/// <inheritdoc />
public string Decrypt(string input, out bool isLatestKey)
{
isLatestKey = false;
if (string.IsNullOrEmpty(input))
{
return(input);
}
byte[] initializationVector = new byte[16];
// Note: Each symbol in a Base32 string is 5 bits.
byte[] buffer = new byte[input.Length * 5 / 8];
if (Base32EncoderDecoder.TryBase32Decode(input, buffer))
{
using (MemoryStream memoryStream = new MemoryStream(buffer))
// Retrieve the IV from the encrypted string.
memoryStream.Read(initializationVector, 0, initializationVector.Length);
// Need just the text to decrypt now, ignoring the IV.
byte[] cipherText = buffer.Skip(initializationVector.Length).ToArray();
string decryptedString = null;
bool decryptionKeyFound = false;
// Try to find the key used in the encryption.
foreach (Key key in _aesEncryptionKeys)
{
if (TryDecryptStringFromBytes(
cipherText,
ConvertHexStringToByteArray(key.Value),
initializationVector,
out decryptedString))
{
decryptionKeyFound = true;
Debug.Assert(_aesEncryptionKeys[0] != null);
if (key.Value == _aesEncryptionKeys[0].Value)
{
isLatestKey = true;
}
break;
}
}
if (!decryptionKeyFound)
{
throw new CryptographicException(Resources.AESCryptographer_Decrypt_DecryptFailed_KeyNotFound);
}
return(decryptedString);
}
// If we get here, decryption failed.
throw new CryptographicException(
// ReSharper disable once AssignNullToNotNullAttribute
string.Format(Resources.AESCryptographer_Decrypt_DecryptFailed_InputNotBase32String, input));
}
/// <inheritdoc />
public string Encrypt(string input)
{
if (string.IsNullOrEmpty(input))
{
return(input);
}
using (AesCryptoServiceProvider aes = new AesCryptoServiceProvider())
{
Key encryptionKey = null;
bool addNewKey = true;
if (_aesEncryptionKeys.Count > 0)
{
// Check if there is any non-Expired keys to use.
bool nonExpiredKeysFound = _aesEncryptionKeys.Count(k => k.Expiry > DateTime.Now) > 0;
if (nonExpiredKeysFound)
{
encryptionKey = _aesEncryptionKeys[0];
addNewKey = false;
}
}
if (addNewKey)
{
const int defaultKeyLifeInDays = 7;
// Use the key automatically generated by the AesCryptoServiceProvider.
// Store it as a hex string.
string value = string.Concat(aes.Key.Select(b => b.ToString("x2")));
// For the expiry, use the number of days specified in the KeyLifeInDays property.
DateTime expiry = DateTime.Now.Add(
TimeSpan.FromDays(_provider != null ? _provider.KeyLifeInDays : defaultKeyLifeInDays));
encryptionKey = new Key(value, expiry);
_aesEncryptionKeys.Add(encryptionKey);
_aesEncryptionKeys = _aesEncryptionKeys.OrderByDescending(k => k.Expiry).ToList();
_provider?.AddKey(encryptionKey);
}
Debug.Assert(encryptionKey != null);
byte[] encrypted = EncryptStringToBytes(input, ConvertHexStringToByteArray(encryptionKey.Value), aes.IV);
return(Base32EncoderDecoder.Base32Encode(encrypted));
}
}
