CIS-1200 SDPSK 1200Bd ("Makhovik", T-230-1A)

updated (23 July 2024)

This transmission, along with a probably spurius emission 600 Hz above, was recorded on 13002.5 KHz (cf) thanks to the remote KiwiSDR located in Azumino-city Nagano, Japan [1].

Fig. 1 - main signal and its spurius

The signal that I assume is the "actual" one and that I analyzed is characterized by a SDPSK (Simmetrical Differential PSK) modulation at a speed of 1200 Baud. Indeed SDPSK is equivalent to π/2 DBPSK or PSK2 with phase rotation: ie, as shown by the transitions in absolute mode, SDPSK assumes that the phase is rotated by +π/2 for bit “0” and by -π/2 for bit “1” thus there is not a 180° turn (transitions do not pass through 0). The information transmitted is encoded in the transition and not in the state. The signal can be demodulated using the differential mode (diff=1).

Fig. 2 - SDPSK modulation

The transmission consists of some segments that differ by the presence or absence of an initial preamble (signals A and B in Figure 3) which consists of a repeated 511-bit length pseudo-random sequence generated by the polynomial x^9+x^5+1 (1) as for the ITU Recommendation O.153 [2] (188-110B "39-tone parallel mode" too uses that sequences).

Fig. 3

 

Fig. 4 - 511 bits length sequence

The presence of such sequences is one of the features of the so-called Makhovik (aka the "flywheel"), a well known Soviet-Mil crypto system. Although someone classifies Makhovik as vocoder, it can can be used for time-multiplexed encryption of both voice and data up to 9600 bps. It's official name is "T-230 bundle ciphering device for teleprinter and  data connections" and was designed to operate in UHF but very often is found in LF and in HF.
After the removal of the initial preamble, the following data block consists of a "common" sequence:

110101100100011110101100100011

followed by 240-bit Initialization Vectors that are sent in 8x30-bit groups, each group repeted three times (Figure 5): these 30-bit groups are another peculiar feature of  the Makhovik system.

010000111011001110010100001110
011101100101000011001010000111
110010100001110010000111011001
001110110010100000111011001010
001110110010100011001010000111
111111111111111000011101100101
001110110010100111011001010000
101100101000011011101100101000

Fig. 5

Segments sent w/out the initial preamble (type B in Figure 3) show exactly the same structure: note as the Initialization Vectors slightly differ (Figure 6): this feature should be further studied (it is probably somehow related to the presence/absence of the initial preamble) but it is necessary to obtain several more recordings.

010000111011001110010100001110
011101100101000011001010000111
110010100001110010000111011001
001110110010100000111011001010
001110110010100011001010000111
111111111111111000011101100101
001110110010100111011001010000
101100101000011011101100101000

010000111011001110010100001110
011101100101000011001010000111
011001010000111100001110110010
111011001010000110010100001110
010100001110110110110010100001
100101000011101001010000111011
111011001010000111111111111111
011101100101000100001110110010

Fig. 6

It's worth noting that in some previous Makhovik recordings I saw differential encoded data & BPSK, while this ones consist of  plain encoded data & SDPSK [3].

update (23 July 2024)
I willingly add a comment sent me by my friend cryptomaster.
The common sequence in Figs 5,6

110101100100011110101100100011

shall be right shifted to appear as

111101011001000111101011001000

which in turn is the repetition of the 15 bits length M-sequence generated by the polynomial x^4+x+1 (Figure 7).

111101011001000

Fig. 7 - the repetition of the 15 bits M-sequence generated by the polynomial x^4+x+1

https://disk.yandex.com/d/Vg5XruORhd8_5A

(1) the use of the polynomial x^9+x^5+1 is quite common in CIS waveforms,see http://i56578-swl.blogspot.com/p/polynomials.html

[1] http://jf0fumkiwi.ddns.net:8073/
[2] https://www.itu.int/rec/T-REC-O.153/en
[3] https://i56578-swl.blogspot.com/search/label/Makhovik 

CIS-1200 BPSK 1200Bd ("Makhovik", T-230-1A)

Good quality CIS-1200 (T-230-1A, BPSK 1200Bd) transmission spotted on 9073.80 KHz (cf) thanks to the ArcticSDR. The transmission consists of a series of encrypted messages, the 240-bit Initialization Vectors are sent in 8x30-bit groups, each group repeted three times (Figure 2).

Fig. 1

Fig. 2

The transmission ends with a long "idling" part consisting of the 511-bit m-sequence generated by the polynomial x^9+x^5+1 (Figure 3). All is ok with previous CIS-1200 recordings [1].

Fig. 3

 

https://disk.yandex.com/d/599vbjcIfpRzrA

 
[1]  https://i56578-swl.blogspot.com/search/label/Makhovik

 

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