2011-12-22 02:22:23 +08:00
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/*
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2012-01-10 06:02:47 +08:00
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Copyright (C) 2011-2012 de4dot@gmail.com
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2011-12-22 02:22:23 +08:00
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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 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.Dotfuscator {
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class StringDecrypter {
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ModuleDefinition module;
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Dictionary<MethodReference, StringDecrypterInfo> stringDecrypterMethods = new Dictionary<MethodReference, StringDecrypterInfo>();
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public class StringDecrypterInfo {
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public MethodDefinition method;
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public int magic;
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public StringDecrypterInfo(MethodDefinition method, int magic) {
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this.method = method;
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this.magic = magic;
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}
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}
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public bool Detected {
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get { return stringDecrypterMethods.Count > 0; }
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}
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public IEnumerable<MethodDefinition> StringDecrypters {
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get {
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var list = new List<MethodDefinition>(stringDecrypterMethods.Count);
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foreach (var info in stringDecrypterMethods)
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list.Add(info.Value.method);
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return list;
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}
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}
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public IEnumerable<StringDecrypterInfo> StringDecrypterInfos {
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get { return stringDecrypterMethods.Values; }
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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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foreach (var type in module.GetTypes())
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findStringDecrypterMethods(type, simpleDeobfuscator);
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}
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void findStringDecrypterMethods(TypeDefinition type, ISimpleDeobfuscator simpleDeobfuscator) {
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foreach (var method in DotNetUtils.findMethods(type.Methods, "System.String", new string[] { "System.String", "System.Int32" })) {
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if (method.Body.HasExceptionHandlers)
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continue;
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var methodCalls = DotNetUtils.getMethodCallCounts(method);
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if (methodCalls.count("System.Char[] System.String::ToCharArray()") != 1)
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continue;
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if (methodCalls.count("System.String System.String::Intern(System.String)") != 1)
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continue;
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simpleDeobfuscator.deobfuscate(method);
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var instructions = method.Body.Instructions;
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for (int i = 0; i <= instructions.Count - 3; i++) {
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var ldci4 = method.Body.Instructions[i];
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if (!DotNetUtils.isLdcI4(ldci4))
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continue;
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if (instructions[i + 1].OpCode.Code != Code.Ldarg_1)
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continue;
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if (instructions[i + 2].OpCode.Code != Code.Add)
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continue;
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var info = new StringDecrypterInfo(method, DotNetUtils.getLdcI4Value(ldci4));
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stringDecrypterMethods[info.method] = info;
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2012-01-04 02:52:40 +08:00
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Log.v("Found string decrypter method: {0}, magic: 0x{1:X8}", Utils.removeNewlines(info.method), info.magic);
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2011-12-22 02:22:23 +08:00
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break;
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}
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}
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}
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public string decrypt(MethodReference method, string encrypted, int value) {
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var info = stringDecrypterMethods[method];
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char[] chars = encrypted.ToCharArray();
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byte key = (byte)(info.magic + value);
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for (int i = 0; i < chars.Length; i++) {
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char c = chars[i];
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byte b1 = (byte)((byte)c ^ key++);
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byte b2 = (byte)((byte)(c >> 8) ^ key++);
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chars[i] = (char)((b1 << 8) | b2);
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}
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return new string(chars);
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}
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}
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}
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