Quantum CryptographyINF-5219029945552Quantum cryptography is the latest technology in the field of cryptography and has proven to be the most secure at the moment. In this article, we will discuss what quantum cryptography is and what makes it more secure and unbreakable. Introduction All our classical computer cryptography methods are basically based on some mathematical calculations which are quite easy to implement in one direction but very difficult to work out in the other direction. . Since the RSA (Rivest-Shamir-Adleman) algorithm, which is one of the first viable and most famous public key cryptosystems, RSA, is based on the large number factorization technique which makes it secure. The difficulty in factoring increases with the number of digits in the RSA key. For example, with today's computers it would take millions of years to calculate a 128-digit number. There are still limitations in classical cryptography, it is purely mathematical and information cannot be separated from its physical representation. In classical physics, we use binary form to store and process data. In the 1980s, C. Bennet, P. Benioff, R. Feynman and others observed that new and very powerful ways of information processing are possible with quantum mechanical systems. This gave birth to the concept of quantum computing. We have algorithms like Shor's algorithm, a quantum computer can decompose a very large number into its prime factors, otherwise the solution may take millions of years. The day quantum cryptography becomes a reality, the aforementioned RSA will become insecure. Luckily, we have some unbreakable code at our disposal. According to Shannon's rules, if the data we will encrypt is much smaller than the key in length and the key itself we...... middle of paper...... the following notations:'+' represents the rectilinear pattern' X' represents the diagonal pattern'-' represents 0 (horizontal polarization quantum state)'/' represents 0 (45 degrees relative to the horizontal polarization state)'|' represents 1 (vertically polarized quantum state)'' represents 1 (45 degrees relative to the vertically polarized state) So, using the qubit representations above, a BB84 transmission for binary 11010011 might look like this:Alice: Bits 1 1 0 1 0 0 1 1Alice: Qubit ↕ ↕ ↔ ↕ ∕ ∕ ↕Bob: Pattern + XX + + XX +Bob: Qubit ↕ ↕ ↔ ∕ ↕Bob: Bit 1 1 1 1 0 0 1 1Key selection √ √ √ √ √Table 1 – Qubit transmission and binary digit selectionAlice sends the first 1 using the scheme +, the second using the scheme X, the first 0 using pattern X, and so on.BB84 Quantum Key Distribution ProtocolPractical Problems with Quantum CryptographyConclusion