A specific X-and-below is required because the RF protocol was reverse-engineered, presented at DEF CON 19 (2011), and the manufacturer locked it down immediately (PSK, gg). The new protocol has not been reverse engineered (this is for Medtronic Minimed)
A newer style of RF pump from a different manufacturer (Insulet OmniPod) has been de-capped and had its protected-mode firmware scanned, and has been disassembled and picked through - and re-flashed firmware has been sent to that pump and works fine, and we understand the cryptographic protection algorithm (we can talk to them) and a great deal of the protocol. That still leaves a massive "forward engineering" and integration efforts that must be non-commercial by nature (because laws)
edit: there are literally 7 of us that have access to the RE'ed firmware repo (it's a private github repo) - PM me if you're interested (there's a really irrelevant NDA that is involved, which I think is spooking wider sharing)
Pump manufacturers are not technology leaders and have no forcing function to create open systems. There is no reason they could not publish the protocol and also allow me to enroll a key (knowingly voiding affected aspects of the warranty) and interact with a device that is legally part of my person.
Of course, this is mostly a USA problem: for other jurisdictions there are open compatible pumps (http://www.sooil.com/eng/product/) that have this, but they are not available (including for insurance support of the consumables) in the USA
Anyway, I would love to help the community with some reverse engineering.
"One of the most frequently asked questions is “I have a 723 pump but it has version 2.5B software version. Has anyone figured out a way to make newer model Medronic pumps compatible? Like flash older version of software onto my 723 2.5B pump?” The answer is “No. The ability to downgrade software versions in the pumps does not exist. It has been investigated and nobody has made any successful progress to that end.”"
I'm curious as to what form the investigation took. Are you aware of an online record of this investigation?
Are compatible pumps rare enough that the need to preserve them is constraining reverse engineering efforts?
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Edit: For those wondering what these things look like, here is the FCC submission including internal photos. FCC is involved because of the integrated wireless link.
https://fccid.io/OH21510
https://fccid.io/OH21510/Internal-Photos/Internal-Photos-239...
Looks like a System-on-a-Chip with separate memory chips? Can't make out the numbers. Opening in GIMP, it looks as if the photo has been doctored to remove chip numbers? That 12-pin unpopulated footprint on the processor board is for a test/JTAG header?