package org.bouncycastle.crypto.digests;


/**
 * Draft FIPS 180-2 implementation of SHA-256. <b>Note:</b> As this is
 * based on a draft this implementation is subject to change.
 *
 * <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
{
    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);

		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;
	}

    public String getAlgorithmName()
    {
        return "SHA-256";
    }

    public int getDigestSize()
    {
        return DIGEST_LENGTH;
    }

    protected void processWord(
        byte[]  in,
        int     inOff)
    {
        X[xOff++] = ((in[inOff] & 0xff) << 24) | ((in[inOff + 1] & 0xff) << 16)
                    | ((in[inOff + 2] & 0xff) << 8) | ((in[inOff + 3] & 0xff)); 

        if (xOff == 16)
        {
            processBlock();
        }
    }

    private void unpackWord(
        int     word,
        byte[]  out,
        int     outOff)
    {
        out[outOff]     = (byte)(word >>> 24);
        out[outOff + 1] = (byte)(word >>> 16);
        out[outOff + 2] = (byte)(word >>> 8);
        out[outOff + 3] = (byte)word;
    }

    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();

        unpackWord(H1, out, outOff);
        unpackWord(H2, out, outOff + 4);
        unpackWord(H3, out, outOff + 8);
        unpackWord(H4, out, outOff + 12);
        unpackWord(H5, out, outOff + 16);
        unpackWord(H6, out, outOff + 20);
        unpackWord(H7, out, outOff + 24);
        unpackWord(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;

		for (int t = 0; t <= 63; t++)
		{
			int		T1, T2;

			T1 = h + Sum1(e) + Ch(e, f, g) + K[t] + X[t];
			T2 = Sum0(a) + Maj(a, b, c);
			h = g;
			g = f;
			f = e;
			e = d + T1;
			d = c;
			c = b;
			b = a;
			a = T1 + T2;
		}

        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 != X.length; i++)
        {
            X[i] = 0;
        }
    }

    private int rotateRight(
        int    x,
        int    n)
    {
        return (x >>> n) | (x << (32 - n));
    }

	/* SHA-256 functions */
    private int Ch(
        int    x,
        int    y,
        int    z)
    {
        return ((x & y) ^ ((~x) & z));
    }

    private int Maj(
        int    x,
        int    y,
        int    z)
    {
        return ((x & y) ^ (x & z) ^ (y & z));
    }

    private int Sum0(
        int    x)
    {
        return rotateRight(x, 2) ^ rotateRight(x, 13) ^ rotateRight(x, 22);
    }

    private int Sum1(
        int    x)
    {
        return rotateRight(x, 6) ^ rotateRight(x, 11) ^ rotateRight(x, 25);
    }

    private int Theta0(
        int    x)
    {
        return rotateRight(x, 7) ^ rotateRight(x, 18) ^ (x >>> 3);
    }

    private int Theta1(
        int    x)
    {
        return rotateRight(x, 17) ^ rotateRight(x, 19) ^ (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
	};
}

