9 December 2016

unid FSK 150Bd/250 with KG-84 encryption


I copied this FSK modem on 06252.2 KHz (cf) on 7 December morning, carrying several messages with a very good signal strength here in JN52 (about 70 dB). The modem use a frequency shift of 250 Hertz and a modulation speed of  150 bps (Figs 1,2).

Fig. 1
Fig. 2
The most interesting thing is that the initial part of the messages contains the 64-bit sync header which is typical of KG-84 encryption
1111101111001110101100001011100011011010010001001100101010000001
followed by the 2 x 64 bit initialization vectors (each vector is repeated four times), as shown in Figs. 3,4:

Fig. 3
Fig. 4
The ending part is most likely a recognized EOM sequence.
The presence of KG-84 leads to think to a NATO country as source, surely - since the signal strength - the site of transmitter is very close to my antenna (center Italy), most likely in the Mediterranean area. 



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