2012-05-26 06:52:38 +08:00
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/*
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Copyright (C) 2011-2012 de4dot@gmail.com
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This file is part of de4dot.
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de4dot is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
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(at your option) any later version.
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de4dot is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with de4dot. If not, see <http://www.gnu.org/licenses/>.
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*/
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using System;
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2012-11-02 22:57:11 +08:00
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using dot10.DotNet;
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using dot10.DotNet.Emit;
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2012-05-26 06:52:38 +08:00
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using de4dot.PE;
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using de4dot.blocks;
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namespace de4dot.code.deobfuscators.CodeWall {
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class MethodsDecrypter {
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static readonly byte[] newCodeHeader = new byte[6] { 0x2B, 4, 0, 0, 0, 0 };
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static readonly byte[] decryptKey = new byte[10] { 0x8D, 0xB5, 0x2C, 0x3A, 0x1F, 0xC7, 0x31, 0xC3, 0xCD, 0x47 };
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2012-11-08 17:40:58 +08:00
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ModuleDefMD module;
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IMethod initMethod;
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2012-05-26 06:52:38 +08:00
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public bool Detected {
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get { return initMethod != null; }
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}
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2012-11-08 17:40:58 +08:00
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public MethodsDecrypter(ModuleDefMD module) {
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2012-05-26 06:52:38 +08:00
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this.module = module;
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}
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public void find() {
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foreach (var cctor in DeobUtils.getInitCctors(module, 3)) {
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if (checkCctor(cctor))
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return;
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}
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}
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2012-11-02 22:57:11 +08:00
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bool checkCctor(MethodDef method) {
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2012-05-26 06:52:38 +08:00
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if (method == null || method.Body == null)
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return false;
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foreach (var instr in method.Body.Instructions) {
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if (instr.OpCode.Code != Code.Call)
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continue;
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2012-11-08 17:40:58 +08:00
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var calledMethod = instr.Operand as IMethod;
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2012-05-26 06:52:38 +08:00
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if (calledMethod == null)
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continue;
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if (calledMethod.DeclaringType.Scope == module)
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return false;
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if (calledMethod.FullName != "System.Void Q::X()")
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return false;
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initMethod = calledMethod;
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return true;
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}
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return false;
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}
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public bool decrypt(PeImage peImage, ref DumpedMethods dumpedMethods) {
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dumpedMethods = new DumpedMethods();
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bool decrypted = false;
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var metadataTables = peImage.Cor20Header.createMetadataTables();
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var methodDef = metadataTables.getMetadataType(MetadataIndex.iMethodDef);
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uint methodDefOffset = methodDef.fileOffset;
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for (int i = 0; i < methodDef.rows; i++, methodDefOffset += methodDef.totalSize) {
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uint bodyRva = peImage.offsetReadUInt32(methodDefOffset);
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if (bodyRva == 0)
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continue;
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uint bodyOffset = peImage.rvaToOffset(bodyRva);
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var dm = new DumpedMethod();
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dm.token = (uint)(0x06000001 + i);
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byte[] code, extraSections;
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peImage.Reader.BaseStream.Position = bodyOffset;
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var mbHeader = MethodBodyParser.parseMethodBody(peImage.Reader, out code, out extraSections);
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if (code.Length < 6 || code[0] != 0x2A || code[1] != 0x2A)
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continue;
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dm.code = code;
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dm.extraSections = extraSections;
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int seed = BitConverter.ToInt32(code, 2);
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Array.Copy(newCodeHeader, code, newCodeHeader.Length);
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if (seed == 0)
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decrypt(code);
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else
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decrypt(code, seed);
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2012-11-07 07:26:36 +08:00
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dm.mdRVA = peImage.offsetRead(methodDefOffset + (uint)methodDef.fields[0].offset, methodDef.fields[0].size);
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2012-05-26 06:52:38 +08:00
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dm.mdImplFlags = peImage.offsetReadUInt16(methodDefOffset + (uint)methodDef.fields[1].offset);
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dm.mdFlags = peImage.offsetReadUInt16(methodDefOffset + (uint)methodDef.fields[2].offset);
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dm.mdName = peImage.offsetRead(methodDefOffset + (uint)methodDef.fields[3].offset, methodDef.fields[3].size);
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dm.mdSignature = peImage.offsetRead(methodDefOffset + (uint)methodDef.fields[4].offset, methodDef.fields[4].size);
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dm.mdParamList = peImage.offsetRead(methodDefOffset + (uint)methodDef.fields[5].offset, methodDef.fields[5].size);
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dm.mhFlags = mbHeader.flags;
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dm.mhMaxStack = mbHeader.maxStack;
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dm.mhCodeSize = (uint)dm.code.Length;
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dm.mhLocalVarSigTok = mbHeader.localVarSigTok;
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dumpedMethods.add(dm);
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decrypted = true;
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}
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return decrypted;
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}
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void decrypt(byte[] data) {
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for (int i = 6; i < data.Length; i++)
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data[i] ^= decryptKey[i % decryptKey.Length];
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}
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void decrypt(byte[] data, int seed) {
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var key = new KeyGenerator(seed).generate(data.Length);
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for (int i = 6; i < data.Length; i++)
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data[i] ^= key[i];
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}
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public void deobfuscate(Blocks blocks) {
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if (initMethod == null)
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return;
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if (blocks.Method.Name != ".cctor")
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return;
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foreach (var block in blocks.MethodBlocks.getAllBlocks()) {
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var instrs = block.Instructions;
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for (int i = 0; i < instrs.Count; i++) {
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var instr = instrs[i];
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if (instr.OpCode.Code != Code.Call)
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continue;
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2012-11-08 17:40:58 +08:00
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var calledMethod = instr.Operand as IMethod;
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if (!MethodEqualityComparer.CompareDeclaringTypes.Equals(calledMethod, initMethod))
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2012-05-26 06:52:38 +08:00
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continue;
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block.remove(i, 1);
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i--;
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}
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}
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}
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}
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}
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