Chapter 7
Password Recovery and

Key Recovery


LexiGuard can be configured during installation to support password recovery and one of a choice of key recovery methods.  Password recovery allows a user who forgot the password of his LexiGuard user account to retrieve the password from a central repository such as a help desk.  Key recovery is a feature of an encryption system that allows authorized persons (the recovery agent or trusted third party), under certain prescribed conditions, to obtain the keys needed to decrypt cyphertext.

Types of Key Recovery Offered by LexiGuard

The  three types of key recovery offered by LexiGuard differ in which key is used by the recovery agent to perform the recovery.
 
Encryption Private Key Escrow  The user's private key generated at the user's machine is sent to a central key escrow database.
Emergency Recovery Key (ERK) Escrow When the user's encryption keys are generated at the user's machine, an extra keypair (the ERK) is also generated. The ERK private key is sent to a central key escrow database. The advantage of putting the ERK into escrow instead of the encryption private key is that the ERK has a password that is generated by a random number method and therefore, the password is more resistant to dictionary attack than the encryption key password chosen by the user.
Master Key Recovery The master key keypair is generated upon initial installation or imported from elsewhere.  The master key public key is  downloadeded to each user's machine.

The Delivery of the Escrow Key to the Key Escrow Database

With the Encryption Private Key and Emergency Recovery Key types of key recovery, the key to be stored in the Key Escrow Database is generated automatically at the user's machine. The private key, together with user name and password, are uploaded to a central key escrow database using an SSL secure link. In a later version of LexiGuard, the choice will be offered to perform the upload automatically or to write the data to a file which can be uploaded manually (via an HTML form or alternatively via ftp).  Currenly only the manual upload method is offered.

With the Master Key Recovery type of key recovery, there is no need to upload the private key since it is not generated at the user machine. However, the user name and password are uploaded to allow the user the password recovery feature.

The user is not be permitted to perform encryption of files until the central key escrow database has sent back confirmation of reception of the private key and other data listed above.

Binding the Recovery Key to the Encrypted File

When key recovery is enabled and the user encrypts a file, a hidden recipient is included automatically in the list of recipients for encryption. This allows the recovery agent to decrypt the file using the appropriate private key. The types of recovery and corresponding hidden recipient are:
  
Encryption Private Key  The user with encryption key is added as a hidden recipient.
Emergency Private Key  The user with emergency key is added as a hidden recipient.
Master Key  A ficticious master user with master key is added as a hidden recipient.

The Recovery Process

The recovery agent can restore the plain-text version of files on the system of a user. To do this, the recovery agent does the following:
  
1.  Retrieve the user login name and password from the key escrow database. Retrieve the key file from the database and output to a floppy, or if Master Key method then use the Master key exported from the administrator PC.
2.  Log into the user machine. If a dialog box asks for the location of the private key keystore, specify the A:\ drive.  If not asked, then choose Preferences from the Edit menu, select the leaf node lexiguard, and next to PrivateKeyPath, type the value "A:\" . 
3.  Select individual files or entire directories and choose Decrypt on the Action menu to decrypt the encrypted files.
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