After the OOB flees from RIP and is being pursued by three fleets, how doesn't their communication with Jefri get intercepted?

Question

So what bugs me is this:
1. there are hints that communication between Jefri and Ravna stops just as the OOB enters the slow zone.
2. the event of 1. happens several days after the OOB flees RIP
3. this whole time the three pursuing fleets (Alliance, Sjandra Kei Commercial Security and the silent fleet of the Blight) are dangerously "near"
4. when the OOB establishes contact with the Olvira they are using heavy encryption (I assume they are not when communicating with Jefri)
5. there are hints in the text that this communication link could be intercepted anyways

So how come not one of the pursuing ships picks up the messages sent from Tines World to the OOB and no one on board is ever worried about that?

Answer 1

There are some clues.

... The Straumers had a backup plan if the rendezvous failed. They intended to signal Relay with their ship's ultrawave.

"Now wait. Just how big is this ship?" Ravna was no physical-layer engineer, but she knew that Relay's backbone tranceivers were actually swarms of antenna elements scattered across several light-years, each element ten-thousand kilometers across.

Blueshell rolled forward and back, a quick gesture of agitation. "We don't know, but it's nothing exceptional. Unless you're looking precisely at it with a large antenna, you'd never detect it from here."

Relay devotes an entire transceiver to searching for Jefri's signal, and although I can't find a reference I got the impression it took a while to find even with those resources.

RIP seems to only be a tenth of the distance from the Tines' world as Relay is, but the OOB has a technical advantage the other fleets likely lack:

Right now the Out of Band II was in the Vrinimi yards getting bottom-lugger enhancements and a huge stock of antenna drones. In one stroke the OOB's value was increased ten-thousand-fold.

Even then, it's no picnic:

Some days, no communication was possible. Other days, when the OOB antenna swarm was tuned in exactly the right direction and when the vagaries of the zone favored it—then Ravna could hear his ship.

I also think it's worth noting that I don't see that any of the fleets have anything to gain by intercepting or even corrupting communications between Jefri and the OOB.

So, I think there are three reasons not to be concerned about the fleets intercepting Jefri's messages:

1. The fleets are likely unaware that the messages even exist, and almost certainly don't have the information necessary to aim their antennas sufficiently.
2. The fleets also probably don't have sufficient antennas to receive the messages even if they were looking in the right place.
3. The fleets have nothing to gain by intercepting the messages anyway.

(Also, you didn't specifically ask about this, but I think it's worth mentioning: Ultrawave is described as "directional", which probably means that the fleets pursuing the OOB would be unable to receive the messages sent from the OOB to the Tines' world.)

Answer 2

It's going to be hard to give a good answer because the author never gives us much by way of detail on how the FTL communications work. The characters just take it for granted rather the way people here-n-now take radio, television, satellite feeds, cell phones, direction microwave comm-links, etc for granted (notice how the technologies I list are all "radio" based, but have very different details).

We know that FTL flight generates detectible signals in the FTL communication band, and we know that the communications system is not heavily disrupted by those signals, which leaves open the possibility that the FTL comm system is tunable or even that it uses frequency hopping or ultra-broadband. That gives us the possibility that the pursuers know that there is communication going on but not the contents.

On a similar note, we also don't know what type of cryptographic system might be in use (we do know that public key crypto is not generally safe in the Beyond).

[pure, unsupported speculation] Jefri was in communication with Relay for a long time before the flight began, so they could conceivable have established a key schedule then (when no one else was looking and it would have taken a Relay-like reciver array to eavesdrop). Indeed, the lander's automation could have done it without human or tine intervention, though this could be a bit of a stretch so close to the Slowness.