| CPC H04L 63/083 (2013.01) | 14 Claims |

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1. A terminal device comprising:
a communication unit connected to a network; and
a processor, wherein the processor is configured to:
send a challenge to an authenticator;
receive the challenge with a signature and a public key from the authenticator;
perform signature verification using the public key;
directly provide a verification result of the signature to an authentication server via the communication unit;
receive a first challenge sent from the authentication server via the communication unit;
send a second challenge different from the first challenge to the authenticator;
receive a signature of the second challenge and a public key from the authenticator;
generate a signature of the first challenge when authentication is successful as a result of performing signature verification using the public key; and
return the signature of the first challenge to the authentication server via the communication unit as a response.
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