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 a Christoph Mayer'post, although he comes to slightly different conclusions (by the way, a next post will deal with French Navy 21-bit period FSK-50Bd/850).
Quoting STANAG-5066 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."
| 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 polynomial x^31+x^3+1.
As seen, STANAG-5065 and KW-46 can be meet also in HF 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: 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).
[2] STANAG-5065 Annex A
