Post-quantum cryptography needs a replacement for Diffie–Hellman that doesn't rely on the discrete-log or factoring problems Shor's algorithm breaks. CSIDH (Commutative Supersingular Isogeny Diffie–Hellman) gets there by walking a graph of elliptic curves connected by small-prime isogenies instead of multiplying group elements. This simulator renders that graph in 3D: Alice and Bob each pick a secret vector of small integers, walk from a shared base curve E0 to their own public curve, exchange those public curves, and then each applies their own secret walk to the curve they received. Because the underlying class-group action is commutative, both walks land on the exact same shared curve — the live vectors, step counters, and the converging gold marker confirm the match in real time.