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Refactor string decrypter

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This commit is contained in:
de4dot 2011-12-21 19:22:23 +01:00
parent d24da2f24c
commit 823d3b07a7
3 changed files with 124 additions and 67 deletions
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1
de4dot.code/de4dot.code.csproj
View File

@ -77,6 +77,7 @@
<Compile Include="deobfuscators\DeobfuscatorInfoBase.cs" />
<Compile Include="deobfuscators\DeobUtils.cs" />
<Compile Include="deobfuscators\Dotfuscator\Deobfuscator.cs" />
<Compile Include="deobfuscators\Dotfuscator\StringDecrypter.cs" />
<Compile Include="deobfuscators\dotNET_Reactor\v3\AntiStrongName.cs" />
<Compile Include="deobfuscators\dotNET_Reactor\v3\ApplicationModeDecrypter.cs" />
<Compile Include="deobfuscators\dotNET_Reactor\v3\ApplicationModeUnpacker.cs" />

82
de4dot.code/deobfuscators/Dotfuscator/Deobfuscator.cs
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@ -19,7 +19,6 @@
using System.Collections.Generic;
using Mono.Cecil;
using Mono.Cecil.Cil;
using de4dot.blocks;
namespace de4dot.code.deobfuscators.Dotfuscator {
@ -50,17 +49,9 @@ namespace de4dot.code.deobfuscators.Dotfuscator {
class Deobfuscator : DeobfuscatorBase {
Options options;
string obfuscatorName = "Dotfuscator";
Dictionary<MethodReference, StringDecrypterInfo> stringDecrypterMethods = new Dictionary<MethodReference, StringDecrypterInfo>();
bool foundDotfuscatorAttribute = false;
class StringDecrypterInfo {
public MethodDefinition method;
public int magic;
public StringDecrypterInfo(MethodDefinition method, int magic) {
this.method = method;
this.magic = magic;
}
}
StringDecrypter stringDecrypter;
bool foundDotfuscatorAttribute = false;
internal class Options : OptionsBase {
}
@ -85,17 +76,18 @@ namespace de4dot.code.deobfuscators.Dotfuscator {
protected override int detectInternal() {
int val = 0;
if (foundDotfuscatorAttribute)
val += 100;
if (stringDecrypterMethods.Count > 0)
val += 10;
int sum = convert(foundDotfuscatorAttribute) +
convert(stringDecrypter.Detected);
if (sum > 0)
val += 100 + 10 * (sum - 1);
return val;
}
protected override void scanForObfuscator() {
stringDecrypter = new StringDecrypter(module);
stringDecrypter.find(DeobfuscatedFile);
findDotfuscatorAttribute();
findStringDecrypterMethods();
}
void findDotfuscatorAttribute() {
@ -120,66 +112,22 @@ namespace de4dot.code.deobfuscators.Dotfuscator {
obfuscatorName = "Dotfuscator " + val.Groups[1].ToString();
}
void findStringDecrypterMethods() {
foreach (var type in module.GetTypes())
findStringDecrypterMethods(type);
}
void findStringDecrypterMethods(TypeDefinition type) {
foreach (var method in DotNetUtils.findMethods(type.Methods, "System.String", new string[] { "System.String", "System.Int32" })) {
if (method.Body.HasExceptionHandlers)
continue;
var methodCalls = DotNetUtils.getMethodCallCounts(method);
if (methodCalls.count("System.Char[] System.String::ToCharArray()") != 1)
continue;
if (methodCalls.count("System.String System.String::Intern(System.String)") != 1)
continue;
DeobfuscatedFile.deobfuscate(method);
var instructions = method.Body.Instructions;
for (int i = 0; i <= instructions.Count - 3; i++) {
var ldci4 = method.Body.Instructions[i];
if (!DotNetUtils.isLdcI4(ldci4))
continue;
if (instructions[i + 1].OpCode.Code != Code.Ldarg_1)
continue;
if (instructions[i + 2].OpCode.Code != Code.Add)
continue;
var info = new StringDecrypterInfo(method, DotNetUtils.getLdcI4Value(ldci4));
Log.v("Found string decrypter method: {0}, magic: 0x{1:X8}", info.method, info.magic);
stringDecrypterMethods[info.method] = info;
staticStringDecrypter.add(info.method, (method2, args) => decryptString(stringDecrypterMethods[method2], (string)args[0], (int)args[1]));
break;
}
}
public override void deobfuscateBegin() {
base.deobfuscateBegin();
foreach (var info in stringDecrypter.StringDecrypterInfos)
staticStringDecrypter.add(info.method, (method, args) => stringDecrypter.decrypt(method, (string)args[0], (int)args[1]));
}
public override void deobfuscateEnd() {
if (Operations.DecryptStrings != OpDecryptString.None) {
foreach (var method in stringDecrypterMethods.Keys)
addMethodToBeRemoved(stringDecrypterMethods[method].method, "String decrypter method");
}
if (Operations.DecryptStrings != OpDecryptString.None)
addMethodsToBeRemoved(stringDecrypter.StringDecrypters, "String decrypter method");
base.deobfuscateEnd();
}
static string decryptString(StringDecrypterInfo info, string encrypted, int value) {
char[] chars = encrypted.ToCharArray();
byte key = (byte)(info.magic + value);
for (int i = 0; i < chars.Length; i++) {
char c = chars[i];
byte b1 = (byte)((byte)c ^ key++);
byte b2 = (byte)((byte)(c >> 8) ^ key++);
chars[i] = (char)((b1 << 8) | b2);
}
return new string(chars);
}
public override IEnumerable<string> getStringDecrypterMethods() {
var list = new List<string>();
foreach (var method in stringDecrypterMethods.Keys)
foreach (var method in stringDecrypter.StringDecrypters)
list.Add(method.MetadataToken.ToInt32().ToString("X8"));
return list;
}

108
de4dot.code/deobfuscators/Dotfuscator/StringDecrypter.cs Normal file
View File

@ -0,0 +1,108 @@
/*
Copyright (C) 2011 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 <http://www.gnu.org/licenses/>.
*/
using System.Collections.Generic;
using Mono.Cecil;
using Mono.Cecil.Cil;
using de4dot.blocks;
namespace de4dot.code.deobfuscators.Dotfuscator {
class StringDecrypter {
ModuleDefinition module;
Dictionary<MethodReference, StringDecrypterInfo> stringDecrypterMethods = new Dictionary<MethodReference, StringDecrypterInfo>();
public class StringDecrypterInfo {
public MethodDefinition method;
public int magic;
public StringDecrypterInfo(MethodDefinition method, int magic) {
this.method = method;
this.magic = magic;
}
}
public bool Detected {
get { return stringDecrypterMethods.Count > 0; }
}
public IEnumerable<MethodDefinition> StringDecrypters {
get {
var list = new List<MethodDefinition>(stringDecrypterMethods.Count);
foreach (var info in stringDecrypterMethods)
list.Add(info.Value.method);
return list;
}
}
public IEnumerable<StringDecrypterInfo> StringDecrypterInfos {
get { return stringDecrypterMethods.Values; }
}
public StringDecrypter(ModuleDefinition module) {
this.module = module;
}
public void find(ISimpleDeobfuscator simpleDeobfuscator) {
foreach (var type in module.GetTypes())
findStringDecrypterMethods(type, simpleDeobfuscator);
}
void findStringDecrypterMethods(TypeDefinition type, ISimpleDeobfuscator simpleDeobfuscator) {
foreach (var method in DotNetUtils.findMethods(type.Methods, "System.String", new string[] { "System.String", "System.Int32" })) {
if (method.Body.HasExceptionHandlers)
continue;
var methodCalls = DotNetUtils.getMethodCallCounts(method);
if (methodCalls.count("System.Char[] System.String::ToCharArray()") != 1)
continue;
if (methodCalls.count("System.String System.String::Intern(System.String)") != 1)
continue;
simpleDeobfuscator.deobfuscate(method);
var instructions = method.Body.Instructions;
for (int i = 0; i <= instructions.Count - 3; i++) {
var ldci4 = method.Body.Instructions[i];
if (!DotNetUtils.isLdcI4(ldci4))
continue;
if (instructions[i + 1].OpCode.Code != Code.Ldarg_1)
continue;
if (instructions[i + 2].OpCode.Code != Code.Add)
continue;
var info = new StringDecrypterInfo(method, DotNetUtils.getLdcI4Value(ldci4));
stringDecrypterMethods[info.method] = info;
Log.v("Found string decrypter method: {0}, magic: 0x{1:X8}", info.method, info.magic);
break;
}
}
}
public string decrypt(MethodReference method, string encrypted, int value) {
var info = stringDecrypterMethods[method];
char[] chars = encrypted.ToCharArray();
byte key = (byte)(info.magic + value);
for (int i = 0; i < chars.Length; i++) {
char c = chars[i];
byte b1 = (byte)((byte)c ^ key++);
byte b2 = (byte)((byte)(c >> 8) ^ key++);
chars[i] = (char)((b1 << 8) | b2);
}
return new string(chars);
}
}
}