def pad(n,replace: true)
      if padding? && replace
          strip_padding.pad(n)
      else
        pad = [n] * n
        return CryptBuffer(bytes + pad )
      end
    end
def pad(n,replace: true)
      if padding? && replace
          strip_padding.pad(n)
      else
        pad = [n] * n
        return CryptBuffer(bytes + pad )
      end
    end
pad an existing buffer with the given amount of bytes
 If a padding already exists, replace: decides whether or not
 to replace it