de4dot-cex/de4dot.code/deobfuscators/ConfuserEx/ResourceDecrypter.cs

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using de4dot.blocks;
using dnlib.DotNet;
using dnlib.DotNet.Emit;

namespace de4dot.code.deobfuscators.ConfuserEx
{
    public class ResourceDecrypter
    {
        private FieldDef _arrayField, _asmField;

        private byte[] _decryptedBytes;
        private readonly ISimpleDeobfuscator _deobfuscator;
        private readonly MethodDef _lzmaMethod;

        private readonly ModuleDef _module;

        public ResourceDecrypter(ModuleDef module, MethodDef lzmaMethod, ISimpleDeobfuscator deobfsucator)
        {
            this._module = module;
            this._lzmaMethod = lzmaMethod;
            _deobfuscator = deobfsucator;
        }

        public bool CanRemoveLzma { get; private set; } = true;

        public TypeDef Type { get; private set; }
        public MethodDef Method { get; private set; }
        public MethodDef AssembyResolveMethod { get; private set; }
        public List<FieldDef> Fields => new List<FieldDef> {_arrayField, _asmField};

        public bool Detected => Method != null && _decryptedBytes != null && _arrayField != null && _asmField != null;

        public void Find()
        {
            var moduleCctor = DotNetUtils.GetModuleTypeCctor(_module);
            if (moduleCctor == null)
                return;
            foreach (var inst in moduleCctor.Body.Instructions)
            {
                if (inst.OpCode != OpCodes.Call)
                    continue;
                if (!(inst.Operand is MethodDef))
                    continue;
                var method = inst.Operand as MethodDef;
                if (!method.HasBody || !method.IsStatic)
                    continue;
                if (!DotNetUtils.IsMethod(method, "System.Void", "()"))
                    continue;
                _deobfuscator.Deobfuscate(method, SimpleDeobfuscatorFlags.Force);
                if (!IsResDecryptInit(method))
                    continue;
                Method = method;
            }
        }

        private bool IsResDecryptInit(MethodDef method)
        {
            var instr = method.Body.Instructions;

            if (instr.Count < 15)
                return false;

            if (!instr[0].IsLdcI4())
                return false;
            if (!instr[1].IsStloc()) //uint num = 96u;
                return false;

            if (!instr[2].IsLdcI4())
                return false;
            if (instr[0].GetLdcI4Value() != instr[2].GetLdcI4Value())
                return false;
            if (instr[3].OpCode != OpCodes.Newarr)
                return false;
            if (instr[3].Operand.ToString() != "System.UInt32")
                return false;
            if (instr[4].OpCode != OpCodes.Dup)
                return false;
            if (instr[5].OpCode != OpCodes.Ldtoken)
                return false;
            var aField = instr[5].Operand as FieldDef;
            if (aField == null)
                return false;
            if (aField.InitialValue == null)
                return false;
            if (aField.Attributes != (FieldAttributes.Assembly | FieldAttributes.Static | FieldAttributes.HasFieldRVA))
                return false;
            if (instr[6].OpCode != OpCodes.Call)
                return false;
            if (instr[6].Operand.ToString() !=
                "System.Void System.Runtime.CompilerServices.RuntimeHelpers::InitializeArray(System.Array,System.RuntimeFieldHandle)"
            )
                return false;
            if (!instr[7].IsStloc()) // uint[] array = new uint[] {.....};
                return false;

            var l = instr.Count;
            if (!instr[l - 10].IsLdloc())
                return false;
            if (instr[l - 9].OpCode != OpCodes.Call)
                return false;
            if (instr[l - 9].Operand != _lzmaMethod)
                return false;
            if (instr[l - 8].OpCode != OpCodes.Call)
                return false;
            if (instr[l - 8].Operand.ToString() !=
                "System.Reflection.Assembly System.Reflection.Assembly::Load(System.Byte[])")
                return false;
            if (instr[l - 7].OpCode != OpCodes.Stsfld) //<Module>.assembly_0 = Assembly.Load(array4);
                return false;
            var asField = instr[l - 7].Operand as FieldDef;
            if (asField == null)
                return false;

            if (instr[l - 6].OpCode != OpCodes.Call)
                return false;
            if (instr[l - 6].Operand.ToString() != "System.AppDomain System.AppDomain::get_CurrentDomain()")
                return false;
            if (instr[l - 5].OpCode != OpCodes.Ldnull)
                return false;
            if (instr[l - 4].OpCode != OpCodes.Ldftn)
                return false;
            var mtd = instr[l - 4].Operand as MethodDef;
            if (mtd == null)
                return false;
            if (!IsAssembyResolveMethod(mtd, asField))
                return false;
            if (instr[l - 3].OpCode != OpCodes.Newobj)
                return false;
            if (instr[l - 2].OpCode != OpCodes.Callvirt
            ) //AppDomain.CurrentDomain.AssemblyResolve += new ResolveEventHandler(<Module>.smethod_1);
                return false;
            try
            {
                DecryptArray(ConvertArray<uint, byte>(aField.InitialValue));
            }
            catch
            {
                CanRemoveLzma = false;
                return false;
            }
            _arrayField = aField;
            Type = DotNetUtils.GetType(_module, aField.FieldSig.Type);
            _asmField = asField;
            AssembyResolveMethod = mtd;
            return true;
        }

        private T[] ConvertArray<T, T1>(T1[] array)
        {
            var l = Marshal.SizeOf(typeof(T));
            var l1 = Marshal.SizeOf(typeof(T1));
            var buffer = new T[array.Length * l1 / l];
            Buffer.BlockCopy(array, 0, buffer, 0, array.Length * l1);
            return buffer;
        }

        private void DecryptArray(uint[] array) //TODO: Automatic detection
        {
            var num = array.Length;
            var array2 = new uint[16];
            var num2 = 825993394u;
            for (var i = 0; i < 16; i++)
            {
                num2 ^= num2 >> 13;
                num2 ^= num2 << 25;
                num2 ^= num2 >> 27;
                array2[i] = num2;
            }
            var num3 = 0;
            var num4 = 0;
            var array3 = new uint[16];
            var array4 = new byte[num * 4u];
            while (num3 < (long) (ulong) num)
            {
                for (var j = 0; j < 16; j++)
                    array3[j] = array[num3 + j];
                array3[0] = array3[0] ^ array2[0];
                array3[1] = array3[1] ^ array2[1];
                array3[2] = array3[2] ^ array2[2];
                array3[3] = array3[3] ^ array2[3];
                array3[4] = array3[4] ^ array2[4];
                array3[5] = array3[5] ^ array2[5];
                array3[6] = array3[6] ^ array2[6];
                array3[7] = array3[7] ^ array2[7];
                array3[8] = array3[8] ^ array2[8];
                array3[9] = array3[9] ^ array2[9];
                array3[10] = array3[10] ^ array2[10];
                array3[11] = array3[11] ^ array2[11];
                array3[12] = array3[12] ^ array2[12];
                array3[13] = array3[13] ^ array2[13];
                array3[14] = array3[14] ^ array2[14];
                array3[15] = array3[15] ^ array2[15];
                for (var k = 0; k < 16; k++)
                {
                    var num5 = array3[k];
                    array4[num4++] = (byte) num5;
                    array4[num4++] = (byte) (num5 >> 8);
                    array4[num4++] = (byte) (num5 >> 16);
                    array4[num4++] = (byte) (num5 >> 24);
                    array2[k] ^= num5;
                }
                num3 += 16;
            }
            _decryptedBytes = Lzma.Decompress(array4);
        }

        private bool IsAssembyResolveMethod(MethodDef method, FieldDef field)
        {
            if (DotNetUtils.IsMethod(method, "", "()"))
                return false;
            _deobfuscator.Deobfuscate(method, SimpleDeobfuscatorFlags.Force);

            var instr = method.Body.Instructions;
            if (instr.Count != 10)
                return false;

            if (instr[0].OpCode != OpCodes.Ldsfld)
                return false;
            if (instr[0].Operand != field)
                return false;
            if (instr[1].OpCode != OpCodes.Callvirt)
                return false;
            if (instr[1].Operand.ToString() != "System.String System.Reflection.Assembly::get_FullName()")
                return false;
            if (!instr[2].IsLdarg())
                return false;
            if (instr[3].OpCode != OpCodes.Callvirt)
                return false;
            if (instr[3].Operand.ToString() != "System.String System.ResolveEventArgs::get_Name()")
                return false;
            if (instr[4].OpCode != OpCodes.Call)
                return false;
            if (instr[4].Operand.ToString() != "System.Boolean System.String::op_Equality(System.String,System.String)")
                return false;
            if (!instr[5].IsBrfalse())
                return false;
            if (instr[6].OpCode != OpCodes.Ldsfld)
                return false;
            if (instr[6].Operand != field)
                return false;
            if (instr[7].OpCode != OpCodes.Ret)
                return false;
            if (instr[8].OpCode != OpCodes.Ldnull)
                return false;
            if (instr[9].OpCode != OpCodes.Ret)
                return false;
            return true;
        }

        public void Fix()
        {
            ModuleDef newModule;
            try
            {
                newModule = ModuleDefMD.Load(_decryptedBytes);
            }
            catch
            {
                CanRemoveLzma = false;
                return;
            }
            var toRemove = new List<Resource>();
            var toAdd = new List<Resource>();
            foreach (var cryptedResource in _module.Resources)
            foreach (var resource in newModule.Resources)
                if (cryptedResource.Name == resource.Name)
                {
                    toRemove.Add(cryptedResource);
                    toAdd.Add(resource);
                }

            foreach (var resToRemove in toRemove)
                _module.Resources.Remove(resToRemove);
            foreach (var resToAdd in toAdd)
                _module.Resources.Add(resToAdd);
        }
    }
}