82 lines
2.8 KiB
Java
82 lines
2.8 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.ctraesclassic;
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import org.bouncycastle.jce.provider.BouncyCastleProvider;
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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.security.Security;
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public class AesCtrDecryptClassic {
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private static boolean BCinitialized = false;
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private void initBCProvider(){
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Security.addProvider(new BouncyCastleProvider());
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BCinitialized = true;
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}
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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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if ( ! BCinitialized)
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initBCProvider();
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byte[] keyArray = hexStrToByteArray(keyString);
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this.ivArray = ivArray;
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key = new SecretKeySpec(keyArray, "AES");
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cipher = Cipher.getInstance("AES/CTR/NoPadding", "BC");
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IvParameterSpec iv = new IvParameterSpec(ivArray.clone());
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cipher.init(Cipher.DECRYPT_MODE, key, iv);
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}
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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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/**
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* Initializes cipher again using updated IV
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* @param blocks - how many blocks from encrypted section start should be skipped. Block size = 0x200
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* */
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public void resetAndSkip(long blocks) throws Exception{
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cipher = Cipher.getInstance("AES/CTR/NoPadding", "BC");
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IvParameterSpec iv = new IvParameterSpec(calculateCtr(blocks * 0x200));
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cipher.init(Cipher.DECRYPT_MODE, key, iv);
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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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return ctr.add(updateTo).toByteArray();
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}
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private byte[] hexStrToByteArray(String s) {
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int len = s.length();
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byte[] data = new byte[len / 2];
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for (int i = 0; i < len; i += 2) {
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data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
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+ Character.digit(s.charAt(i+1), 16));
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}
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return data;
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}
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}
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