Thanks, changing the shunt resistor (2x47 Ohm, 5v supply) did help, but I did need to filter the power supply (via the LC filter on https://wiki.newae.com/CW308_UFO_Target) to remove remaining noise, which would otherwise be hidden in the traces, as below:
(Also, I wonder if the other components on your target board are affecting the power measurement?)
Here’s where it gets a bit wierd though - after software filtering and aligning the traces, I did a t-test on the last bit of ciphertext. I’ve found strong correlation, on the last bit only - and from what I can see, past the end of the crypto operation (the t-test spike at the start of the trace is a false positive, created by the alignment process).
Not sure if this helps at all - truth told, I’m a bit puzzled by this result (are you getting the same, for any bits?). I’ll keep studying the algorithm and reading code, let’s see where it goes.