lunedì 23 ottobre 2017


This is a 2G-ALE traffic example recorded some days ago.

The first signal ( red box ) is a MIL188-141A waveform ( also known as Automatic Link Establishment ALE ). During this procedure between the two stations there is an exchange of information about the quality of the received signal. After establishing the connection, the stations can continue with a low speed data exchange or alternatively, the ALE system can manually or automatically switch tasks to a system of different transmission FSK or PSK for high-speed or even voice data transmission. In this case is used a an high speed modem - PSK waveform ( yellow box ).

Looking the ACF value we can get some info about the system used. 200ms are typical of a MIL188-110A ( this is a necessary but not sufficient condition ! ).

After a brief analysis of the bits stream ( with a bits analyzer ), I found a 10 bits structure: 2 bits are used as packet frame delimiter and the last 8 bits are encrypted data.

Looking the first bits sequence we can identify the tipical "fingerprint" of the "Harris Citadel" encryption (*).

(*) source about Harris Citadel encryption: i56578_swl

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