context: /*
      Copyright (C) 2011-2015 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;
  using dnlib.IO;
  using de4dot.blocks;
  
  namespace de4dot.code.deobfuscators.CodeVeil {
  	class MethodsDecrypter {
  		MainType mainType;
  		IDecrypter decrypter;
  
  		interface IDecrypter {
  			void Initialize(byte[] methodsData);
  			bool Decrypt(ref DataReader fileDataReader, DumpedMethod dm);
  		}
  
  		class Decrypter : IDecrypter {
  			DataReader methodsDataReader;
  
  			public virtual void Initialize(byte[] methodsData) => methodsDataReader = ByteArrayDataReaderFactory.CreateReader(methodsData);
  
  			public virtual bool Decrypt(ref DataReader fileDataReader, DumpedMethod dm) {
  				if (fileDataReader.ReadByte() != 0x2A)
  					return false;	// Not a RET
  				methodsDataReader.Position = fileDataReader.ReadCompressedUInt32();
  
  				dm.mhCodeSize = methodsDataReader.ReadCompressedUInt32();
  				dm.code = methodsDataReader.ReadBytes((int)dm.mhCodeSize);
  				if ((dm.mhFlags & 8) != 0)
  					dm.extraSections = MethodBodyParser.ReadExtraSections(ref methodsDataReader);
  
  				if (!DecryptCode(dm))
  					return false;
  
  				return true;
  			}
  
  			protected virtual bool DecryptCode(DumpedMethod dm) => true;
  		}
  
  		class DecrypterV5 : Decrypter {
  			byte[] decryptKey;
  
  			public override void Initialize(byte[] methodsData) {
  				var data = DeobUtils.Inflate(methodsData, true);
  				decryptKey = BitConverter.GetBytes(BitConverter.ToUInt32(data, 0));
  
  				var newMethodsData = new byte[data.Length - 4];
  				Array.Copy(data, 4, newMethodsData, 0, newMethodsData.Length);
  				base.Initialize(newMethodsData);
  			}
  
  			protected override bool DecryptCode(DumpedMethod dm) {
  				var code = dm.code;
  				for (int i = 0; i < code.Length; i++) {
  					for (int j = 0; j < 4 && i + j < code.Length; j++)
  						code[i + j] ^= decryptKey[j];
  				}
  
  				return true;
  			}
  		}
  
  		public bool Detected => decrypter != null;
  		public MethodsDecrypter(MainType mainType) => this.mainType = mainType;
  		public MethodsDecrypter(MainType mainType, MethodsDecrypter oldOne) => this.mainType = mainType;
  
  		public void Find() {
  			if (!mainType.Detected)
  				return;
  
  			switch (mainType.Version) {
  			case ObfuscatorVersion.Unknown:
  				break;
  
  			case ObfuscatorVersion.V3:
  			case ObfuscatorVersion.V4_0:
  			case ObfuscatorVersion.V4_1:
  				decrypter = new Decrypter();
  				break;
  
  			case ObfuscatorVersion.V5_0:
  				decrypter = new DecrypterV5();
  				break;
  
  			default:
  				throw new ApplicationException("Unknown version");
  			}
  		}
  
  		public bool Decrypt(byte[] fileData, ref DumpedMethods dumpedMethods) {
  			if (decrypter == null)
  				return false;
  
  			using (var peImage = new MyPEImage(fileData)) {
  				if (peImage.Sections.Count <= 0)
  					return false;
  
  				var methodsData = FindMethodsData(peImage, fileData);
  				if (methodsData == null)
  					return false;
  
  				decrypter.Initialize(methodsData);
  
  				dumpedMethods = CreateDumpedMethods(peImage, fileData, methodsData);
  				if (dumpedMethods == null)
  					return false;
  			}
  
  			return true;
  		}
  
  		DumpedMethods CreateDumpedMethods(MyPEImage peImage, byte[] fileData, byte[] methodsData) {
  			var dumpedMethods = new DumpedMethods();
  
  			/*var methodsDataReader = ByteArrayDataReaderFactory.CreateReader(methodsData);*/
  			var fileDataReader = ByteArrayDataReaderFactory.CreateReader(fileData);
  
  			var methodDef = peImage.Metadata.TablesStream.MethodTable;
  			for (uint rid = 1; rid <= methodDef.Rows; rid++) {
  				var dm = new DumpedMethod();
  
  				peImage.ReadMethodTableRowTo(dm, rid);
  				if (dm.mdRVA == 0)
  					continue;
  				uint bodyOffset = peImage.RvaToOffset(dm.mdRVA);
  
  				byte b = peImage.OffsetReadByte(bodyOffset);
  				uint codeOffset;
  				if ((b & 3) == 2) {
  					if (b != 2)
  						continue;	// not zero byte code size
  
  					dm.mhFlags = 2;
  					dm.mhMaxStack = 8;
  					dm.mhLocalVarSigTok = 0;
  					codeOffset = bodyOffset + 1;
  				}
  				else {
  					if (peImage.OffsetReadUInt32(bodyOffset + 4) != 0)
  						continue;	// not zero byte code size
  
  					dm.mhFlags = peImage.OffsetReadUInt16(bodyOffset);
  					dm.mhMaxStack = peImage.OffsetReadUInt16(bodyOffset + 2);
  					dm.mhLocalVarSigTok = peImage.OffsetReadUInt32(bodyOffset + 8);
  					codeOffset = bodyOffset + (uint)(dm.mhFlags >> 12) * 4;
  				}
  				fileDataReader.Position = codeOffset;
  
  				if (!decrypter.Decrypt(ref fileDataReader, dm))
  					continue;
  
  				dumpedMethods.Add(dm);
  			}
  
  			return dumpedMethods;
  		}
  
  		// xor eax, eax / inc eax / pop esi edi edx ecx ebx / leave / ret 0Ch or 10h
  		static byte[] initializeMethodEnd = new byte[] {
  			0x33, 0xC0, 0x40, 0x5E, 0x5F, 0x5A, 0x59, 0x5B, 0xC9, 0xC2,
  		};
  		byte[] FindMethodsData(MyPEImage peImage, byte[] fileData) {
  			var section = peImage.Sections[0];
  
  			var reader = ByteArrayDataReaderFactory.CreateReader(fileData);
  
  			const int RVA_EXECUTIVE_OFFSET = 1 * 4;
  			const int ENC_CODE_OFFSET = 6 * 4;
  			int lastOffset = Math.Min(fileData.Length, (int)(section.PointerToRawData + section.SizeOfRawData));
  			for (int offset = GetStartOffset(peImage); offset < lastOffset; ) {
  				offset = FindSig(fileData, offset, lastOffset, initializeMethodEnd);
  				if (offset < 0)
  					return null;
  				offset += initializeMethodEnd.Length;
  
  				short retImm16 = BitConverter.ToInt16(fileData, offset);
  				if (retImm16 != 0x0C && retImm16 != 0x10)
  					continue;
  				offset += 2;
  				if (offset + ENC_CODE_OFFSET + 4 > lastOffset)
  					return null;
  
  				// rva is 0 when the assembly has been embedded
  				uint rva = BitConverter.ToUInt32(fileData, offset + RVA_EXECUTIVE_OFFSET);
  				if (rva != 0 && mainType.Rvas.IndexOf(rva) < 0)
  					continue;
  
  				int relOffs = BitConverter.ToInt32(fileData, offset + ENC_CODE_OFFSET);
  				if (relOffs <= 0 || relOffs >= section.SizeOfRawData)
  					continue;
  				reader.Position = section.PointerToRawData + (uint)relOffs;
  
  				int size = (int)reader.ReadCompressedUInt32();
  				int endOffset = relOffs + size;
  				if (endOffset < relOffs || endOffset > section.SizeOfRawData)
  					continue;
  
  				return reader.ReadBytes(size);
  			}
  
  			return null;
  		}
  
  		int GetStartOffset(MyPEImage peImage) {
  			int minOffset = int.MaxValue;
  			foreach (var rva in mainType.Rvas) {
  				int rvaOffs = (int)peImage.RvaToOffset((uint)rva);
  
gt: 				if (rvaOffs < minOffset)