COMMUNICATION APPARATUS, COMMUNICATION METHOD AND PROGRAM

摘要

A communication apparatus for encrypting and transmitting a "piece" that means herein a part of data.  The communication apparatus receives a first encrypted piece, which is a piece encrypted by another communication apparatus, first apparatus identifying information, which has been assigned to the other communication apparatus, and first temporary information generated by the other communication apparatus when the first encrypted piece is generated by the other communication apparatus.  The communication apparatus then associates the first encrypted piece, first apparatus identifying information and first temporary information with one another, stores the thus associated first encrypted piece, first apparatus identifying information and first temporary information, and further stores second apparatus identifying information assigned to the communication apparatus itself.  The communication apparatus generates and uses second temporary information, which may be different each time the second temporary information is generated, to generate a temporary symmetric key.  The communication apparatus decides the first part of the first encrypted piece which is to be encrypted, and uses the temporary symmetric key to further encrypt the first part, thereby outputting a second encrypted piece.  The communication apparatus then transmits the second encrypted piece, first apparatus identifying information, second apparatus identifying information, first temporary information and second temporary information.