/*
 * Copyright (c) 2013, 2018, 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
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 */

/*
 * (C) Copyright IBM Corp. 2013
 */

package com.sun.crypto.provider;

import java.nio.ByteBuffer;
import java.nio.ByteOrder;
import javax.crypto.IllegalBlockSizeException;
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.  With a given cipher object and initial counter
block, a counter mode operation is performed.  Blocksize is limited
to 16 bytes.
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).
The counter mode operations can be intrinsified and parallelized
by using CounterMode.implCrypt() if HotSpot VM supports it on the
architecture.
This function is used in the implementation of GCM mode.
Since:
1.8/**
 * This class represents the GCTR function defined in NIST 800-38D
 * under section 6.5.  With a given cipher object and initial counter
 * block, a counter mode operation is performed.  Blocksize is limited
 * to 16 bytes.
 *
 * 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).
 *
 * The counter mode operations can be intrinsified and parallelized
 * by using CounterMode.implCrypt() if HotSpot VM supports it on the
 * architecture.
 *
 * <p>This function is used in the implementation of GCM mode.
 *
 * @since 1.8
 */
final class GCTR extends CounterMode {

    GCTR(SymmetricCipher cipher, byte[] initialCounterBlk) {
        super(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 + ")");
        }

        iv = initialCounterBlk;
        reset();
    }

    @Override
    String getFeedback() {
        return "GCTR";
    }

    // return the number of blocks until the lower 32 bits roll over
    private long blocksUntilRollover() {
        ByteBuffer buf = ByteBuffer.wrap(counter, counter.length - 4, 4);
        buf.order(ByteOrder.BIG_ENDIAN);
        long ctr32 = 0xFFFFFFFFL & buf.getInt();
        long blocksLeft = (1L << 32) - ctr32;
        return blocksLeft;
    }

    // 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");
        }

        long blocksLeft = blocksUntilRollover();
        int numOfCompleteBlocks = inLen / AES_BLOCK_SIZE;
        if (numOfCompleteBlocks >= blocksLeft) {
            // Counter Mode encryption cannot be used because counter will
            // roll over incorrectly. Use GCM-specific code instead.
            byte[] encryptedCntr = new byte[AES_BLOCK_SIZE];
            for (int i = 0; i < numOfCompleteBlocks; i++) {
                embeddedCipher.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;
        } else {
            return encrypt(in, inOfs, inLen, out, outOfs);
        }
    }

    // input can be arbitrary size when calling doFinal
    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];
                    embeddedCipher.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;
    }
}