/*
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.Text;
using Mono.Cecil;
using Mono.Cecil.Cil;
using Mono.Cecil.Metadata;
using de4dot.blocks;
namespace de4dot.code.deobfuscators.DeepSea {
class StringDecrypter {
ModuleDefinition module;
MethodDefinitionAndDeclaringTypeDict methodToInfo = new MethodDefinitionAndDeclaringTypeDict();
DecrypterVersion version = DecrypterVersion.Unknown;
public enum DecrypterVersion {
Unknown,
V1_3,
V4_0,
V4_1,
}
interface IDecrypterInfo {
DecrypterVersion Version { get; }
MethodDefinition Method { get; }
string decrypt(object[] args);
void cleanup();
}
static short[] findKey(MethodDefinition initMethod, FieldDefinition keyField) {
var fields = new FieldDefinitionAndDeclaringTypeDict();
fields.add(keyField, true);
return findKey(initMethod, fields);
}
static short[] findKey(MethodDefinition initMethod, FieldDefinitionAndDeclaringTypeDict fields) {
var instrs = initMethod.Body.Instructions;
for (int i = 0; i < instrs.Count - 2; i++) {
var ldci4 = instrs[i];
if (!DotNetUtils.isLdcI4(ldci4))
continue;
var newarr = instrs[i + 1];
if (newarr.OpCode.Code != Code.Newarr)
continue;
if (newarr.Operand.ToString() != "System.Char")
continue;
var stloc = instrs[i + 2];
if (!DotNetUtils.isStloc(stloc))
continue;
var local = DotNetUtils.getLocalVar(initMethod.Body.Variables, stloc);
int startInitIndex = i;
i++;
var array = ArrayFinder.getInitializedInt16Array(DotNetUtils.getLdcI4Value(ldci4), initMethod, ref i);
if (array == null)
continue;
var field = getStoreField(initMethod, startInitIndex, local);
if (field == null)
continue;
if (fields.find(field))
return array;
}
return null;
}
static FieldDefinition getStoreField(MethodDefinition method, int startIndex, VariableDefinition local) {
var instrs = method.Body.Instructions;
for (int i = 0; i < instrs.Count - 1; i++) {
var ldloc = instrs[i];
if (!DotNetUtils.isLdloc(ldloc))
continue;
if (DotNetUtils.getLocalVar(method.Body.Variables, ldloc) != local)
continue;
var stsfld = instrs[i + 1];
if (stsfld.OpCode.Code != Code.Stsfld)
continue;
return stsfld.Operand as FieldDefinition;
}
return null;
}
static bool findMagic(MethodDefinition method, out int magic) {
int arg1, arg2;
return findMagic(method, out arg1, out arg2, out magic);
}
static bool findMagic(MethodDefinition method, out int arg1, out int arg2, out int magic) {
var instrs = method.Body.Instructions;
for (int i = 0; i < instrs.Count - 3; i++) {
if ((arg1 = DotNetUtils.getArgIndex(instrs[i])) < 0)
continue;
var ldci4 = instrs[i + 1];
if (!DotNetUtils.isLdcI4(ldci4))
continue;
if (instrs[i + 2].OpCode.Code != Code.Xor)
continue;
if ((arg2 = DotNetUtils.getArgIndex(instrs[i + 3])) < 0)
continue;
magic = DotNetUtils.getLdcI4Value(ldci4);
return true;
}
arg1 = arg2 = 0;
magic = 0;
return false;
}
class DecrypterInfo41 : IDecrypterInfo {
MethodDefinition cctor;
int magic;
int arg1, arg2;
FieldDefinitionAndDeclaringTypeDict fields;
ArrayInfo arrayInfo;
ushort[] encryptedData;
short[] key;
int keyShift;
bool isTrial;
class ArrayInfo {
public int sizeInElems;
public TypeReference elementType;
public FieldDefinition initField;
public FieldDefinition field;
public ArrayInfo(int sizeInElems, TypeReference elementType, FieldDefinition initField, FieldDefinition field) {
this.sizeInElems = sizeInElems;
this.elementType = elementType;
this.initField = initField;
this.field = field;
}
}
public DecrypterVersion Version {
get { return DecrypterVersion.V4_1; }
}
public MethodDefinition Method { get; private set; }
public DecrypterInfo41(MethodDefinition cctor, MethodDefinition method) {
this.cctor = cctor;
Method = method;
}
public static bool isPossibleDecrypterMethod(MethodDefinition method) {
if (!checkMethodSignature(method))
return false;
var fields = getFields(method);
if (fields == null || fields.Count != 3)
return false;
return true;
}
static bool checkMethodSignature(MethodDefinition method) {
if (method.MethodReturnType.ReturnType.EType != ElementType.String)
return false;
int count = 0;
foreach (var arg in method.Parameters) {
if (arg.ParameterType.EType == ElementType.I4)
count++;
}
return count >= 2;
}
static FieldDefinitionAndDeclaringTypeDict getFields(MethodDefinition method) {
var fields = new FieldDefinitionAndDeclaringTypeDict();
foreach (var instr in method.Body.Instructions) {
if (instr.OpCode.Code != Code.Ldsfld && instr.OpCode.Code != Code.Stsfld)
continue;
var field = instr.Operand as FieldDefinition;
if (field == null)
continue;
if (field.DeclaringType != method.DeclaringType)
continue;
fields.add(field, true);
}
return fields;
}
public bool initialize() {
if (!findMagic(Method, out arg1, out arg2, out magic))
return false;
fields = getFields(Method);
if (fields == null)
return false;
arrayInfo = getArrayInfo(cctor);
if (arrayInfo == null)
return false;
if (arrayInfo.initField.InitialValue.Length % 2 == 1)
return false;
encryptedData = new ushort[arrayInfo.initField.InitialValue.Length / 2];
Buffer.BlockCopy(arrayInfo.initField.InitialValue, 0, encryptedData, 0, arrayInfo.initField.InitialValue.Length);
isTrial = !DeobUtils.hasInteger(Method, 0xFFF0);
keyShift = findKeyShift(cctor);
key = findKey();
if (key == null || key.Length == 0)
return false;
return true;
}
int findKeyShift(MethodDefinition method) {
var instrs = method.Body.Instructions;
for (int i = 0; i < instrs.Count - 3; i++) {
int index = i;
var ldci4 = instrs[index++];
if (!DotNetUtils.isLdcI4(ldci4))
continue;
if (DotNetUtils.getLdcI4Value(ldci4) != 0xFF)
continue;
if (instrs[index++].OpCode.Code != Code.And)
continue;
if (instrs[index++].OpCode.Code != Code.Dup)
continue;
var ldci4_2 = instrs[index++];
if (!DotNetUtils.isLdcI4(ldci4_2))
continue;
if (findNextFieldUse(method, index) < 0)
continue;
return DotNetUtils.getLdcI4Value(ldci4_2);
}
return -1;
}
int findNextFieldUse(MethodDefinition method, int index) {
var instrs = method.Body.Instructions;
for (int i = index; i < instrs.Count; i++) {
var instr = instrs[i];
if (instr.OpCode.Code != Code.Ldsfld && instr.OpCode.Code != Code.Stsfld)
continue;
var field = instr.Operand as FieldReference;
if (!fields.find(field))
return -1;
return i;
}
return -1;
}
ArrayInfo getArrayInfo(MethodDefinition method) {
var instructions = method.Body.Instructions;
for (int i = 0; i < instructions.Count; i++) {
var ldci4_arraySizeInBytes = instructions[i];
if (!DotNetUtils.isLdcI4(ldci4_arraySizeInBytes))
continue;
i++;
var instrs = DotNetUtils.getInstructions(instructions, i, OpCodes.Newarr, OpCodes.Dup, OpCodes.Ldtoken, OpCodes.Call, OpCodes.Stsfld);
if (instrs == null)
continue;
int sizeInBytes = DotNetUtils.getLdcI4Value(ldci4_arraySizeInBytes);
var elementType = instrs[0].Operand as TypeReference;
var initField = instrs[2].Operand as FieldDefinition;
var field = instrs[4].Operand as FieldDefinition;
if (elementType == null)
continue;
if (initField == null || initField.InitialValue == null || initField.InitialValue.Length == 0)
continue;
if (!fields.find(field))
continue;
return new ArrayInfo(sizeInBytes, elementType, initField, field);
}
return null;
}
short[] findKey() {
if (cctor.Module.Assembly == null)
return null;
var pkt = cctor.Module.Assembly.Name.PublicKeyToken;
if (pkt != null && pkt.Length > 0)
return getPublicKeyTokenKey(pkt);
return findKey(cctor);
}
short[] findKey(MethodDefinition initMethod) {
return StringDecrypter.findKey(initMethod, fields);
}
short[] getPublicKeyTokenKey(byte[] publicKeyToken) {
if (keyShift < 0)
throw new ApplicationException("Could not find shift value");
var key = new short[publicKeyToken.Length];
for (int i = 0; i < publicKeyToken.Length; i++) {
int b = publicKeyToken[i];
key[i] = (short)((b << keyShift) ^ b);
}
return key;
}
public string decrypt(object[] args) {
if (isTrial)
return decryptTrial((int)args[arg1], (int)args[arg2]);
return decryptRetail((int)args[arg1], (int)args[arg2]);
}
string decryptTrial(int magic2, int magic3) {
int offset = magic ^ magic2 ^ magic3;
var keyChar = encryptedData[offset + 1];
int cachedIndex = encryptedData[offset] ^ keyChar;
int numChars = ((keyChar ^ encryptedData[offset + 2]) << 16) + (keyChar ^ encryptedData[offset + 3]);
offset += 4;
var sb = new StringBuilder(numChars);
for (int i = 0; i < numChars; i++)
sb.Append((char)(keyChar ^ encryptedData[offset + i] ^ key[(offset + i) % key.Length]));
return sb.ToString();
}
string decryptRetail(int magic2, int magic3) {
int offset = magic ^ magic2 ^ magic3;
var keyChar = encryptedData[offset + 2];
int cachedIndex = encryptedData[offset + 1] ^ keyChar;
int flags = encryptedData[offset] ^ keyChar;
int numChars = (flags >> 1) & ~7 | (flags & 7);
if ((flags & 8) != 0) {
numChars <<= 15;
numChars |= encryptedData[offset + 3] ^ keyChar;
offset++;
}
offset += 3;
var sb = new StringBuilder(numChars);
for (int i = 0; i < numChars; i++)
sb.Append((char)(keyChar ^ encryptedData[offset + numChars - i - 1] ^ key[(i + 1 + offset) % key.Length]));
return sb.ToString();
}
public void cleanup() {
arrayInfo.initField.InitialValue = new byte[1];
arrayInfo.initField.FieldType = arrayInfo.initField.Module.TypeSystem.Byte;
}
}
class DecrypterInfo40 : IDecrypterInfo {
MethodDefinition cctor;
int magic;
FieldDefinition cachedStringsField;
FieldDefinition keyField;
FieldDefinition encryptedStringsField;
FieldDefinition encryptedDataField;
short[] key;
ushort[] encryptedData;
public MethodDefinition Method { get; private set; }
public DecrypterVersion Version {
get { return DecrypterVersion.V4_0; }
}
public DecrypterInfo40(MethodDefinition cctor, MethodDefinition method) {
this.cctor = cctor;
this.Method = method;
}
public static bool isPossibleDecrypterMethod(MethodDefinition method) {
if (!checkFields(method.DeclaringType.Fields))
return false;
return DotNetUtils.isMethod(method, "System.String", "(System.Int32,System.Int32)");
}
public bool initialize() {
if (!findMagic(Method, out magic))
return false;
var charArrayFields = findFields();
if (charArrayFields == null || charArrayFields.Count != 2)
return false;
encryptedStringsField = findEncryptedStrings(cctor, charArrayFields, out encryptedDataField);
if (encryptedStringsField == null)
return false;
if (encryptedDataField.InitialValue.Length % 2 == 1)
return false;
encryptedData = new ushort[encryptedDataField.InitialValue.Length / 2];
Buffer.BlockCopy(encryptedDataField.InitialValue, 0, encryptedData, 0, encryptedDataField.InitialValue.Length);
charArrayFields.Remove(encryptedStringsField);
keyField = charArrayFields[0];
key = findKey();
if (key == null || key.Length == 0)
return false;
return true;
}
List findFields() {
var charArrayFields = new List();
foreach (var instr in Method.Body.Instructions) {
if (instr.OpCode.Code != Code.Stsfld && instr.OpCode.Code != Code.Ldsfld)
continue;
var field = instr.Operand as FieldDefinition;
if (field == null)
continue;
if (!MemberReferenceHelper.compareTypes(Method.DeclaringType, field.DeclaringType))
continue;
switch (field.FieldType.FullName) {
case "System.Char[]":
if (!charArrayFields.Contains(field))
charArrayFields.Add(field);
break;
case "System.String[]":
if (cachedStringsField != null && cachedStringsField != field)
return null;
cachedStringsField = field;
break;
default:
break;
}
}
if (cachedStringsField == null)
return null;
return charArrayFields;
}
static FieldDefinition findEncryptedStrings(MethodDefinition initMethod, List ourFields, out FieldDefinition dataField) {
for (int i = 0; i < initMethod.Body.Instructions.Count; i++) {
var instrs = DotNetUtils.getInstructions(initMethod.Body.Instructions, i, OpCodes.Ldtoken, OpCodes.Call, OpCodes.Stsfld);
if (instrs == null)
continue;
dataField = instrs[0].Operand as FieldDefinition;
if (dataField == null || dataField.InitialValue == null || dataField.InitialValue.Length == 0)
continue;
var savedField = instrs[2].Operand as FieldDefinition;
if (savedField == null || !matches(ourFields, savedField))
continue;
return savedField;
}
dataField = null;
return null;
}
static bool matches(IEnumerable ourFields, FieldReference field) {
foreach (var ourField in ourFields) {
if (MemberReferenceHelper.compareFieldReferenceAndDeclaringType(ourField, field))
return true;
}
return false;
}
short[] findKey() {
if (cctor.Module.Assembly == null)
return null;
var pkt = cctor.Module.Assembly.Name.PublicKeyToken;
if (pkt != null && pkt.Length > 0)
return getPublicKeyTokenKey(pkt);
return findKey(cctor);
}
short[] findKey(MethodDefinition initMethod) {
return StringDecrypter.findKey(initMethod, keyField);
}
static short[] getPublicKeyTokenKey(byte[] publicKeyToken) {
var key = new short[publicKeyToken.Length];
for (int i = 0; i < publicKeyToken.Length; i++) {
int b = publicKeyToken[i];
key[i] = (short)((b << 4) ^ b);
}
return key;
}
public string decrypt(object[] args) {
return decrypt((int)args[0], (int)args[1]);
}
string decrypt(int magic2, int magic3) {
int index = magic ^ magic2 ^ magic3;
int cachedIndex = encryptedData[index++];
int stringLen = encryptedData[index++] + ((int)encryptedData[index++] << 16);
var sb = new StringBuilder(stringLen);
for (int i = 0; i < stringLen; i++)
sb.Append((char)(encryptedData[index++] ^ key[cachedIndex++ % key.Length]));
return sb.ToString();
}
public void cleanup() {
encryptedDataField.InitialValue = new byte[1];
encryptedDataField.FieldType = encryptedDataField.Module.TypeSystem.Byte;
}
}
class DecrypterInfo13 : IDecrypterInfo {
MethodDefinition cctor;
FieldDefinition cachedStringsField;
FieldDefinition keyField;
int magic;
string[] encryptedStrings;
short[] key;
public MethodDefinition Method { get; private set; }
public DecrypterVersion Version {
get { return DecrypterVersion.V1_3; }
}
public static bool isPossibleDecrypterMethod(MethodDefinition method) {
if (!checkFields(method.DeclaringType.Fields))
return false;
return DotNetUtils.isMethod(method, "System.String", "(System.Int32)");
}
public DecrypterInfo13(MethodDefinition cctor, MethodDefinition method) {
this.cctor = cctor;
this.Method = method;
}
public string decrypt(object[] args) {
return decrypt((int)args[0]);
}
string decrypt(int magic2) {
var es = encryptedStrings[magic ^ magic2];
var sb = new StringBuilder(es.Length);
for (int i = 0; i < es.Length; i++)
sb.Append((char)(es[i] ^ key[(magic2 + i) % key.Length]));
return sb.ToString();
}
public bool initialize() {
if (!findMagic(Method, out magic))
return false;
if (!findFields())
return false;
if (!findEncryptedStrings(Method))
return false;
key = findKey();
if (key == null || key.Length == 0)
return false;
return true;
}
bool findFields() {
foreach (var instr in Method.Body.Instructions) {
if (instr.OpCode.Code != Code.Stsfld && instr.OpCode.Code != Code.Ldsfld)
continue;
var field = instr.Operand as FieldDefinition;
if (field == null)
continue;
if (!MemberReferenceHelper.compareTypes(Method.DeclaringType, field.DeclaringType))
continue;
switch (field.FieldType.FullName) {
case "System.Char[]":
if (keyField != null && keyField != field)
return false;
keyField = field;
break;
case "System.String[]":
if (cachedStringsField != null && cachedStringsField != field)
return false;
cachedStringsField = field;
break;
default:
break;
}
}
return keyField != null && cachedStringsField != null;
}
short[] findKey() {
if (cctor.Module.Assembly == null)
return null;
var pkt = cctor.Module.Assembly.Name.PublicKeyToken;
if (pkt != null && pkt.Length > 0)
return getPublicKeyTokenKey(pkt);
return findKey(cctor);
}
short[] findKey(MethodDefinition initMethod) {
return StringDecrypter.findKey(initMethod, keyField);
}
static short[] getPublicKeyTokenKey(byte[] publicKeyToken) {
var key = new short[publicKeyToken.Length];
for (int i = 0; i < publicKeyToken.Length; i++) {
int b = publicKeyToken[i];
key[i] = (short)((b << 4) ^ b);
}
return key;
}
static bool findMagic(MethodDefinition method, out int magic) {
var instrs = method.Body.Instructions;
for (int i = 0; i < instrs.Count - 2; i++) {
var ldarg = instrs[i];
if (DotNetUtils.getArgIndex(ldarg) < 0)
continue;
var ldci4 = instrs[i + 1];
if (!DotNetUtils.isLdcI4(ldci4))
continue;
if (instrs[i + 2].OpCode.Code != Code.Xor)
continue;
magic = DotNetUtils.getLdcI4Value(ldci4);
return true;
}
magic = 0;
return false;
}
bool findEncryptedStrings(MethodDefinition method) {
var switchInstr = getOnlySwitchInstruction(method);
if (switchInstr == null)
return false;
var targets = (Instruction[])switchInstr.Operand;
encryptedStrings = new string[targets.Length];
for (int i = 0; i < targets.Length; i++) {
var target = targets[i];
if (target.OpCode.Code != Code.Ldstr)
return false;
encryptedStrings[i] = (string)target.Operand;
}
return true;
}
static Instruction getOnlySwitchInstruction(MethodDefinition method) {
Instruction switchInstr = null;
foreach (var instr in method.Body.Instructions) {
if (instr.OpCode.Code != Code.Switch)
continue;
if (switchInstr != null)
return null;
switchInstr = instr;
}
return switchInstr;
}
public void cleanup() {
}
public override string ToString() {
return string.Format("M:{0:X8} N:{1}", magic, encryptedStrings.Length);
}
}
public bool Detected {
get { return methodToInfo.Count != 0; }
}
public DecrypterVersion Version {
get { return version; }
}
public List DecrypterMethods {
get {
var methods = new List(methodToInfo.Count);
foreach (var info in methodToInfo.getValues())
methods.Add(info.Method);
return methods;
}
}
public StringDecrypter(ModuleDefinition module) {
this.module = module;
}
public void find(ISimpleDeobfuscator simpleDeobfuscator) {
if (module.Assembly == null)
return;
bool hasPublicKeyToken = module.Assembly.Name.PublicKeyToken != null && module.Assembly.Name.PublicKeyToken.Length != 0;
foreach (var type in module.GetTypes()) {
var cctor = DotNetUtils.getMethod(type, ".cctor");
if (cctor == null)
continue;
bool deobfuscatedCctor = false;
foreach (var method in type.Methods) {
if (!method.IsStatic || method.Body == null)
continue;
IDecrypterInfo info = null;
if (DecrypterInfo13.isPossibleDecrypterMethod(method)) {
deobfuscateCctor(simpleDeobfuscator, cctor, ref deobfuscatedCctor, hasPublicKeyToken);
simpleDeobfuscator.deobfuscate(method);
info = getInfoV13(cctor, method);
}
else if (DecrypterInfo40.isPossibleDecrypterMethod(method)) {
deobfuscateCctor(simpleDeobfuscator, cctor, ref deobfuscatedCctor, hasPublicKeyToken);
simpleDeobfuscator.deobfuscate(method);
info = getInfoV40(cctor, method);
}
else if (DecrypterInfo41.isPossibleDecrypterMethod(method)) {
deobfuscateCctor(simpleDeobfuscator, cctor, ref deobfuscatedCctor, hasPublicKeyToken);
simpleDeobfuscator.deobfuscate(method);
info = getInfoV41(cctor, method);
}
if (info == null)
continue;
methodToInfo.add(method, info);
version = info.Version;
}
}
}
static void deobfuscateCctor(ISimpleDeobfuscator simpleDeobfuscator, MethodDefinition cctor, ref bool deobfuscatedCctor, bool hasPublicKeyToken) {
if (deobfuscatedCctor || hasPublicKeyToken)
return;
simpleDeobfuscator.deobfuscate(cctor);
deobfuscatedCctor = true;
}
static bool checkFields(IEnumerable fields) {
bool foundCharAry = false, foundStringAry = false;
foreach (var field in fields) {
if (foundCharAry && foundStringAry)
break;
switch (field.FieldType.FullName) {
case "System.Char[]":
foundCharAry = true;
break;
case "System.String[]":
foundStringAry = true;
break;
}
}
return foundCharAry && foundStringAry;
}
DecrypterInfo13 getInfoV13(MethodDefinition cctor, MethodDefinition method) {
var info = new DecrypterInfo13(cctor, method);
if (!info.initialize())
return null;
return info;
}
DecrypterInfo40 getInfoV40(MethodDefinition cctor, MethodDefinition method) {
var info = new DecrypterInfo40(cctor, method);
if (!info.initialize())
return null;
return info;
}
DecrypterInfo41 getInfoV41(MethodDefinition cctor, MethodDefinition method) {
var info = new DecrypterInfo41(cctor, method);
if (!info.initialize())
return null;
return info;
}
public string decrypt(MethodReference method, object[] args) {
var info = methodToInfo.find(method);
return info.decrypt(args);
}
public void cleanup() {
foreach (var info in methodToInfo.getValues())
info.cleanup();
}
}
}