28 June 2018

COMSEC transmissions using a S4285 variant (poss. Croatian-Mil)

Encrypted transmissions on 6931.0/usb which use a slightly modified 4285 waveform with 4 preamble tones and running 600bps/Short sub-mode. Transmissions are between two stations in simplex, are quite frequent during the daytime and are not preceded by ALE or voice calls: probably it's not a network but rather a PtP link where peers are tuned on the same frequency.
Fig. 1
The COMSEC preamble in some way resembles 188-220D and in my guess it consists of 3 parts:

A) 60-bit Frame Sync (110000100000111000101111001011011101101001001011111010101100)
B) 5 x 128-bit encoded Initialization Vector
C) 64-bit idling sequence (time to load the key?)

preamble is then followed by the encrypted block (D) which ends with "01" sequences (E).
Fig. 2
Fig. 3
All the TDoA multilaterations I've done indicate the region of Split in Croatia, also this post  suggests the same source. Unfortunately it was not possible to use TDoA more effectively: the signals have mostly short airtime and there are no close GPS'ed SDRs to both the west and east.

Fig. 4
It's worth noting that the same add of the 4 initial tones is also visible in the 110A waveform recorded on October,2 2017; in that recording the same 128-bit protocol was detected:

Fig. 5

27 June 2018

CIS-14 FSK 96Bd/500

Although the name FSK 96Bd/500, the used shift of this sytem is 480 Hz. Speed is 96Bd and the two 5-bit data words are bit-interleaved according to the CIS-14 format; first two bits are the system bits: t_a and t_b: 0 = traffic, 1 = idle (or no traffic). As you can see in the demodulate stream, only channel b transports data (figure 1). It's probably a test transmission since data are in clear-text mode and consist of a "classic" Russian test sequence "GA VIL BY CITRUS? DA,NO FALX"  (figure 2), something like "the brown fox jumps over the lazy dog".

Fig. 1
Fig. 2
Another example of a CIS-14 96Bd/500 bit-interleaved is shown in figure 3

Fig. 3

22 June 2018

redefining T-207 (CIS-14) checksums

T-207 (T-207, T-207 2M "VIKTORIA" - Soviet teletype encryption device) is a multiplexed two channels "system" that is used in several CIS waveforms. Since the lack of official documentation it's difficult to say much more about the T207: guys from radioscanner talk about "equipment" as a in-line ciphering device while ex DDR STASI archives refer to T207 as an "encryption algorithm".
CIS-14 (also known as as TORG 14) is a designation of a transmission mode: a full duplex system using FSK at several speeds (42.1Bd, 47.5Bd, 48Bd, 50Bd, 70.5Bd, 72Bd, 83.3Bd, 84.21Bd, 94.11Bd, 96Bd, 100Bd, 144Bd, 192Bd, 200Bd, 288Bd, ...) and shifts. Data of two independent data channels can be processed; they are in MTK-2 alphabet (Russian [Cyrillic] Third-shift ITA-2, sometimes also called "ITA-2 Cyrillic M2") thus have 5 bits per character, but are transmitted in 14-bit frames, each containing two characters.
As shown in figure 1, the data code words (A in the figure) of the two channels are amended with two leading "channel state" bits and then either word-interleaved (case B) or bit-interleaved (case C). Two parity bits are calculated over the complete 12-bit frame generated and expand it to the final 14-bit frame. The two bits indicating the channel state signify whether the channel contains traffic(bit = 0) or idle (bit = 1) sequences at the moment.
Fig. 1 - 14 bit frame (from R&S Manual of transmitting methods)
Additionally, a variant of CIS-14 has been observed using frames of 28 bits. As can be seen in figure 2, after having established the 14-bit frame(s) (B) form the datawords (A) as explained above, two of these frames are bit-interleaved (C) to the new28-bit frame.

Fig. 2 - 28 bit frame (from R&S Manual of transmitting methods)
Note that although T207 is "hardware" while CIS-14 is a transmission mode, I use T207 in this blog as an implicit reference to CIS-14.

software tools (download)
- The Octave script T207_detect.m  has been used for the check of T207/CIS-14 mode:
- The Octave script T207_detect_e.m also extracts the two world and bit interleaved channels:
(the two Octave scripts are coded by me and Christoph, you will need GNU Octave package [1] to run them)
- The software CIS14-C.exe (coded by cryptomaster) can be used to etract the two 5-bit channels from a 10-bit stream C-interleaved:

As said in a previous posts, T207 detection had to be manually spotted by processing the demodulated bitstream and checking if it matches the criteria described in this post in radioscanner forum: the Octave scripts are now improved and detects the presence of T207 checksums in a given bit stream and for each permutation of the checksum bits.  T207_detect scripts are very useful since encrypted CIS-14 messages have ACF=0 and anonymous demodulated streams, clear-text messages instead may be recognized as CIS-14 by the "solid" columns of the channel state bits.

I run the script against several waveforms and the results are very interesting.So far, I found two checksum modes termed "3" or [3120] and "20" or [0312]:

T207/CIS-14 verified waveforms (so far)
(note that some waveforms  can be coded with both the two checksums)

checksum mode 3 [3120]:
VFT 3x100Bd/1440, VFT 6x100Bd/120
FSK 50Bd/1000, FSK 100Bd/500 
F7B 100Bd/1000 (on one channel)

checksum mode 20 [0312]:
VFT 3x100Bd/1440, VFT 6x100Bd/120
FSK 50Bd/1000, FSK 96Bd/500, FSK 96Bd/1000
FSK 100Bd/500, FSK 100Bd/1000, FSK 100Bd/2000
F7B 96Bd/500 (on one channel), F7B 100Bd/1000 (on one channel) 


15 June 2018

STANAG-4539: unexpected data rate of 12800 bps

Long transmission (hours) of STANAG-4539 8PSK 2400 Bd bursts spotted on 14 June morning on 7807.2/usb:  each burst lasting 1680 ms and composed of 13 x 287 tribit symbols frames. It's interesting to note the uncoded 12800 bps speed detected by the 5710-A modem: using 8PSK at a modulation rate of 2400Bd, the the maximum data rate obtainable is 4800 bps (7200 bps on-air) therefore there is something wrong somewhere (a data rate of 12800 bps is obtainable using QAM64 modulation at 2400 Bd). STANAG-4539 is an "auto-baud" waveform, so perhaps they use a modified preamble that misleads the modem.
A run of TDoA multilateration says Cornwall (UK) as Tx location, possibly UK MoD DHFCS tests from St.Eval? 

Fig. 1
Fig. 2
Fig. 3


12 June 2018

TDMA waveforms (STANAG-4539 Annex D,...) and NILE/Link-22

Recently, some friends and me happened to run into QPSK and 8PSK burst waveforms that are among those described by STANAG-4539 for TDMA operations (Time Division Multiple Access) and that are used by NILE/Link-22. Even if I do not have a direct confirmation, my prudent guess is that it is probably about Link-22 transmissions.

In TDMA mode each user is allowed to transmit only within specified time intervals (Time Slots) so that different users transmit in differents time slots. When users transmit, they occupy the whole frequency bandwidth (separation among users is performed in the time domain). 
According to S-4539 D, a TDMA slot is the high level structure in which information will be transmitted/received and it is composed of a Preamble, a certain number of Media Code Frames and a Guard Time (Fig. 1).

Fig. 1 - TDMA Slot Time
A Media Code Frame is composed of 270 symbols to be transmitted/ received at the modulation rate of 2400 baud and following a certain waveform structure (Traffic Waveform) with different waveforms and modulation. Each Traffic Waveform is composed of a sequence of different DATA blocks and Mini Probe (MP) blocks: the DATA block contains coded user information symbols and the MP block contains known training symbols to be used by the equaliser. There are two different types of PSK modulations: QPSK and 8PSK. The QPSK modulation is used for preamble transmission, QPSK or 8PSK are used for Media Code Frame transmission.
As far as I know, and from S-4539 D, the 270 symbols of a Media Code Frame are arranged according the used Traffic Waveforms (TWF): 

TWF1: 4 sections with 48 data and 19/20 probes 
TWF2: 8 sections with 18 data and 15/16 probes
TWF3: 4 sections with 48 data and 19/20 probes
TWF4 to WF7: 1 section with 240 data and 30 probes 8PSK 
TWF?: 3 sections with 60 data and 30 probes 

That said, the  270 symbols (length of the Media Code Frame) sent at 2400 symbols/sec, regardless the used Traffic Waveform, should produce an ACF value of 112.5ms.
The analysis of the signals was therefore targeted at checking that ACF value, the structure of the Media Code Frames (Traffic Waveforms) and some other possible regularities among the signals. Unfortunately I have only the annex D of S-4539 which specifies only the first three Traffic Waveforms while from some advertising on the internet, Fig. 2, one can see that they can be up to 18 (Annex G).

Fig. 2 - STANAG-4539/Link-22 Traffic Waveforms
The lack of official documentation means that these signals can not be identified exactly as Link-22, but there is a good chance that they will be.

QPSK modulations
Below an interesting  4 Media Code Frame slots transmission (Fig. 4). Each Media Code Frame (270 symbols, 112.5ms) seems composed of 3 packages with 60 data and 30 probes (Fig. 5)

Fig. 4 - 4 Media Code Frame slots
Fig. 5 - Traffic Waveform composed of 3 packages
In Fig.6 is shown a Media Code Frame that uses a Traffic Waveform composed of only 1 package (TWF 1-7) followed by a 3 packages Traffic Waveform (37.5ms).

Fig. 6

8PSK modulations
In this sample the Media Code Frame uses a Traffic Waveform composed of two packages (Fig. 7)

Fig. 7 - 2 packages Traffic Waveform

As verified by KarapuZ, all the analyzed signals have the same preamble: here below, Figs. 8 and 9, an example of two signals (8PSK and QPSK)

Fig. 8
Fig. 9
(to be continued)

10 June 2018

CIS-12 TDoA measurements using GPS time-stamped IQ samples from KiwiSDRs

TDOA (Time Difference Of Arrival), also known as multilateration, is a well-established technique for the geolocation of RF emitters. Using three or more receivers, TDOA algorithms locate a signal source from the different arrival times at the receivers.
In this case, TDoA measurements are related to a CIS-12 signal (modem AT-3004D) spotted this morning on 11414.0 KHz/usb and use GPS time-stamped IQ samples from four KiwiSDRs: F1JEK (JN05hs, southwestern France), SV3EXP (KM07qx, west Greece), UR5VIB (KN68DL, central Ukriane) and KHIMKI (KO85qw, near Moscow city Russia). 
Cross correlations suggest the Crimean peninsula as the area of Tx antenna. Since CIS-12 is widely used by Rus-Ny, it's quite reasonable to assume that the Tx be in Sevastopol, Black Sea fleet HQ. Note the scattering in the correlations involving the French SDR (F1JEK) which are due to multipath propagation.


Plots are obtained using my (old) Ubuntu 12.06 LTS updated to gcc 6.6 and gnuplot 4.4; TDoA algorithms implemented by Christoph mayer:
and GNU Octave, scientific programming language, version 4.4:

5 June 2018

Nokia msg terminal + Tadiran HF equipment

Transmission picked up some days ago by my friend AngazU using the SM2BYC Kiwi sdr. The signal is composed of an initial tone followed by a preamble consisting of F7B modulation (apparently MFSK-4) and two simultaneous FSK modulations (Fig. 1). As suggest by cryptomaster and KarapuZ, this is an interesting example of a Nokia Adaptive MSG Terminal which is used along with a Tadiran HF equipment that presumably provides an active noise cancellation feature (Tadiran DCS, Digital-Coded Squelch).

Fig. 1 - waveforms
The upper FSK 125Bd/290 delivers the same 84-bit pattern and it's interesting to note that the last 84-bit sequence is sent in opposite polarity:  perhaps signalling the last group/block of data (sent in the lower FSK).  The same parameters (FSK and 84-bit pattern length) has been discussed here in radioscanner:
Although, of course, we can be wrong because a specific description of this function was not found TADIRAN HF modems.

The lower FSK 300Bd/780, after the initial 1-0 sync sequence pattern, delivers data and seems to have a 16-bit period. After differential demodulation the stream exhibits 8 solid bits columns in a 16-bit period and once removed the stream does not have a clearly defined period (Fig. 2).

Fig. 2 - bitstreams
Cryptomaster is inclined to the Machester modulation but I get errors in both the phase conventions (G.E.Thomas and IEEE 802), and he pointed me that the signal has a constant preamble whicH is not coded using Manchester (Fig. 3) and causes mistakes in decoding.

Fig. 3

As for as I can see, the same F7B + FSK125Bd structure is sent first but without the lower FSK300Bd (Fig. 4). The patterns are the same in the two FSK125Bd streams, perhaps it is used to initialize the (supposed) Tadiran noise blanker function?


3 June 2018

MIL 188-110C App.D: 9KHz/7200Bd & 12KHz/9600Bd

9KHz/7200Bd & 12KHz/9600Bd WBHF waveforms spotted on 9 MHz band. Both the ACFs show a value of 120ms that corresponds to 864 symbols for the 7200 Bd waveform (768 uk + 96k) and 1152 symbols for the 9600 waveform (1024 uk + 128 k).

The extra spikes in ACF diagrams, more evident in CCF, in my guess are due to the cyclically rotated version of the mini-probe which is utilized to identify the long interleaver block boundary (MIL 188-110D #D.5.2.2). Note that 2 data block make 4608-bit blocks (768x2x3) and 21 data blocks make 64512-bit block (1024x21x3), therefore the CCF spikes are related since 64512/4608=14