What about ssh over port 80? I realize that would have to be set up in advance from outside the country, but the question is are they using port numbers to aid in their filtering or deep packet inspection?

If they are dropping all encrypted connections, it doesn't matter what port you use for ssh, it'll be dropped.

How do they know it's encrypted? I mean would they block something that looks like gibberish but was plain text over port 80?

I like that idea. You could encode a block of octets with plain words. "\xC3\x08\x00\x23\xFA" would then actually travel on the wire as "Was named prefer to use the other especially in, every cast a chuckle on neithout getting. Into useful informash speech makes removing a featuring a move or usage actual considered!", and be decoded back at the other end. You'd have to use common words so it looks as innocuous as possible.

I doubt you'd need to go to such lengths, otherwise you wouldn't be able to transmit binary data such as images, either.

If.

That is why I asked the question.

They drop all secure connections. For security reasons, I had to access a VPS on port 33 (instead of 22), and in the past couple months I've been unable to do so.

That's an interesting data point, but port 33 is rarely used so deep packet inspection is still relatively cheap. I'd really like someone to test on port 80, then I'd believe that it's 100% coverage with deep packet inspection.

They have to be using ports. Deep packet inspection is far too expensive to do on a massive scale.