public static byte[] HKDF(byte[] salt, byte[] prk, byte[] info, int length)
{
var hmac = new HmacSha256(salt);
var key = hmac.ComputeHash(prk);
return(HKDFSecondStep(key, info, length));
}
public static byte[] HKDFSecondStep(byte[] key, byte[] info, int length)
{
var hmac = new HmacSha256(key);
var infoAndOne = info.Concat(new byte[] { 0x01 }).ToArray();
var result = hmac.ComputeHash(infoAndOne);
if (result.Length > length)
{
Array.Resize(ref result, length);
}
return(result);
}