/// <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));
}
private void btnDecrypt_Click(object sender, EventArgs e)
{
string ToDecrypt = "";
try
{
try { ToDecrypt = FilePath + lbFiles.SelectedItem.ToString(); }
catch (Exception) { MessageBox.Show("You must select an item to encrypt or decrypt!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error); return; }
if (string.IsNullOrWhiteSpace(txtPassword.Text))
{
MessageBox.Show("You must enter a password to decrypt or encrypt files!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error); return;
}
string Password = txtPassword.Text;
if (Path.GetExtension(ToDecrypt).ToLower() == ".locked")
{
}
else
{
MessageBox.Show("File is already decrypted!", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error); return;
}
string Output = FilePath + Path.GetFileNameWithoutExtension(ToDecrypt);
Rijndael.Decrypt(ToDecrypt, Output, txtPassword.Text, KS);
File.Delete(ToDecrypt);
WriteToConsole("Decrypted file successfully");
} catch { File.Delete(FilePath + Path.GetFileNameWithoutExtension(ToDecrypt)); }
}