Книга: Windows Server 2012 R2 Storage, Security, & Networking Pocket Consultant

Understanding encryption and the encrypting file system

Understanding encryption and the encrypting file system

File encryption is supported on a per-folder or per-file basis. Any file placed in a folder marked for encryption is automatically encrypted. Files in encrypted format can be read only by the person who encrypted the file. Before other users can read an encrypted file, the user must decrypt the file or grant special access to the file by adding a user’s encryption key to the file.

Every encrypted file has the unique encryption key of the user who created the file or currently has ownership of the file. An encrypted file can be copied, moved, backed up, restored, or renamed just like any other file, and in most cases these actions don’t affect the encryption of the data. (For details, see “Working with encrypted files and folders” later in this chapter.) The user who encrypts a file always has access to the file, provided that the user’s public-key certificate is available on the computer that she is using. For this user, the encryption and decryption process is handled automatically and is transparent.

EFS is the process that handles encryption and decryption. The default setup for EFS allows users to encrypt files without needing special permission. Files are encrypted by using a public/private key that EFS automatically generates on a peruser basis.

Encryption certificates are stored as part of the data in user profiles. If a user works with multiple computers and wants to use encryption, an administrator needs to configure a roaming profile for that user. A roaming profile ensures that the user’s profile data and public-key certificates are accessible from other computers. Without this, users won’t be able to access their encrypted files on another computer.

SECURITY ALERT An alternative to a roaming profile is to copy the user’s encryption certificate to the computers that the user uses. You can do this by using the certificate backup and restore process discussed in “Backing up and restoring the system state” in Chapter 11, “Data backup and recovery.” Simply back up the certificate on the user’s original computer, and then restore the certificate on each of the other computers the user logs on to.

EFS has a built-in data recovery system to guard against data loss. This recovery system ensures that encrypted data can be recovered if a user’s public-key certificate is lost or deleted. The most common scenario for this is when a user leaves the company and the associated user account is deleted. A manager might have been able to log on to the user’s account, check files, and save important files to other folders, but if the user account has been deleted, encrypted files will be accessible only if the encryption is removed or if the files are moved to an exFAT, FAT, or FAT32 volume (where encryption isn’t supported).

To access encrypted files after the user account has been deleted, you need to use a recovery agent. Recovery agents have access to the file encryption key necessary to unlock data in encrypted files. To protect sensitive data, however, recovery agents don’t have access to a user’s private key or any private key information.

Windows Server won’t encrypt files without designated EFS recovery agents.

Therefore, recovery agents are designated automatically, and the necessary recovery certificates are generated automatically as well. This ensures that encrypted files can always be recovered.

EFS recovery agents are configured at two levels:

? Domain The recovery agent for a domain is configured automatically when the first Windows Server domain controller is installed. By default, the recovery agent is the domain administrator. Through Group Policy, domain administrators can designate additional recovery agents. Domain administrators can also delegate recovery agent privileges to designated security administrators.

? Local computer When a computer is part of a workgroup or in a standalone configuration, the recovery agent is the administrator of the local computer by default. Additional recovery agents can be designated. Further, if you want local recovery agents in a domain environment rather than domain-level recovery agents, you must delete the recovery policy from Group Policy for the domain.

You can delete recovery agents if you don’t want them to be used. However, if you delete all recovery agents, EFS will no longer encrypt files. One or more recovery agents must be configured for EFS to function.

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