Abstract: A communication system is provided, including a plurality of terminal devices and a root certification authority. Each of the plurality of terminal devices includes a certification authority key generation unit, a certification authority public key certificate acquisition unit that acquires a certification authority public key certificate, a certification authority key storage unit, a transmission unit, and a verification unit that verifies the certification authority public key certificate with a root certification authority public key certificate, and verifies a user in a case where the verification succeeds. The root certification authority includes a root certification authority key storage unit, a communication unit, and a certification authority public key certificate generation unit that generates the certification authority public key certificate by encrypting the certification authority public key with the root certification authority secret key.

Abstract: A communication device includes: a first subscriber identification unit that stores first subscriber identification unit identification information associated with user identification information; and a communication unit that communicates with another communication device, the other communication device including a second subscriber identification unit that stores second subscriber identification unit identification information associated with user identification information.

Abstract: A communication system is provided, including a plurality of terminal devices and a root certification authority. Each of the plurality of terminal devices includes a certification authority key generation unit, a certification authority public key certificate acquisition unit that acquires a certification authority public key certificate, a certification authority key storage unit, a transmission unit, and a verification unit that verifies the certification authority public key certificate with a root certification authority public key certificate, and verifies a user in a case where the verification succeeds. The root certification authority includes a root certification authority key storage unit, a communication unit, and a certification authority public key certificate generation unit that generates the certification authority public key certificate by encrypting the certification authority public key with the root certification authority secret key.

Abstract: A communication device includes: a first subscriber identification unit that stores first subscriber identification unit identification information associated with user identification information; and a communication unit that communicates with another communication device, the other communication device including a second subscriber identification unit that stores second subscriber identification unit identification information associated with user identification information.

Abstract: A communication system and a security assurance device are proposed, which are capable of assuring that a target party for communication is implementing security countermeasures. A server 3 transmits information 104 necessary for AC issuance to a security assurance authority 2. The security assurance authority 2 verifies the security of the server 3 during communication based upon this information necessary for AC issuance 104. And, when the security of the server 3 during communication is confirmed, the security assurance authority 2 issues an AC 105 which proves the security of the server 3 during communication, and transmits it to the server 3. Upon receipt of this AC 105, the server 3 transmits the AC 105 to a client 4, according to a connection request from the client 4. And, upon receipt of this AC 105, the client 4 verifies the security during communication of the server 3, based upon the AC 105.

Abstract: A communication system and a security assurance device are proposed, which are capable of assuring that a target party for communication is implementing security countermeasures. A server 3 transmits information 104 necessary for AC issuance to a security assurance authority 2. The security assurance authority 2 verifies the security of the server 3 during communication based upon this information necessary for AC issuance 104. And, when the security of the server 3 during communication is confirmed, the security assurance authority 2 issues an AC 105 which proves the security of the server 3 during communication, and transmits it to the server 3. Upon receipt of this AC 105, the server 3 transmits the AC 105 to a client 4, according to a connection request from the client 4. And, upon receipt of this AC 105, the client 4 verifies the security during communication of the server 3, based upon the AC 105.