/// <remarks>
/// Create keying material using a two stage generator
/// </remarks>
private byte[] GetBlock()
{
// generate seed; 2x input block per NIST sp800-90b
byte[] seed = _seedEngine.GetBytes((_hashEngine.BlockSize * 2));
if (_hashEngine.GetType().Equals(typeof(SHA512)) || _hashEngine.GetType().Equals(typeof(SHA256)))
{
// hmac key size is digest hash size: rfc 2104
byte[] key = _seedEngine.GetBytes(_hashEngine.DigestSize);
// set hmac to *not* dispose of underlying digest
using (HMAC mac = new HMAC(_hashEngine, key, false))
return(mac.ComputeMac(seed));
}
else
{
// other implemented digests do not require hmac
return(_hashEngine.ComputeHash(seed));
}
}