internal static void TestTampering(ITest test, IAeadCipher cipher, ICipherParameters parameters)
{
byte[] plaintext = new byte[1000];
for (int i = 0; i < plaintext.Length; i++)
{
plaintext[i] = (byte)i;
}
cipher.Init(true, parameters);
byte[] ciphertext = new byte[cipher.GetOutputSize(plaintext.Length)];
int len = cipher.ProcessBytes(plaintext, 0, plaintext.Length, ciphertext, 0);
cipher.DoFinal(ciphertext, len);
int macLength = cipher.GetMac().Length;
// Test tampering with a single byte
cipher.Init(false, parameters);
byte[] tampered = new byte[ciphertext.Length];
byte[] output = new byte[plaintext.Length];
Array.Copy(ciphertext, 0, tampered, 0, tampered.Length);
tampered[0] += 1;
cipher.ProcessBytes(tampered, 0, tampered.Length, output, 0);
try
{
cipher.DoFinal(output, 0);
throw new TestFailedException(
new SimpleTestResult(false, test + " : tampering of ciphertext not detected."));
}
catch (InvalidCipherTextException e)
{
// Expected
}
// Test truncation of ciphertext to < tag length
cipher.Init(false, parameters);
byte[] truncated = new byte[macLength - 1];
Array.Copy(ciphertext, 0, truncated, 0, truncated.Length);
cipher.ProcessBytes(truncated, 0, truncated.Length, output, 0);
try
{
cipher.DoFinal(output, 0);
Fail(test, "tampering of ciphertext not detected.");
}
catch (InvalidCipherTextException e)
{
// Expected
}
}
/**
* return the size of the output buffer required for an update plus a
* doFinal with an input of len bytes.
*
* @param len the length of the input.
* @return the space required to accommodate a call to update and doFinal
* with len bytes of input.
*/
public override int GetOutputSize(
int length)
{
return(cipher.GetOutputSize(length));
}