SLIDE 28 Pre-Quantum Cryptograpghy Quantum Attacks on Classical Cryptosystems Quantum Cryptography Post-Quantum Cryptography Solving Hard Problems by Quantum Computers Death of Classical Public Key Cryptography Need for QKD
Period finding problem
Let f : {0, 1, 2, . . . , M − 1} → {0, 1, 2, . . . , M − 1} be a periodic function of period r, meaning that f (x) = f (x + r) ∀x ∈ {0, 1, 2, . . . , M − 1} and the values f (x), f (x + 1), f (x + 2), . . . , f (x + r − 1) are all distinct. For simplicity, one can assume that M = 2m that r ≤ M/2. Finding the unknown period is a hard problem in classical computing.
Goutam Paul The death and rebirth of classical cryptography in a quantum world Slide 14 of 28