116 lines
3.8 KiB
C#
116 lines
3.8 KiB
C#
/*
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Copyright (C) 2011-2015 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 dnlib.DotNet;
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using dnlib.DotNet.Emit;
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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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ModuleDefMD module;
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MethodDefAndDeclaringTypeDict<StringDecrypterInfo> stringDecrypterMethods = new MethodDefAndDeclaringTypeDict<StringDecrypterInfo>();
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public class StringDecrypterInfo {
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public MethodDef method;
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public int magic;
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public StringDecrypterInfo(MethodDef 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<MethodDef> StringDecrypters {
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get {
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var list = new List<MethodDef>(stringDecrypterMethods.Count);
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foreach (var info in stringDecrypterMethods.GetValues())
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list.Add(info.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.GetValues(); }
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}
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public StringDecrypter(ModuleDefMD 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(TypeDef 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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if (DotNetUtils.GetMethodCalls(method, "System.Char[] System.String::ToCharArray()") != 1)
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continue;
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if (DotNetUtils.GetMethodCalls(method, "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 instrs = method.Body.Instructions;
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for (int i = 0; i < instrs.Count - 3; i++) {
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var ldarg = instrs[i];
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if (!ldarg.IsLdarg() || ldarg.GetParameterIndex() != 0)
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continue;
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var callvirt = instrs[i + 1];
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if (callvirt.OpCode.Code != Code.Callvirt)
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continue;
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var calledMethod = callvirt.Operand as MemberRef;
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if (calledMethod == null || calledMethod.FullName != "System.Char[] System.String::ToCharArray()")
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continue;
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var stloc = instrs[i + 2];
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if (!stloc.IsStloc())
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continue;
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var ldci4 = instrs[i + 3];
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if (!ldci4.IsLdcI4())
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continue;
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var info = new StringDecrypterInfo(method, ldci4.GetLdcI4Value());
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stringDecrypterMethods.Add(info.method, info);
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Logger.v("Found string decrypter method: {0}, magic: 0x{1:X8}", Utils.RemoveNewlines(info.method), info.magic);
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break;
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}
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}
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}
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public string Decrypt(IMethod method, string encrypted, int value) {
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var info = stringDecrypterMethods.FindAny(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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