Operation Manual

IP Masquerading at the Network Adapter
73 NT/MPRI – 4 Special NT/MPRI Settings
Data are encrypted on the level of the transport protocol (PPP). Encryp-
tion on this level is based on the RFC standard, making it interoperable
for all transmissions using PPP over ISDN. The advantage of this meth-
od is that data compression also takes place on this level, so that data
can be compressed first and then encrypted.
Data are encrypted with the Twofish algorithm. The Twofish algorithm
encrypts symmetrically in accordance with the Secret Key procedure.
Here “symmetrical” means that the same key is used to encode and to
decode the data. Only the sender and the recipient know the secret
key.
The key has a length of 128-256 bits. Because it is generated when a
connection is established, it is known to the sender. Transmission is
necessary to make it known to the recipient. Because the key must re-
main secret on the way from the sender to the recipient, it is encrypted
as well. Because the key is encrypted using a separate application
which is not a component of the NT/MPRI, it can be adapted to your in-
dividual needs. The NT/MPRI can access external routines which en-
code the key over the Crypt Provider API. An example application illus-
trating this procedure is included on the NT/MPRI CD.
4.7 IP Masquerading at the Network Adapter
IP filter profiles and masquerading profiles can be activated for each of
the network adapters used by the NT/MPRI in the “Configuration /
Server Settings / Network Adapters” menu. Using these profiles make
sense when the NT/MPRI connects via network adapter to an IP net-
work that offers insufficient security mechanisms, for instance, to the
Internet. The NT/MPRI also uses a network adapter to connect to the In-
ternet via ADSL, but in this case a PPPoE channel is established. This
means that the only way to activate filter and masquerading profiles is
by configuring the settings for the ADSL destination accordingly.
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