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private readonly byte[] key = new byte[] { xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx };
private readonly byte[] iv = new byte[] { xx, xx, xx, xx, xx, xx, xx, xx };                    

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string input = "12345";

MemoryStream mstream = new MemoryStream();
CryptoStream cstream = new CryptoStream(mstream, new TripleDESCryptoServiceProvider().CreateEncryptor(this.key, this.iv), CryptoStreamMode.Write);

byte[] toEncrypt = new UnicodeEncoding().GetBytes(input);
cstream.Write(toEncrypt, 0, toEncrypt.Length);
cstream.FlushFinalBlock();
byte[] ret = mstream.ToArray();
                        
cstream.Close();
mstream.Close();

RegistryKey wreg = Registry.CurrentUser.CreateSubKey("Software\\Test");
wreg.SetValue("testentry", ret);                    

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RegistryKey regreader = Registry.CurrentUser.OpenSubKey("Software\\Test", true);

byte[] rread = (byte[])regreader.GetValue("testentry");

MemoryStream nmstream = new MemoryStream();
CryptoStream ncstream = new CryptoStream(nmstream, new TripleDESCryptoServiceProvider().CreateDecryptor(this.key, this.iv), CryptoStreamMode.Read);
byte[] fromEncrypt = new byte[rread.Length];

ncstream.Read(fromEncrypt, 0, fromEncrypt.Length);  // Hier bekomme ich den Fehler "Bad Data"

string result = new UnicodeEncoding().GetString(fromEncrypt);                    

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wreg.SetValue("testentry", ret, RegistryValueKind.Binary);