SHAPING THE FUTURE SATELLITE OF COMMUNICATIONS
8.2.2 Security Approach
To control access to the transmission, the DSNG model requires the direct entry of
a Session Word at the transmitter and receiver. The sender and receiver(s) of the
transmission share the session word, such that only the intended parties will
receive the transmission. This is outlined as follows:
1. The Session Word is entered at the DSNG unit in the field, or at the transmitting
earth station;
2. The Session Word is entered at the receiving IRDs;
3. If the Session Words are the same, then the IRDs are able to decrypt the
broadcast;
4. If the Session Words are different, then the broadcast is not received.
The security requirements for fixed contribution systems are somewhat different to
the DSNG model. The secure exchange of session wordss fundamental to such
systems and is achievable by encrypting them.
8.2.3 Modes of Operation
The Newtec Scrambler supports the following three modes of operation:
• Mode 0: No scrambling;
• Mode 1: All components are scrambled with a fixed Control Word (CW),
derived from a clear Session Word (SW);
• Mode E: All components are scrambled by a fixed CW, derived from an
Encrypted Session Word (ESW).
The scrambling mechanism, as defined in the DVB-CSA specification, is applied at
the Transport level only.
A Conditional Access Table (CAT) is present in the multiplex for BISS Mode 1
and BISS-E, although the table shall be empty as no Entitlement Management
Message (EMM) stream will be present.
For BISS Mode 0 the Scrambler disables the scrambling operation. In this mode,
there will be no CA_descriptor in the Programme Map Table (PMT) and no
Entitlement Control Message (ECM) stream. The Transport_Scrambling_Control
bits of the Transport Packets will be set to “00”.
A scrambler supports a number of modes of operation according
to a specific hierarchy. The Newtec Scrambler provides support
for Mode E and therefore also supports Modes 0 and 1.
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