/*

 * Copyright (c) 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

 * questions.

 */

/*

 * (C) Copyright IBM Corp. 2013

 */

package com.sun.crypto.provider;

import java.security.*;

import javax.crypto.*;

import static com.sun.crypto.provider.AESConstants.AES_BLOCK_SIZE;

/**

 * This class represents the GCTR function defined in NIST 800-38D

 * under section 6.5. It needs to be constructed w/ an initialized

 * cipher object, and initial counter block(ICB). Given an input X

 * of arbitrary length, it processes and returns an output which has

 * the same length as X. The invariants of this class are:

 *

 * (1) The length of intialCounterBlk (and also of its clones, e.g.,

 * fields counter and counterSave) is equal to AES_BLOCK_SIZE.

 *

 * (2) After construction, the field counter never becomes null, it

 * always contains a byte array of length AES_BLOCK_SIZE.

 *

 * If any invariant is broken, failures can occur because the

 * AESCrypt.encryptBlock method can be intrinsified on the HotSpot VM

 * (see JDK-8067648 for details).

 *

 * <p>This function is used in the implementation of GCM mode.

 *

 * @since 1.8

 */

final class GCTR {

    // these fields should not change after the object has been constructed

    private final SymmetricCipher aes;

    private final byte[] icb;

    // the current counter value

    private byte[] counter;

    // needed for save/restore calls

    private byte[] counterSave = null;

    // NOTE: cipher should already be initialized

    GCTR(SymmetricCipher cipher, byte[] initialCounterBlk) {

        this.aes = cipher;

        if (initialCounterBlk.length != AES_BLOCK_SIZE) {

            throw new RuntimeException("length of initial counter block (" + initialCounterBlk.length +

                                       ") not equal to AES_BLOCK_SIZE (" + AES_BLOCK_SIZE + ")");

        }

        this.icb = initialCounterBlk;

        this.counter = icb.clone();

    }

    // input must be multiples of 128-bit blocks when calling update

    int update(byte[] in, int inOfs, int inLen, byte[] out, int outOfs) {

        if (inLen - inOfs > in.length) {

            throw new RuntimeException("input length out of bound");

        }

        if (inLen < 0 || inLen % AES_BLOCK_SIZE != 0) {

            throw new RuntimeException("input length unsupported");

        }

        if (out.length - outOfs < inLen) {

            throw new RuntimeException("output buffer too small");

        }

        byte[] encryptedCntr = new byte[AES_BLOCK_SIZE];

        int numOfCompleteBlocks = inLen / AES_BLOCK_SIZE;

        for (int i = 0; i < numOfCompleteBlocks; i++) {

            aes.encryptBlock(counter, 0, encryptedCntr, 0);

            for (int n = 0; n < AES_BLOCK_SIZE; n++) {

                int index = (i * AES_BLOCK_SIZE + n);

                out[outOfs + index] =

                    (byte) ((in[inOfs + index] ^ encryptedCntr[n]));

            }

            GaloisCounterMode.increment32(counter);

        }

        return inLen;

    }

    // input can be arbitrary size when calling doFinal

    protected int doFinal(byte[] in, int inOfs, int inLen, byte[] out,

                          int outOfs) throws IllegalBlockSizeException {

        try {

            if (inLen < 0) {

                throw new IllegalBlockSizeException("Negative input size!");

            } else if (inLen > 0) {

                int lastBlockSize = inLen % AES_BLOCK_SIZE;

                int completeBlkLen = inLen - lastBlockSize;

                // process the complete blocks first

                update(in, inOfs, completeBlkLen, out, outOfs);

                if (lastBlockSize != 0) {

                    // do the last partial block

                    byte[] encryptedCntr = new byte[AES_BLOCK_SIZE];

                    aes.encryptBlock(counter, 0, encryptedCntr, 0);

                    for (int n = 0; n < lastBlockSize; n++) {

                        out[outOfs + completeBlkLen + n] =

                            (byte) ((in[inOfs + completeBlkLen + n] ^

                                     encryptedCntr[n]));

                    }

                }

            }

        } finally {

            reset();

        }

        return inLen;

    }

    /**

     * Resets the content of this object to when it's first constructed.

     */

    void reset() {

        System.arraycopy(icb, 0, counter, 0, icb.length);

        counterSave = null;

    }

    /**

     * Save the current content of this object.

     */

    void save() {

        this.counterSave = this.counter.clone();

    }

    /**

     * Restores the content of this object to the previous saved one.

     */

    void restore() {

        if (this.counterSave != null) {

            this.counter = this.counterSave;

        }

    }

}