Elliptic Curves: From Torus to Pendulum
Same law, three worlds: \(y^2 = x^3+ax+b\) adds points by chord-tangent. Over $\mathbb{C}$ the curve is a torus; a pendulum's $(\theta,p)$ phase flow wraps that torus.
Quantum Fourier Transform & Shor's Algorithm
Physics turns periodicity into constructive interference. QFT sums phasors $e^{2\pi i kx/M}$; peaks land at multiples of $M/r$, revealing the period that breaks RSA.
Diffie-Hellman on Circles and Curves
Same protocol, different groups. Classic DH multiplies on the circle $e^{2\pi i a/p}$; ECDH adds points on an elliptic curve. Hardness comes from the group, not the wire.
Why the Triangle Works
Mathematics provides
Abelian groups, elliptic curves, and Fourier analysis. The chord-tangent law, $E(\mathbb{C})\cong \mathbb{C}/\Lambda$, and characters $e^{2\pi i kx/N}$ are the same algebraic structures in different costumes.
Physics provides
Hamiltonian phase space, action-angle variables, and quantum interference. A pendulum winds a torus; a quantum computer sums phasors—both are physical realizations of group translations.
Cryptography uses
Hard problems: factoring, DLP, ECDLP. It builds protocols from math, then physics tests them. When quantum period-finding wins, math responds with lattices and isogenies—closing the loop.
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