public virtual void Init(
bool forEncryption,
ICipherParameters parameters)
{
this.forEncryption = forEncryption;
byte[] nonce;
ICipherParameters keyParam;
if (parameters is AeadParameters)
{
AeadParameters param = (AeadParameters)parameters;
nonce = param.GetNonce();
initialAssociatedText = param.GetAssociatedText();
macSize = param.MacSize / 8;
keyParam = param.Key;
}
else if (parameters is ParametersWithIV)
{
ParametersWithIV param = (ParametersWithIV)parameters;
nonce = param.GetIV();
initialAssociatedText = null;
macSize = mac.GetMacSize() / 2;
keyParam = param.Parameters;
}
else
{
throw new ArgumentException("invalid parameters passed to EAX");
}
byte[] tag = new byte[blockSize];
// Key reuse implemented in CBC mode of underlying CMac
mac.Init(keyParam);
tag[blockSize - 1] = (byte)Tag.N;
mac.BlockUpdate(tag, 0, blockSize);
mac.BlockUpdate(nonce, 0, nonce.Length);
mac.DoFinal(nonceMac, 0);
tag[blockSize - 1] = (byte)Tag.H;
mac.BlockUpdate(tag, 0, blockSize);
if (initialAssociatedText != null)
{
ProcessAadBytes(initialAssociatedText, 0, initialAssociatedText.Length);
}
// Same BlockCipher underlies this and the mac, so reuse last key on cipher
cipher.Init(true, new ParametersWithIV(null, nonceMac));
}
