265 lines
7.3 KiB
C#
265 lines
7.3 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.Collections.Generic;
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using System.Text;
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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.DeepSea {
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class StringDecrypter {
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ModuleDefinition module;
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MethodDefinitionAndDeclaringTypeDict<DecrypterInfo> methodToInfo = new MethodDefinitionAndDeclaringTypeDict<DecrypterInfo>();
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class DecrypterInfo {
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MethodDefinition cctor;
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public MethodDefinition method;
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FieldDefinition cachedStringsField;
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FieldDefinition keyField;
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int magic;
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string[] encryptedStrings;
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short[] key;
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public DecrypterInfo(MethodDefinition cctor, MethodDefinition method) {
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this.cctor = cctor;
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this.method = method;
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}
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public string decrypt(int magic2) {
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var es = encryptedStrings[magic ^ magic2];
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var sb = new StringBuilder(es.Length);
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for (int i = 0; i < es.Length; i++)
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sb.Append((char)(es[i] ^ key[(magic2 + i) % key.Length]));
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return sb.ToString();
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}
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public bool initialize() {
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if (!findMagic(method, out magic))
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return false;
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if (!findFields())
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return false;
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if (!findEncryptedStrings(method))
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return false;
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key = findKey();
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if (key.Length == 0)
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return false;
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return true;
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}
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bool findFields() {
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foreach (var instr in method.Body.Instructions) {
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if (instr.OpCode.Code != Code.Stsfld && instr.OpCode.Code != Code.Ldsfld)
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continue;
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var field = instr.Operand as FieldDefinition;
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if (field == null)
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continue;
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if (!MemberReferenceHelper.compareTypes(method.DeclaringType, field.DeclaringType))
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continue;
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switch (field.FieldType.FullName) {
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case "System.Char[]":
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if (keyField != null && keyField != field)
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return false;
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keyField = field;
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break;
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case "System.String[]":
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if (cachedStringsField != null && cachedStringsField != field)
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return false;
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cachedStringsField = field;
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break;
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default:
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break;
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}
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}
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return keyField != null && cachedStringsField != null;
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}
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short[] findKey() {
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var pkt = cctor.Module.Assembly.Name.PublicKeyToken;
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if (pkt != null && pkt.Length > 0)
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return getPublicKeyTokenKey(pkt);
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return findKey(cctor);
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}
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short[] findKey(MethodDefinition initMethod) {
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var instrs = initMethod.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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var newarr = instrs[i + 1];
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if (newarr.OpCode.Code != Code.Newarr)
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continue;
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if (newarr.Operand.ToString() != "System.Char")
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continue;
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i++;
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var array = ArrayFinder.getInitializedInt16Array(DotNetUtils.getLdcI4Value(ldci4), initMethod, ref i);
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if (array == null)
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continue;
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i++;
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if (i >= instrs.Count)
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return null;
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var stsfld = instrs[i];
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if (stsfld.OpCode.Code != Code.Stsfld)
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continue;
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if (MemberReferenceHelper.compareFieldReferenceAndDeclaringType(keyField, stsfld.Operand as FieldReference))
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return array;
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}
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return null;
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}
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static short[] getPublicKeyTokenKey(byte[] publicKeyToken) {
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var key = new short[publicKeyToken.Length];
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for (int i = 0; i < publicKeyToken.Length; i++) {
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int b = publicKeyToken[i];
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key[i] = (short)((b << 4) ^ b);
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}
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return key;
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}
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static bool findMagic(MethodDefinition method, out int magic) {
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var instrs = method.Body.Instructions;
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for (int i = 0; i < instrs.Count - 2; i++) {
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var ldarg = instrs[i];
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if (DotNetUtils.getArgIndex(ldarg) != 0)
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continue;
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var ldci4 = instrs[i + 1];
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if (!DotNetUtils.isLdcI4(ldci4))
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continue;
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if (instrs[i + 2].OpCode.Code != Code.Xor)
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continue;
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magic = DotNetUtils.getLdcI4Value(ldci4);
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return true;
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}
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magic = 0;
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return false;
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}
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bool findEncryptedStrings(MethodDefinition method) {
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var switchInstr = getOnlySwitchInstruction(method);
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if (switchInstr == null)
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return false;
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var targets = (Instruction[])switchInstr.Operand;
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encryptedStrings = new string[targets.Length];
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for (int i = 0; i < targets.Length; i++) {
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var target = targets[i];
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if (target.OpCode.Code != Code.Ldstr)
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return false;
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encryptedStrings[i] = (string)target.Operand;
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}
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return true;
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}
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static Instruction getOnlySwitchInstruction(MethodDefinition method) {
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Instruction switchInstr = null;
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foreach (var instr in method.Body.Instructions) {
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if (instr.OpCode.Code != Code.Switch)
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continue;
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if (switchInstr != null)
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return null;
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switchInstr = instr;
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}
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return switchInstr;
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}
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public override string ToString() {
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return string.Format("M:{0:X8} N:{1}", magic, encryptedStrings.Length);
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}
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}
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public bool Detected {
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get { return methodToInfo.Count != 0; }
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}
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public List<MethodDefinition> DecrypterMethods {
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get {
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var methods = new List<MethodDefinition>(methodToInfo.Count);
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foreach (var info in methodToInfo.getValues())
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methods.Add(info.method);
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return methods;
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}
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}
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public StringDecrypter(ModuleDefinition module) {
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this.module = module;
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}
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public void find(ISimpleDeobfuscator simpleDeobfuscator) {
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bool hasPublicKeyToken = module.Assembly.Name.PublicKeyToken != null && module.Assembly.Name.PublicKeyToken.Length != 0;
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foreach (var type in module.GetTypes()) {
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if (!checkFields(type.Fields))
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continue;
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var cctor = DotNetUtils.getMethod(type, ".cctor");
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if (cctor == null)
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continue;
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if (!hasPublicKeyToken)
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simpleDeobfuscator.deobfuscate(cctor);
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foreach (var method in DotNetUtils.findMethods(type.Methods, "System.String", new string[] { "System.Int32" }, true)) {
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simpleDeobfuscator.deobfuscate(method);
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var info = getInfo(cctor, method);
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if (info == null)
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continue;
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methodToInfo.add(method, info);
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}
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}
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}
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static bool checkFields(IEnumerable<FieldDefinition> fields) {
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bool foundCharAry = false, foundStringAry = false;
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foreach (var field in fields) {
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if (foundCharAry && foundStringAry)
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break;
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switch (field.FieldType.FullName) {
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case "System.Char[]":
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foundCharAry = true;
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break;
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case "System.String[]":
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foundStringAry = true;
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break;
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}
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}
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return foundCharAry && foundStringAry;
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}
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DecrypterInfo getInfo(MethodDefinition cctor, MethodDefinition method) {
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if (method == null || method.Body == null)
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return null;
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var info = new DecrypterInfo(cctor, method);
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if (!info.initialize())
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return null;
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return info;
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}
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public string decrypt(MethodReference method, int magic2) {
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var info = methodToInfo.find(method);
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return info.decrypt(magic2);
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}
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}
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}
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