A distribution of bending principal strains giving a target shape of a curved surface is obtained, and a calculation grid is divided along the direction of the bending principal strains. The base portion has an axis and a bore coincident with the axis. Using a public key of the conversion server, a predetermined restricted condition, and a secret key for decryption of the message, the recipient terminal generates a delegation key allowing decryption of the message under the restricted condition and passes the delegation key to the agent terminal. The exposed cord length is user-controllable by lockably spooling excess cord length into a rotatable spool reservoir attached to the handle member.