/// <summary>
/// Decrypts authenticated ciphertext using the Rijndael cipher in CBC mode with a password derived
/// HMAC SHA-512 salt.
/// </summary>
/// <param name="etmCiphertext">The EtM ciphertext to decrypt.</param>
/// <param name="password">The password to decrypt the EtM ciphertext with.</param>
/// <param name="keySize">The size of the cipher key used to create the EtM ciphertext.</param>
/// <returns>The plaintext.</returns>
public static new string Decrypt(byte[] etmCiphertext, string password, KeySize keySize)
{
// Generate AE keys
var keyRing = AeKeyRing.Generate(password);
// Extract the ciphertext and MAC from the EtM ciphertext
var mac = new byte[keyRing.MacKey.Length];
var ciphertext = new byte[etmCiphertext.Length - mac.Length];
using (var ms = new MemoryStream(etmCiphertext))
{
// Extract the ciphertext
ms.Read(ciphertext, 0, ciphertext.Length);
// Extract the MAC
ms.Read(mac, 0, mac.Length);
}
// Calculate the MAC from the ciphertext
var newMac = CalculateMac(ciphertext, keyRing.MacKey);
// Authenticate ciphertext
if (!mac.SequenceEqual(newMac))
{
throw new Exception("Authentication failed!");
}
// Decrypt the ciphertext
return(Rijndael.Decrypt(ciphertext, keyRing.CipherKey, keySize));
}
