À l'aide de Rijndael pour crypter/décrypter des fichiers

J'ai besoin de transférer des fichiers xml et ils doivent être chiffrées. J'ai trouvé quelques exemples pense que je suis proche, mais quand j'déchiffrer le fichier je me retrouve avec des caractères indésirables. Il y a quelques posts à ce sujet mais je n'ai vu aucun qui va exactement de l'aide. Voici le chiffrer et de déchiffrer le code.

private void EncryptFile(string inputFile, string outputFile, string key) {
try {
byte[] keyBytes;
keyBytes = Encoding.Unicode.GetBytes(key);
Rfc2898DeriveBytes derivedKey = new Rfc2898DeriveBytes(key, keyBytes);
RijndaelManaged rijndaelCSP = new RijndaelManaged();
rijndaelCSP.Key = derivedKey.GetBytes(rijndaelCSP.KeySize / 8);
rijndaelCSP.IV = derivedKey.GetBytes(rijndaelCSP.BlockSize / 8);
ICryptoTransform encryptor = rijndaelCSP.CreateEncryptor();
FileStream inputFileStream = new FileStream(inputFile, FileMode.Open, FileAccess.Read);
byte[] inputFileData = new byte[(int)inputFileStream.Length];
inputFileStream.Read(inputFileData, 0, (int)inputFileStream.Length);
FileStream outputFileStream = new FileStream(outputFile, FileMode.Create, FileAccess.Write);
CryptoStream encryptStream = new CryptoStream(outputFileStream, encryptor, CryptoStreamMode.Write);
encryptStream.Write(inputFileData, 0, (int)inputFileStream.Length);
encryptStream.FlushFinalBlock();
rijndaelCSP.Clear();
encryptStream.Close();
inputFileStream.Close();
outputFileStream.Close();
}
catch (Exception ex) {
MessageBox.Show(ex.Message, "Encryption Failed!", MessageBoxButtons.OK, MessageBoxIcon.Error);
return;
}
MessageBox.Show("File Encryption Complete!");
}
private void DecryptFile(string inputFile, string outputFile, string key) {
try {
byte[] keyBytes = Encoding.Unicode.GetBytes(key);
Rfc2898DeriveBytes derivedKey = new Rfc2898DeriveBytes(key, keyBytes);
RijndaelManaged rijndaelCSP = new RijndaelManaged();
rijndaelCSP.Key = derivedKey.GetBytes(rijndaelCSP.KeySize / 8);
rijndaelCSP.IV = derivedKey.GetBytes(rijndaelCSP.BlockSize / 8);
ICryptoTransform decryptor = rijndaelCSP.CreateDecryptor();
FileStream inputFileStream = new FileStream(inputFile, FileMode.Open, FileAccess.Read);
CryptoStream decryptStream = new CryptoStream(inputFileStream, decryptor, CryptoStreamMode.Read);
byte[] inputFileData = new byte[(int)inputFileStream.Length];
decryptStream.Read(inputFileData, 0, (int)inputFileStream.Length);
FileStream outputFileStream = new FileStream(outputFile, FileMode.Create, FileAccess.Write);
outputFileStream.Write(inputFileData, 0, inputFileData.Length);
outputFileStream.Flush();
rijndaelCSP.Clear();
decryptStream.Close();
inputFileStream.Close();
outputFileStream.Close();
}
catch (Exception ex) {
MessageBox.Show(ex.Message, "Decryption Failed!", MessageBoxButtons.OK, MessageBoxIcon.Error);
return;
}
MessageBox.Show("File Decryption Complete!");
}

Je me retrouve avec

<?xml version="1.0" encoding="UTF-8"?>
<transaction>
<header>
<qOrderNumber></qOrderNumber>
<qRequestDate></qRequestDate>
<testOrder></testOrder>
<qCustomerNumber></qCustomerNumber>
<transactionStatus></transactionStatus>
</header>
<lines>
<line>
<productID></productID>
<serialNumber></serialNumber>
</line>
<line> 
<productID></productID>
<serialNumber></serialNumber>
</line>
</lines>
</transaction>NULNULNULNULNULNUL