Neil Armstrong, products director at BT-owned ISP PlusNet, said: "It isn't possible for us to tell if a customer is downloading a copyright file or not unless we specifically 'snoop' every packet on the customer's line.
"We would obviously only do this where we have a proper request from the relevant legal authority to do so, and even then it is unlikely we would be able to see inside encrypted payloads."
The most popular BitTorrent client, uTorrent, can be configured to use RC4 encryption to obscure torrent streams and header information. Armstrong said that although future DPI gear may be able to grab some header detail, the music or movie itself is likely to remain inaccessible.
So-called content filtering software from Audible Magic cannot peer inside encrypted packets, either.
The rapid acceleration in encryption isn't limited to BitTorrenters. Estimates say torrent traffic accounts for about between 50 and 60 per cent of all file-sharing. Usenet, which the RIAA recently said is a bigger offender than Kazaa-type services, accounts for about another 25 per cent. It's set to see more scrambled files shared over it, too, as providers including Giganews now offer SSL encryption.
Paul Sanders, part of the team of music and ISP veterans behind PlayLouder, the first "Media Service Provider", which will let subscribers share music freely and legally in exchange for a small premium on the monthly broadband bill, sounded the alarm. "I think this trend is absolutely a warning to those people in the music industry who believe they can win this war," he said.
"There's got to be a commercial settlement. Both sides [ISPs and the record industry] are destroying the value in music." Sanders believes the much-debated blanket licence and download services that are "better than free" are one the way out of the arms race with determined freeloaders.
Even if BitTorrent encryption can be defeated somehow, there's another P2P protocol on the horizon. It's being specifically designed to dodge monitoring systems. ®