Aastra 9143i Series Administrator's Manual page 725

To make changes to the configuration files, the System Administrator must save
the original files.
The security feature described above prevents unauthorized parties from reading
or writing the contents of the <MAC>.tuz file. It also provides the following:
• Prevents users from using the <MAC>.tuz file that does not match the user's
phone MAC address.
• Renders the <MAC>.tuz file invalid if the user renames the file.
• Works with IP phone releases prior to Release 2.2.
• Provides compatibility between the previous encryption routine and the new
decryption routine.
41-001160-03, Rev 00, Releaes 2.4
Note: If the use of encrypted configuration files is enabled (via
security.tuz or pre-provisioned on the IP phone) the aastra.cfg and
<mac>.cfg files are ignored, and only the encrypted equivalent files
aastra.tuz and <mac>.tuz are read.
Encrypted Files on the IP Phone
Encrypted Files on the IP Phone
7-3