SHA-3 / Keccak — Java Implementation

A from-scratch implementation of the SHA-3 hash function family in Java, following the FIPS 202 standard.

Overview

SHA-3 is based on the Keccak sponge construction, which applies a permutation function (Keccak-p) to absorb the input and squeeze out the digest. This implementation covers all four standardized variants:

Variant	Digest size	Capacity
SHA3-224	224 bits	448 bits
SHA3-256	256 bits	512 bits
SHA3-384	384 bits	768 bits
SHA3-512	512 bits	1024 bits

Structure

The Keccak-p permutation is built from five step mappings applied each round:

• θ (Theta) — XORs each bit with the parity of two columns
• ρ (Rho) — rotates each lane by a fixed offset
• π (Pi) — rearranges the positions of the lanes
• χ (Chi) — applies a non-linear function to each row
• ι (Iota) — XORs lane (0,0) with a round constant

Usage

Compile and run

javac Sha3.java && java -cp . Sha3

API

All methods take and return binary strings (sequences of '0' and '1'). Use the provided HexToBin and BinToHex helpers to convert to/from hex.

String input = Sha3.HexToBin("A3A3A3...");
String digest = Sha3.BinToHex(Sha3.SHA3_256(input));

Test Vectors

The test() method verifies the implementation against the official NIST test vectors from FIPS 202, including:

• Empty input
• 1600-bit input (A3 repeated 200 times)

Run the main class to execute all tests. Expected output is true for each variant.

Reference

• FIPS 202 — SHA-3 Standard
• Keccak reference