Tor 0.4.1.x introduced circuit padding, to make it harder for network observers to recognize client onion service requests. Tor's circuit padding defense is in a similar position. Unfortunately, that defense is only available for relays running supported versions. One example is the Denial of Service defenses that we rolled out at the start of 2018 as an emergency reaction to a large scale attack on the network. And they can also make it harder to roll out some new features. Outdated relays make it harder for us to roll out important fixes. Any relay in the network that runs an obsolete version puts network stability and security at risk. Unfortunately, End-Of-Life relays have some negative impacts on the network. We may also fix smaller bugs that significantly impact user experience. Maintaining these versions means that the Network Team intends to fix major stability issues, security vulnerabilities, and portability regressions. There are a total of 85 different Tor versions, from alpha to stable, in use by relays today.Ĭurrently the Tor Network Team maintains 5 Tor version series: These relay versions represent roughly 5 years of Tor development. Other cutting edge relays are running our latest code in nightly builds and alpha releases. These relays are running Tor software versions that go all the way back to the 0.2.4.x series, which was released on December 10th 2013. Today, the Tor network is composed of more than 6000 relays.

Tor project hopes replace code