To provide a communication system capable of easily maintaining a state, wherein normal authentication can be permitted, while maintaining security.

When a lower level apparatus 20 is requested by a higher level apparatus 10 to conduct communication, the lower level apparatus 20 provides two kinds of digital certificates to which different valid terms are set as certificates for receiving authentication from the higher level apparatus 10, that is, the lower level apparatus 20 provides a regular public key certificate, whose valid term is shorter in the two certificates when communication is requested to a regular processing URL and provides a rescue public key certificate, whose valid term is longer in the two certificates when communication is requested to a rescue URL. Then when communication is conducted with the rescue URL, wherein the rescue public key certificate is provided, processings related to requirements, other than the requirements related to setting the regular public key certificate, are inhibited.

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