/*
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.Collections.Generic;
using dnlib.DotNet;
using dnlib.DotNet.Emit;
using de4dot.blocks;
namespace de4dot.code.deobfuscators.SmartAssembly {
enum StringDecrypterVersion {
V1,
V2,
V3,
V4,
Unknown,
}
class StringDecrypterInfo {
ModuleDefMD module;
ResourceDecrypter resourceDecrypter;
TypeDef stringsEncodingClass;
EmbeddedResource stringsResource;
int stringOffset;
MethodDef simpleZipTypeMethod;
MethodDef stringDecrypterMethod;
StringDecrypterVersion decrypterVersion;
public StringDecrypterVersion DecrypterVersion {
get { return decrypterVersion; }
}
public TypeDef GetStringDelegate { get; set; }
public TypeDef StringsType { get; set; }
public MethodDef CreateStringDelegateMethod { get; set; }
public TypeDef StringsEncodingClass {
get { return stringsEncodingClass; }
}
public bool CanDecrypt {
get { return resourceDecrypter == null || resourceDecrypter.CanDecrypt; }
}
public MethodDef SimpleZipTypeMethod {
get { return simpleZipTypeMethod; }
}
public EmbeddedResource StringsResource {
get { return stringsResource; }
}
public int StringOffset {
get { return stringOffset; }
}
public bool StringsEncrypted {
get { return simpleZipTypeMethod != null; }
}
public MethodDef StringDecrypterMethod {
get { return stringDecrypterMethod; }
}
public StringDecrypterInfo(ModuleDefMD module, TypeDef stringsEncodingClass) {
this.module = module;
this.stringsEncodingClass = stringsEncodingClass;
}
static string[] fields2x = new string[] {
"System.IO.Stream",
"System.Int32",
};
static string[] fields3x = new string[] {
"System.Byte[]",
"System.Int32",
};
StringDecrypterVersion GuessVersion(MethodDef cctor) {
var fieldTypes = new FieldTypes(stringsEncodingClass);
if (fieldTypes.Exactly(fields2x))
return StringDecrypterVersion.V2;
if (cctor == null)
return StringDecrypterVersion.V1;
if (fieldTypes.Exactly(fields3x))
return StringDecrypterVersion.V3;
return StringDecrypterVersion.Unknown;
}
public bool Initialize(IDeobfuscator deob, ISimpleDeobfuscator simpleDeobfuscator) {
var cctor = stringsEncodingClass.FindStaticConstructor();
if (cctor != null)
simpleDeobfuscator.Deobfuscate(cctor);
decrypterVersion = GuessVersion(cctor);
if (!FindDecrypterMethod())
throw new ApplicationException("Could not find string decrypter method");
if (!FindStringsResource(deob, simpleDeobfuscator, cctor))
return false;
if (decrypterVersion <= StringDecrypterVersion.V3) {
MethodDef initMethod;
if (decrypterVersion == StringDecrypterVersion.V3)
initMethod = cctor;
else if (decrypterVersion == StringDecrypterVersion.V2)
initMethod = stringDecrypterMethod;
else
initMethod = stringDecrypterMethod;
stringOffset = 0;
if (decrypterVersion != StringDecrypterVersion.V1) {
if (CallsGetPublicKeyToken(initMethod)) {
var pkt = PublicKeyBase.ToPublicKeyToken(module.Assembly.PublicKeyToken);
if (!PublicKeyBase.IsNullOrEmpty2(pkt)) {
for (int i = 0; i < pkt.Data.Length - 1; i += 2)
stringOffset ^= ((int)pkt.Data[i] << 8) + pkt.Data[i + 1];
}
}
if (DeobUtils.HasInteger(initMethod, 0xFFFFFF) &&
DeobUtils.HasInteger(initMethod, 0xFFFF)) {
stringOffset ^= ((stringDecrypterMethod.MDToken.ToInt32() & 0xFFFFFF) - 1) % 0xFFFF;
}
}
}
else {
var offsetVal = FindOffsetValue(cctor);
if (offsetVal == null)
throw new ApplicationException("Could not find string offset");
stringOffset = offsetVal.Value;
decrypterVersion = StringDecrypterVersion.V4;
}
simpleZipTypeMethod = FindSimpleZipTypeMethod(cctor) ?? FindSimpleZipTypeMethod(stringDecrypterMethod);
if (simpleZipTypeMethod != null)
resourceDecrypter = new ResourceDecrypter(new ResourceDecrypterInfo(module, simpleZipTypeMethod, simpleDeobfuscator));
return true;
}
bool CallsGetPublicKeyToken(MethodDef method) {
foreach (var calledMethod in DotNetUtils.GetMethodCalls(method)) {
if (calledMethod.ToString() == "System.Byte[] System.Reflection.AssemblyName::GetPublicKeyToken()")
return true;
}
return false;
}
bool FindStringsResource(IDeobfuscator deob, ISimpleDeobfuscator simpleDeobfuscator, MethodDef cctor) {
if (stringsResource != null)
return true;
if (decrypterVersion <= StringDecrypterVersion.V3) {
stringsResource = DotNetUtils.GetResource(module, (module.Mvid ?? Guid.NewGuid()).ToString("B")) as EmbeddedResource;
if (stringsResource != null)
return true;
}
if (FindStringsResource2(deob, simpleDeobfuscator, cctor))
return true;
if (FindStringsResource2(deob, simpleDeobfuscator, stringDecrypterMethod))
return true;
return false;
}
bool FindStringsResource2(IDeobfuscator deob, ISimpleDeobfuscator simpleDeobfuscator, MethodDef initMethod) {
if (initMethod == null)
return false;
stringsResource = FindStringResource(initMethod);
if (stringsResource != null)
return true;
simpleDeobfuscator.DecryptStrings(initMethod, deob);
stringsResource = FindStringResource(initMethod);
if (stringsResource != null)
return true;
return false;
}
public byte[] Decrypt() {
if (!CanDecrypt)
throw new ApplicationException("Can't decrypt strings");
return resourceDecrypter.Decrypt(stringsResource);
}
// Find the embedded resource where all the strings are encrypted
EmbeddedResource FindStringResource(MethodDef method) {
foreach (var s in DotNetUtils.GetCodeStrings(method)) {
if (s == null)
continue;
var resource = DotNetUtils.GetResource(module, s) as EmbeddedResource;
if (resource != null)
return resource;
}
return null;
}
// Find the string decrypter string offset value or null if none found
int? FindOffsetValue(MethodDef method) {
var fieldDict = new FieldDefAndDeclaringTypeDict();
foreach (var field in method.DeclaringType.Fields)
fieldDict.Add(field, field);
var offsetField = FindOffsetField(method);
if (offsetField == null)
return null;
return FindOffsetValue(method, (FieldDef)fieldDict.Find(offsetField), fieldDict);
}
IField FindOffsetField(MethodDef method) {
var instructions = method.Body.Instructions;
for (int i = 0; i <= instructions.Count - 2; i++) {
var ldsfld = instructions[i];
if (ldsfld.OpCode.Code != Code.Ldsfld)
continue;
var field = ldsfld.Operand as IField;
if (field == null || field.FieldSig.GetFieldType().GetElementType() != ElementType.String)
continue;
if (!new SigComparer().Equals(stringsEncodingClass, field.DeclaringType))
continue;
var call = instructions[i + 1];
if (call.OpCode.Code != Code.Call)
continue;
var calledMethod = call.Operand as IMethod;
if (!DotNetUtils.IsMethod(calledMethod, "System.Int32", "(System.String)"))
continue;
return field;
}
return null;
}
int? FindOffsetValue(MethodDef method, FieldDef offsetField, FieldDefAndDeclaringTypeDict fields) {
var instructions = method.Body.Instructions;
for (int i = 0; i <= instructions.Count - 2; i++) {
var ldstr = instructions[i];
if (ldstr.OpCode.Code != Code.Ldstr)
continue;
var stringVal = ldstr.Operand as string;
if (stringVal == null)
continue;
var stsfld = instructions[i + 1];
if (stsfld.OpCode.Code != Code.Stsfld)
continue;
var field = stsfld.Operand as IField;
if (field == null || fields.Find(field) != offsetField)
continue;
int value;
if (!int.TryParse(stringVal, System.Globalization.NumberStyles.Integer, null, out value))
continue;
return value;
}
return null;
}
bool FindDecrypterMethod() {
if (stringDecrypterMethod != null)
return true;
var methods = new List(DotNetUtils.FindMethods(stringsEncodingClass.Methods, "System.String", new string[] { "System.Int32" }));
if (methods.Count != 1)
return false;
stringDecrypterMethod = methods[0];
return true;
}
MethodDef FindSimpleZipTypeMethod(MethodDef method) {
if (method == null || method.Body == null)
return null;
var instructions = method.Body.Instructions;
for (int i = 0; i <= instructions.Count - 2; i++) {
var call = instructions[i];
if (call.OpCode.Code != Code.Call)
continue;
var calledMethod = call.Operand as MethodDef;
if (calledMethod == null)
continue;
if (!DotNetUtils.IsMethod(calledMethod, "System.Byte[]", "(System.Byte[])"))
continue;
var stsfld = instructions[i + 1];
if (stsfld.OpCode.Code != Code.Stsfld)
continue;
var field = stsfld.Operand as IField;
if (field == null || field.FieldSig.GetFieldType().GetFullName() != "System.Byte[]")
continue;
if (!new SigComparer().Equals(stringsEncodingClass, field.DeclaringType))
continue;
return calledMethod;
}
return null;
}
public IEnumerable GetAllStringDelegateFields() {
if (GetStringDelegate == null)
yield break;
foreach (var type in module.GetTypes()) {
foreach (var field in type.Fields) {
if (field.FieldType.TryGetTypeDef() == GetStringDelegate)
yield return field;
}
}
}
public void RemoveInitCode(Blocks blocks) {
if (CreateStringDelegateMethod == null)
return;
if (CreateStringDelegateMethod.Parameters.Count != 0)
RemoveInitCode_v2(blocks);
else
RemoveInitCode_v1(blocks);
}
void RemoveInitCode_v1(Blocks blocks) {
foreach (var block in blocks.MethodBlocks.GetAllBlocks()) {
var instructions = block.Instructions;
for (int i = 0; i < instructions.Count; i++) {
var call = instructions[i];
if (call.OpCode != OpCodes.Call)
continue;
var method = call.Operand as IMethod;
if (!MethodEqualityComparer.CompareDeclaringTypes.Equals(method, CreateStringDelegateMethod))
continue;
block.Remove(i, 1);
break;
}
}
}
void RemoveInitCode_v2(Blocks blocks) {
foreach (var block in blocks.MethodBlocks.GetAllBlocks()) {
var instructions = block.Instructions;
for (int i = 0; i <= instructions.Count - 3; i++) {
var ldtoken = instructions[i];
if (ldtoken.OpCode != OpCodes.Ldtoken)
continue;
if (!new SigComparer().Equals(blocks.Method.DeclaringType, ldtoken.Operand as ITypeDefOrRef))
continue;
var call1 = instructions[i + 1];
if (call1.OpCode != OpCodes.Call)
continue;
var method1 = call1.Operand as IMethod;
if (method1 == null || method1.ToString() != "System.Type System.Type::GetTypeFromHandle(System.RuntimeTypeHandle)")
continue;
var call2 = instructions[i + 2];
if (call2.OpCode != OpCodes.Call)
continue;
var method2 = call2.Operand as IMethod;
if (!MethodEqualityComparer.CompareDeclaringTypes.Equals(method2, CreateStringDelegateMethod))
continue;
block.Remove(i, 3);
break;
}
}
}
}
}