/*
Copyright (C) 2011-2012 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;
using System.Collections.Generic;
using System.Globalization;
using System.Security.Cryptography;
using System.Text;
using System.Text.RegularExpressions;
using Mono.Cecil;
using Mono.Cecil.Cil;
using de4dot.blocks;
namespace de4dot.code.deobfuscators.Skater_NET {
class StringDecrypter {
ModuleDefinition module;
TypeDefinition decrypterType;
MethodDefinition decrypterCctor;
byte[] key;
byte[] iv;
FieldDefinitionAndDeclaringTypeDict fieldToDecryptedString = new FieldDefinitionAndDeclaringTypeDict();
public bool Detected {
get { return decrypterType != null; }
}
public TypeDefinition Type {
get { return decrypterType; }
}
public StringDecrypter(ModuleDefinition module) {
this.module = module;
}
public void find() {
foreach (var type in module.Types) {
if (type.HasProperties || type.HasEvents)
continue;
var cctor = DotNetUtils.getMethod(type, ".cctor");
if (cctor == null)
continue;
if (checkType(type)) {
decrypterType = type;
decrypterCctor = cctor;
return;
}
}
}
public void initialize() {
if (decrypterCctor == null)
return;
var instrs = decrypterCctor.Body.Instructions;
for (int i = 0; i < instrs.Count - 4; i++) {
var ldstr = instrs[i];
if (ldstr.OpCode.Code != Code.Ldstr)
continue;
var encryptedString = ldstr.Operand as string;
if (encryptedString == null)
continue;
if (instrs[i + 1].OpCode.Code != Code.Stsfld)
continue;
if (instrs[i + 2].OpCode.Code != Code.Ldsfld)
continue;
if (instrs[i + 3].OpCode.Code != Code.Call)
continue;
if (instrs[i + 4].OpCode.Code != Code.Stsfld)
continue;
var field = instrs[i + 4].Operand as FieldDefinition;
if (field == null)
continue;
if (!MemberReferenceHelper.compareTypes(field.DeclaringType, decrypterType))
continue;
var decryptedString = Encoding.Unicode.GetString(DeobUtils.des3Decrypt(Convert.FromBase64String(encryptedString), key, iv));
fieldToDecryptedString.add(field, decryptedString);
}
}
bool checkType(TypeDefinition type) {
foreach (var method in type.Methods) {
if (!method.IsStatic || method.Body == null)
continue;
if (!DotNetUtils.isMethod(method, "System.String", "(System.String)"))
continue;
var salt = getSalt(method);
if (salt == null)
continue;
var password = getPassword(method);
if (string.IsNullOrEmpty(password))
continue;
var passwordBytes = new PasswordDeriveBytes(password, salt);
key = passwordBytes.GetBytes(16);
iv = passwordBytes.GetBytes(8);
return true;
}
return false;
}
static byte[] getSalt(MethodDefinition method) {
foreach (var s in DotNetUtils.getCodeStrings(method)) {
var saltAry = fixSalt(s);
if (saltAry != null)
return saltAry;
}
return null;
}
static byte[] fixSalt(string s) {
if (s.Length < 10 || s.Length > 30 || s.Length / 2 * 2 != s.Length)
return null;
var ary = s.ToCharArray();
Array.Reverse(ary);
for (int i = 0; i < ary.Length; i++)
ary[i]--;
var s2 = new string(ary);
var saltAry = new byte[(int)Math.Round((double)s2.Length / 2 - 1) + 1];
for (int i = 0; i < saltAry.Length; i++) {
int result;
if (!int.TryParse(s2.Substring(i * 2, 2), NumberStyles.AllowHexSpecifier, null, out result))
return null;
saltAry[i] = (byte)result;
}
return saltAry;
}
string getPassword(MethodDefinition decryptMethod) {
foreach (var info in DotNetUtils.getCalledMethods(module, decryptMethod)) {
var method = info.Item2;
if (!method.IsStatic || method.Body == null)
continue;
if (!MemberReferenceHelper.compareTypes(method.DeclaringType, decryptMethod.DeclaringType))
continue;
if (!DotNetUtils.isMethod(method, "System.String", "()"))
continue;
var hexChars = getPassword2(method);
if (string.IsNullOrEmpty(hexChars))
continue;
var password = fixPassword(hexChars);
if (string.IsNullOrEmpty(password))
continue;
return password;
}
return null;
}
string fixPassword(string hexChars) {
var ary = hexChars.Trim().Split(' ');
string password = "";
for (int i = 0; i < ary.Length; i++) {
int result;
if (!int.TryParse(ary[i], NumberStyles.AllowHexSpecifier, null, out result))
return null;
password += (char)result;
}
return password;
}
string getPassword2(MethodDefinition method) {
string password = "";
foreach (var info in DotNetUtils.getCalledMethods(module, method)) {
var s = getPassword3(info.Item2);
if (string.IsNullOrEmpty(s))
return null;
password += s;
}
return password;
}
string getPassword3(MethodDefinition method) {
var strings = new List(DotNetUtils.getCodeStrings(method));
if (strings.Count != 1)
return null;
var s = strings[0];
if (!Regex.IsMatch(s, @"^[a-fA-F0-9]{2} $"))
return null;
return s;
}
public void deobfuscate(Blocks blocks) {
foreach (var block in blocks.MethodBlocks.getAllBlocks()) {
var instrs = block.Instructions;
for (int i = 0; i < instrs.Count; i++) {
var instr = instrs[i];
if (instr.OpCode.Code != Code.Ldsfld)
continue;
var field = instr.Operand as FieldReference;
if (field == null)
continue;
var decrypted = fieldToDecryptedString.find(field);
if (decrypted == null)
continue;
instrs[i] = new Instr(Instruction.Create(OpCodes.Ldstr, decrypted));
Log.v("Decrypted string: {0}", Utils.toCsharpString(decrypted));
}
}
}
}
}