/*

 * Copyright 1996-2007 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.ssl;

import java.security.InvalidKeyException;

import java.security.NoSuchAlgorithmException;

import java.nio.ByteBuffer;

import javax.crypto.Mac;

import javax.crypto.SecretKey;

import sun.security.ssl.CipherSuite.MacAlg;

import static sun.security.ssl.CipherSuite.*;

/**

 * This class computes the "Message Authentication Code" (MAC) for each

 * SSL message.  This is essentially a shared-secret signature, used to

 * provide integrity protection for SSL messages.  The MAC is actually

 * one of several keyed hashes, as associated with the cipher suite and

 * protocol version.  (SSL v3.0 uses one construct, TLS uses another.)

 *

 * <P>NOTE: MAC computation is the only place in the SSL protocol that the

 * sequence number is used.  It's also reset to zero with each change of

 * a cipher spec, so this is the only place this state is needed.

 *

 * @author David Brownell

 * @author Andreas Sterbenz

 */

final class MAC {

    final static MAC NULL = new MAC();

    // Value of the null MAC is fixed

    private static final byte nullMAC[] = new byte[0];

    // internal identifier for the MAC algorithm

    private final MacAlg        macAlg;

    // stuff defined by the kind of MAC algorithm

    private final int           macSize;

    // JCE Mac object

    private final Mac mac;

    // byte array containing the additional information we MAC in each record

    // (see below)

    private final byte[] block;

    // sequence number + record type + + record length

    private static final int BLOCK_SIZE_SSL = 8 + 1 + 2;

    // sequence number + record type + protocol version + record length

    private static final int BLOCK_SIZE_TLS = 8 + 1 + 2 + 2;

    // offset of record type in block

    private static final int BLOCK_OFFSET_TYPE    = 8;

    // offset of protocol version number in block (TLS only)

    private static final int BLOCK_OFFSET_VERSION = 8 + 1;

    private MAC() {

        macSize = 0;

        macAlg = M_NULL;

        mac = null;

        block = null;

    }

    /**

     * Set up, configured for the given SSL/TLS MAC type and version.

     */

    MAC(MacAlg macAlg, ProtocolVersion protocolVersion, SecretKey key)

            throws NoSuchAlgorithmException, InvalidKeyException {

        this.macAlg = macAlg;

        this.macSize = macAlg.size;

        String algorithm;

        boolean tls = (protocolVersion.v >= ProtocolVersion.TLS10.v);

        if (macAlg == M_MD5) {

            algorithm = tls ? "HmacMD5" : "SslMacMD5";

        } else if (macAlg == M_SHA) {

            algorithm = tls ? "HmacSHA1" : "SslMacSHA1";

        } else {

            throw new RuntimeException("Unknown Mac " + macAlg);

        }

        mac = JsseJce.getMac(algorithm);

        mac.init(key);

        if (tls) {

            block = new byte[BLOCK_SIZE_TLS];

            block[BLOCK_OFFSET_VERSION]   = protocolVersion.major;

            block[BLOCK_OFFSET_VERSION+1] = protocolVersion.minor;

        } else {

            block = new byte[BLOCK_SIZE_SSL];

        }

    }

    /**

     * Returns the length of the MAC.

     */

    int MAClen() {

        return macSize;

    }

    /**

     * Computes and returns the MAC for the data in this byte array.

     *

     * @param type record type

     * @param buf compressed record on which the MAC is computed

     * @param offset start of compressed record data

     * @param len the size of the compressed record

     */

    final byte[] compute(byte type, byte buf[], int offset, int len) {

        return compute(type, null, buf, offset, len);

    }

    /**

     * Compute and returns the MAC for the remaining data

     * in this ByteBuffer.

     *

     * On return, the bb position == limit, and limit will

     * have not changed.

     *

     * @param type record type

     * @param bb a ByteBuffer in which the position and limit

     *          demarcate the data to be MAC'd.

     */

    final byte[] compute(byte type, ByteBuffer bb) {

        return compute(type, bb, null, 0, bb.remaining());

    }

    // increment the sequence number in the block array

    // it is a 64-bit number stored in big-endian format

    private void incrementSequenceNumber() {

        int k = 7;

        while ((k >= 0) && (++block[k] == 0)) {

            k--;

        }

    }

    /*

     * Compute based on either buffer type, either bb.position/limit

     * or buf/offset/len.

     */

    private byte[] compute(byte type, ByteBuffer bb, byte[] buf, int offset, int len) {

        if (macSize == 0) {

            return nullMAC;

        }

        block[BLOCK_OFFSET_TYPE] = type;

        block[block.length - 2]  = (byte)(len >> 8);

        block[block.length - 1]  = (byte)(len     );

        mac.update(block);

        incrementSequenceNumber();

        // content

        if (bb != null) {

            mac.update(bb);

        } else {

            mac.update(buf, offset, len);

        }

        return mac.doFinal();

    }

}