part 7.5 Rogue Trader
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The Rogue Trader has arrived at a pirate shipyard after escaping from the Inquisition. He seems to be rather discouraged at the Inquisition's chase of his ship.

Repairs and recruitment of pirate crew are underway. He has agreed to provide equipment, primarily military in nature, in exchange for the payment for repairs and wages of his crew.

Week 3
The Rogue Trader has completed repairs and has recruited excess crew on both ship and is jumping to an uninhabited system in order to set up an independent mining operation using the nanobots and the plans for an asteroid miner. He intends to use the excess crew to run the miner to feed the nanobot construction.

Of note is an astropathic message he sent from his ship while in transit. The message also uses a one-time pad encoding that he performed from memory and so is undecipherable. Nevertheless, we suspect it is related to the first message he received.
The string is attached, request for all Culture vessels to monitor astropathic choirs for the outgoing string.

Rogue Trader - Decoded Messages (note that one-time pads are of fixed length, in this case, 180 characters not including message headers)
Incoming: INQUISITION SUSPECTS XENOTECH USE, AVOID INVESTIGATION AT ALL COSTS. DETAILS ON XENOTECH DESIRED AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA

Outgoing: INVESTIGATION AVOIDED. INQUISITION ON TAIL, WILL TURN PIRATE UNDERCOVER. DETAILS TOO LONG TO NOTE, OF IMMENSE IMPORTANCE. REQUEST ASSISTANCE AAA AAAAA AAAAA AAAAA AAAAA AAAAA AAAAA

Decoded messages provided for your viewing, the Culture does not know of these. The outgoing message hasn't arrived yet.

The message channel consists of multiple backup safeties, including using a circuitous routing of the Astropathic choirs that spans a good portion of the galaxy (each endpoint decodes the transmission header to find the next endpoint, similar to bouncing messages through proxies in RL internet; and 'trusted' endpoints are used).
The final astropathic choir is on a self-sufficient mini-space station in interstellar space. Incoming messages, aka. the message the RT sends, will be moved by warp to a specific deaddrop location in interstellar space (the message capsule is cooled to microwave background before being released and made from radar absorbent material. It's essentially invisible unless you know exactly where to use a Lidar pulse to find a strangely large object for interstellar space)
Then a 'message received' astropathic signal (also in code, something like 'AAA') sent to the actual receiver who then goes and gets it.
The final astropathic choir is a handpicked choir that is known for total loyalty, and still that choir is the weakest link in the chain. Everyone else only knows exactly one piece of information. But these guys know two, the existence of high security messages and which choir they need to send a simple three letter code to when they pick something up.
Obviously, the one-time pads don't exist anymore except in the heads of the two communicating people. Not to mention, 'chaff' messages are also mixed into the chain where various astropathic choirs just send random strings at random times of the same length as each one time pad around random endpoints in a similar bouncing pattern.

All in all, they can't send long messages and it does take a week for it to travel one way, but this is about the most secure method for making messages untraceable by just about anyone. Including the Culture or any other curious inquisitors.

*rolls dice* hmm, interesting.