de4dot-cex/de4dot.code/deobfuscators/CliSecure/MethodsDecrypter.cs

/*
    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;
using System.Collections.Generic;
using Mono.MyStuff;

namespace de4dot.deobfuscators.CliSecure {
	class CodeHeader {
		public byte[] signature;
		public byte[] decryptionKey;
		public uint totalCodeSize;
		public uint numMethods;
		public uint methodDefTableOffset;
		public uint methodDefElemSize;
	}

	struct MethodInfo {
		public uint codeOffs, codeSize, flags, localVarSigTok;

		public MethodInfo(uint codeOffs, uint codeSize, uint flags, uint localVarSigTok) {
			this.codeOffs = codeOffs;
			this.codeSize = codeSize;
			this.flags = flags;
			this.localVarSigTok = localVarSigTok;
		}

		public override string ToString() {
			return string.Format("{0:X8} {1:X8} {2:X8} {3:X8}", codeOffs, codeSize, flags, localVarSigTok);
		}
	}

	class MethodsDecrypter {
		static byte[] SIGNATURE = new byte[16] { 0x08, 0x44, 0x65, 0xE1, 0x8C, 0x82, 0x13, 0x4C, 0x9C, 0x85, 0xB4, 0x17, 0xDA, 0x51, 0xAD, 0x25 };
		PE.PeImage peImage;
		CodeHeader codeHeader = new CodeHeader();
		uint endOfMetadata;

		public bool decrypt(PE.PeImage peImage, ref Dictionary<uint, DumpedMethod> dumpedMethods) {
			this.peImage = peImage;

			endOfMetadata = peImage.rvaToOffset(peImage.Cor20Header.metadataDirectory.virtualAddress + peImage.Cor20Header.metadataDirectory.size);
			uint offset = endOfMetadata;
			if (!readCodeHeader(offset))
				return false;

			var methodInfos = getMethodInfos(offset + 0x30 + codeHeader.totalCodeSize);
			var metadataTables = peImage.Cor20Header.createMetadataTables();
			var methodDefTable = metadataTables.getMetadataType(PE.MetadataIndex.iMethodDef);

			offset = methodDefTable.fileOffset - methodDefTable.totalSize;
			foreach (var methodInfo in methodInfos) {
				offset += methodDefTable.totalSize;
				if (methodInfo.flags == 0 || methodInfo.localVarSigTok == 0)
					continue;
				uint rva = peImage.offsetReadUInt32(offset);
				peImage.writeUint16(rva, (ushort)methodInfo.flags);
				peImage.writeUint32(rva + 8, methodInfo.localVarSigTok);
			}

			dumpedMethods = new Dictionary<uint, DumpedMethod>();
			offset = methodDefTable.fileOffset;
			for (int i = 0; i < methodInfos.Count; i++, offset += methodDefTable.totalSize) {
				var methodInfo = methodInfos[i];
				if (methodInfo.codeOffs == 0)
					continue;

				var dm = new DumpedMethod();
				dm.token = 0x06000001 + (uint)i;

				uint rva = peImage.offsetReadUInt32(offset);
				dm.mdImplFlags = peImage.offsetReadUInt16(offset + (uint)methodDefTable.fields[1].offset);
				dm.mdFlags = peImage.offsetReadUInt16(offset + (uint)methodDefTable.fields[2].offset);
				dm.mdName = peImage.offsetRead(offset + (uint)methodDefTable.fields[3].offset, methodDefTable.fields[3].size);
				dm.mdSignature = peImage.offsetRead(offset + (uint)methodDefTable.fields[4].offset, methodDefTable.fields[4].size);
				dm.mdParamList = peImage.offsetRead(offset + (uint)methodDefTable.fields[5].offset, methodDefTable.fields[5].size);

				dm.code = getDecryptedCode(methodInfo);

				if ((peImage.readByte(rva) & 3) == 2) {
					dm.mhFlags = 2;
					dm.mhMaxStack = 8;
					dm.mhCodeSize = (uint)dm.code.Length;
					dm.mhLocalVarSigTok = 0;
				}
				else {
					dm.mhFlags = peImage.readUInt16(rva);
					dm.mhMaxStack = peImage.readUInt16(rva + 2);
					dm.mhCodeSize = (uint)dm.code.Length;
					dm.mhLocalVarSigTok = peImage.readUInt32(rva + 8);
				}

				dumpedMethods[dm.token] = dm;
			}

			return true;
		}

		byte[] getDecryptedCode(MethodInfo methodInfo) {
			byte[] data = peImage.offsetReadBytes(endOfMetadata + methodInfo.codeOffs, (int)methodInfo.codeSize);
			for (int i = 0; i < data.Length; i++) {
				byte b = data[i];
				b ^= codeHeader.decryptionKey[(methodInfo.codeOffs - 0x30 + i) % 16];
				b ^= codeHeader.decryptionKey[(methodInfo.codeOffs - 0x30 + i + 7) % 16];
				data[i] = b;
			}

			int codeOffset, codeSize;
			if ((data[0] & 3) == 2) {
				codeOffset = 1;
				codeSize = data[0] >> 2;
			}
			else {
				codeOffset = 4 * (data[1] >> 4);
				codeSize = BitConverter.ToInt32(data, 4);
			}

			var code = new byte[codeSize];
			Array.Copy(data, codeOffset, code, 0, codeSize);
			return code;
		}

		bool readCodeHeader(uint offset) {
			codeHeader.signature = peImage.offsetReadBytes(offset, 16);
			if (!Utils.compare(SIGNATURE, codeHeader.signature))
				return false;
			codeHeader.decryptionKey = peImage.offsetReadBytes(offset + 0x10, 16);
			codeHeader.totalCodeSize = peImage.offsetReadUInt32(offset + 0x20);
			codeHeader.numMethods = peImage.offsetReadUInt32(offset + 0x24);
			codeHeader.methodDefTableOffset = peImage.offsetReadUInt32(offset + 0x28);
			codeHeader.methodDefElemSize = peImage.offsetReadUInt32(offset + 0x2C);

			if (codeHeader.totalCodeSize > 0x10000000)
				throw new ApplicationException("Invalid total code size");
			if (codeHeader.numMethods > 512*1024)
				throw new ApplicationException("Invalid num methods");

			return true;
		}

		List<MethodInfo> getMethodInfos(uint offset) {
			var methodInfos = new List<MethodInfo>((int)codeHeader.numMethods);
			for (int i = 0; i < (int)codeHeader.numMethods; i++, offset += 16) {
				uint codeOffs = peImage.offsetReadUInt32(offset);
				uint codeSize = peImage.offsetReadUInt32(offset + 4);
				uint flags = peImage.offsetReadUInt32(offset + 8);
				uint localVarSigTok = peImage.offsetReadUInt32(offset + 12);
				methodInfos.Add(new MethodInfo(codeOffs, codeSize, flags, localVarSigTok));
			}
			return methodInfos;
		}
	}
}