Alice bob eve quantum cryptography pdf

Alice, bob, and eve a b alice bob alice wants to send a secret message binary string to bob she cannot risk eve learning it e my account number is 33049519a. The following is an example of how quantum cryptography can be used to securely distribute keys. This is achievable using delayedchoice quantum cryptography. It enables two parties to produce a shared random bit string known only to them, which can be used as a key to encrypt and decrypt messages. Alice prepares photons randomly with either rectilinear or circular polarizations. Cryptography names alice, bob, eve nancys baby names. Eve already having access to the medium is a worse case to alice and bob than the eve not having access. Quantum cryptography is based on the framework of quantum physics, and it is meant to solve the problem of key distribution, which is an essential. A talk on quantum cryptography, or how alice outwits eve. Quantum cryptography and security of information systems. Since their invention in 1978, they have at once been called inseparable, and have been the subject of numerous divorces, travels, and torments.

These two lectures are an introduction to quantum key distribution qkd. Quantum cryptography university of california, berkeley. Untrusted communication channels this is a story about alice and bob. Quantum key distribution comprises a quantum channel and a public classical authenticated channel. Quantum communication alice sends the data to bob, recording which filter is used for which bit bob receives the data and records which filters was used for each bit bob sends the filters that he used for decoding each and sends the listing of filters back to alice over the classic channel e. Alice chooses n bits randomly and informs bob alice and bob compare their results for these n bits if more than an acceptable number disagree, they abort evidence of eve s tampering or a noisy channel. Basic quantum cryptography gerald scharitzer vienna university of technology institute of automation 24.

Alice and bob are the worlds most famous cryptographic couple. Alice and bob are fictional characters commonly used as a placeholder name in cryptology, as well as science and engineering literature. The information includes the secret key that the sender usually dubbed alice in descriptions of quantum cryptography transmits to a receiver named bob. Vinzenz vogel, viola hansjakob qsit fs 2015 students presentations paper by lars lydersen et. A brief introduction of quantum cryptography for engineers bing qi, li qian, hoikwong lo. Introduction to quantum cryptography norwegian creations. In quantum cryptography, individual quanta are prepared in nonorthogonal quantum states to encode and carry information about cryptographic keys. If alice and bob send a key to each other through such an insecure channel, then they cannot prove if eve has made a copy of it or not.

Eve represents this attacker, and eve has access to the medium. Alice and bob work far apart on a topsecret project, and, because of this, they need to exchange topsecret information using a communication medium. Alice, bob, and eve cryptography overview coursera. In the ensuing years, other characters have joined their cryptographic family. Therefore, the notion quantum key distribution is more accurate than quantum cryptography. If eve performs measurements on the transmitted quanta, alice and bob will discover the eavesdropping in the public communica tion. Over the past 20 years we have seen classical cryptography evolve to quantum cryptography, a branch of quantum information theory. Quantum channel alice bob first stage first stage the quantum channel alice will communicate over the quantum channel by sending 0s and 1s, each encoded as a quantum polarization state of an individual photon.

Suppose that alice and bob can communicate through a classical channel, and a third party eve is able to monitor the communications on that. In practice, eve gaining access to the medium may be a nontrivial task, and deter the attack. Alice, decides to take two college courses, one in. By reading the photon, eve alters the photons quantum state, which introduces errors into the quantum key. Pramod pandya, in cyber security and it infrastructure protection, 2014. In this way, an eavesdropper can acquire information about the key only at the risk of causing a detectable disturbance.

Alice shares with bob very hard to be factorized ex 257885161. Alice wants to send a private message to bob, and the only easy way they have to communicate is via postal mail. Unfortunately, alice is pretty sure that the postman is reading the mail she sends. Quantum cryptography an overview sciencedirect topics. In cryptography for communications, the names alice, bob and eve are frequently used to describe an everyday scenario. Quantum cryptography 10 of 32 bennett and brassards bb84 quantum key distribution the bb84 protocol builds on wqm to achieve truly secret key distribution. We note that the polarization state of an individual photon is an element. It is assumed that the eavesdropper eve has access to both the quantum. Subsequently, they have become common archetypes in many scientific and. The bb84 protocol of quantum cryptography is based on transmission of single.

Alice and bob exchange parity bits to correct their mismatches. A brief introduction of quantum cryptography for engineers bing qi 1,2, li qian 1,2, hoikwong lo 1,2, 3,4 1 center for quantum information and quantu m control, university of toronto. Quantum cryptography nitp 2003 10 bb84 qkd protocol with high probability, alice and bob have 2n successes to check for eve s interference. A brief introduction of quantum cryptography for engineers bing qi, li qian, hoikwong lo classical cryptography vs quantum cryptography. As a universal convention in quantum cryptography, alice sends quantum states to bob through a quantum channel. The third person is known as eve who eavesdrops the public channel used by alice and bob. An important and unique property of quantum cryptography is the ability of the. In 1984 bennett and brassard proposed a scheme for quantum cryptography based on the idea that alice can send qubits to bob through a quantum channel, and that in addition alice and bob can communicate through a public classical channel ordinary telephone, email. Public key cryptography, and establishing a secure channel, explained using physical means. Whether eve can decode the message or not depends on what resources we give her, and this point raises the.

The security of quantum cryptography john preskill, caltech biedenharn lecture 2 8 september 2005. For example, one simple solution could e facetoface meeting between alice andb bob. Eve alice begins by sending a message to bob using a photon gun to send a. Pdf a brief introduction of quantum cryptography for.

Secure communication based on quantum cryptography, will serve as a. Freespace quantum cryptography experimental quantum physics. Alice sends a copy of the key to bob alice eve bob problem. Secure key distribution with quantum communication transmission error correction.

Then alice uses the secret key to encrypt the message she wants to transmit. For this to be possible, alice and bob must have some secret information that eve ignores, otherwise eve could simply run the same algorithms that alice does, and thus be able to read the messages received by alice and to communicate with bob impersonating alice. This alerts alice and bob that someone is listening and the key has been compromised, so they discard the key. Publickey cryptography diffiehellman 76 classically, this difficulty can be overcome by public key cryptography.

Alice and bob decide in public on an acceptable key length including a sensible. Can only guarantee that eve does not know too many bits out of the remaining n. Introduction to quantum cryptography and secretkey. Banach, computer science, university of manchester. Alice has to send bob a new key that isnt compromised, and then bob can use that key. Alice chooses n bits randomly and informs bob alice and bob compare their results for these n bits if more than an acceptable number disagree, they abort evidence of eves tampering or a noisy channel. Alice and bob share bits a,b,c,d eve know one of these bits. Quantum cryptography nitp 2003 10 bb84 qkd protocol with high probability, alice and bob have 2n successes to check for eves interference. Quantum cryptography applications in electronic commerce. Cryptography names alice, bob, eve since the late 1970s, cryptographers have been using personal names instead of labels like person a and person b to describe various communications scenarios. Alice and bob wish to communicate without the archvillainess eve eavesdropping on their conversation. Quantum cryptography department of computer science.

In the classical symmetrickey cryptography setting, alice and bob have met before and. Each photon in a state with polarization corresponding to 1 or 0, but with randomly chosen basis. Quantum key distribution a perfectly secure cryptosystem. Consequently, the last step in a qc protoc ol uses classi. Alice, decides to take two college courses, one in cryptography, the other in quantum mechanics. The oldest and best known cryptographic scheme, bb84, is due to bennett. This example includes a sender, alice, a receiver, bob, and a malicious eavesdropper, eve alice begins by sending a message to bob using a photon gun to send a stream of photons randomly chosen in one of four. Quantum cryptography uses quantum mechanics to guarantee secure communication. Bob measures the state of the photons he receives, with each state measured with respect to randomly chosen basis. The bestknown and developed application of quantum cryptography is quantum key distribution qkd, which is the process of using quantum communication to establish a shared key between two parties alice and bob, for example without a third party eve learning anything about that key, even if eve can eavesdrop on all communication between alice and bob. Quantum cryptography makes it possible that two parties, in this case alice and bob, share a random key in a secure way.