Data recovery help for non-booting teracube 2e

I have a Teracube 2e (2020 SN), and it recently stopped booting. I can connect to it with SP Flash and download partitions, but fastboot doesn’t see it, and dmesg reports that the USB connection keeps closing itself after a few seconds. And, unfortunately, throughout all of this, the screen remains stubbornly blank, so I’m not even sure if I’m reaching any of the boot/recovery menus with various combinations of the power and volume buttons. Potentially, I’m facing a case of a/b booting, but with the display apparently non-responsive, it’s difficult to tell what’s going on (and without fastboot, I’m not sure that’s fixable anyway).

At this point, barring more clever troubleshooting ideas, I’d just like to copy off the data on the data partition and then send off the phone for repair/replacement. Unfortunately, while I can dump the user_data partition just fine, it’s encrypted. I have my PIN, of course, so then the question is how to find the encryption key, decrypt it with the PIN, and then use the decrypted key in turn to decrypt the dumped user_data.

Any suggestions (either about booting or decrypting) would be most appreciated.

I have a hunch that it may not be possible to decrypt data like this, however I’m checking with the Devs if there is a way.

Have you tried flashing the factory OS again using SP Flash (in download mode and with userdata partition unchecked)?

Thanks for the reply.

I have not yet tried reflashing the OS; I was holding off because I wasn’t sure precisely where the encryption keys were stored, and didn’t want to accidentally blow them away. I suppose the thing to do would be to dump all the other partitions just in case, and then proceed with a system-only flash.

I will update with my progress.

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So, I am sad to report that, after a reflash minus userdata, the situation remains unchanged (the display is non-responsive and the phone appears not to boot), and dmesg shows the same set of messages, namely:

[45717.857156] usb 1-5: new high-speed USB device number 23 using xhci_hcd
[45718.009822] usb 1-5: New USB device found, idVendor=0e8d, idProduct=2000, bcdDevice= 1.00
[45718.009828] usb 1-5: New USB device strings: Mfr=1, Product=2, SerialNumber=0
[45718.009830] usb 1-5: Product: MT65xx Preloader
[45718.009833] usb 1-5: Manufacturer: MediaTek
[45718.032744] cdc_acm 1-5:1.1: Zero length descriptor references
[45718.032752] cdc_acm: probe of 1-5:1.1 failed with error -22
[45718.072869] cdc_acm 1-5:1.0: ttyACM0: USB ACM device
[45720.681203] usb 1-5: USB disconnect, device number 23

(this repeats every ~5-10 seconds while the phone is connected, with device number incrementing)

I was just wondering if you’d had any luck talking to the devs about this. I did find a file entitled “encrypted-key” in a folder called “unencrypted” in the root of the userdata partition, along with files that identify the encryption type as AES 256 XTS (which makes sense with what I know of encryption on Android), but I’ve been unable to determine how to decrypt that key with my PIN.

Sorry - I did get their response. Unfortunately, It is not possible to decrypt the user data off the phone.