CPU time. The required Diffie–Hellman keys to achieve a security equal to AES would have been much bigger or require elliptic curve cryptography, making the handshake more expensive in terms of used CPU time. Effectiveness Analysis of the BitTorrent protocol encryption (a.k.a. MSE) has shown that statistical measurements of packet sizes and packet directions of the first 100 packets in a TCP session can be used to identify the obfuscated protocol with over 96% accuracy. Criticism Bram Cohen, the inventor of BitTorrent, opposed adding encryption to the BitTorrent protocol. Cohen stated he was worried that encryption could create incompatibility between clients. He also stressed the point that the majority of ISPs don't block the torrent protocol. In 2006 Cohen wrote "I rather suspect that some developer has gotten rate limited by his ISP, and is more interested in trying to hack around his ISP's limitations than in the performance of the internet as a whole". Many BitTorrent community users responded strongly against Cohen's accusations. Cohen later added encrypted connections to his Mainline client with the ability to receive but not originate them. Notably, when μTorrent was purchased by BitTorrent, Inc. and then became the next mainline release, the ability to originate encrypted connections was retained, but it became turned off by default. In an interview in 2007, Cohen stated "The so-called 'encryption' of BitTorrent traffic isn't really encryption, it's obfuscation. It provides no anonymity whatsoever, and only temporarily evades traffic shaping." Notes References External links "Message Stream Encryption". Vuze. "ISPs that shape BitTorrent". Vuze. "BitTorrent End to End Encryption and Bandwidth Throttling - Part I" with µTorrent developers. Slyck News. "BitTorrent End to End Encryption and Bandwidth Throttling - Part II" with Azureus developers Slyck News. "BitTorrent and End to End Encryption". Slashdot. "Tracker Peer Obfuscation". BitTorrent.org. "Identifying the Message Stream Encryption (MSE) protocol" for Statistical Protocol IDentification. SourceForge. "Block P2P Traffic on a Cisco IOS Router using NBAR". Cisco. "Aria2c VPN/Proxy Tutorial". GoTux. BitTorrent Cryptographic protocols