Provable security of the modified encrypting file system for Microsoft Windows

EFS is the encryption mechanism for Microsoft Windows. In this paper, by introducing two additional hash functions, we present a security-improved variant of the original EFS scheme. The minor modification has almost negligible effect on the performance of the operating system. Then we apply the Fujisaki-Okamoto´s technique to prove its security against adaptive chosen ciphertext attacks in the random oracle model. Compared with the more confidence in the security for EFS in Microsoft Windows, the minor modification and the minor cost incremental is worthwhile, we believe.