247 lines
6.9 KiB
C#
247 lines
6.9 KiB
C#
/*
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Copyright (C) 2011-2012 de4dot@gmail.com
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This file is part of de4dot.
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de4dot 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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de4dot 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 de4dot. If not, see <http://www.gnu.org/licenses/>.
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*/
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using System;
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using System.IO;
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using Mono.Cecil;
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using Mono.Cecil.Cil;
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using de4dot.blocks;
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namespace de4dot.code.deobfuscators.CodeVeil {
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class StringDecrypter {
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ModuleDefinition module;
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MainType mainType;
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TypeDefinition decrypterType;
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FieldDefinition stringDataField;
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MethodDefinition initMethod;
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MethodDefinition decrypterMethod;
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string[] decryptedStrings;
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public bool Detected {
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get { return decrypterType != null; }
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}
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public TypeDefinition Type {
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get { return decrypterType; }
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}
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public MethodDefinition InitMethod {
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get { return initMethod; }
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}
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public MethodDefinition DecryptMethod {
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get { return decrypterMethod; }
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}
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public StringDecrypter(ModuleDefinition module, MainType mainType) {
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this.module = module;
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this.mainType = mainType;
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}
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public StringDecrypter(ModuleDefinition module, MainType mainType, StringDecrypter oldOne) {
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this.module = module;
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this.mainType = mainType;
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this.decrypterType = lookup(oldOne.decrypterType, "Could not find string decrypter type");
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this.stringDataField = lookup(oldOne.stringDataField, "Could not find string data field");
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this.initMethod = lookup(oldOne.initMethod, "Could not find string decrypter init method");
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this.decrypterMethod = lookup(oldOne.decrypterMethod, "Could not find string decrypter method");
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}
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T lookup<T>(T def, string errorMessage) where T : MemberReference {
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return DeobUtils.lookup(module, def, errorMessage);
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}
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public void find() {
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var cctor = DotNetUtils.getModuleTypeCctor(module);
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if (cctor == null)
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return;
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// V3-V4 calls string decrypter init method in <Module>::.cctor().
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if (find(cctor))
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return;
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findV5(cctor);
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}
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bool find(MethodDefinition method) {
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if (method == null || method.Body == null || !method.IsStatic)
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return false;
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var instrs = method.Body.Instructions;
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for (int i = 0; i < instrs.Count; i++) {
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var call = instrs[i];
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if (call.OpCode.Code != Code.Call)
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continue;
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var initMethodTmp = call.Operand as MethodDefinition;
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if (initMethodTmp == null || initMethodTmp.Body == null || !initMethodTmp.IsStatic)
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continue;
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if (!DotNetUtils.isMethod(initMethodTmp, "System.Void", "()"))
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continue;
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if (!checkType(initMethodTmp.DeclaringType))
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continue;
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decrypterType = initMethodTmp.DeclaringType;
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initMethod = initMethodTmp;
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return true;
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}
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return false;
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}
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// The main decrypter type calls the string decrypter init method inside its init method
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void findV5(MethodDefinition method) {
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if (!mainType.Detected)
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return;
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foreach (var calledMethod in DotNetUtils.getCalledMethods(module, mainType.InitMethod)) {
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if (find(calledMethod))
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return;
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}
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}
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bool checkType(TypeDefinition type) {
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if (!type.HasNestedTypes)
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return false;
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var stringDataFieldTmp = checkFields(type);
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if (stringDataFieldTmp == null)
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return false;
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var fieldType = DotNetUtils.getType(module, stringDataFieldTmp.FieldType);
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if (fieldType == null || type.NestedTypes.IndexOf(fieldType) < 0)
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return false;
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var decrypterMethodTmp = getDecrypterMethod(type);
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if (decrypterMethodTmp == null)
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return false;
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stringDataField = stringDataFieldTmp;
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decrypterMethod = decrypterMethodTmp;
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return true;
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}
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static MethodDefinition getDecrypterMethod(TypeDefinition type) {
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MethodDefinition foundMethod = null;
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foreach (var method in type.Methods) {
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if (method.Body == null || !method.IsStatic)
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continue;
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if (!DotNetUtils.isMethod(method, "System.String", "(System.Int32)"))
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continue;
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if (foundMethod != null)
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return null;
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foundMethod = method;
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}
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return foundMethod;
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}
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static string[] requiredFields = new string[] {
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"System.Byte[]",
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"System.Int32",
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"System.Int32[]",
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"System.String[]",
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"System.UInt32[]",
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};
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FieldDefinition checkFields(TypeDefinition type) {
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if (!new FieldTypes(type).all(requiredFields))
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return null;
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FieldDefinition stringData = null;
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foreach (var field in type.Fields) {
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if (field.RVA != 0) {
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if (stringData != null)
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return null;
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stringData = field;
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continue;
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}
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}
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if (stringData == null)
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return null;
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var data = stringData.InitialValue;
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if (data == null || data.Length == 0 || data.Length % 4 != 0)
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return null;
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return stringData;
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}
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public void initialize() {
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if (initMethod == null || stringDataField == null)
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return;
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var key = getKey(initMethod);
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if (key == null)
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throw new ApplicationException("Could not find string decrypter key");
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decryptStrings(key);
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stringDataField.FieldType = module.TypeSystem.Byte;
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stringDataField.InitialValue = new byte[1];
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}
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static uint[] getKey(MethodDefinition method) {
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var instrs = method.Body.Instructions;
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for (int i = 0; i < instrs.Count - 1; i++) {
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var ldci4 = instrs[i];
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if (!DotNetUtils.isLdcI4(ldci4))
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continue;
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if (DotNetUtils.getLdcI4Value(ldci4) != 4)
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continue;
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if (instrs[i + 1].OpCode.Code != Code.Newarr)
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continue;
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i++;
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var key = ArrayFinder.getInitializedUInt32Array(4, method, ref i);
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if (key == null)
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continue;
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return key;
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}
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return null;
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}
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void decryptStrings(uint[] key) {
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var data = stringDataField.InitialValue;
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var encryptedData = new uint[data.Length / 4];
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Buffer.BlockCopy(data, 0, encryptedData, 0, data.Length);
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DeobUtils.xxteaDecrypt(encryptedData, key);
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var decryptedData = new byte[data.Length];
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Buffer.BlockCopy(encryptedData, 0, decryptedData, 0, data.Length);
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var inflated = DeobUtils.inflate(decryptedData, 0, decryptedData.Length, true);
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var reader = new BinaryReader(new MemoryStream(inflated));
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int deflatedLength = DeobUtils.readVariableLengthInt32(reader);
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int numStrings = DeobUtils.readVariableLengthInt32(reader);
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decryptedStrings = new string[numStrings];
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var offsets = new int[numStrings];
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for (int i = 0; i < numStrings; i++)
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offsets[i] = DeobUtils.readVariableLengthInt32(reader);
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int startOffset = (int)reader.BaseStream.Position;
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for (int i = 0; i < numStrings; i++) {
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reader.BaseStream.Position = startOffset + offsets[i];
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decryptedStrings[i] = reader.ReadString();
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}
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}
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public string decrypt(int index) {
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return decryptedStrings[index];
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}
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}
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}
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