A few years ago, I wrote a client (tortunnel) that connects directly to Tor exit nodes and pretends to be a full circuit, allowing you to use Tor exit nodes as

A few years ago, I wrote a client (tortunnel) that connects directly to Tor exit nodes and pretends to be a full circuit, allowing you to use Tor exit nodes as one hop proxies. I'm sure that things have changed since then, but I got to know the protocol while writing that, and my recollection was that Tor traffic would be easy to detect: 1) Most people aren't using bridge nodes, and are instead connecting to Tor nodes publicly listed in the consensus. No DPI necessary. 2) Tor clients/servers used to signal their intent by including "special" cipher suite combinations in the TLS handshake. IIRC, they later switched to doing a "normal" looking TLS handshake with an immediate TLS renegotiation once the outer handshake was complete. That's a very distinctive traffic pattern. 3) All writes were translated into cells that were padded to 512 bytes. So by design, all Tor traffic looks the same. 4) The circuits were much longer lived than a standard TLS connection. My sense was that Tor was originally designed to use TLS for innocuous egress filtering compatibility, rather than for explicit censorship resistance.