/*
Copyright (C) 2011-2014 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.Text;
using System.Collections.Generic;
using dnlib.PE;
using dnlib.DotNet;
using dnlib.DotNet.Emit;
using de4dot.blocks;
namespace de4dot.code.deobfuscators.dotNET_Reactor.v4 {
class StringDecrypter {
ModuleDefMD module;
EncryptedResource encryptedResource;
List decrypterInfos = new List();
MethodDef otherStringDecrypter;
byte[] decryptedData;
MyPEImage peImage;
byte[] fileData;
StringDecrypterVersion stringDecrypterVersion;
enum StringDecrypterVersion {
UNKNOWN = 0,
VER_37, // 3.7-
VER_38, // 3.8+
}
public class DecrypterInfo {
public MethodDef method;
public byte[] key;
public byte[] iv;
public DecrypterInfo(MethodDef method, byte[] key, byte[] iv) {
this.method = method;
this.key = key;
this.iv = iv;
}
}
public bool Detected {
get { return encryptedResource.Method != null; }
}
public TypeDef DecrypterType {
get { return encryptedResource.Type; }
}
public EmbeddedResource Resource {
get { return encryptedResource.Resource; }
}
public IEnumerable DecrypterInfos {
get { return decrypterInfos; }
}
public MethodDef OtherStringDecrypter {
get { return otherStringDecrypter; }
}
public StringDecrypter(ModuleDefMD module) {
this.module = module;
this.encryptedResource = new EncryptedResource(module);
}
public StringDecrypter(ModuleDefMD module, StringDecrypter oldOne) {
this.module = module;
this.stringDecrypterVersion = oldOne.stringDecrypterVersion;
this.encryptedResource = new EncryptedResource(module, oldOne.encryptedResource);
foreach (var oldInfo in oldOne.decrypterInfos) {
var method = Lookup(oldInfo.method, "Could not find string decrypter method");
decrypterInfos.Add(new DecrypterInfo(method, oldInfo.key, oldInfo.iv));
}
otherStringDecrypter = Lookup(oldOne.otherStringDecrypter, "Could not find string decrypter method");
}
T Lookup(T def, string errorMessage) where T : class, ICodedToken {
return DeobUtils.Lookup(module, def, errorMessage);
}
public void Find(ISimpleDeobfuscator simpleDeobfuscator) {
var additionalTypes = new string[] {
"System.String",
};
EmbeddedResource stringsResource = null;
foreach (var type in module.Types) {
if (decrypterInfos.Count > 0)
break;
if (type.BaseType == null || type.BaseType.FullName != "System.Object")
continue;
foreach (var method in type.Methods) {
if (!method.IsStatic || !method.HasBody)
continue;
if (!DotNetUtils.IsMethod(method, "System.String", "(System.Int32)"))
continue;
if (!encryptedResource.CouldBeResourceDecrypter(method, additionalTypes))
continue;
var resource = DotNetUtils.GetResource(module, DotNetUtils.GetCodeStrings(method)) as EmbeddedResource;
if (resource == null)
throw new ApplicationException("Could not find strings resource");
if (stringsResource != null && stringsResource != resource)
throw new ApplicationException("Two different string resources found");
stringsResource = resource;
encryptedResource.Method = method;
var info = new DecrypterInfo(method, null, null);
simpleDeobfuscator.Deobfuscate(info.method);
FindKeyIv(info.method, out info.key, out info.iv);
decrypterInfos.Add(info);
}
}
if (decrypterInfos.Count > 0)
FindOtherStringDecrypter(decrypterInfos[0].method.DeclaringType);
}
void FindOtherStringDecrypter(TypeDef type) {
foreach (var method in type.Methods) {
if (!method.IsStatic || !method.HasBody)
continue;
var sig = method.MethodSig;
if (sig == null)
continue;
if (sig.RetType.GetElementType() != ElementType.String)
continue;
if (sig.Params.Count != 1)
continue;
if (sig.Params[0].GetElementType() != ElementType.Object &&
sig.Params[0].GetElementType() != ElementType.String)
continue;
otherStringDecrypter = method;
return;
}
}
public void Initialize(MyPEImage peImage, byte[] fileData, ISimpleDeobfuscator simpleDeobfuscator) {
if (encryptedResource.Method == null)
return;
this.peImage = peImage;
this.fileData = fileData;
encryptedResource.Initialize(simpleDeobfuscator);
if (!encryptedResource.FoundResource)
return;
Logger.v("Adding string decrypter. Resource: {0}", Utils.ToCsharpString(encryptedResource.Resource.Name));
decryptedData = encryptedResource.Decrypt();
}
void FindKeyIv(MethodDef method, out byte[] key, out byte[] iv) {
key = null;
iv = null;
var requiredTypes = new string[] {
"System.Byte[]",
"System.IO.MemoryStream",
"System.Security.Cryptography.CryptoStream",
"System.Security.Cryptography.Rijndael",
};
foreach (var calledMethod in DotNetUtils.GetCalledMethods(module, method)) {
if (calledMethod.DeclaringType != method.DeclaringType)
continue;
if (calledMethod.MethodSig.GetRetType().GetFullName() != "System.Byte[]")
continue;
var localTypes = new LocalTypes(calledMethod);
if (!localTypes.All(requiredTypes))
continue;
var instructions = calledMethod.Body.Instructions;
byte[] newKey = null, newIv = null;
for (int i = 0; i < instructions.Count && (newKey == null || newIv == null); i++) {
var instr = instructions[i];
if (instr.OpCode.Code != Code.Ldtoken)
continue;
var field = instr.Operand as FieldDef;
if (field == null)
continue;
if (field.InitialValue == null)
continue;
if (field.InitialValue.Length == 32)
newKey = field.InitialValue;
else if (field.InitialValue.Length == 16)
newIv = field.InitialValue;
}
if (newKey == null || newIv == null)
continue;
InitializeStringDecrypterVersion(method);
key = newKey;
iv = newIv;
return;
}
}
void InitializeStringDecrypterVersion(MethodDef method) {
var localTypes = new LocalTypes(method);
if (localTypes.Exists("System.IntPtr"))
stringDecrypterVersion = StringDecrypterVersion.VER_38;
else
stringDecrypterVersion = StringDecrypterVersion.VER_37;
}
DecrypterInfo GetDecrypterInfo(MethodDef method) {
foreach (var info in decrypterInfos) {
if (info.method == method)
return info;
}
throw new ApplicationException("Invalid string decrypter method");
}
public string Decrypt(MethodDef method, int offset) {
var info = GetDecrypterInfo(method);
if (info.key == null) {
int length = BitConverter.ToInt32(decryptedData, offset);
return Encoding.Unicode.GetString(decryptedData, offset + 4, length);
}
else {
byte[] encryptedStringData;
if (stringDecrypterVersion == StringDecrypterVersion.VER_37) {
int fileOffset = BitConverter.ToInt32(decryptedData, offset);
int length = BitConverter.ToInt32(fileData, fileOffset);
encryptedStringData = new byte[length];
Array.Copy(fileData, fileOffset + 4, encryptedStringData, 0, length);
}
else if (stringDecrypterVersion == StringDecrypterVersion.VER_38) {
uint rva = BitConverter.ToUInt32(decryptedData, offset);
int length = peImage.ReadInt32(rva);
encryptedStringData = peImage.ReadBytes(rva + 4, length);
}
else
throw new ApplicationException("Unknown string decrypter version");
return Encoding.Unicode.GetString(DeobUtils.AesDecrypt(encryptedStringData, info.key, info.iv));
}
}
public string Decrypt(string s) {
return Encoding.Unicode.GetString(Convert.FromBase64String(s));
}
}
}