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The AWS SDK for Java with support for OSGi. The AWS SDK for Java provides Java APIs for building software on AWS' cost-effective, scalable, and reliable infrastructure products. The AWS Java SDK allows developers to code against APIs for all of Amazon's infrastructure web services (Amazon S3, Amazon EC2, Amazon SQS, Amazon Relational Database Service, Amazon AutoScaling, etc).

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/*
 * Copyright 2013-2016 Amazon.com, Inc. or its affiliates. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License").
 * You may not use this file except in compliance with the License.
 * A copy of the License is located at
 *
 *  http://aws.amazon.com/apache2.0
 *
 * or in the "license" file accompanying this file. This file is distributed
 * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
 * express or implied. See the License for the specific language governing
 * permissions and limitations under the License.
 */
package com.amazonaws.services.s3.internal.crypto;

class AesCtr extends ContentCryptoScheme {
    @Override String getKeyGeneratorAlgorithm() { return AES_GCM.getKeyGeneratorAlgorithm(); }
    @Override String getCipherAlgorithm() { return "AES/CTR/NoPadding"; }
    @Override int getKeyLengthInBits() { return AES_GCM.getKeyLengthInBits(); }
    @Override int getBlockSizeInBytes() { return AES_GCM.getBlockSizeInBytes(); }
    @Override int getIVLengthInBytes() { return 16; }
    @Override long getMaxPlaintextSize() {  return MAX_CTR_BYTES;  }

    @Override
    byte[] adjustIV(byte[] iv, long byteOffset) {
        // currently only support iv of length 12 for AES/GCM.
        // Anything else is quite a bit complicated.
        if (iv.length != 12)
            throw new UnsupportedOperationException();
        final int blockSize = getBlockSizeInBytes();
        final long blockOffset = byteOffset / blockSize;
        if (blockOffset * blockSize != byteOffset) {
            throw new IllegalArgumentException(
                    "Expecting byteOffset to be multiple of 16, but got blockOffset="
                            + blockOffset + ", blockSize=" + blockSize
                            + ", byteOffset=" + byteOffset);
        }
        byte[] J0 = computeJ0(iv);
        return incrementBlocks(J0, blockOffset);
    }

    /**
     * See 
     * NIST Special Publication 800-38D. for the definition of J0, the
     * "pre-counter block".
     * 
     * Reference: GCMBlockCipher.java
     */
     private byte[] computeJ0(byte[] nonce) {
         final int blockSize = getBlockSizeInBytes();
         byte[] J0 = new byte[blockSize];
         System.arraycopy(nonce, 0, J0, 0, nonce.length);
         J0[blockSize - 1] = 0x01;
         return incrementBlocks(J0, 1);
     }
}