MHFCS FSK 600Bd/850 with KW-46 encryption

Quite good FSK 600Bd/850 signal centered on 10405 KHz, from Australian MHFCS, heard some days ago around 1630z using iw2nke KiwiSDR (center Italy). As reported in UDXF logs by Eddy Waters [1] [2], Australian Defence Force (ADF) has changed the previous dual channel system (ISB) to two single channel with 4 KHz spacings: the lower of the 2 frequencies has a speed of 600 baud, while the higher is 50 baud. The shift in both cases is 850 Hz. As in the waterfall above, I did not hear the 50bd FSK signal 4 KHz above (i.e. on 10409 KHz): maybe it's missing? Eddy also logged 10405 KHz frequency reporting ADF MHFCS Humpty Doo as location of the Tx.

Fig. 1 - main parameters

 

After arranged the demodulated stream into a 7-bit format, it's possible to detect the presence of the sequence called "Fibonacci bits" originated by the polynomial x^31+x^3+1 and which reveals the use of KW-46 crypto device (Fig. 2) as per STANAG-5065 Annex-A.
 

Fig. 2 - 7-bit frame delimited by KW-46 sync bit

Sometimes an FSK 50Bd/340Hz transmission has been seen within the 600Bd/340Hz signal so in these cases they operate in ISB mode: according Eddy Waters from UDXF, the USB side is called "Rockwell 700B" while the LSB side is called "Rockwell CPU100" (Fig. 3). 

 

Fig.3

Just a tip: in order to identify the MHFCS transmissions, in addition to the dial frequencies listed  here (remember that they use a 1500Hz offset above the indicated carrier) and to the shift and speed parameteres (tipically 600Bd/340Hz), think that these MSK signals exhibit a quite unique sign when inspecting the harmonics  using the SA 'involutions' tool. In this case, you will see the presence of several spectral lines in the 7^ power (Fig. 4).

Fig. 4

[1] https://groups.io/g/UDXF/message/85118

[2] https://groups.io/g/UDXF/message/85361

https://yadi.sk/d/bW0grViPPif1KA

 

STANAG-5065 MSK300, LF shore-to-ship surface broadcast

Nice catch of a STANAG-5065 MSK300 signal picked up by a colleague using the Alicante Kiwisdr on 145.0 KHz. By the way, we wish here to thanks the owner of Alicante kiwisdr for his kindness allowing the use of his sdr uninterruptedly for long periods.

The signal is transmitted from Guardamar de Segura in Spain (also known as "Torreta de Guardamar" [1]) currently operated by the Spanish Infanteria de Marina to convey messages to submarines. The use of the S5065 Low Frequency MSK300 waveform (surface broadcast) and the "mission" of Guardamar site, suggest that these transmissions could be intended for surfaced submarines or submarines cruising at periscope depth.  

 

Fig. 1- TDoA results (left), Tx location obscured by Google Earth (right)

While other broadcast stations for submarines such as DHO38 or NSY transmit continuously, Guardamar only transmits if there is traffic to send, and, since the low bandwidth that characterizes the LF band, transmissions may last for some more than an hour. Most likely the Thales TRC 2556 VLF/LF digital multi-channel receiver is used aboard [2].

As said, the S5065 MSK 300Bd/150 is the used waveform:

Fig. 2 - MSK 300Bd/150Hz waveform

Messages use 7-bit START-STOP ITA2 (Baudot) code which is then encrypted using the KW-46 crypto equipment (KWT-46 transmitter and the KWR-46 receiver hase the code name Vallor). Encryption results in bits 1 to 6 being encrypted and bit 7 (STOP) being replaced with a deterministic unencrypted Fibonacci bit defined by the polynomial x^31+x^3+1 which provides synchronization to the receive KW-46 equipment. 

In MSK300 mode the encrypted data from KW-46 are coded into a (13,12) Wagner error coding scheme and then applied to the MSK modulator (as seen here, processing for STANAG-5065 FSK operations does not include Wagner encoding). As shown in Figure 3, the encoding includes blocking the information into 2 character groups, substituting a parity bit for every second Fibonacci bit to form a (13,12) Wagner odd parity code block (odd numbers of 1s) over 12 informations bits (Fibonacci bit excluded).

Fig. 3 - (13,12) Wagner encoding of KW-46 encrypted stream

In MSK modulations the intelligence is contained in the phase shifts and is not consistent with the frequency shifts, thus the signal can't be demodulated using a generic FSK demodulator.

Fig. 4 - MSK300 phase-plane (before equalization)

After some unsuccessful demodulation attempts I asked my friend Christoph Mayer for help, he too checked the S5065 waveform and kindly sent me an MSK demodulator written by him and re-coded for Octave. The results of the analysis of the modulated stream, shown in Fig. 5 after left shifted, perfectly matches the schema of Figure 3.

Fig. 5 -  S5065 MSK300 stream after demodulation

It's very interesting to note that both the sequence obtained with n F-bits and that obtained with n/2 (n/2 -1) F-bits are attributable to the same polynomial x^31+x^3+1, my guess is that this feature maybe helps the initial synchronization of the FEC process detecting the position of the Wagner odd parity bits.

[1] https://en.wikipedia.org/wiki/Torreta_de_Guardamar

[2] https://www.thalesgroup.com/.../vlflf-digital-multichannel-receiver

NATO naval broadcast and KW-46 encryption

This post follows up and completes the one of Christoph where he noticed the presence of LFSR delimited 7-bit frames in STANAG-4285 payloads using GNU Octave scripts.
Given that: 

1) the HF waveform STANAG-4285 is largely used for NATO naval broadcasts;

2) the markers consist of the bits of pseudo-random sequence generated by the polynomial x^31+x^3+1, as specified by STANAG-5630 and already seen in FSK 50Bd/850;

3) those bits (termed "Fibonacci bits") are used by KW-46 cryptographic equipment to provide  synchronization; 

we can assume that NATO naval broadcasts are secured with KW-46 encryption (code name Vallor). 

We analyzed several STANAG-4285 transmissions in both 600L and 1200L sub-modes picked up in well-known frequencies belonging to British, Danish, Dutch, French, German, Norwegian and Spanish Navy as (frequency USB/S4285 sub-mode):

 
05361.8/600L
07554.6/1200L
08170.2/600L
08408.2/600L
08612.2/600L
09095.0/1200L
10186.2/1200L
10264.1/1200L
10733.3/600L
11538.3/600L
12958.3/600L
13057.7/600L
13410.1/1200L  

 
and in all we verified the presence of the Fibonacci bits.

STANAG-4285 bitstreams after deinterleaving and convolutional decoding
Fibonacci bits (before descrambling) 

By the way, NATO naval broadcast consists of a continuous coded stream of data which is typically be transmitted over multiple HF frequencies at the same time, providing an uninterrupted data flow from shore to ships. In the absence of messages to be transmitted, "jam" messages (pseduo-random chars) is injected into the data stream.

28 May update
NATO RATT (4481-F) 75Bd/850, same story as above, ie:
"taps" 1000000000000000000000000000100 = polynomial x^31+x^3+1 = KW-46 encryption. 
This stream has been processed using Octave scripts and Christoph's C++ code.

 

Exploring FSK 50Bd/850 transmissions for STANAG-5065 and KW-46 encryption

Although STANAG-5065 indicates the standards required for naval LF shore-to-ship broadcast with KW-46 encryption devices [1], some implementations of this standards can also be found in HF waveforms such as the FSK 50Bd/850. I came up with the idea to depeen after reading an interesting Christoph Mayer' post .

Quoting STANAG-5065 Annex A, BASEBAND PROCESSING [2]: 

"Encryption and decryption sall be provided by KW-46 interoperable cryptographic equipment operating in the 6.0 Stepped Digital mode. Encryption by the KW-46 equipment sall be coded in the 7-0 unit SART-TOP ITA2 alphabet. Encryption by the KW-46 equipment will result in bits 1 through 6 being encrypted and bit 7 (STOP) being replaced with an unencrypted and deterministic Fibonacci bit", where "Fibonacci bits = Deterministic unencrypted bits used by the KW-46 interoperable cryptographic equipment to provide synchronization defined by the polynomial x^31+x^3+1."

7-bit frame delimited by KW-46 sync bit

x	x	x	x	x	x	KW-46
1	2	3	4	5	6	7

The goal was to arrange the demodulated bits (courtesy of Christoph) into a 7-bit format stream and then process each column of the stream in order to find a descrambler polynomial - if any - that was the same as the one indicated in STANAG-5065 standard. As expected, only the bit-7 column can be successfully descrambled using the LFSR described by the polynomial x^31+x^3+1.

As seen,  STANAG-5065 and KW-46 can be meet also in HF secured naval broadcasts with the commonly used FSK waveform 50Bd/850Hz. For what concerns the users, such signals were recorded on 4905, 4985, 7455 and 16123 Khz (all CFs) using KiwiSDRs located at DF0KL and at Newport,OR: user is probably US Navy.

 [1] In the late 1980's, the KW-46 simplex cryptosystem was introduced in order to provide communications security (COMSEC) for naval broadcasts to naval fleets (Fleet Broadcast). Formally, this equipment is called "Fleet Broadcast Security Equipment, TSEC/KW-46". The  KW-46 consists of the KWT-46 transmitter and the KWR-46 receiver (code name Vallor).

http://www.jproc.ca/crypto/kw46.html

[2] STANAG-5065 Annex A