Microsoft Technology Licensing, LLC

Hiroshi Yasukawa

Takashi Kurosawa

To facilitate protected distribution of digital data files, the files are segmented, and each segment (e.g. disk sector) is encrypted separately. Some segments can be left unencrypted, speeding access since less decryption is required. Different segments can utilize different encryption techniques, increasing protection against unauthorized decryption. A table stored in association with the encrypted data provides authorized users with data identifying the encrypted segments, and the form of encryption used. Decryption is accomplished with a layered set of operating system software that operates in conjunction with said table. Specialized APIs aren't used; applications programs are provided with unencrypted data using conventional APIs. Internal interfaces, invisible to the APIS, intercept normal processing calls (e.g READs) and direct them to internal decryption software that returns decrypted data back to the APIs.

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Tokyo, Japan

Hiroshi Yasukawa