iOS Question Hmac SHA512 question.

Public Sub HMACSHA512(key As String, input As String, key_is_hex_string As Boolean) As String
    Dim no As NativeObject = Me
    Dim keyb() As Byte
    Dim bc As ByteConverter
    If key_is_hex_string Then
        keyb = bc.HexToBytes(key)
    Else
        keyb = key.GetBytes("UTF8")
    End If
    Dim res As Object = no.RunMethod("hmacForKeyAndData::", Array(no.ArrayToNSData(keyb), no.ArrayToNSData(input.GetBytes("utf8"))))
    Dim resb() As Byte = no.NSDataToArray(res)
    Return bc.HexFromBytes(resb).ToLowerCase
End Sub