STANAG-4285 async 1200bps test transmissions from Turkey

For about a week I monitored STANAG-4285 1200bps async transmissions heard on several frequencies in the 6 MHz band according to Table I; after April 23th the transmissions have stopped (at least in the 6 MHz band and until today). About the used frequencies, I have not found any match either in the UDXF group logs database or in other resources on the web.

Table I

The transmissions take place with a cycle of about 2 minutes and 25 seconds and seem to use a kind of "call/reply" mode between two stations a,b (since the different strength of the signals); don't know who's the caller and who's the called, but I noticed different patterns depending on the monitored day, as for example in Fig. 1

Fig. 1

The use of two frequencies was also observed (Fig. 2). Obviously it is automated transmissions or controlled by software. Messages, net of 32 bits each for SOM & EOM, have the same length each day, e.g. 8832/5760 bits (caller/called); user-data are encrypted and then transmitted using the 8N1 framing (Fig. 2). Note that the Turkish S-4285 async transmissions I have met so far used the 5N1.5 framing.

Fig. 2 - (the different durations of the signals on the left depend on the waterfall rate that has been selected)

As from Table I, the STANAG-4285 submode 1200bps/L was used from April 15th to April 19th, then the submode 1200bps/S was used.

The direction finding (TDoA) results indicate an area of southern Turkey as a possible transmitter site (Fig. 3); results may be a bit incorrect since the short durations of the signals, anyway it's quite credible. Such a location, along with the transmission schedule and with the encryption algorithm, allows for some observations and comments.

Fig. 3

As seen, the contents of the messages are encrypted but the encryption algorithm does not correspond to the known ones such as KG-84/BID and KW-46/KIV-7 therefore the use of a "national algorithm" can be assumed. TÜBİTAK (Technological Research Council of Turkey) National Electronic and Cryptology Research Institute (UEKAE) developed secure communication solutions in terms of cryptographic algorithms, protocols, and architecture as well as data encryption devices such as the MİLON family (MİLON-4A was also approved by NATO) [1] [2]. It is reasonable to think that these transmissions, as well as other encrypted transmissions from Turkish Armed Forces which are reported in this blog, use such encryption systems.

Fig. 4 - some encryption devices by TUBITAK
(https://bilgem.tubitak.gov.tr/.../corporate_presentation_v7-2019.04.09.pdf)

The way these transmissions are conducted suggests that they are tests. STANAG-4285 is now a consolidated and widely used waveform and therefore the tests could concern the installation of a new HF system (maybe a MRL system?). There is also another somewhat "suggestive" hypothesis: on-field tests of a SCA-based 4285 waveform on proprietary advanced SDR transceivers. Indeed, TUBITAK UEKAE ported two different waveforms to the Spectrum's flexComm SDR-4000 for demonstration to the Turkish Ministry of Defense: an implementation of STANAG-4285 for high frequency (HF) radio links and APCO Project 25 (P25) for public safety links [3].

https://yadi.sk/d/wpMhMwaNpa9NXg
https://yadi.sk/d/OnFVfIPiiBbwlA

[1] https://www.hurriyet.com.tr/gundem/natonun-kripto-cihazlari-tubitaktan-9191151
[2] https://bilgem.tubitak.gov.tr/.../corporate_presentation_v7-2019.04.09.pdf
[3] https://pdfs.semanticscholar.org/

MFSK-4with mixed offsets mode (likely Ukr nets)

Some days ago my friend Mike (mco) sent me an interesting record about a seeming MFSK-4 signal (fig. 1) originating north of Rivne, Ukraine; such (duplex) transmissions are frequently heard on 13873.55, 15833.55, 15863.55, 16354.55, 17412.55, 17442.55 & 17469.55 KHz (Rivne TX).

Fig. 1

This sample I think it's a  combined mode in which the used offsets and speeds are: -1200 -400 +400 +1200 400Bd, -750 -250 +250 +750 250Bd, and -600 -200 +200 +600 200Bd; anyway, it's to be noticed a change of the center frequency between the first and the second mode (Figs 2,3).

Fig. 2

Fig. 3

"They use a wide range of frequencies and I've not noted all of them. This list seems ok but it certainly include Main stn freqs and also side B stations ones and some are missing. They are working full duplex with abroad stations according to multiple TDoAs. So far I've seen them using MFSK-4 with 50/100 80/160 100/200 125/250 160/320 200/400 250/500 400/800 500/1000 settings" my friend Linkz say.

Fig. 4 - TDoA Tx site (thanks to Mike)

https://yadi.sk/d/WQrHjOlxMkH48A
[1] http://resources.rohde-schwarz-usa.com/c/manual-of-transmissi-2

few comments on the secured 50-75Bd/850 FSK transmissions

 The post you are looking for has been moved here

Again about the 3-bit format STANAG-4481F transmissions

(cryptomaster, I56578. KarapuZ)

STANAG-4481F on 18370 KHz from NPN US Navy, Guam

This is an update and just some remarks to a previous post post which I reference for background. All frequencies are CF (tuning + 2k).

1) the signal

Discussing the signal together, my friend cryptomaster had the suspect that a 50 bps data flow is transmitted using a device which is designed to transmit only with a speed of 75 bps: it could be correct.  The ratio 75/50 is equal to 1.5 thus each "original" bit is repeated 1.5 times. The bit editors work with an integer number of bits (they can't represent half bit) thus the 1.5 bit view is possible only by aggregating two consecutive frames and then getting an integer number of 3 consecutive bits (i.e. 1.5 x 2): thus the 3-bit structure that we see (it's the same of the async 5N1.5 framing which is represented as a 15-bit pattern, i.e. 7.5 x 2). Therefore the bits of the stream are allocated as follows:

A S-4481F transmission lasting 10 seconds produces 750 bits that can be arranged into a 3 x 250 bits pattern; by removing one column we get 2 x 250 = 500 bits that just match a 50bps transmission of the same duration (10 seconds).
But what about the M-sequence generated by the polynomial x^31+x^3+1 ? Notice that the Wagner(13,12) coding, which is used for example in STANAG-5065, replaces each second Fibonacci bit with the parity bit: well, the new Fibocaccci sequence bits (the half of the original one!) still belongs to the same polynomial x^31+x^3+1 (see this post).
Indeed, filtering out the replicated third bits from a 75bps demodulated stream  and resizing the resulting stream into a 7-bit pattern, it turns out that we get an usual KW-46 encrypted 7-bit stream (Fig. 1).

Fig. 1

In the light of the above, I analyzed again the signals in order to verify what we hypothesized and found above. I compared a signal from NSY Niscemi recorded on 6383 KHz (3-bit pattern S-4481F) and another one from NAU Isabela 12120 KHz (plain S-4481F) by using the modified quadrature amplitude detector of SA software: you can valuate the different results (Fig. 2).

Fig. 2

Even more interesting: all the signals from Niscemi show the extra harmonics EXCEPT the signal on 6942 KHz which is correctly modulated (Fig. 3) and coincidentally does not has the 3-bit pattern (Fig. 8).

Fig. 3

Then I selected the 50 Hz clock from the NSY signal and subsequently I demodulate it by using the synch'ed FSK demodulator: the test was successful and replicated the same results that I found using the theory and manipulating the bitstreams (Fig. 4). So, 50 bps seems to be the right working speed.

Fig.4

If our analysis is correct and we are right, it seems that they use the 75 bps STANAG-4481F waveform to send 50 bps streams (?!). We do not know the reason but probably you can  do this. In synchronous transmissions the DTE usually provides the transmit clock to the modem but perhaps they could use a modem - e.g. like the Harris RF-5710A - which can recover the clock automatically from the incoming transmit data (transmit clock set to "DATA" or in "recovery mode").

As proved, decoding those signals using standards modes, or changing the speeds to 50 bps, unfortunately does not work: the only successful way is to sync the FSK demodulator to the 50 Hz clock of the signals. Since we are talking about shore-to-ship broadcast, I wonder how the receive ships may manage these transmissions.

2) the source

(monitoring was carried out according to a list of frequencies from logs and in any case not 24/7)
a) Using remote KiwiSDRs, and with the help of my friend Mike "mco", I checked several S-4481F transmissions  but - at present day - only those from NSY and AJE exhibit the odd 3-bit pattern we are talking about. Below the current list of the successful frequencies:

5120.5 NSY
6383.0 NSY
7545.5 NSY
8145.0 NSY, AJE
8204.5 NSY

It's to notice that most of the times the NSY frequencies are logged as "NSY Sigonella": well, NAVCOMTELSTA (U.S. NAVAL COMPUTER AND TELECOMMUNICATIONS STATION) Sicily, located in Naval Air Station Sigonella, manages the Naval Radio Transmitter Facility Niscemi, housing LF/HF transmitters [1][2]. Same story about AJE Barford St.John that probably is sometimes reported as Croughton, nearby (6 miles distant) [3][4]. 

b) Interestingly, 8145 KHz is shared by NSY and AJE; often I have been able to see contemporary broadcasts and same contents (Figs 5,6). The modified AM detector shows the same results as the ones of Fig. 3

Fig.5

Fig.6

The modified AM detector shows the same results as the ones of Fig. 3:

Fig. 7

 c) According to the Tx sites (NSY in Italy and AJE in UK) this type of traffic is beamed only by some European stations. 

d) As said above, I also spotted a S-4481F transmission on 6942 KHz that DF points to southern Sicily, thus it's again NSY. However, this signal does not have the expected 3-bit structure although it's contemporaneous to another S-4481F transmission beamed from NSY on 6383 Khz (Figs 8,9). So, it seems that most of the 3-bit structured signals come from NSY,  but not all those coming from NSY have that feature. Still not heard S-4881F transmissions on the other NSY frequencies 10974 and 15018 KHz.

Fig.8

Fig.9

https://yadi.sk/d/ZhGp8Ay7Jk4UEA

[1] https://www.public.navy.mil/.../art00145_NCTS-Sicily.aspx
[2] https://www.public.navy.mil/fltfor/navcomtelsta/...
[3] http://www.fraw.org.uk/frn/cw/barford-site.html
[4] https://picryl.com/media/...

Makhovik (T-230) secured CIS PSK2/1200Bd

This post is an update and a correction to a previous post to which reference. I want to thank an anonymous reader who in his comment to that post suggested to use differential PSK2 decoding.

In that post I verified the use of Makhovik crypto system (T-230 bundle ciphering device for teleprinter and data connections) in CIS-12 transmissions as well as in CIS PSK2/1200Bd (CIS-1200) transmissions. One of Makhovik's features that can be considered as a signature, in addition to the characteristic 30-bit Message Indicators, is the use of 511-bit pseudo-random sequences generated by the primitive polynomial x^9+x^5+1. These sequences follow the ITU Recommendation O.153 [1] and are primarily intended for error measurements at bitrates up to 14400bps  and synchronization purposes (188-110B "39-tone parallel mode" too uses that pattern).

I searched just these 511-bit sequences in three different CIS-1200 recordings (files psk2_a, psk2_b, and psk2_c) and the search was successful in all the three files but I did not find the right sequences, and then the generator polynomial x^9+x^5+1, in the _a recording (Fig. 1).

Fig. 1

As said above, an anonymous reader suggested to use differential decoding for the _a file: well, I took his advice and results are interesting: as shown in Fig. 2, after the differential decoding the bitstream have the right 511-bit sequences generated by the polynomial x^9+x^5+1 !

Fig. 2 - psk2_a diff. decoded bitstream

This is a further indication in favor of the use of  Makovik encryption with the CIS-1200 waveform,  in these cases the modem T-230-1A (a single channel version of T-230) should have been used. 

As usual, further recordings are needed.

psk2_a_diff.bin 

[1] https://www.itu.int/rec/T-REC-O.153/en