Quantum Algorithms for Some Hidden Shift Problems

Almost all of the most successful quantum algorithms discovered to date exploit the ability of the Fourier transform to recover subgroup structures of functions, especially periodicity. The fact that Fourier transforms can also be used to capture shift structure has received far less attention in the context of quantum computation. In this paper, we present three examples of "unknown shift" problems that can be solved efficiently on a quantum computer using the quantum Fourier transform. For one of these problems, the shifted Legendre symbol problem, we give evidence that the problem is hard to solve classically, by showing a reduction from breaking algebraically homomorphic cryptosystems. We also define the hidden coset problem, which generalizes the hidden shift problem and the hidden subgroup problem. This framework provides a unified way of viewing the ability of the Fourier transform to capture subgroup and shift structure

An Exposition on Peter Shor's Polynomial-Time Factoring Algorithm and Its Effects on Post-Quantum Cryptography

When building cryptosystems, cryptographers focus on finding problems that are not believed to be solvable in polynomial-time. Some of the most popular problems they have found are the Discrete Logarithm Problem and Integer Factoring. The former is used in Diffie-Hellman Key Exachange (DHK) and El Gamal encryption, while the latter is used in RSA. El Gamal and DHK are both very popular, but RSA is more prevalent due to its efficiency. Nevertheless, it is plausible that in the next few decades, all three of these systems will likely be useless due to the advances made by Peter Shor in quantum computing. This paper will explain the details of how Shor’s algorithm works and how it accomplishes the above. It will also feature a redesign of the proof of Jeffrey Miller (1975) that efficiently reduces from order finding in a group of order N to factoring N. Hopefully, doing so will aid future students in their studies of quantum algorithms and Post-Quantum Cryptography

The Key to Cryptography: The RSA Algorithm

Cryptography is the study of codes, as well as the art of writing and solving them. It has been a growing area of study for the past 40 years. Now that most information is sent and received through the internet, people need ways to protect what they send. Some of the most commonly used cryptosystems today include a public key. Some public keys are based around using two large, random prime numbers combined together to help encrypt messages. The purpose of this project was to test the strength of the RSA cryptosystem public key. This public key is created by taking the product of two large prime numbers. We needed to find a way to factor this number and see how long it would take to factor it. So we coded several factoring algorithms to test this. The algorithms that were implemented to factor are Trial Division, Pollard’s Rho, and the Quadratic Sieve. Using these algorithms we were able to find the threshold for decrypting large prime numbers used in Cryptography