System and method for authentication

A non-transitory computer-readable medium with instructions stored therein which upon execution instruct at least one processor to:

• receive a subscription request from a user terminal, the subscription request including a group code and a plaintext e-mail address;
• store the plaintext e-mail address included in the subscription request in a table for subscription;
• when the group code and the plaintext e-mail address correspond to each other, perform a group authentication procedure on the user terminal and processing the group authentication procedure as being successful;
• when the group authentication procedure for the user terminal is processed successfully:
• issue an authentication key for the subscription request and storing the authentication key in the table for subscription;
• transmit the authentication key to the user terminal;
• receive, from the user terminal, member information including an encrypted plaintext e-mail address of the user with the authentication key;
• search the plaintext e-mail address using the authentication key in the table for subscription;
• encrypt the searched plaintext e-mail address using the same encryption logic used when an encrypted e-mail address recorded in the table for redundancy removal is encrypted;
• and
• check whether the encrypted searched plaintext e-mail address exists in a table for redundancy removal;
• when the encrypted searched plaintext e-mail address exists in the table for redundancy removal, transmit a redundancy message to the user terminal;
• when the encrypted searched plaintext e-mail address is not in the table for redundancy removal:
• issue a member session key and e-mail session key;
• store the encrypted searched plaintext e-mail address and e-mail session key in the table for redundancy removal;
• store the encrypted plaintext e-mail address in the member information and the member session key in a table for members;
• transmit the member session key and the e-mail session key, to the user terminal;
• and
• delete the data of the table for subscription for the subscription request;
• and
• provide a service requested by the user terminal in response to a service request including the member session key and the e-mail session key, only when the member session key is exist in the table for members and the e-mail session key is exist in the table for redundancy removal.