretty amazing particles. bit as well. This means that to crack a 128-bit key, the possible They have no mass, they're the smallest measure of light, numbers used can reach upward to the 1038 power. That's a lot and they can exist in all of their possible states at once, of possible numbers for the correct combination to the key. The called the wave function. This means that whatever keys used in modern cryptography are so large, in fact, that a direction a photon can spin in -- say, diagonally, vertically billion computers working in conjunction with each processing and horizontally -- it does all at once. Light in this state is a billion calculations per second would still take a trillion years called unpolarized. This is exactly the same as if you to definitively crack a key [source: Dartmouth College]. This constantly moved east, west, north, south, and up-and- isn't a problem now, but it soon will be. down at the same time. Current computers will be replaced in the near future with quantum computers, which exploit the properties of The foundation of quantum physics is the physics on the immensely small quantum scale.Since they can unpredictability factor. This unpredictability is pretty much operate on the quantum level, these computers are expected to defined by Heisenberg's Uncertainty Principle. This principle be able to perform calculations and operate at speeds no says, essentially, that it's impossible to know both an object's computer in use now could possibly achieve. So the codes that position and velocity -- at the same time. But when dealing with would take a trillion years to break with conventional photons for encryption, Heisenberg's principle can be used to our computers could possibly be cracked in much less time with advantage. To create a photon, quantum cryptographers use quantum computers. This means that secret-key cryptology LEDs -- light emitting diodes, a source of unpolarized light. (SKC) looks to be the preferred method of transferring ciphers LEDs are capable of creating just one photon at a time, which is in the future. But SKC has its problems as well. The chief how a string of photons can be created, rather than a wild burst. problem with SKC is how the two users agree on what secret Through the use of polarization filters, we can force the photon key to use. The problem with secret-key cryptology is that to take one state or another -- or polarize it. If we use a vertical there's almost always a place for an unwanted third party to polarizing filter situated beyond a LED, we can polarize the Sahrdaya College Of Engineering and Technology 5 QUANTUM CRYPTOGRAPHY AND ITS ADVANCES photons that emerge: The photons that aren't absorbed will emerge on the other side with a vertical spin ( | ). The thing about photons is that once they're polarized, they can't be accurately measured again, except by a filter like the one that initially produced their current spin. So if a photon with a vertical spin is measured through a diagonal filter, either the photon won't pass through the filter or the filter will affect the photon's behavior, causing it to take a diagonal spin. In this sense, the information on the photon's original Fig. 2 Photons as keys. polarization is lost, and so, too, is any information attached to the photon's spin. This is where binary code comes into play. Each type of a photon's spin represents one piece of information -- usually a 1 or a 0, for binary code. This code uses strings of 1s and 0s to create a coherent message. For example, 1110010011 could correspond to h-e-l-l-o. So a binary code can be assigned to each photon -- for example, a photon that has a vertical spin ( | ) can be assigned a 1. Alice can send her photons through randomly chosen filters and record the polarization of each photon. Fig 1 Polarization of photons. She will then know what photon polarizations Bob should receive. When Alice sends Bob her photons using an LED, she'll randomly polarize them through either the X or the + Using Quantum cryptology Quantum cryptography uses photons to transmit a key. Once the key is transmitted, coding and encoding using the normal secret-key method can take place. But how does a photon become a key? How do you attach information to a photon's spin? filters, so that each polarized photon has one of four possible states: (|), (--), (/) or (\ ) . As Bob receives these photons, he decides whether to measure each with either his + or X filter -- he can't use both filters together. Keep in mind, Bob has no idea what filter to use for each photon, he's guessing for each one. After the entire transmission, Bob and Alice have a non-encrypted discussion about the transmission. Sahrdaya College Of Engineering and Technology 6 QUANTUM CRYPTOGRAPHY AND ITS ADVANCES The reason this conversation can be public is translated into English, Spanish, Navajo, prime numbers or because of the way it's carried out. Bob calls Alice and tells her anything else the Bob and Alice use as codes for the keys which filter he used for each photon, and she tells him whether used in their encryption. it was the correct or incorrect filter to use. Their conversation may sound a little like this: Bob: Plus Alice: Correct Bob: Plus Alice: Incorrect Bob: X Alice: Correct Since Bob isn't saying what his measurements are -only the type of filter he used -- a third party listening in on their conversation can't determine what the actual photon sequence is. Fig 4.3 Interception Detection Here's an example. Say Alice sent one photon as a ( / ) and Bob says he used a + filter to measure it. Alice will say The goal of quantum cryptology is to thwart "incorrect" to Bob. But if Bob says he used an X filter to measure that particular photon, Alice will say "correct." A person listening will only know that that particular photon could be either a ( / ) or a ( ), but not which one definitively. attempts by a third party to eavesdrop on the encrypted message. In cryptology, an eavesdropper is referred to as Eve. In modern cryptology, Eve (E) can passively Bob will know that his measurements are correct, because a (--) photon traveling through a + filter will remain polarized as a (--) photon after it passes through the filter. After their odd conversation, Alice and Bob both throw out the results from Bob's incorrect guesses. This leaves Alice and Bob with identical strings of polarized protons. It my look a little like this: -- / | | | / -- -- | | | -- / | … and so on. To Alice and Bob, this is a meaningless string of photons. But once binary code is applied, the photons become a message. Bob and Alice can agree on binary assignments, say 1 for photons polarized as ( \ ) and ( -- ) and 0 for photons polarized like ( / ) and ( | ). This means that their string of photons now intercept Alice and Bob's encrypted message -- she can get her hands on the encrypted message and work to decode it without Bob and Alice knowing she has their message. Eve can accomplish this in different ways, such as wiretapping Bob or Alice's phone or reading their secure emails. Quantum cryptology is the first cryptology that safeguards against passive interception. Since we can't measure a photon without affecting its behavior, Heisenberg's Uncertainty Principle emerges when Eve makes her own eavesdrop measurements. looks like this: 11110000011110001010. Which can in turn be Sahrdaya College Of Engineering and Technology 7 QUANTUM CRYPTOGRAPHY AND ITS ADVANCES Here's an example. If Alice sends Bob a series of polarized photons, and Eve has set up a filter of her own to photon has been measured by a third party, who inadvertently altered it. intercept the photons, Eve is in the same boat as Bob: Neither has any idea what the polarizations of the photons Alice sent Alice and Bob can further protect their are. Like Bob, Eve can only guess which filter orientation transmission by discussing some of the exact correct (for example an X filter or a + filter) she should use to results measure the photons. measurements. This is called a parity check. If the after they've discarded the incorrect chosen examples of Bob's measurements are all correct After Eve has measured the photons by randomly - meaning the pairs of Alice's transmitted photons and selecting filters to determine their spin, she will pass them Bob's received photons all match up -- then their down the line to Bob using her own LED with a filter set to message is secure. the alignment she chose to measure the original photon. She Bob and Alice can then discard these discussed does to cover up her presence and the fact that she intercepted measurements and use the remaining secret measurements the photon message. But due to the Heisenberg Uncertainty as their key. If discrepancies are found, they should occur Principle, Eve's presence will be detected. in 50 percent of the parity checks. Since Eve will have By measuring the photons, Eve inevitably altered altered about 25 percent of the photons through her some of them.Say Alice sent to Bob one photon polarized to measurements, Bob and Alice can reduce the likelihood a ( -- ) spin, and Eve intercepts the photon. But Eve has that Eve has the remaining correct information down to a incorrectly chosen to use an X filter to measure the photon. If one-in-a-million chance by conducting 20 parity checks Bob randomly (and correctly) chooses to use a + filter to measure the original photon, he will find it's polarized in PROBLEMS OF QUANTUM CRYPTOLOGY either a ( / ) or ( \) position. Bob will believe he chose Despite all of the security it offers, quantum incorrectly until he has his conversation with Alice about the cryptology also has a few fundamental flaws. Chief among filter choice. these flaws is the length under which the system will work: It’s too short. After all of the photons are received by Bob, and The original quantum cryptography system, he and Alice have their conversation about the filters used to built in 1989 by Charles Bennett, Gilles Brassard and John determine the polarizations, discrepancies will emerge if Eve Smolin, sent a key over a distance of 36 centimeters has intercepted the message. In the example of the ( -- ) [source: Scientific American]. Since then, newer models photon that Alice sent, Bob will tell her that he used a + have reached a distance of 150 kilometers (about 93 filter. miles). Alice will tell him this is correct, but Bob will But this is still far short of the distance know that the photon he received didn't measure as ( -- ) or ( | requirements needed to transmit information with modern ). Due to this discrepancy, Bob and Alice will know that their computer and telecommunication systems. Sahrdaya College Of Engineering and Technology 8 QUANTUM CRYPTOGRAPHY AND ITS ADVANCES The reason why the length of quantum cryptology capability is so short is because of interference. A photon’s spin can be changed when it bounces off other particles, and so when it's received, it may no longer be polarized the way it was originally intended to be. This means that a 1 may come through as a 0 -- this is the probability factor at work in quantum physics. As the distance a photon must travel to carry its binary message is increased, so, too, is the chance that it will meet other particles and be influenced by them. Fig 4.4 Spooky Action Of Photon SOLUTION DEVELOPED One group of Austrian researchers may have solved this problem. This team used what Albert Einstein called “spooky action at a distance.” This observation of quantum physics is based on the entanglement of photons. At the quantum level, photons can come to depend on one another after undergoing some particle reactions, and their states become entangled. This entanglement doesn’t mean that the two photons are physically connected, but they become connected in a way that physicists still don't understand. In entangled pairs, each photon has the opposite spin of the other -- for example, ( / ) and (\ ). If the spin of one is measured, the spin of the other can be deduced. What’s strange (or “spooky”) about the entangled pairs is that they remain entangled, even when they’re separated at a distance. The Austrian team put a photon from an entangled Even though it’s existed just a few years so far, quantum cryptography may have already been cracked. A group of researchers from Massachusetts Institute of Technology took advantage of another property of entanglement. In this form, two states of a single photon become related, rather than the properties of two separate photons. By entangling the photons the team intercepted, they were able to measure one property of the photon and make an educated guess of what the measurement of another property -- like its spin -- would be. By not measuring the photon’s spin, they were able to identify its direction without affecting it. So the photon traveled down the line to its intended recipient none the wiser. pair at each end of a fiber optic cable. When one photon was measured in one polarization, its entangled counterpart took the opposite polarization, meaning the polarization the other photon would take could be predicted. It transmitted its information to its entangled partner. This could solve the distance problem of quantum cryptography, since there is now a method to help predict the actions of entangled photons. Sahrdaya College Of Engineering and Technology The MIT researchers admit that their eavesdropping method may not hold up to other systems, but that with a little more research, it could be perfected. Hopefully, quantum cryptology will be able to stay one step ahead as decoding methods continue to advance. 9 QUANTUM CRYPTOGRAPHY AND ITS ADVANCES POSITION BASED QUANTUM CRYPTOGRAPHY A central task in position-based cryptography is Here the study of position-based cryptography in the the problem of position-verfication. We have a prover P at quantum setting is investigated. The aim is to use the position pos, wishing to convince a set of verifiers V0; : : : geographical position of a party as its only credential. This has ; Vk (at different points in geographical space) that he (i.e. interesting applications, e.g., it enables two military bases to the prover) is indeed at that position pos. The prover can communicate over insecure channels and without having any run an interactive protocol with the verifiers in order to do pre-shared key, with the guarantee that only parties within the this. The main technique for such a protocol is known as bases learn the content of the conversation. distance bounding. A verifier sends a random nonce to P and measures the time taken for P to reply back with this There are schemes for several important positionbased cryptographic tasks: position-verification, value. Assuming that communication is bounded by the speed of light, this technique gives an upper bound on the authentication, and key distance of P from the verifier. exchange, and we prove them unconditionally secure, i.e., The set of verifiers cannot distinguish between the case when without assuming any restriction on the adversaries (beyond they are interacting with an honest prover at pos and the case when they the laws of quantum mechanics). Unlike key-distribution, are interacting with multiple colluding dishonest provers, none of whom which is possible under cryptographic hardness assumptions are at position pos. Their impossibility result holds even if we make alone, position-based cryptography is impossible under any computational hardness assumptions, and it also rules out most other hardness assumptions. Thus, this is the first example of a interesting position-based cryptographic tasks. A model in which verifiers cryptographic task that we are aware of which is impossible in can broadcast large bursts of information and there is a bound on the the standard complexity-based setting but becomes possible amount of information that the set of adversaries can retrieve. (this model when using quantum methods. We also present schemes for is known as the Bounded Retrieval Model (BRM)). which we can merely conjecture security; proving them secure (or insecure) remains an interesting challenge. In this model, constructs information- theoretically secure protocols for the task of position The results open up a fascinating new direction of verification as well as position-based key exchange quantum cryptography where security of protocols is solely (wherein the verifiers, in addition to verifying the position based on the laws of physics. claim of a prover, also exchange a secret key with the prover). The BRM has its drawbacks. Firstly, it requires The goal of position-based cryptography is to use the verifiers to be able to broadcast large bursts of the geographical position of a party as its only “credential”. For information and this might be difficult to do; secondly, and example, one would like to send a message to a party at a perhaps more importantly, the bound on the amount of geographical position pos with the guarantee that the party can information that an adversary retrieves might be hard to decrypt the message only if he or she is physically present at impose. pos. Sahrdaya College Of Engineering and Technology 10 QUANTUM CRYPTOGRAPHY AND ITS ADVANCES This work, initiates the study of position-based classical cryptography and quantum cryptography, in cryptography in the quantum setting. By going to the that the latter offers unconditional security whereas the quantum setting, one may be able to circumvent the former does not offer any security if the adversary is impossibility result thanks to the following observation. If unrestricted. some information is encoded into a quantum state, then the It should be stressed that our work exhibits far greater above attack fails due to the no-cloning principle: the power of quantum world then what QKD vs. classical key adversary can either store the quantum state or send it to a agreement colluding adversary (or do something in-between, like store informationtheoretic security, while standard key agreements part of it), but not both. Thus, going to the quantum setting provide only computational security. However, one can argue that may indeed be a promising approach. We put forward computational security, in some cases, given sufficiently strong quantum cryptographic schemes for several position-based cryptographic hardness assumptions is “good enough” and there is tasks: no need for more costly quantum implementation. demonstrates. In particular, QKD provides position-verification, authentication, and key In contrast, position-based key agreement (as well as exchange, and we prove these scheme unconditionally other position-based cryptographic tasks) are provably impossible secure against an arbitrary coalition of adversaries. to achieve in the classical cryptographic setting, even if we As already mentioned, a position-verification scheme can be used to convince the verifiers V0; : : : ; Vk assume that P is different from NP and there are cryptographically hard problems that are provably impossible to break. of the geographic position pos of P. A position-based This demonstrates an existence of a task that is authentication scheme on the other hand convinces the impossible in the classical setting and is readily realizable verifiers that a message m originates from P at position pos. using quantum communication. An additional attractive Finally, a position-based key exchange scheme ensures that feature of all our solutions is that our schemes merely the verifiers share a secret key with P at position pos, and require one of the verifiers, V0, to prepare individual anyone that is not at position pos does not have any qubits and send them to P, and P needs to measure them information regarding the key. immediately upon arrival. If this is possible, and the key is sufficiently long, then perfectly secure communication with a device No quantum computation is needed, and all other communication may be classical. only located in a certain position is possible. This scheme prove security for the above tasks Classical cryptographic protocols in a quantum world without any restriction on the power of the adversaries; they may have unbounded classical and quantum memory, and Our main contribution is showing the existence they may have unbounded computing power; the only of classical two-party protocols for the secure evaluation assumption is that the laws of quantum mechanics hold. (SFE) of any polynomial-time function that are secure Therefore, our results show that position-based against quantum attacks under reasonable computational quantum cryptography is one of the rare examples besides assumptions (for example, it suffices that the learning with QKD for which there is a strong separation between errors problem be hard for quantum polynomial time). Sahrdaya College Of Engineering and Technology 11 QUANTUM CRYPTOGRAPHY AND ITS ADVANCES We show that a large class of classical security The need to secure our data is the prime aim of most analyses remain valid in the presence of quantum attackers as firms.One of the most advanced techniques used for solving this long as the underlying computational primitives (encryption issue is ‘cryptology’. Cryptology means the encoding of our schemes, pseudorandom generators, etc) resist quantum attack. sensitive information into forms unrecognizable by others. But In what follows, we distinguish two basic settings: in the stand- traditional cryptology methods have a lot of flaws. And that is alone setting, protocols are designed to be run in isolation, where the necessity of Quantum Cryptology lies. without other protocols running simultaneously; in network It is very important that potential intruders (and their settings, the protocols must remain secure even when the corresponding activities) are taken into consideration before honest participants are running many other protocols (or copies devising a security system. This is exactly what Quantum of the same protocol) concurrently. Protocols that are secure in Cryptology helps in. arbitrary network settings are called universally composable. Photons being the keys of transmission can be highly unpredictable by a third party. By observing the spin of these Modeling stand-alone security with quantum adversaries: photons interception by unauthorized parties can be detected. This We describe a security model for two party makes Quantum Cryptology one of the most efficient means of protocols in the presence of a quantum attackers. Proving ‘hiding’ data. Another feature of Quantum Cryptology is that it is security in this model amounts to showing that a protocol for purely physics, while all the other present cryptography computing a function f behaves indistinguishably from an techniques are based on mathematics. “ideal” protocol in which of is computed by a trusted third Current computers will be replaced in the near future party. Our model captures both classical and quantum with quantum computers, which exploit the properties of physics protocols, though we only apply it to classical ones. The new on the immensely small quantum scale. Since they can operate on model is significantly more general than existing stand-alone the quantum level, these computers are expected to be able to models of security. This allows us to design protocols perform calculations and operate at speeds no computer in use assuming that all participants share a uniformly random now could possibly achieve. So the codes that would take a trillion common reference string (CRS). By the modular composition years to break with conventional computers could possibly be theorem, we can then use the DL coin-flipping protocol to cracked in much less time with quantum computers. generate the CRS. Hopefully these computers will be able to increase the speed of decoding into just minutes and thus make cryptography worthwhile and encourage the CONCLUSIONS AND FUTURE WORKS widespread use of cryptology in everyday life. Position Based Quantum Cryptology is In this computer-centric era, the relevance of security systems have increased to great heights. Though present day security systems offer a good level of protection, they are incapable of providing a “trustworthy” technique being developed to enhance the present quantum cryptography scenario. It is based on sending confidential encoded data to a specific person seated in a specific position of geographical earth. This ensures environment and are vulnerable to unexpected attacks or third party interception. Sahrdaya College Of Engineering and Technology 12 QUANTUM CRYPTOGRAPHY AND ITS ADVANCES “Position-based quantum cryptography,” that our secure data does not fall into wrong hands. It avoids possible interceptions and unauthorized access. 2010, (full version), ArXiv eprints/ Presently, cryptography is used only by the 1005.1750. higher level authorities such as in government affairs and military. Soon, it could reach down to the common man, helping him secure his data from intruders [9] N. Chandran, B. Kanukurthi, R. Ostrovsky, and L. Reyzin, “Privacy and amplification with asymptotically optimal entropy loss,” in STOC’10. eavesdroppers. New York: ACM Press, 2010, pp. 785– REFERENCES [1] Proceedings of the International Conference “CRYPTO-2011” and “ CRYPTO-2010” 794. [10] V. Giovannetti, S. Lloyd, and L. Maccone, “Quantum cryptographic ranging,” Journal of Optics B, vol. 4, no. http://www.iacr.org/conferences/crypto2011/acceptedpapers-list.htm 4, p. 042319, Aug 2002. [11] R. A. Malaney, “Location-dependent communications using quantum [2] entanglement,” Phys. Rev. A, vol. 81, no. N. Chandran, V. Goyal, R. Moriarty, and R. Ostrovsky, “Position Based Cryptography,” in CRYPTO’09. Springer, 2009, p. 407, full version: http://eprint.iacr.org/2009/364. [3] S. Brands and D. Chaum, “Distance-bounding protocols,” in EUROCRYPT’ 4, p. 042319, Apr 2010. [12] http://enggseminars.blogspot.com/2009/02/quantumc ryptography.html [13] http://e-articles.info/e/a/title/Quantum- Cryptography/ . 93. Springer, 1994, pp. 344–359. [4] http://www.springerlink.com/content/l7235j1368005068/ [5] H. Buhrman, S. Fehr, and C. Schaffner, unpublished results, 2010. [6] http://www.garykessler.net/library/crypto.html#purpose [7] A. S. Holevo, “Information-theoretical aspects of quantum measurement,” Problemy Peredaˇci Informacii, vol. 9, no. 2, pp. 31–42 [8] N. Chandran, S. Fehr, R. Gelles, V. Goyal, and R. Ostrovsky, Sahrdaya College Of Engineering and Technology 13