101 lines
2.6 KiB
C#
101 lines
2.6 KiB
C#
/*
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Copyright (C) 2011-2015 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.Text;
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using dnlib.DotNet;
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using de4dot.blocks;
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namespace de4dot.code.deobfuscators.Xenocode {
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class StringDecrypter {
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const int STRING_DECRYPTER_KEY_CONST = 1789;
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ModuleDefMD module;
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TypeDef stringDecrypterType;
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MethodDef stringDecrypterMethod;
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public bool Detected {
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get { return stringDecrypterMethod != null; }
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}
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public TypeDef Type {
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get { return stringDecrypterType; }
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}
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public MethodDef Method {
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get { return stringDecrypterMethod; }
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}
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public StringDecrypter(ModuleDefMD module) {
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this.module = module;
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}
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public void Find() {
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foreach (var type in module.Types) {
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if (type.HasFields)
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continue;
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if (type.Methods.Count < 1 || type.Methods.Count > 3)
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continue;
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if (type.HasProperties || type.HasEvents)
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continue;
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MethodDef method = null;
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foreach (var m in type.Methods) {
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if (m.Name == ".ctor" || m.Name == ".cctor")
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continue;
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if (DotNetUtils.IsMethod(m, "System.String", "(System.String,System.Int32)")) {
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method = m;
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continue;
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}
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method = null;
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break;
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}
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if (method == null || method.Body == null)
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continue;
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bool foundConstant = false;
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foreach (var instr in method.Body.Instructions) {
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if (instr.IsLdcI4() && instr.GetLdcI4Value() == STRING_DECRYPTER_KEY_CONST) {
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foundConstant = true;
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break;
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}
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}
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if (!foundConstant)
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continue;
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stringDecrypterType = type;
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stringDecrypterMethod = method;
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break;
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}
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}
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public string Decrypt(string es, int magic) {
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int newLen = es.Length / 4;
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var sb = new StringBuilder(newLen);
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for (int i = 0; i < newLen * 4; i += 4) {
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char c = (char)((es[i] - 'a') +
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((es[i + 1] - 'a') << 4) +
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((es[i + 2] - 'a') << 8) +
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((es[i + 3] - 'a') << 12) - magic);
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magic += STRING_DECRYPTER_KEY_CONST;
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sb.Append(c);
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}
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return sb.ToString();
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}
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}
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}
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