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7.1.
Introduction
The two most important aspects using encryption are:
e Prevent tapping of sensitive information.
e Restrict system access.
Encryption is in general based upon scrambling the transmitted data
using an algorithm that provides sufficient security against
descrambling. The algorithm used in the modems, is the well known
DES standard. Only the key used to encrypt and decrypt data must
be kept secret. The DES algorithm is today the most common and
accepted encryption method.
Your modem always uses error correction in asynchronous DES
mode. This function ensures error free data receiption before
decryption. Data compression is active in DES mode, because data
is compressed before they are encrypted. LAPM/V.42 bis is the
preferred operation mode, MNP is only supported for backward
compatibility.
When using encryption and character format 7E1 or 701 (7 data bit,
odd parity and 1 stop-bit) between DTE and modem, the character
format between the modems (on-line) should be set-up to 8N1 (8
data bit, no parity and 1 stop bit). This is set-up with the command
+&G and writing to register +S6. See description of command and
registers in this manual.
7.2
Security
To obtain maximum security, you should read the following user
requirements:
e Encryption keys and possible copies of the keys must be stored
unavailable to others.
e Keys should be upgraded at regular intervals. If anyone should
know one of the keys, the access is only valid until a new one is
distributed. Make sure the routine for distributing keys are safe
enough.
e It is important that all keys have the same probability, the key
should therefore be chosen at random.
Make your security precautions depending of the sensivity of the
information to be transmitted. It may be sufficient to distribute the
keys verbally or by mail and to keep the modems in a safe location.
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