1Tor 2--- 3 4Tor protocol can use SSL to hide itself. These are examples: 5 6TCP 37.128.208.46:9001 <-> 172.16.253.130:2078 [VLAN: 0][proto: 91/SSL][132 pkts/93834 bytes][SSL client: www.jwrpsthzrih.com] 7TCP 172.16.253.130:2021 <-> 75.147.140.249:443 [VLAN: 0][proto: 91/SSL][28 pkts/8053 bytes][SSL client: www.5akw23dx.com] 8TCP 172.16.253.130:2077 <-> 77.247.181.163:443 [VLAN: 0][proto: 91/SSL][136 pkts/94329 bytes][SSL client: www.fk4pprq42hsvl2wey.com] 9 10It can be detected by analyzing the SSL client certificate and checking the name that does not match to a real host in 11addition of being a bit weird. As doing DNS resolution is not a task for nDPI we let applications do and then recognize 12SSL-tunnelled connections. 13 14See http://www.netresec.com/?page=Blog&month=2013-04&post=Detecting-TOR-Communication-in-Network-Traffic 15 16For this reason nDPI uses a heuristic, non-DNS based, approach to detect tor communications. If possible, apps 17should validate the certificate using the DNS. This is not something nDPI can afford to do for performance 18reasons 19