def next_cek(key)
      decrypted_key, new_alg = alg.next_cek(key, enc)
      new_jwe = JOSE::JWE.from_map(to_map)
      new_jwe.alg = new_alg
      return decrypted_key, new_jwe
    end
def next_cek(key)
      decrypted_key, new_alg = alg.next_cek(key, enc)
      new_jwe = JOSE::JWE.from_map(to_map)
      new_jwe.alg = new_alg
      return decrypted_key, new_jwe
    end
Returns the next `cek` using the `jwk` and the `"alg"` and `"enc"` specified by the `jwe`.

 @param [JOSE::JWK, [JOSE::JWK, JOSE::JWK]] key
 @return [[String, JOSE::JWE]]