package org.bouncycastle.crypto.digests;

import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.Digest;
import org.bouncycastle.crypto.params.KeyParameter;
import org.bouncycastle.crypto.params.ParametersWithSBox;
import org.bouncycastle.crypto.engines.GOST28147Engine;

/**
 * implementation of GOST R 34.11-94
 */
public class GOST3411Digest
    implements Digest
{
    private static final int    DIGEST_LENGTH = 32;

    private byte[]   H = new byte[32], L = new byte[32],
                     M = new byte[32], Sum = new byte[32];
    private byte[][] C = new byte[4][32];

    private byte[]  xBuf = new byte[32];
    private int  xBufOff;
    private long byteCount;
    
    private BlockCipher cipher = new GOST28147Engine();

    /**
     * Standard constructor
     */
    public GOST3411Digest()
    {
        cipher.init(true, new ParametersWithSBox(null, GOST28147Engine.getSBox("D-A")));
        
        reset();
    }

    /**
     * Copy constructor.  This will copy the state of the provided
     * message digest.
     */
    public GOST3411Digest(GOST3411Digest t)
    {
        cipher.init(true, new ParametersWithSBox(null, GOST28147Engine.getSBox("D-A")));
        
        reset();

        System.arraycopy(t.H, 0, this.H, 0, t.H.length);
        System.arraycopy(t.L, 0, this.L, 0, t.L.length);
        System.arraycopy(t.M, 0, this.M, 0, t.M.length);
        System.arraycopy(t.Sum, 0, this.Sum, 0, t.Sum.length);
        System.arraycopy(t.C[1], 0, this.C[1], 0, t.C[1].length);
        System.arraycopy(t.C[2], 0, this.C[2], 0, t.C[2].length);
        System.arraycopy(t.C[3], 0, this.C[3], 0, t.C[3].length);
        System.arraycopy(t.xBuf, 0, this.xBuf, 0, t.xBuf.length);
        
        this.xBufOff = t.xBufOff;
        this.byteCount = t.byteCount;
    }

    public String getAlgorithmName()
    {
        return "GOST3411";
    }

    public int getDigestSize()
    {
        return DIGEST_LENGTH;
    }

    public void update(byte in)
    {
        xBuf[xBufOff++] = in;
        if (xBufOff == xBuf.length)
        {
            sumByteArray(xBuf); // calc sum M
            processBlock(xBuf, 0);
            xBufOff = 0;
        }
        byteCount++;
    }

    public void update(byte[] in, int inOff, int len)
    {
        while ((xBufOff != 0) && (len > 0))
        {
            update(in[inOff]);
            inOff++;
            len--;
        }

        while (len > xBuf.length)
        {
            System.arraycopy(in, inOff, xBuf, 0, xBuf.length);

            sumByteArray(xBuf); // calc sum M
            processBlock(xBuf, 0);
            inOff += xBuf.length;
            len -= xBuf.length;
            byteCount += xBuf.length;
        }

        // load in the remainder.
        while (len > 0)
        {
            update(in[inOff]);
            inOff++;
            len--;
        }
    }

    // (i + 1 + 4(k - 1)) = 8i + k      i = 0-3, k = 1-8
    private byte[] K = new byte[32];

    private byte[] P(byte[] in)
    {
        for(int k = 0; k < 8; k++)
        {
            K[0 + 4*k] = in[ 0 + k];
            K[1 + 4*k] = in[ 8 + k];
            K[2 + 4*k] = in[16 + k];
            K[3 + 4*k] = in[24 + k];
        }

        return K;
    }

    //A (x) = (x0 ^ x1) || x3 || x2 || x1
    byte[] a = new byte[8];
    private byte[] A(byte[] in)
    {
        for(int j=0; j<8; j++) a[j]=(byte)(in[j] ^ in[j+8]);

        System.arraycopy(in, 8, in, 0, 24);
        System.arraycopy(a, 0, in, 24, 8);

        return in;
    }

    //Encrypt function, ECB mode
    private void E(byte[] key, byte[] s, int sOff, byte[] in, int inOff)
    {
        cipher.init(true, new KeyParameter(key));
        
        cipher.processBlock(in, inOff, s, sOff);
    }

    // (in:) n16||..||n1 ==> (out:) n1^n2^n3^n4^n13^n16||n16||..||n2
    short[] wS = new short[16], w_S = new short[16];

    private void fw(byte[] in)
    {
        cpyBytesToShort(in, wS);
        w_S[15] = (short)(wS[0] ^ wS[1] ^ wS[2] ^ wS[3] ^ wS[12] ^ wS[15]);
        for(int i = 14; i >= 0; i--) w_S[i] = wS[i+1];
        cpyShortToBytes(w_S, in);
    }

    // block processing
    byte[] S = new byte[32];
    byte[] U = new byte[32], V = new byte[32], W = new byte[32];

    protected void processBlock(byte[] in, int inOff)
    {
        System.arraycopy(in, inOff, M, 0, 32);

        //key step 1
        int i=0;
        // H = h3 || h2 || h1 || h0
        // S = s3 || s2 || s1 || s0
        System.arraycopy(H, 0, U, 0, 32);
        System.arraycopy(M, 0, V, 0, 32);
        for(int j=0; j<32; j++) W[j] = (byte)(U[j]^V[j]);
        // Encrypt gost28147-ECB
        E(P(W), S, 0, H, 0); // s0 = EK0 [h0]

        //keys step 2,3,4
        for (i=1; i<4; i++)
        {
            byte[] tmpA = A(U);
            for (int j=0; j<32; j++) U[j] = (byte)(tmpA[j] ^ C[i][j]);
            V = A(A(V));
            for (int j=0; j<32; j++) W[j] = (byte)(U[j]^V[j]);
            // Encrypt gost28147-ECB
            E(P(W), S, i * 8, H, i * 8); // si = EKi [hi]
        }

        // x(M, H) = y61(H^y(M^y12(S)))
        for(int n = 0; n < 12; n++) fw(S);
        for(int n = 0; n < 32; n++) S[n] = (byte)(S[n] ^ M[n]);
        fw(S);
        for(int n = 0; n < 32; n++) S[n] = (byte)(H[n] ^ S[n]);
        for(int n = 0; n < 61; n++) fw(S);
        for(int j=0; j < H.length; j++) H[j] = S[j];
    }

    private void finish()
    {
        LongToBytes(byteCount * 8, L, 0); // get length into L (byteCount * 8 = bitCount)

        while (xBufOff != 0) update((byte)0);

        processBlock(L, 0);
        processBlock(Sum, 0);
    }

    public int doFinal(
        byte[]  out,
        int     outOff)
    {
        finish();

        for(int i=0; i<H.length; i++) out[i+outOff] = H[i];

        reset();

        return DIGEST_LENGTH;
    }

    /**
     * reset the chaining variables to the IV values.
     */
    private static byte[]  C2 = {
       0x00,(byte)0xFF,0x00,(byte)0xFF,0x00,(byte)0xFF,0x00,(byte)0xFF,
       (byte)0xFF,0x00,(byte)0xFF,0x00,(byte)0xFF,0x00,(byte)0xFF,0x00,
       0x00,(byte)0xFF,(byte)0xFF,0x00,(byte)0xFF,0x00,0x00,(byte)0xFF,
       (byte)0xFF,0x00,0x00,0x00,(byte)0xFF,(byte)0xFF,0x00,(byte)0xFF};

    public void reset()
    {
        byteCount = 0;
        xBufOff = 0;

        for(int i=0; i<H.length; i++) H[i] = 0;  // start vector H
        for(int i=0; i<L.length; i++) L[i] = 0;
        for(int i=0; i<M.length; i++) M[i] = 0;
        for(int i=0; i<C[1].length; i++) C[1][i] = 0;  // real index C = +1 because index array with 0.
        for(int i=0; i<C[3].length; i++) C[3][i] = 0;
        for(int i=0; i<Sum.length; i++) Sum[i] = 0;
        for(int i = 0; i < xBuf.length; i++ ) xBuf[i] = 0;

        System.arraycopy(C2, 0, C[2], 0, C2.length);
    }

    //  256 bitsblock modul -> (Sum + a mod (2^256))
    private void sumByteArray(byte[] in)
    {
        int carry = 0;

        for (int i = 0; i != Sum.length; i++)
        {
            int sum = (Sum[i] & 0xff) + (in[i] & 0xff) + carry;

            Sum[i] = (byte)sum;

            carry = sum >>> 8;
        }
    }

    private void LongToBytes( long r, byte[] out, int outOff)
    {
        out[outOff + 7] = (byte)(r >> 56);
        out[outOff + 6] = (byte)(r >> 48);
        out[outOff + 5] = (byte)(r >> 40);
        out[outOff + 4] = (byte)(r >> 32);
        out[outOff + 3] = (byte)(r >> 24);
        out[outOff + 2] = (byte)(r >> 16);
        out[outOff + 1] = (byte)(r >> 8);
        out[outOff] = (byte)r;
    }

    private void cpyBytesToShort(byte[] S, short[] wS)
    {
        for(int i=0; i<S.length/2; i++){
            wS[i] = (short)(((S[i*2+1]<<8)&0xFF00)|(S[i*2]&0xFF));
        }
    }

    private void cpyShortToBytes(short[] wS, byte[] S)
    {
        for(int i=0; i<S.length/2; i++){
            S[i*2 + 1] = (byte)(wS[i] >> 8);
            S[i*2] = (byte)wS[i];
        }
    }
}
