ZKDF(zkey, label):
  /* Calculate the blinding factor */
  PRK_h := HKDF-Extract("key-derivation", zkey)
  h := HKDF-Expand(PRK_h, label || "gns", 512 / 8)
  /* Ensure that h == h mod L */
  h := h mod L

  zkey' := h * zkey
  return zkey'