A communication terminal which is capable of reducing load of a server apparatus by reutilizing a message key to be used for encrypting a message is provided. The communication terminal includes a session key storage part which stores a session key which is shared with another communication terminal and which is not shared with the server apparatus, a message key generating part which generates a message key, a message key storage part which stores the message key to be reutilized in association with a message key identifier, a message encrypting part which generates a message encrypted text based on a common key cryptosystem using the message and the message key, a message key encrypting part which generates a message key encrypted text based on a common key cryptosystem which can perform re-encryption using the session key and the message key, and an encrypted text transmitting part which transmits a group identifier which is an identifier of a group to which an own terminal belongs, the message key encrypted text or the message key identifier, and the message encrypted text to the server apparatus.