/*
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.Collections.Generic;
using System.Text;
using Mono.Cecil;
using Mono.Cecil.Cil;
using de4dot.blocks;
namespace de4dot.code.deobfuscators.DeepSea {
class StringDecrypter {
ModuleDefinition module;
MethodDefinitionAndDeclaringTypeDict methodToInfo = new MethodDefinitionAndDeclaringTypeDict();
class DecrypterInfo {
MethodDefinition cctor;
public MethodDefinition method;
FieldDefinition cachedStringsField;
FieldDefinition keyField;
int magic;
string[] encryptedStrings;
short[] key;
public DecrypterInfo(MethodDefinition cctor, MethodDefinition method) {
this.cctor = cctor;
this.method = method;
}
public 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.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() {
var pkt = cctor.Module.Assembly.Name.PublicKeyToken;
if (pkt != null && pkt.Length > 0)
return getPublicKeyTokenKey(pkt);
return findKey(cctor);
}
short[] findKey(MethodDefinition initMethod) {
var instrs = initMethod.Body.Instructions;
for (int i = 0; i < instrs.Count - 1; 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;
i++;
var array = ArrayFinder.getInitializedInt16Array(DotNetUtils.getLdcI4Value(ldci4), initMethod, ref i);
if (array == null)
continue;
i++;
if (i >= instrs.Count)
return null;
var stsfld = instrs[i];
if (stsfld.OpCode.Code != Code.Stsfld)
continue;
if (MemberReferenceHelper.compareFieldReferenceAndDeclaringType(keyField, stsfld.Operand as FieldReference))
return array;
}
return null;
}
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 override string ToString() {
return string.Format("M:{0:X8} N:{1}", magic, encryptedStrings.Length);
}
}
public bool Detected {
get { return methodToInfo.Count != 0; }
}
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) {
bool hasPublicKeyToken = module.Assembly.Name.PublicKeyToken != null && module.Assembly.Name.PublicKeyToken.Length != 0;
foreach (var type in module.GetTypes()) {
if (!checkFields(type.Fields))
continue;
var cctor = DotNetUtils.getMethod(type, ".cctor");
if (cctor == null)
continue;
if (!hasPublicKeyToken)
simpleDeobfuscator.deobfuscate(cctor);
foreach (var method in DotNetUtils.findMethods(type.Methods, "System.String", new string[] { "System.Int32" }, true)) {
simpleDeobfuscator.deobfuscate(method);
var info = getInfo(cctor, method);
if (info == null)
continue;
methodToInfo.add(method, info);
}
}
}
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;
}
DecrypterInfo getInfo(MethodDefinition cctor, MethodDefinition method) {
if (method == null || method.Body == null)
return null;
var info = new DecrypterInfo(cctor, method);
if (!info.initialize())
return null;
return info;
}
public string decrypt(MethodReference method, int magic2) {
var info = methodToInfo.find(method);
return info.decrypt(magic2);
}
}
}