74 lines
2.5 KiB
Java
74 lines
2.5 KiB
Java
/*
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Copyright 2019-2023 Dmitry Isaenko
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This file is part of libKonogonka.
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libKonogonka is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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libKonogonka is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with libKonogonka. If not, see <https://www.gnu.org/licenses/>.
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*/
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package libKonogonka.aesctr;
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import libKonogonka.Converter;
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import javax.crypto.Cipher;
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import javax.crypto.spec.IvParameterSpec;
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import javax.crypto.spec.SecretKeySpec;
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import java.math.BigInteger;
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import java.nio.Buffer;
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import java.nio.ByteBuffer;
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public class AesCtrDecryptClassic extends AesCtrDecrypt {
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private final SecretKeySpec key;
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private final byte[] ivArray;
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private Cipher cipher;
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public AesCtrDecryptClassic(String keyString, byte[] ivArray) throws Exception{
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super();
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this.key = new SecretKeySpec(Converter.hexStringToByteArray(keyString), "AES");
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this.ivArray = ivArray;
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reset();
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}
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@Override
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public byte[] decryptNext(byte[] encryptedData) {
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return cipher.update(encryptedData);
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}
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@Override
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public void resetAndSkip(long blockCount) throws Exception{
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reset(calculateCtr(blockCount * 0x200));
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}
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private byte[] calculateCtr(long offset){
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BigInteger ctr = new BigInteger(ivArray);
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BigInteger updateTo = BigInteger.valueOf(offset / 0x10L);
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byte[] ctrCalculated = ctr.add(updateTo).toByteArray();
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if (ctrCalculated.length != 0x10) {
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ByteBuffer ctrByteBuffer = ByteBuffer.allocate(0x10);
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((Buffer) ctrByteBuffer).position(0x10 - ctrCalculated.length);
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ctrByteBuffer.put(ctrCalculated);
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return ctrByteBuffer.array();
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}
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return ctrCalculated;
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}
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@Override
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public void reset() throws Exception{
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reset(ivArray.clone());
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}
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private void reset(byte[] updatedIvArray) throws Exception{
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cipher = Cipher.getInstance("AES/CTR/NoPadding", "BC");
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IvParameterSpec iv = new IvParameterSpec(updatedIvArray);
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cipher.init(Cipher.DECRYPT_MODE, key, iv);
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}
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}
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