Feistel Cipher: Rounds and the Avalanche Effect

This simulator builds a real 16-bit Feistel-network block cipher — the same round structure used by DES — and renders every round as a 3D tower of glowing bits. Type a plaintext block and a key in hexadecimal, choose how many rounds to run, and step or play through the encryption to watch the substitution-box round function scramble the block layer by layer. Toggling the avalanche twin flips a single input bit and re-runs the identical key schedule alongside the original, so you can watch two nearly-identical blocks diverge into unrecognizably different ciphertexts — a live demonstration of why a well-designed cipher makes a one-bit change ripple through roughly half the output.