/*

 * Copyright (c) 2012, 2013, Oracle and/or its affiliates. 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.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

 * or visit www.oracle.com if you need additional information or have any

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 */

package sun.security.ssl;

import java.util.Arrays;

/**

 * This class represents an SSL/TLS message authentication token,

 * which encapsulates a sequence number and ensures that attempts to

 * delete or reorder messages can be detected.

 *

 * Each SSL/TLS connection state contains a sequence number, which

 * is maintained separately for read and write states.  The sequence

 * number MUST be set to zero whenever a connection state is made the

 * active state.  Sequence numbers are of type uint64 and may not

 * exceed 2^64-1.  Sequence numbers do not wrap.  If a SSL/TLS

 * implementation would need to wrap a sequence number, it must

 * renegotiate instead.  A sequence number is incremented after each

 * record: specifically, the first record transmitted under a

 * particular connection state MUST use sequence number 0.

 */

class Authenticator {

    // byte array containing the additional authentication information for

    // each record

    private final byte[] block;

    // the block size of SSL v3.0:

    // sequence number + record type + + record length

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

    // the block size of TLS v1.0 and later:

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

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

    /**

     * Default construct, no message authentication token is initialized.

     *

     * Note that this construct can only be called for null MAC

     */

    Authenticator() {

        block = new byte[0];

    }

    /**

     * Constructs the message authentication token for the specified

     * SSL/TLS protocol.

     */

    Authenticator(ProtocolVersion protocolVersion) {

        if (protocolVersion.v >= ProtocolVersion.TLS10.v) {

            block = new byte[BLOCK_SIZE_TLS];

            block[9] = protocolVersion.major;

            block[10] = protocolVersion.minor;

        } else {

            block = new byte[BLOCK_SIZE_SSL];

        }

    }

    /**

     * Checks whether the sequence number is close to wrap.

     *

     * Sequence numbers are of type uint64 and may not exceed 2^64-1.

     * Sequence numbers do not wrap. When the sequence number is near

     * to wrap, we need to close the connection immediately.

     *

     * @return true if the sequence number is close to wrap

     */

    final boolean seqNumOverflow() {

        /*

         * Conservatively, we don't allow more records to be generated

         * when there are only 2^8 sequence numbers left.

         */

        return (block.length != 0 &&

                block[0] == (byte)0xFF && block[1] == (byte)0xFF &&

                block[2] == (byte)0xFF && block[3] == (byte)0xFF &&

                block[4] == (byte)0xFF && block[5] == (byte)0xFF &&

                block[6] == (byte)0xFF);

    }

    /**

     * Checks whether the sequence number close to renew.

     *

     * Sequence numbers are of type uint64 and may not exceed 2^64-1.

     * Sequence numbers do not wrap.  If a TLS

     * implementation would need to wrap a sequence number, it must

     * renegotiate instead.

     *

     * @return true if the sequence number is huge enough to renew

     */

    final boolean seqNumIsHuge() {

        /*

         * Conservatively, we should ask for renegotiation when there are

         * only 2^48 sequence numbers left.

         */

        return (block.length != 0 &&

                block[0] == (byte)0xFF && block[1] == (byte)0xFF);

    }

    /**

     * Gets the current sequence number.

     *

     * @return the byte array of the current sequence number

     */

    final byte[] sequenceNumber() {

        return Arrays.copyOf(block, 8);

    }

    /**

     * Acquires the current message authentication information with the

     * specified record type and fragment length, and then increases the

     * sequence number.

     *

     * @param  type the record type

     * @param  length the fragment of the record

     * @return the byte array of the current message authentication information

     */

    final byte[] acquireAuthenticationBytes(byte type, int length) {

        byte[] copy = block.clone();

        if (block.length != 0) {

            copy[8] = type;

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

            copy[copy.length - 1] = (byte)(length);

            /*

             * Increase the sequence number in the block array

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

             */

            int k = 7;

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

                k--;

            }

        }

        return copy;

    }

}