### Quantum Cryptography

1. The art and science of concealing the messages to introduce secrecy in information security is recognized as cryptography. Word Cryptography comes from greek word: Cryptography=Krypto + graphene “Secret Writing”.
2. WHAT IS QUANTUM?
3. A quantum is a minimum amount of any physical entity involved in an interaction. The fundamental notion that a physical property may be "quantized" is referred to as "the hypothesis of quantization". Word Quantum comes from Latin ‘quantus’ means “how great”.
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5. Science of exploiting quantum mechanical properties to perform cryptographic tasks. Method of coding information based on quantum mechanics, which is said to be unbreakable. . It uses current knowledge of physics to develop a cryptosystem i.e. not able to be defeated .
6. History Proposed first by Stephen Wiesner in 1970’s. Uses Heisenberg's uncertainty principle formulated in 1927.
7. Quantum Key Distribution Process of using quantum communication to establish a shared key between two parties without a third party learning anything about that key, even if Eve can eavesdrop on all communication between Alice and Bob. If Eve tries to learn information about the key being established, key establishment will fail causing Alice and Bob to notice.
8. How Quantum Cryptography Works?  QKD uses quantum mechanics to guarantee secure communication.  Enables two parties to produce a shared random secret key known only to them, which used to encrypt and decrypt messages. In quantum computing, a qubit or quantum bit is a unit of quantum information. The state of a qubit can be in a ‘superposition' of 0 and 1 simultaneously.
9. QUANTUM PROPERTIES
10. a) • A single photon is emitted from a light source and passes through a linear polarizer, in this case - horizontal. That process creates a qubit with horizontal polarization.
11. b) • When the horizontally-polarized photon passes through a horizontally/vertically-oriented polarizing beamsplitter, it always retains its horizontal polarization.
12. c) • If that horizontally-polarized photon passes through a diagonally-oriented polarizing beamsplitter: -There is a 50% probability of finding the photon at one of the exits. -The photon will only be detected at one of the exits. -The polarization of the photon will have changed to the corresponding diagonal polarization.
13. Spin values
14. BB84 Protocol • Relies on quantum indeterminism and no-cloning theorem. • Can be used between Alice and Bob to “negotiate” a key through a quantum channel + a classical channel. • Key is generated on-the-fly.
15. The BB84 Protocol’s steps 1) Key transmission through the quantum channel . 2) Error correction 3) Key distillation
16. Eve Possible Attacks Cloning the photon Intercept-resend Intercept the public classical channel Spoofing attack through the public channel
17. Why Quantum Cryptography? • only known method for transmitting a secret key over distance that is secure in principle and based on the laws of physics.
18. Why Quantum Cryptography So Secure? • The quantum no-cloning theorem states that an unknown quantum state cannot be cloned. • In a quantum system, which can be in one of two states, any attempt to measure the quantum state will disturb the system. A quantum message that is intercepted and read by an eavesdropper will reproduce in a confused and distorted way and useless to the intended recipient of the message. • The effects produced by measuring a quantum property are irreversible.
19. Weaknesses and Limitation of Quantum Cryptography Only works along unbroken and relatively short fiber optic cables. Doesn’t solve authentication problem. Doesn’t address some of the weakest links in data security such as human corruptibility and key storage. Relatively high cost.
20. Advantages Virtually Un-hackable Simple to use Less resources needed to maintain it Used to detect eavesdropping in Quantum Key Distribution
21. Disadvantages The signal is currently limited to 90 miles. Could replace a lot of jobs.
22. Conclusion Due to the high cost of implementation and the adequacy of current cryptological methods, it is unlikely that quantum cryptography will be in widespread use for several years.

### Notas del editor

1.  the smallest possible discrete unit of any physical property, such as energy or matter.