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Chapter 7
Password Recovery and
Key Recovery
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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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