/*
 * Copyright 2002-2006 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
 * CA 95054 USA or visit www.sun.com if you need additional information or
 * have any questions.
 */

package sun.security.provider;

import static sun.security.provider.ByteArrayAccess.*;

/**
 * This class implements the Secure Hash Algorithm SHA-256 developed by
 * the National Institute of Standards and Technology along with the
 * National Security Agency.
 *
 * <p>It implements java.security.MessageDigestSpi, and can be used
 * through Java Cryptography Architecture (JCA), as a pluggable
 * MessageDigest implementation.
 *
 * @since       1.4.2
 * @author      Valerie Peng
 * @author      Andreas Sterbenz
 */
public final class SHA2 extends DigestBase {

    private static final int ITERATION = 64;
    // Constants for each round
    private static final int[] ROUND_CONSTS = {
        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
    };

    // buffer used by implCompress()
    private final int[] W;

    // state of this object
    private final int[] state;

    /**
     * Creates a new SHA object.
     */
    public SHA2() {
        super("SHA-256", 32, 64);
        state = new int[8];
        W = new int[64];
        implReset();
    }

    /**
     * Creates a SHA2 object.with state (for cloning)
     */
    private SHA2(SHA2 base) {
        super(base);
        this.state = base.state.clone();
        this.W = new int[64];
    }

    public Object clone() {
        return new SHA2(this);
    }

    /**
     * Resets the buffers and hash value to start a new hash.
     */
    void implReset() {
        state[0] = 0x6a09e667;
        state[1] = 0xbb67ae85;
        state[2] = 0x3c6ef372;
        state[3] = 0xa54ff53a;
        state[4] = 0x510e527f;
        state[5] = 0x9b05688c;
        state[6] = 0x1f83d9ab;
        state[7] = 0x5be0cd19;
    }

    void implDigest(byte[] out, int ofs) {
        long bitsProcessed = bytesProcessed << 3;

        int index = (int)bytesProcessed & 0x3f;
        int padLen = (index < 56) ? (56 - index) : (120 - index);
        engineUpdate(padding, 0, padLen);

        i2bBig4((int)(bitsProcessed >>> 32), buffer, 56);
        i2bBig4((int)bitsProcessed, buffer, 60);
        implCompress(buffer, 0);

        i2bBig(state, 0, out, ofs, 32);
    }

    /**
     * logical function ch(x,y,z) as defined in spec:
     * @return (x and y) xor ((complement x) and z)
     * @param x int
     * @param y int
     * @param z int
     */
    private static int lf_ch(int x, int y, int z) {
        return (x & y) ^ ((~x) & z);
    }

    /**
     * logical function maj(x,y,z) as defined in spec:
     * @return (x and y) xor (x and z) xor (y and z)
     * @param x int
     * @param y int
     * @param z int
     */
    private static int lf_maj(int x, int y, int z) {
        return (x & y) ^ (x & z) ^ (y & z);
    }

    /**
     * logical function R(x,s) - right shift
     * @return x right shift for s times
     * @param x int
     * @param s int
     */
    private static int lf_R( int x, int s ) {
        return (x >>> s);
    }

    /**
     * logical function S(x,s) - right rotation
     * @return x circular right shift for s times
     * @param x int
     * @param s int
     */
    private static int lf_S(int x, int s) {
        return (x >>> s) | (x << (32 - s));
    }

    /**
     * logical function sigma0(x) - xor of results of right rotations
     * @return S(x,2) xor S(x,13) xor S(x,22)
     * @param x int
     */
    private static int lf_sigma0(int x) {
        return lf_S(x, 2) ^ lf_S(x, 13) ^ lf_S(x, 22);
    }

    /**
     * logical function sigma1(x) - xor of results of right rotations
     * @return S(x,6) xor S(x,11) xor S(x,25)
     * @param x int
     */
    private static int lf_sigma1(int x) {
        return lf_S( x, 6 ) ^ lf_S( x, 11 ) ^ lf_S( x, 25 );
    }

    /**
     * logical function delta0(x) - xor of results of right shifts/rotations
     * @return int
     * @param x int
     */
    private static int lf_delta0(int x) {
        return lf_S(x, 7) ^ lf_S(x, 18) ^ lf_R(x, 3);
    }

    /**
     * logical function delta1(x) - xor of results of right shifts/rotations
     * @return int
     * @param x int
     */
    private static int lf_delta1(int x) {
        return lf_S(x, 17) ^ lf_S(x, 19) ^ lf_R(x, 10);
    }

    /**
     * Process the current block to update the state variable state.
     */
    void implCompress(byte[] buf, int ofs) {
        b2iBig64(buf, ofs, W);

        // The first 16 ints are from the byte stream, compute the rest of
        // the W[]'s
        for (int t = 16; t < ITERATION; t++) {
            W[t] = lf_delta1(W[t-2]) + W[t-7] + lf_delta0(W[t-15])
                   + W[t-16];
        }

        int a = state[0];
        int b = state[1];
        int c = state[2];
        int d = state[3];
        int e = state[4];
        int f = state[5];
        int g = state[6];
        int h = state[7];

        for (int i = 0; i < ITERATION; i++) {
            int T1 = h + lf_sigma1(e) + lf_ch(e,f,g) + ROUND_CONSTS[i] + W[i];
            int T2 = lf_sigma0(a) + lf_maj(a,b,c);
            h = g;
            g = f;
            f = e;
            e = d + T1;
            d = c;
            c = b;
            b = a;
            a = T1 + T2;
        }
        state[0] += a;
        state[1] += b;
        state[2] += c;
        state[3] += d;
        state[4] += e;
        state[5] += f;
        state[6] += g;
        state[7] += h;
    }

}