/// <inheritdoc/>
public byte[] Unprotect(string protectedData)
{
// Extract encrypted key and encrypted data
string[] parts = protectedData.Split(Separator);
if (parts.Length != 3)
{
throw new Exception("Invalid format of protected data");
}
byte[] encryptedStoredKey = CryptoUtils.Base64StringToBytes(parts[0]);
byte[] nonce = CryptoUtils.Base64StringToBytes(parts[1]);
byte[] protectedDataPart = CryptoUtils.Base64StringToBytes(parts[2]);
// Unprotect the random key with OS support
byte[] storedKey = null;
try
{
if (KeysExistInKeyStore())
{
Cipher cipher = Cipher.GetInstance("RSA/ECB/PKCS1Padding"); // ECB mode is not used by RSA
IKey privateKey = GetPrivateKeyFromKeyStore();
cipher.Init(CipherMode.DecryptMode, privateKey);
storedKey = cipher.DoFinal(encryptedStoredKey);
}
}
catch (Exception)
{
storedKey = null;
}
// Fallback to obfuscated key
if (storedKey == null)
{
storedKey = CryptoUtils.Deobfuscate(encryptedStoredKey, CryptoUtils.StringToSecureString(Obcake));
}
// Decrypt the data with the random key
ISymmetricEncryptionAlgorithm decryptor;
byte[] result;
try
{
decryptor = new BouncyCastleXChaCha20();
result = decryptor.Decrypt(protectedDataPart, storedKey, nonce);
}
catch (Exception)
{
// Fallback to twofish, which was used before 3.2021
decryptor = new BouncyCastleTwofishGcm();
result = decryptor.Decrypt(protectedDataPart, storedKey, nonce);
}
return(result);
}
public void EnsureCompatibilityToLibsodiumXChaCha20()
{
// Ensure that a once stored cipher can always be decrypted even after changes in the liberary.
// This cypher was created with libsodium.
string base64Cipher = "q8w/Zotsi3ZJp2eaAnFmMiAGgko+N2TkNgunS5+bDRNqrBBoN+XMQPSt7ojO4ODMP3Rf3aoYMNeJFL2/ZqK3AngIuQ==";
byte[] cipher = CryptoUtils.Base64StringToBytes(base64Cipher);
ISymmetricEncryptionAlgorithm decryptor = new BouncyCastleXChaCha20();
ICryptoRandomService randomGenerator = CommonMocksAndStubs.CryptoRandomService(88);
byte[] key = randomGenerator.GetRandomBytes(decryptor.ExpectedKeySize);
byte[] nonce = randomGenerator.GetRandomBytes(decryptor.ExpectedNonceSize);
string decryptedMessage = CryptoUtils.BytesToString(decryptor.Decrypt(cipher, key, nonce));
Assert.AreEqual("The brown fox jumps over the lazy 🐢🖐🏿 doc.", decryptedMessage);
}
