Java tutorial
package org.bouncycastle.crypto.macs; import org.bouncycastle.crypto.BlockCipher; import org.bouncycastle.crypto.CipherParameters; import org.bouncycastle.crypto.DataLengthException; import org.bouncycastle.crypto.Mac; import org.bouncycastle.crypto.OutputLengthException; import org.bouncycastle.crypto.generators.Poly1305KeyGenerator; import org.bouncycastle.crypto.params.KeyParameter; import org.bouncycastle.crypto.params.ParametersWithIV; import org.bouncycastle.util.Pack; /** * Poly1305 message authentication code, designed by D. J. Bernstein. * <p> * Poly1305 computes a 128-bit (16 bytes) authenticator, using a 128 bit nonce and a 256 bit key * consisting of a 128 bit key applied to an underlying cipher, and a 128 bit key (with 106 * effective key bits) used in the authenticator. * <p> * The polynomial calculation in this implementation is adapted from the public domain <a * href="https://github.com/floodyberry/poly1305-donna">poly1305-donna-unrolled</a> C implementation * by Andrew M (@floodyberry). * @see Poly1305KeyGenerator */ public class Poly1305 implements Mac { private static final int BLOCK_SIZE = 16; private final BlockCipher cipher; private final byte[] singleByte = new byte[1]; // Initialised state /** Polynomial key */ private int r0, r1, r2, r3, r4; /** Precomputed 5 * r[1..4] */ private int s1, s2, s3, s4; /** Encrypted nonce */ private int k0, k1, k2, k3; // Accumulating state /** Current block of buffered input */ private final byte[] currentBlock = new byte[BLOCK_SIZE]; /** Current offset in input buffer */ private int currentBlockOffset = 0; /** Polynomial accumulator */ private int h0, h1, h2, h3, h4; /** * Constructs a Poly1305 MAC, where the key passed to init() will be used directly. */ public Poly1305() { this.cipher = null; } /** * Constructs a Poly1305 MAC, using a 128 bit block cipher. */ public Poly1305(final BlockCipher cipher) { if (cipher.getBlockSize() != BLOCK_SIZE) { throw new IllegalArgumentException("Poly1305 requires a 128 bit block cipher."); } this.cipher = cipher; } /** * Initialises the Poly1305 MAC. * * @param params if used with a block cipher, then a {@link ParametersWithIV} containing a 128 bit * nonce and a {@link KeyParameter} with a 256 bit key complying to the * {@link Poly1305KeyGenerator Poly1305 key format}, otherwise just the * {@link KeyParameter}. */ public void init(CipherParameters params) throws IllegalArgumentException { byte[] nonce = null; if (cipher != null) { if (!(params instanceof ParametersWithIV)) { throw new IllegalArgumentException("Poly1305 requires an IV when used with a block cipher."); } ParametersWithIV ivParams = (ParametersWithIV) params; nonce = ivParams.getIV(); params = ivParams.getParameters(); } if (!(params instanceof KeyParameter)) { throw new IllegalArgumentException("Poly1305 requires a key."); } KeyParameter keyParams = (KeyParameter) params; setKey(keyParams.getKey(), nonce); reset(); } private void setKey(final byte[] key, final byte[] nonce) { if (key.length != 32) { throw new IllegalArgumentException("Poly1305 key must be 256 bits."); } if (cipher != null && (nonce == null || nonce.length != BLOCK_SIZE)) { throw new IllegalArgumentException("Poly1305 requires a 128 bit IV."); } // Extract r portion of key (and "clamp" the values) int t0 = Pack.littleEndianToInt(key, 0); int t1 = Pack.littleEndianToInt(key, 4); int t2 = Pack.littleEndianToInt(key, 8); int t3 = Pack.littleEndianToInt(key, 12); // NOTE: The masks perform the key "clamping" implicitly r0 = t0 & 0x03FFFFFF; r1 = ((t0 >>> 26) | (t1 << 6)) & 0x03FFFF03; r2 = ((t1 >>> 20) | (t2 << 12)) & 0x03FFC0FF; r3 = ((t2 >>> 14) | (t3 << 18)) & 0x03F03FFF; r4 = (t3 >>> 8) & 0x000FFFFF; // Precompute multipliers s1 = r1 * 5; s2 = r2 * 5; s3 = r3 * 5; s4 = r4 * 5; final byte[] kBytes; final int kOff; if (cipher == null) { kBytes = key; kOff = BLOCK_SIZE; } else { // Compute encrypted nonce kBytes = new byte[BLOCK_SIZE]; kOff = 0; cipher.init(true, new KeyParameter(key, BLOCK_SIZE, BLOCK_SIZE)); cipher.processBlock(nonce, 0, kBytes, 0); } k0 = Pack.littleEndianToInt(kBytes, kOff + 0); k1 = Pack.littleEndianToInt(kBytes, kOff + 4); k2 = Pack.littleEndianToInt(kBytes, kOff + 8); k3 = Pack.littleEndianToInt(kBytes, kOff + 12); } public String getAlgorithmName() { return cipher == null ? "Poly1305" : "Poly1305-" + cipher.getAlgorithmName(); } public int getMacSize() { return BLOCK_SIZE; } public void update(final byte in) throws IllegalStateException { singleByte[0] = in; update(singleByte, 0, 1); } public void update(final byte[] in, final int inOff, final int len) throws DataLengthException, IllegalStateException { int copied = 0; while (len > copied) { if (currentBlockOffset == BLOCK_SIZE) { processBlock(); currentBlockOffset = 0; } int toCopy = Math.min((len - copied), BLOCK_SIZE - currentBlockOffset); System.arraycopy(in, copied + inOff, currentBlock, currentBlockOffset, toCopy); copied += toCopy; currentBlockOffset += toCopy; } } private void processBlock() { if (currentBlockOffset < BLOCK_SIZE) { currentBlock[currentBlockOffset] = 1; for (int i = currentBlockOffset + 1; i < BLOCK_SIZE; i++) { currentBlock[i] = 0; } } final long t0 = 0xffffffffL & Pack.littleEndianToInt(currentBlock, 0); final long t1 = 0xffffffffL & Pack.littleEndianToInt(currentBlock, 4); final long t2 = 0xffffffffL & Pack.littleEndianToInt(currentBlock, 8); final long t3 = 0xffffffffL & Pack.littleEndianToInt(currentBlock, 12); h0 += t0 & 0x3ffffff; h1 += (((t1 << 32) | t0) >>> 26) & 0x3ffffff; h2 += (((t2 << 32) | t1) >>> 20) & 0x3ffffff; h3 += (((t3 << 32) | t2) >>> 14) & 0x3ffffff; h4 += (t3 >>> 8); if (currentBlockOffset == BLOCK_SIZE) { h4 += (1 << 24); } long tp0 = mul32x32_64(h0, r0) + mul32x32_64(h1, s4) + mul32x32_64(h2, s3) + mul32x32_64(h3, s2) + mul32x32_64(h4, s1); long tp1 = mul32x32_64(h0, r1) + mul32x32_64(h1, r0) + mul32x32_64(h2, s4) + mul32x32_64(h3, s3) + mul32x32_64(h4, s2); long tp2 = mul32x32_64(h0, r2) + mul32x32_64(h1, r1) + mul32x32_64(h2, r0) + mul32x32_64(h3, s4) + mul32x32_64(h4, s3); long tp3 = mul32x32_64(h0, r3) + mul32x32_64(h1, r2) + mul32x32_64(h2, r1) + mul32x32_64(h3, r0) + mul32x32_64(h4, s4); long tp4 = mul32x32_64(h0, r4) + mul32x32_64(h1, r3) + mul32x32_64(h2, r2) + mul32x32_64(h3, r1) + mul32x32_64(h4, r0); h0 = (int) tp0 & 0x3ffffff; tp1 += (tp0 >>> 26); h1 = (int) tp1 & 0x3ffffff; tp2 += (tp1 >>> 26); h2 = (int) tp2 & 0x3ffffff; tp3 += (tp2 >>> 26); h3 = (int) tp3 & 0x3ffffff; tp4 += (tp3 >>> 26); h4 = (int) tp4 & 0x3ffffff; h0 += (int) (tp4 >>> 26) * 5; h1 += (h0 >>> 26); h0 &= 0x3ffffff; } public int doFinal(final byte[] out, final int outOff) throws DataLengthException, IllegalStateException { if (outOff + BLOCK_SIZE > out.length) { throw new OutputLengthException("Output buffer is too short."); } if (currentBlockOffset > 0) { // Process padded final block processBlock(); } h1 += (h0 >>> 26); h0 &= 0x3ffffff; h2 += (h1 >>> 26); h1 &= 0x3ffffff; h3 += (h2 >>> 26); h2 &= 0x3ffffff; h4 += (h3 >>> 26); h3 &= 0x3ffffff; h0 += (h4 >>> 26) * 5; h4 &= 0x3ffffff; h1 += (h0 >>> 26); h0 &= 0x3ffffff; int g0, g1, g2, g3, g4, b; g0 = h0 + 5; b = g0 >>> 26; g0 &= 0x3ffffff; g1 = h1 + b; b = g1 >>> 26; g1 &= 0x3ffffff; g2 = h2 + b; b = g2 >>> 26; g2 &= 0x3ffffff; g3 = h3 + b; b = g3 >>> 26; g3 &= 0x3ffffff; g4 = h4 + b - (1 << 26); b = (g4 >>> 31) - 1; int nb = ~b; h0 = (h0 & nb) | (g0 & b); h1 = (h1 & nb) | (g1 & b); h2 = (h2 & nb) | (g2 & b); h3 = (h3 & nb) | (g3 & b); h4 = (h4 & nb) | (g4 & b); long f0, f1, f2, f3; f0 = (((h0) | (h1 << 26)) & 0xffffffffl) + (0xffffffffL & k0); f1 = (((h1 >>> 6) | (h2 << 20)) & 0xffffffffl) + (0xffffffffL & k1); f2 = (((h2 >>> 12) | (h3 << 14)) & 0xffffffffl) + (0xffffffffL & k2); f3 = (((h3 >>> 18) | (h4 << 8)) & 0xffffffffl) + (0xffffffffL & k3); Pack.intToLittleEndian((int) f0, out, outOff); f1 += (f0 >>> 32); Pack.intToLittleEndian((int) f1, out, outOff + 4); f2 += (f1 >>> 32); Pack.intToLittleEndian((int) f2, out, outOff + 8); f3 += (f2 >>> 32); Pack.intToLittleEndian((int) f3, out, outOff + 12); reset(); return BLOCK_SIZE; } public void reset() { currentBlockOffset = 0; h0 = h1 = h2 = h3 = h4 = 0; } private static final long mul32x32_64(int i1, int i2) { return (i1 & 0xFFFFFFFFL) * i2; } }