/*
Copyright (C) 2011 de4dot@gmail.com
This file is part of de4dot.
de4dot is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
de4dot is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with de4dot. If not, see .
*/
using System.Collections.Generic;
using Mono.Cecil;
using Mono.Cecil.Cil;
using de4dot.blocks;
namespace de4dot.code.deobfuscators.Dotfuscator {
class StringDecrypter {
ModuleDefinition module;
Dictionary stringDecrypterMethods = new Dictionary();
public class StringDecrypterInfo {
public MethodDefinition method;
public int magic;
public StringDecrypterInfo(MethodDefinition method, int magic) {
this.method = method;
this.magic = magic;
}
}
public bool Detected {
get { return stringDecrypterMethods.Count > 0; }
}
public IEnumerable StringDecrypters {
get {
var list = new List(stringDecrypterMethods.Count);
foreach (var info in stringDecrypterMethods)
list.Add(info.Value.method);
return list;
}
}
public IEnumerable StringDecrypterInfos {
get { return stringDecrypterMethods.Values; }
}
public StringDecrypter(ModuleDefinition module) {
this.module = module;
}
public void find(ISimpleDeobfuscator simpleDeobfuscator) {
foreach (var type in module.GetTypes())
findStringDecrypterMethods(type, simpleDeobfuscator);
}
void findStringDecrypterMethods(TypeDefinition type, ISimpleDeobfuscator simpleDeobfuscator) {
foreach (var method in DotNetUtils.findMethods(type.Methods, "System.String", new string[] { "System.String", "System.Int32" })) {
if (method.Body.HasExceptionHandlers)
continue;
var methodCalls = DotNetUtils.getMethodCallCounts(method);
if (methodCalls.count("System.Char[] System.String::ToCharArray()") != 1)
continue;
if (methodCalls.count("System.String System.String::Intern(System.String)") != 1)
continue;
simpleDeobfuscator.deobfuscate(method);
var instructions = method.Body.Instructions;
for (int i = 0; i <= instructions.Count - 3; i++) {
var ldci4 = method.Body.Instructions[i];
if (!DotNetUtils.isLdcI4(ldci4))
continue;
if (instructions[i + 1].OpCode.Code != Code.Ldarg_1)
continue;
if (instructions[i + 2].OpCode.Code != Code.Add)
continue;
var info = new StringDecrypterInfo(method, DotNetUtils.getLdcI4Value(ldci4));
stringDecrypterMethods[info.method] = info;
Log.v("Found string decrypter method: {0}, magic: 0x{1:X8}", Utils.removeNewlines(info.method), info.magic);
break;
}
}
}
public string decrypt(MethodReference method, string encrypted, int value) {
var info = stringDecrypterMethods[method];
char[] chars = encrypted.ToCharArray();
byte key = (byte)(info.magic + value);
for (int i = 0; i < chars.Length; i++) {
char c = chars[i];
byte b1 = (byte)((byte)c ^ key++);
byte b2 = (byte)((byte)(c >> 8) ^ key++);
chars[i] = (char)((b1 << 8) | b2);
}
return new string(chars);
}
}
}