├── .gitattributes ├── .gitignore ├── ThemidaStringDecryptor.sln └── ThemidaStringDecryptor ├── Program.cs └── ThemidaStringDecryptor.csproj /.gitattributes: -------------------------------------------------------------------------------- 1 | ############################################################################### 2 | # Set default behavior to automatically normalize line endings. 3 | ############################################################################### 4 | * text=auto 5 | 6 | ############################################################################### 7 | # Set default behavior for command prompt diff. 8 | # 9 | # This is need for earlier builds of msysgit that does not have it on by 10 | # default for csharp files. 11 | # Note: This is only used by command line 12 | ############################################################################### 13 | #*.cs diff=csharp 14 | 15 | ############################################################################### 16 | # Set the merge driver for project and solution files 17 | # 18 | # Merging from the command prompt will add diff markers to the files if there 19 | # are conflicts (Merging from VS is not affected by the settings below, in VS 20 | # the diff markers are never inserted). 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2 | using AsmResolver.DotNet; 3 | using AsmResolver.DotNet.Builder; 4 | using AsmResolver.DotNet.Code.Cil; 5 | using AsmResolver.PE.DotNet.Builder; 6 | using AsmResolver.PE.DotNet.Cil; 7 | using AsmResolver.PE.DotNet.Metadata.Tables.Rows; 8 | using System; 9 | using System.Linq; 10 | using System.Text; 11 | 12 | namespace ThemidaStringDecryptor 13 | { 14 | internal class Program 15 | { 16 | private static int ResolveArithmethics(CilCode code, int a, int b) 17 | { 18 | return code switch 19 | { 20 | CilCode.And => a & b, 21 | CilCode.Or => a | b, 22 | _ => a ^ b, 23 | }; 24 | } 25 | static void Main(string[] args) 26 | { 27 | ModuleDefinition module = ModuleDefinition.FromFile(args[0]); 28 | System.Collections.Generic.IEnumerable types = module.GetAllTypes(); 29 | TypeDefinition stringDecryptType = types.FirstOrDefault(x => x.FullName.Contains("PrivateImpl")); 30 | 31 | int resolveStringMethod = stringDecryptType.Methods.FirstOrDefault(x => x.Parameters.Count == 3).MetadataToken.ToInt32(); 32 | 33 | CilInstructionCollection stringDecryptTypeCtorInstructions = stringDecryptType.GetStaticConstructor().CilMethodBody.Instructions; 34 | 35 | byte[] decryptArray = ((DataSegment)((FieldDefinition)stringDecryptTypeCtorInstructions[6].Operand).FieldRva).ToArray(); 36 | 37 | var firsArithmetic = stringDecryptTypeCtorInstructions[18].OpCode.Code; 38 | var secondNumber = stringDecryptTypeCtorInstructions[19].GetLdcI4Constant(); 39 | var secondArithmetic = stringDecryptTypeCtorInstructions[20].OpCode.Code; 40 | 41 | for (int i = 0; i < decryptArray.Length; i++) 42 | { 43 | decryptArray[i] = (byte)(ResolveArithmethics(secondArithmetic , ResolveArithmethics(firsArithmetic, decryptArray[i], i), secondNumber) ); 44 | } 45 | 46 | foreach (var moduleMethods in types.SelectMany(type => type.Methods.Where(md => md.HasMethodBody))) 47 | { 48 | for (int i = 0; i < moduleMethods.CilMethodBody.Instructions.Count; i++) 49 | { 50 | CilInstruction methodInstructions = moduleMethods.CilMethodBody.Instructions[i]; 51 | if (methodInstructions.OpCode.Code != CilCode.Call || methodInstructions.Operand is not MethodDefinition) 52 | continue; 53 | 54 | MethodDefinition proxyMethod = (MethodDefinition)methodInstructions.Operand; 55 | if (proxyMethod.Signature.ReturnType.ElementType != ElementType.String) 56 | continue; 57 | 58 | CilInstructionCollection proxyMethodInstructions = (proxyMethod).CilMethodBody.Instructions; 59 | if (proxyMethodInstructions.Count != 11 || ((MethodDefinition)proxyMethodInstructions[9].Operand).MetadataToken.ToInt32() != resolveStringMethod) 60 | continue; 61 | 62 | moduleMethods.CilMethodBody.Instructions[i] = new CilInstruction(CilOpCodes.Ldstr, Encoding.UTF8.GetString(decryptArray, proxyMethodInstructions[7].GetLdcI4Constant(), proxyMethodInstructions[8].GetLdcI4Constant())); 63 | Console.WriteLine(moduleMethods.CilMethodBody.Instructions[i]); 64 | } 65 | } 66 | new ManagedPEFileBuilder().CreateFile(new ManagedPEImageBuilder().CreateImage(module).ConstructedImage).Write("out.exe"); 67 | } 68 | 69 | } 70 | } 71 | -------------------------------------------------------------------------------- /ThemidaStringDecryptor/ThemidaStringDecryptor.csproj: -------------------------------------------------------------------------------- 1 | 2 | 3 | 4 | Exe 5 | net5.0 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | --------------------------------------------------------------------------------