There's an extremely wide range of adversaries between "potentially capable of MITMing a network I use" and "potentially capable of screwing with my OS/browser's CA roots or actively acquiring and misusing an illegally obtained valid TLS cert for ubuntu.com".
Sure, most nation states can craft whatever TLS cert they want, with only some risk of bad press if they get caught signing a ubuntu.com TLS cert fraudulently via a CA they control/coerce. If those people are my adversary I'm screwed. "YOU'RE STILL GONNA GET MOSSAD'D UPON!"
A TLS connection for the download (and the gpg signature) protects against people like the disgruntled hotel IT guy, the kid futzing with the cafe wifi, an evil housemate, some crappy rooted IoT shit somebody hooked up to the wifi, an overly curious coworker or corporate IT drone, the red team in a company pen test.
I've heard the arguments here - that it's a difficult problem for all the mirror operators to add ssl certs, that it'll stop downloads being cacheable, etc. But I didn't really buy those arguments 5 years ago, and these days, with LetsEncrypt and HSTS - I think those arguments are even more bogus than they were in 2015...
Sure, most nation states can craft whatever TLS cert they want, with only some risk of bad press if they get caught signing a ubuntu.com TLS cert fraudulently via a CA they control/coerce. If those people are my adversary I'm screwed. "YOU'RE STILL GONNA GET MOSSAD'D UPON!"
A TLS connection for the download (and the gpg signature) protects against people like the disgruntled hotel IT guy, the kid futzing with the cafe wifi, an evil housemate, some crappy rooted IoT shit somebody hooked up to the wifi, an overly curious coworker or corporate IT drone, the red team in a company pen test.
I've heard the arguments here - that it's a difficult problem for all the mirror operators to add ssl certs, that it'll stop downloads being cacheable, etc. But I didn't really buy those arguments 5 years ago, and these days, with LetsEncrypt and HSTS - I think those arguments are even more bogus than they were in 2015...