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Feistel Network: The Structure Behind DES

Interactive 3D Feistel-network cipher: split a 16-bit block into two halves, run it through a real round function with key schedule and S-box substitution, and watch a single flipped input bit cascade into an avalanche of changed output bits round by round.

Cryptography3DModerate60 FPS📱 Mobile-adapted⇄ 2D version

Most classical block ciphers, including DES, are built from a Feistel network: a block is split into two halves that swap places every round while one half is mixed with the other through a round function keyed off a schedule derived from a master key. This simulator runs a real 16-bit Feistel cipher — rotate, XOR with a round key, substitute through an S-box, permute — for up to 16 rounds, and runs two plaintexts side by side that differ in exactly one bit. Watching the avalanche meter climb toward 50% shows, concretely, why a well-designed cipher makes a single flipped input bit unpredictable in every output bit after only a few rounds.

⚙ Under the hood

An interactive 3D Feistel-cipher block: split a 16-bit block into two halves, run it through a real round function with a key schedule and S-box substitution, and watch a single flipped input bit cascade into an avalanche of changed output bits round by round.

cryptographyfeistel-networkblock-cipherdesavalanche-effectcomputer-science

3D · Three.js / WebGL renderer · 60 FPS target · runs fully client-side, no install