401 lines
11 KiB
C#
401 lines
11 KiB
C#
/*
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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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using System.Collections.Generic;
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using System.IO;
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using System.IO.Compression;
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using System.Security.Cryptography;
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using Mono.Cecil;
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using Mono.Cecil.Cil;
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using de4dot.blocks;
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namespace de4dot.code.deobfuscators.CryptoObfuscator {
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class ResourceDecrypter {
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const int BUFLEN = 0x8000;
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ModuleDefinition module;
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TypeDefinition resourceDecrypterType;
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byte[] buffer1 = new byte[BUFLEN];
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byte[] buffer2 = new byte[BUFLEN];
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byte desEncryptedFlag;
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byte deflatedFlag;
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byte bitwiseNotEncryptedFlag;
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FrameworkType frameworkType;
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bool flipFlagsBits;
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int skipBytes;
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public ResourceDecrypter(ModuleDefinition module, ISimpleDeobfuscator simpleDeobfuscator) {
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this.module = module;
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frameworkType = DotNetUtils.getFrameworkType(module);
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find(simpleDeobfuscator);
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}
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void find(ISimpleDeobfuscator simpleDeobfuscator) {
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switch (frameworkType) {
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case FrameworkType.Desktop:
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if (module.Runtime >= TargetRuntime.Net_2_0)
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findDesktopOrCompactFramework();
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else
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findDesktopOrCompactFrameworkV1();
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break;
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case FrameworkType.Silverlight:
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findSilverlight();
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break;
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case FrameworkType.CompactFramework:
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if (module.Runtime >= TargetRuntime.Net_2_0) {
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if (findDesktopOrCompactFramework())
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break;
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}
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findDesktopOrCompactFrameworkV1();
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break;
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}
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initializeHeaderInfo(simpleDeobfuscator);
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}
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static string[] requiredTypes = new string[] {
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"System.IO.MemoryStream",
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"System.Object",
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"System.Int32",
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};
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bool findDesktopOrCompactFramework() {
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resourceDecrypterType = null;
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foreach (var type in module.Types) {
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if (type.Fields.Count != 5)
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continue;
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if (!new FieldTypes(type).exactly(requiredTypes))
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continue;
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var cctor = DotNetUtils.getMethod(type, ".cctor");
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if (cctor == null)
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continue;
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if (!checkCctor(cctor))
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continue;
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resourceDecrypterType = type;
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return true;
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}
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return false;
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}
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bool checkCctor(MethodDefinition cctor) {
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if (cctor.Body == null)
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return false;
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int stsfldCount = 0;
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foreach (var instr in cctor.Body.Instructions) {
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if (instr.OpCode.Code == Code.Stsfld) {
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var field = instr.Operand as FieldReference;
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if (!MemberReferenceHelper.compareTypes(cctor.DeclaringType, field.DeclaringType))
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return false;
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stsfldCount++;
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}
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}
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return stsfldCount >= cctor.DeclaringType.Fields.Count;
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}
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static string[] requiredLocals_v1 = new string[] {
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"System.Boolean",
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"System.Byte",
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"System.Byte[]",
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"System.Int32",
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"System.Security.Cryptography.DESCryptoServiceProvider",
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};
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bool findDesktopOrCompactFrameworkV1() {
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resourceDecrypterType = null;
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foreach (var type in module.Types) {
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if (type.Fields.Count != 0)
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continue;
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var method = getDecrypterMethod(type);
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if (method == null)
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continue;
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if (!new LocalTypes(method).exactly(requiredLocals_v1))
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continue;
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if (!DotNetUtils.callsMethod(method, "System.Int64", "()"))
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continue;
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if (!DotNetUtils.callsMethod(method, "System.Int32", "(System.Byte[],System.Int32,System.Int32)"))
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continue;
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if (!DotNetUtils.callsMethod(method, "System.Void", "(System.Array,System.Int32,System.Array,System.Int32,System.Int32)"))
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continue;
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if (!DotNetUtils.callsMethod(method, "System.Security.Cryptography.ICryptoTransform", "()"))
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continue;
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if (!DotNetUtils.callsMethod(method, "System.Byte[]", "(System.Byte[],System.Int32,System.Int32)"))
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continue;
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resourceDecrypterType = type;
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return true;
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}
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return false;
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}
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static string[] requiredLocals_sl = new string[] {
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"System.Byte",
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"System.Byte[]",
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"System.Int32",
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};
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void findSilverlight() {
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foreach (var type in module.Types) {
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if (type.Fields.Count > 0)
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continue;
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if (type.HasNestedTypes || type.HasGenericParameters)
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continue;
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var method = getDecrypterMethod(type);
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if (method == null)
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continue;
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if (!new LocalTypes(method).exactly(requiredLocals_sl))
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continue;
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resourceDecrypterType = type;
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break;
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}
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}
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void initializeHeaderInfo(ISimpleDeobfuscator simpleDeobfuscator) {
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skipBytes = 0;
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if (resourceDecrypterType != null) {
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if (updateFlags(getDecrypterMethod(), simpleDeobfuscator))
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return;
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}
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desEncryptedFlag = 1;
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deflatedFlag = 2;
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bitwiseNotEncryptedFlag = 4;
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}
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static bool checkFlipBits(MethodDefinition method) {
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var instrs = method.Body.Instructions;
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for (int i = 0; i < instrs.Count - 1; i++) {
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var ldloc = instrs[i];
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if (!DotNetUtils.isLdloc(ldloc))
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continue;
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var local = DotNetUtils.getLocalVar(method.Body.Variables, ldloc);
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if (local == null || !local.VariableType.IsPrimitive)
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continue;
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var not = instrs[i + 1];
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if (not.OpCode.Code != Code.Not)
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continue;
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return true;
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}
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return false;
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}
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bool updateFlags(MethodDefinition method, ISimpleDeobfuscator simpleDeobfuscator) {
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if (method == null || method.Body == null)
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return false;
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var constants = new List<int>();
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simpleDeobfuscator.deobfuscate(method);
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var instructions = method.Body.Instructions;
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for (int i = 2; i < instructions.Count; i++) {
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var and = instructions[i];
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if (and.OpCode.Code != Code.And)
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continue;
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var ldci4 = instructions[i - 1];
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if (!DotNetUtils.isLdcI4(ldci4))
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continue;
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int flagValue = DotNetUtils.getLdcI4Value(ldci4);
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if (!isFlag(flagValue))
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continue;
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var ldloc = instructions[i - 2];
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if (!DotNetUtils.isLdloc(ldloc))
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continue;
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var local = DotNetUtils.getLocalVar(method.Body.Variables, ldloc);
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if (!local.VariableType.IsPrimitive)
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continue;
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constants.Add(flagValue);
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}
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flipFlagsBits = checkFlipBits(method);
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skipBytes = getHeaderSkipBytes(method);
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switch (frameworkType) {
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case FrameworkType.Desktop:
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if (module.Runtime >= TargetRuntime.Net_2_0) {
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if (constants.Count == 2) {
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desEncryptedFlag = (byte)constants[0];
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deflatedFlag = (byte)constants[1];
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return true;
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}
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}
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else {
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if (constants.Count == 1) {
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desEncryptedFlag = (byte)constants[0];
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return true;
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}
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}
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break;
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case FrameworkType.Silverlight:
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if (constants.Count == 1) {
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bitwiseNotEncryptedFlag = (byte)constants[0];
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return true;
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}
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break;
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case FrameworkType.CompactFramework:
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if (constants.Count == 1) {
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desEncryptedFlag = (byte)constants[0];
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return true;
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}
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break;
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}
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return false;
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}
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static int getHeaderSkipBytes(MethodDefinition method) {
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var instrs = method.Body.Instructions;
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for (int i = 0; i < instrs.Count - 1; i++) {
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var ldci4 = instrs[i];
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if (!DotNetUtils.isLdcI4(ldci4))
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continue;
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if (DotNetUtils.getLdcI4Value(ldci4) != 2)
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continue;
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var blt = instrs[i + 1];
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if (blt.OpCode.Code != Code.Blt && blt.OpCode.Code != Code.Blt_S)
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continue;
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return 1;
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}
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return 0;
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}
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static bool isFlag(int value) {
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for (uint tmp = (uint)value; tmp != 0; tmp >>= 1) {
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if ((tmp & 1) != 0)
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return tmp == 1;
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}
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return false;
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}
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MethodDefinition getDecrypterMethod() {
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return getDecrypterMethod(resourceDecrypterType);
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}
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static MethodDefinition getDecrypterMethod(TypeDefinition type) {
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foreach (var method in type.Methods) {
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if (DotNetUtils.isMethod(method, "System.Byte[]", "(System.IO.Stream)"))
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return method;
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if (DotNetUtils.isMethod(method, "System.Byte[]", "(System.Int32,System.IO.Stream)"))
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return method;
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}
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return null;
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}
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public byte[] decrypt(Stream resourceStream) {
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byte flags = (byte)resourceStream.ReadByte();
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if (flipFlagsBits)
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flags = (byte)~flags;
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Stream sourceStream = resourceStream;
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int sourceStreamOffset = 1;
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bool didSomething = false;
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sourceStream.Position += skipBytes;
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sourceStreamOffset += skipBytes;
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byte allFlags = (byte)(desEncryptedFlag | deflatedFlag | bitwiseNotEncryptedFlag);
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if ((flags & ~allFlags) != 0)
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Log.w("Found unknown resource encryption flags: 0x{0:X2}", flags);
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if ((flags & desEncryptedFlag) != 0) {
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var memStream = new MemoryStream((int)resourceStream.Length);
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using (var provider = new DESCryptoServiceProvider()) {
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var iv = new byte[8];
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sourceStream.Read(iv, 0, 8);
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provider.IV = iv;
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provider.Key = getKey(sourceStream);
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using (var transform = provider.CreateDecryptor()) {
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while (true) {
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int count = sourceStream.Read(buffer1, 0, buffer1.Length);
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if (count <= 0)
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break;
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int count2 = transform.TransformBlock(buffer1, 0, count, buffer2, 0);
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memStream.Write(buffer2, 0, count2);
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}
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var finalData = transform.TransformFinalBlock(buffer1, 0, 0);
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memStream.Write(finalData, 0, finalData.Length);
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}
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}
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sourceStream = memStream;
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sourceStreamOffset = 0;
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didSomething = true;
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}
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if ((flags & deflatedFlag) != 0) {
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var memStream = new MemoryStream((int)resourceStream.Length);
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sourceStream.Position = sourceStreamOffset;
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using (var inflater = new DeflateStream(sourceStream, CompressionMode.Decompress)) {
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while (true) {
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int count = inflater.Read(buffer1, 0, buffer1.Length);
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if (count <= 0)
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break;
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memStream.Write(buffer1, 0, count);
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}
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}
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sourceStream = memStream;
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sourceStreamOffset = 0;
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didSomething = true;
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}
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if ((flags & bitwiseNotEncryptedFlag) != 0) {
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var memStream = new MemoryStream((int)resourceStream.Length);
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sourceStream.Position = sourceStreamOffset;
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for (int i = sourceStreamOffset; i < sourceStream.Length; i++)
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memStream.WriteByte((byte)~sourceStream.ReadByte());
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sourceStream = memStream;
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sourceStreamOffset = 0;
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didSomething = true;
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}
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if (didSomething && sourceStream is MemoryStream) {
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var memStream = (MemoryStream)sourceStream;
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return memStream.ToArray();
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}
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else {
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int len = (int)(sourceStream.Length - sourceStream.Position);
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byte[] data = new byte[len];
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sourceStream.Read(data, 0, len);
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return data;
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}
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}
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byte[] getKey(Stream resourceStream) {
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byte[] key = new byte[8];
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resourceStream.Read(key, 0, key.Length);
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for (int i = 0; i < key.Length; i++) {
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if (key[i] != 0)
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return key;
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}
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key = module.Assembly.Name.PublicKeyToken;
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if (key == null)
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throw new ApplicationException("PublicKeyToken is null, can't decrypt resources");
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return key;
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}
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}
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}
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