Nowadays, Internet/Intranet, WWW and E-mail are widely used. Therefore usable security systems based on encryption are desired.
In this paper, we propose multimedia information partial encryption systems which enable free selection of confidential information of processing data on a screen, and encrypting them. Therefore, we can construct encryption systems which are superior in view of both confidence and operation. For example, in a text, only part of confidential information is encrypted and further translated into text mode which is ASCII code, and then returned into the text. Therefore, the text including encrypted data can be handled easily as a text file by ordinary word processors. Also, in databases, users can execute encrypting/decrypting data of each items when data are entered. These systems can also be used for images, spreadsheets, and digital signatures. Each part of confidential information has its own security level and a unique encrypting key. In these systems, security levels adapted to business organizations can be allocated, for example, a user in charge or the company president can have the highest security level.