Old topic, but I have the same problem, with the same software developer. Instead of timeshift, I’m trying to install the aptik software. But it uses the same repo and key. My question is regarding the last post. The instructions linked above have the following steps:
Try this, assuming you’re using Ubuntu:
1 In your web browser, go to http://keyserver.ubuntu.com:11371/pk...39676F7613768D
2 Copy the pgp public key block, including the lines saying “begin pgp public key block” and “end pgp public key block”
3 Paste it into a text file and save it anywhere.
4 Open System->Administration->Software Sources, put in your password if asked, and click on the Authentication tab
5 Press the Import Key File button, select the file you just saved, and press OK
How do I do the equivalent of step 4 in PureOS?
Thanks.