Paper Abstract
"When sending highly confidential information by e-mail, there is a method of attaching a ZIP file encrypted with a password to the e-mail, and then sending the password for decryption separately by e-mail, which is the same channel. We named this method “Ostrich ZIP”. While Ostrich ZIP method is used to protect information through encryption and to prevent misdirection, its meaning is sometimes questioned. However, it is difficult to say that these discussions have been organized. In this paper, the advantages, disadvantages, and threats of Ostrich ZIP are summarized based on these discussions, and the current situation is clarified by surveying the environment related to Ostrich ZIP. In addition, we construct an information leakage event model for file sharing when sending and receiving e-mails, and evaluate and discuss the information leakage risk of ostrich ZIP and alternative measures based on the model. Finally, the background of the use of the ostrich ZIP is discussed from institutional and other perspectives, adding another perspective along with the information leakage risk results. This paper will be provided as a comprehensive risk assessment of the ostrich ZIP."

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