Cryptographic File Systems, Part Two: Implementation

    Date14 Apr 2003
    CategoryCryptography
    3563
    Posted ByAnthony Pell
    This is the second article in a two-part series looking at cryptographic filesystems. The first article in this series covered the background on cryptographic filesystems from the underlying concepts to some of the mechanics of those systems. This article will cover . . . This is the second article in a two-part series looking at cryptographic filesystems. The first article in this series covered the background on cryptographic filesystems from the underlying concepts to some of the mechanics of those systems. This article will cover implementation. The focus will be on implementing the Microsoft's EFS under Windows 2000 and the Linux CryptoAPI.

    One point to clarify from the first article involves the note that Microsoft's EFS does not support using a password-based symmetric algorithm. This is due to the concern that such schemes are weaker because of their susceptibility to dictionary attacks. While technically accurate, the fact remains that the public portion of the user's X.509v3 certificate (which is used to encrypt the File Encryption Key, or FEK, used by EFS) is used to encrypt the FEK. To decrypt the FEK requires the use of password or passphrase and unless password-based logon is disabled completely this password or passphrase is typically the user's domain password.

    Microsoft's Windows 2000 product introduced the encrypting file system (EFS) to the Windows product line. While third party add-on encrypting software has been available for some time, EFS was the integration of such a concept into Windows 2000. Under Windows 2000, EFS supports the DESX algorithm only. With Windows XP that encryption algorithm now includes 3DES as well and will eventually include the Advanced Encryption Standard (AES) algorithm.

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