Java tutorial
package org.bouncycastle.crypto.digests; import org.bouncycastle.util.Memoable; import org.bouncycastle.util.Pack; /** * FIPS 180-2 implementation of SHA-256. * * <pre> * block word digest * SHA-1 512 32 160 * SHA-256 512 32 256 * SHA-384 1024 64 384 * SHA-512 1024 64 512 * </pre> */ public class SHA256Digest extends GeneralDigest implements EncodableDigest { private static final int DIGEST_LENGTH = 32; private int H1, H2, H3, H4, H5, H6, H7, H8; private int[] X = new int[64]; private int xOff; /** * Standard constructor */ public SHA256Digest() { reset(); } /** * Copy constructor. This will copy the state of the provided * message digest. */ public SHA256Digest(SHA256Digest t) { super(t); copyIn(t); } private void copyIn(SHA256Digest t) { super.copyIn(t); H1 = t.H1; H2 = t.H2; H3 = t.H3; H4 = t.H4; H5 = t.H5; H6 = t.H6; H7 = t.H7; H8 = t.H8; System.arraycopy(t.X, 0, X, 0, t.X.length); xOff = t.xOff; } /** * State constructor - create a digest initialised with the state of a previous one. * * @param encodedState the encoded state from the originating digest. */ public SHA256Digest(byte[] encodedState) { super(encodedState); H1 = Pack.bigEndianToInt(encodedState, 16); H2 = Pack.bigEndianToInt(encodedState, 20); H3 = Pack.bigEndianToInt(encodedState, 24); H4 = Pack.bigEndianToInt(encodedState, 28); H5 = Pack.bigEndianToInt(encodedState, 32); H6 = Pack.bigEndianToInt(encodedState, 36); H7 = Pack.bigEndianToInt(encodedState, 40); H8 = Pack.bigEndianToInt(encodedState, 44); xOff = Pack.bigEndianToInt(encodedState, 48); for (int i = 0; i != xOff; i++) { X[i] = Pack.bigEndianToInt(encodedState, 52 + (i * 4)); } } public String getAlgorithmName() { return "SHA-256"; } public int getDigestSize() { return DIGEST_LENGTH; } protected void processWord(byte[] in, int inOff) { // Note: Inlined for performance // X[xOff] = Pack.bigEndianToInt(in, inOff); int n = in[inOff] << 24; n |= (in[++inOff] & 0xff) << 16; n |= (in[++inOff] & 0xff) << 8; n |= (in[++inOff] & 0xff); X[xOff] = n; if (++xOff == 16) { processBlock(); } } protected void processLength(long bitLength) { if (xOff > 14) { processBlock(); } X[14] = (int) (bitLength >>> 32); X[15] = (int) (bitLength & 0xffffffff); } public int doFinal(byte[] out, int outOff) { finish(); Pack.intToBigEndian(H1, out, outOff); Pack.intToBigEndian(H2, out, outOff + 4); Pack.intToBigEndian(H3, out, outOff + 8); Pack.intToBigEndian(H4, out, outOff + 12); Pack.intToBigEndian(H5, out, outOff + 16); Pack.intToBigEndian(H6, out, outOff + 20); Pack.intToBigEndian(H7, out, outOff + 24); Pack.intToBigEndian(H8, out, outOff + 28); reset(); return DIGEST_LENGTH; } /** * reset the chaining variables */ public void reset() { super.reset(); /* SHA-256 initial hash value * The first 32 bits of the fractional parts of the square roots * of the first eight prime numbers */ H1 = 0x6a09e667; H2 = 0xbb67ae85; H3 = 0x3c6ef372; H4 = 0xa54ff53a; H5 = 0x510e527f; H6 = 0x9b05688c; H7 = 0x1f83d9ab; H8 = 0x5be0cd19; xOff = 0; for (int i = 0; i != X.length; i++) { X[i] = 0; } } protected void processBlock() { // // expand 16 word block into 64 word blocks. // for (int t = 16; t <= 63; t++) { X[t] = Theta1(X[t - 2]) + X[t - 7] + Theta0(X[t - 15]) + X[t - 16]; } // // set up working variables. // int a = H1; int b = H2; int c = H3; int d = H4; int e = H5; int f = H6; int g = H7; int h = H8; int t = 0; for (int i = 0; i < 8; i++) { // t = 8 * i h += Sum1(e) + Ch(e, f, g) + K[t] + X[t]; d += h; h += Sum0(a) + Maj(a, b, c); ++t; // t = 8 * i + 1 g += Sum1(d) + Ch(d, e, f) + K[t] + X[t]; c += g; g += Sum0(h) + Maj(h, a, b); ++t; // t = 8 * i + 2 f += Sum1(c) + Ch(c, d, e) + K[t] + X[t]; b += f; f += Sum0(g) + Maj(g, h, a); ++t; // t = 8 * i + 3 e += Sum1(b) + Ch(b, c, d) + K[t] + X[t]; a += e; e += Sum0(f) + Maj(f, g, h); ++t; // t = 8 * i + 4 d += Sum1(a) + Ch(a, b, c) + K[t] + X[t]; h += d; d += Sum0(e) + Maj(e, f, g); ++t; // t = 8 * i + 5 c += Sum1(h) + Ch(h, a, b) + K[t] + X[t]; g += c; c += Sum0(d) + Maj(d, e, f); ++t; // t = 8 * i + 6 b += Sum1(g) + Ch(g, h, a) + K[t] + X[t]; f += b; b += Sum0(c) + Maj(c, d, e); ++t; // t = 8 * i + 7 a += Sum1(f) + Ch(f, g, h) + K[t] + X[t]; e += a; a += Sum0(b) + Maj(b, c, d); ++t; } H1 += a; H2 += b; H3 += c; H4 += d; H5 += e; H6 += f; H7 += g; H8 += h; // // reset the offset and clean out the word buffer. // xOff = 0; for (int i = 0; i < 16; i++) { X[i] = 0; } } /* SHA-256 functions */ private static int Ch(int x, int y, int z) { return (x & y) ^ ((~x) & z); // return z ^ (x & (y ^ z)); } private static int Maj(int x, int y, int z) { // return (x & y) ^ (x & z) ^ (y & z); return (x & y) | (z & (x ^ y)); } private static int Sum0(int x) { return ((x >>> 2) | (x << 30)) ^ ((x >>> 13) | (x << 19)) ^ ((x >>> 22) | (x << 10)); } private static int Sum1(int x) { return ((x >>> 6) | (x << 26)) ^ ((x >>> 11) | (x << 21)) ^ ((x >>> 25) | (x << 7)); } private static int Theta0(int x) { return ((x >>> 7) | (x << 25)) ^ ((x >>> 18) | (x << 14)) ^ (x >>> 3); } private static int Theta1(int x) { return ((x >>> 17) | (x << 15)) ^ ((x >>> 19) | (x << 13)) ^ (x >>> 10); } /* SHA-256 Constants * (represent the first 32 bits of the fractional parts of the * cube roots of the first sixty-four prime numbers) */ static final int K[] = { 0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5, 0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174, 0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da, 0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967, 0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85, 0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070, 0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3, 0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2 }; public Memoable copy() { return new SHA256Digest(this); } public void reset(Memoable other) { SHA256Digest d = (SHA256Digest) other; copyIn(d); } public byte[] getEncodedState() { byte[] state = new byte[52 + xOff * 4]; super.populateState(state); Pack.intToBigEndian(H1, state, 16); Pack.intToBigEndian(H2, state, 20); Pack.intToBigEndian(H3, state, 24); Pack.intToBigEndian(H4, state, 28); Pack.intToBigEndian(H5, state, 32); Pack.intToBigEndian(H6, state, 36); Pack.intToBigEndian(H7, state, 40); Pack.intToBigEndian(H8, state, 44); Pack.intToBigEndian(xOff, state, 48); for (int i = 0; i != xOff; i++) { Pack.intToBigEndian(X[i], state, 52 + (i * 4)); } return state; } }