16 January 2023

4529.75 KHz (cf), yet another async 5N1 STANAG-4481F (to replace 4539.7 KHz?)

Some days ago my dear friend Karapuz noted the transmission of STANAG-4481F segments centered on 4529.75 KHz, data were transferred using 5N1 framing and apparently not in clear text. In the following days I monitored, albeit occasionally, the channel until the transmissions started to be continuous (Figure 1).

Fig. 1

Analyzing the bitstream after the start/stop bits have been removed, it turns out that the messages are sent in protected mode using KG-84/KIV-7 encryption... as it was expected since the used protocol (S-4481F, 75Bd/850). As already noted in other similar STANAG-4481F transmissions, the 128-bit Initialization Vector is splitted in two 64-bit groups and each group is repeated twice rather than four times (as instead it's used to do in STANAG-4285 transmissions).

Fig. 2 - notice the presence of the KG-84 64-bit sync sequence and the 128-bit Initialization Vector (after the removal of the start/stop bits)

As happened for the 4539.7 KHz channel, in the same way the 4529.7KHz channel started with test transmissions and then switched to the usual secured broadcast [1]. TDoA runs indicate the DHFCS site in Crimond UK.


[1] https://i56578-swl.blogspot.com/2021/09/async-5n1-stanag-4481f-likely-tests-or.html