Patent ID: 8266445

Claim:
An encrypted communication system, comprising an encrypting device for creating an encrypted document from a plain document and a decrypting device for decrypting the encrypted document to obtain the plain document, wherein the encrypting device comprises: an encrypting role information storage device for storing encrypting role information that is configured with a plurality of encrypting keys corresponding to levels of authorized powers of viewers as well as key IDs for identifying the encrypting keys; an encrypting process device which grasps an encrypting range designated from the plain document, and encrypts the encrypting range with a key selected among the plurality of encrypting keys configuring the encrypting role information; an encrypting information creating device for creating encrypting information that includes: a front position and a rear position in the plain document to which the encryption processing is executed, and the key ID corresponding to the encrypting key that is applied for the encrypting range; and an encrypted document creating device for creating the encrypted document by combining the encrypting information with the document that has been encrypted, and the decrypting device comprises: a decrypting role information storage device for storing decrypting role information that is configured with an encrypting key corresponding to a viewer and a key ID corresponding to the encrypting key; a separating device for separating and extracting the encrypting information and an encrypted document main body from the encrypted document; an encrypting key loading device for loading, from the decrypting role information storage device, the encrypting key corresponding to the key ID of the encrypting information extracted by the separating device; and a decrypting processing device for decrypting the range between the front end position and the rear end position in the encrypted document main body by using the encrypting key that corresponds to the range, the encrypting and decrypting devices comprise: wherein a role information obtaining device obtains the role information from a role information managing server at prescribed intervals, and updates the role information to be the latest so that the encrypting keys can remain valid within an effective period; and wherein the effective periods for the encrypted keys are set in the encrypting role information and the decrypting role information by using the effective start dates and the effective end dates enabling encryption and decryption to be executed only within the effective periods but not outside the effective periods.