I’ve always found Bram Cohen, author of the BitTorrent protocol, very fascinating, perhaps mainly because he’s allowed myself and countless others the ability to share content in ways still yet to be imagined.

So whenever he shares his thoughts on BitTorrent I always sit up and take notice.

In this case it’s nothing spectacular, but he does give a simple explanation of why BitTorrent performs so well why dispelling the myth that content popularity drives download speeds.

He writes:

There’s a classic fallacy because if one person stands up during a concert they get a better view, then if everybody stood up during a concert they’d all get a better view. This is of course is not true – they wind up slightly worse off by all standing, because they all compete with each other for a view. The same thing happens with downloading from a server. In general, web servers will give about the same rate to every client downloading from them, so if you open many more connections than everybody else you get a greater proportion of the bandwidth and hence a better rate. But you do so simply by taking bandwidth from other downloaders. The overall supply of upload is unchange, it’s simply being shuffled around. If everybody does the same thing it results in overall slightly worse performance and you’re basically back where you started, but with a bunch of headaches tacked on.

So why does BitTorrent perform so well? Quite simply, because it does a better job of finding more places to do uploading. Any peer which is downloading is in general willing to upload as well, and their uplink is usually unutilized, so if you can get a peer to start uploading as soon as it starts downloading, and keep uploading as long as possible, and saturate its link while it’s uploading, then overall performance will be better. It doesn’t necessarily help to transfer over more connections, or make more different things available at the same time, or use error correcting codes. In fact, all of those are a complex tradeoff between benefits and costs, with the net result being that small amounts of them can help reliability and robustness, but in general it’s good to keep things simple and be polite to the network.

On the internet, the formula is bytes downloaded = bytes uploaded. It’s that simple.

Indeed it is.

jared@zeropaid.com

In both Northern and Southern California yesterday, representatives of BitTorrent Inc provided key insights into their current state of affairs and also hinted at its future.

At the Online Media, Marketing, and Advertising Conference and Expo (OMMA) that was held in Hollywood, CA, a panel session called “Big Media–Disintermediated” was conducted where Eric Patterson, vice president and general manager of consumer services for BitTorrent Inc., said that it will be looking to launch a new ad-supported Net TV service by years end.

He said that “We see us moving to an advertising-supported model at the end of the year so people can consume TV shows in the same way they consume programs on television.”

This announcement could be aimed at the new Joost service which has already lined up Viacom as a provider of TV and film content for the ad-supported streaming Net TV service.

Up in Northern California Bram Cohen was a keynote speaker at the New Video Summit in San Jose, where he was interviewed by Andreas Kluth of the Economist.

The BitTorrent Entertainment Network has been dogged by problems with the way that content DRM restrictions have both hampered playback, as well as discouraged many to switch from pirating the content DRM-free from BitTorrent tracker sites and to purchasing the content from their site.

Bram Cohen said that he feels that DRM software and the implementation of it in Windows is to blame for slowing the shift of video to the Internet.

He said that We’ve got a problem we share with everyone. Content owners want a DRM, consumers know what a DRM is and they don’t like it.”

“We are using Windows DRM because it is the only solution that has been vetted widely, but we are not happy with how it affects playback from a technology point of view it sometimes makes playback not work,” Cohen continued.

The BitTorrent Entertainment Network is now infamous from playback and download problems. It was noted before how some have even had difficulty getting content to play in Windows Media Player 11, and how others have paid for a song download that they could never get to download properly.

Now to be fair, Cohen knows that the DRM is only hamstringing his efforts, noting previously that “We are not happy with the user interface implications” of digital rights management, or DRM. It’s an unfortunate thing. We would really like to strip it all away.

Unfortunately for him, I don’t see the movie studios giving into that one anytime soon. Who likes DRM more than content owners?

The last bit of commentary that Cohen provided at the NVS in San Jose was about how BitTorrent Inc. now has the largest catalog of digital video on the Web. This may be the case as iTunes is still limited to Lionsgate, Disney, and ABC but, it seems as though iTunes has better managed the potential of its catalog thus far than has the BitTorrent Entertainment Network. I guess time will tell but, the DRM issue will need to be addressed first and foremost. Perhaps some sort of Zune partnering would help it succeed, as the iPod, iTunes player and content combination seems to be the key. But, will anybody be willing to buy a Zune for this reason alone?

In any event, its good to see that BitTorrent Inc. has become complacent with their new BitTorrent Entertainment Network and are still thinking outside the box to make it succeed. Now if only they could get content providers oTV episodes will cost $1.99, which is a similar to the price charged on competing sites such as Apple’s iTunes.ff their back long enough to make it the best that it could possibly be.

digg_url = ‘http://digg.com/tech_news/BitTorrent_Entertainment_Network_to_launch_ad_supported_NetTV_service’;

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SOULXTC: “walkin’ the streets of P2P”

Tools for exploiting the weak system used by private BitTorrent trackers to monitor user ratios are becoming increasingly user-friendly and available. Despite being a widely publicised problem for nearly a year, there are still no obvious solutions.

The exploit was first publicly highlighted in September last year, at Xyflar.

RatioMaster, who develops cheating software, explained to Zeropaid. “Private trackers keep statistics about how much you’re uploading and downloading. Those stats reported by each client. There are many ways to report wrong statistics.”

(CLICK ON IMAGE TO ENLARGE)

Private BitTorrent trackers rely on individual clients for information on how much the client has uploaded. Due to the decentralised nature of a BitTorrent swarm, trackers are unable to monitor the actual uploaded and downloaded data, so have to rely on the each client being honest.

By interrupting messages to the tracker, cheaters can change the reported upload and download statistics.

Xyflar explained how to exploit this weakness last year. By using freely available software, the site demonstrated how to increase the amount of uploaded data reported, hence giving a better ratio.

Despite being reported by major technology and file sharing websites, the exploit’s publication did not cause the predicted flood of leechers. Arguably this is because the exploit requires unfamiliar software and lots of time to execute. Each time a user wants to fake their upload, they must “catch” and then edit a packet sent to the tracker. Falsify the upload by too much, and anti-leeching scripts will catch the exploiter. Falsify by too little and the exploiter would need to catch and edit too many packets to make the exploit feasible.

This process has been automated by groups of cheaters, mostly in small communities who require a minimum number of forum posts to access the files. Steadily these cheats are becoming more readily available from a new wave of developers.

Theoretically, since the exploit does not require any abnormal code to be sent to trackers, the exploit is virtually impossible to detect.

Seba14 develops freely available hacked versions of uTorrent to help people with slow or restricted upload. Using his software is no different to using the standard version of uTorrent, making it shockingly easy to use. The software cheats by multiplying any upload by a factor of ten. He told Zeropaid, “If you use leecher mods carefully, the admin’s of tracker sites have no chance to detect you at this time, because the tracker scripts don’t know if the sending data of mods is real or fake, they see only a number.”

Another developer called RatioMaster creates ratio cheating software of the same name. Unlike the uTorrent hack by Seba14, his software is free standing and does not actually download or upload any data. Instead, a randomized speed within user defined parameters is reported to the tracker. RatioMaster automatically cuts off if the number of leechers on the torrent falls below a given figure.

RatioMaster is more cautious than Seba14 about the possibility of being caught.

“Some trackers have some anti-cheating scripts, which work on some cases of particularly suspicious reporting, like for example someone uploading too many too fast. If an anti-cheating script is good, I believe it can catch 90% of cheaters,” he told Zeropaid, before conceding, “Most of the time they ban people who don’t even cheat.”

Zeropaid tested both pieces of software at Torrentleech.org, Ilovetorrents.com, Filelist.org, Bitsoup.org and Oink. RatioMaster was set to spoof as Azureus. All testing was done at semi-realistic upload speeds.

Despite reaching a ratio of nearly 15 on some sites, the only ban came from Oink. This came after RatioMaster was left running for a long period of time, without the minimum leech safety catch enabled.

“It’s impossible for all users to have ratio above 1. In reality 99% of users can barely stay above 0.5 by seeding 24/7,” said RatioMaster.

“Good tracker scripts can calculate the average upload speed between the tracker updates and so find ‘heavy’ cheating. Scripts exist which show the admin which users have an upload speed more than specifically value,” Seba14 explained. “So the admin can ask the user, ‘what’s your connection?’, if the user lies, then the admin can do nothing.”

Feelings about the availability of this software run strong, as people feel that any leeching is anti-P2P. In an extreme case, one post on the RatioMaster forums compares the developers to child molesters.

However, Seba14 is defensive of releasing his software publicly. “Because the mods on my blog are free for all, the tracker administrators can test them and search for a way to detect them. Maybe they will find something,” he said.

RatioMaster agrees that increased availability of the software will lead to more solutions. “Some of the private trackers will employ anti-cheating measures that will catch most cheaters, it’s not that hard,” he justified.

However, no adequate solutions to stop people leeching have been implemented yet, despite the exploit being publicly known for nearly a year now.

Since the exploit relies on standard protocol code, the only solution may be to change the BitTorrent protocol to force clients to inform the tracker how much it has downloaded from each peer. Although the large private tracker sites could easily afford this, for many bandwidth is at a premium. Furthermore, that would leave users vulnerable to hacks developed to deliberately get other users banned.

“The only way to protect private trackers is by banning all clients which have modifications. Another way is the programming of an own client for each tracker,” Seba14 suggests. However, many sites already ban a long list of clients and are reluctant to ban popular clients like Azureus and uTorrent.

RatioMaster feels that stopping leeching is the wrong focus. Administrators should instead focus on encouraging seeding.

“Tools like mine and other cheating utilities and modifications will hopefully make torrent trackers consider applying things that encourage people to share,” he rationalized. “Lately torrent sites that really care about users more than about money have started to apply mods that encourage actual sharing. Like a mod that improves your ratio regardless of how much you upload, just by seeding (even if nobody leeching from you), so it encourage people to seed. Otherwise you can seed for days, but if nobody is downloading from you, your ratio will be the same.”

In the short term it does not look like there is going to be the doomsday scenario of leechers flooding and destroying private trackers. Like the rest of file sharing, the site owners will need to rely on good human nature for the sharing.

Zeropaid spoke to a contact close to the administrators of large private trackers, but the administrators refused comment.

***Special thanks to Michael Ingram

Digg It!!

Some private BitTorrent trackers monitor their members to ensure users upload as much as they download. Supporters say monitoring the upload/download ratio encourages sharing, resulting in faster download speeds. Those who do not reach the minimum ratio are normally banned from using the tracker.

To monitor user ratios’, trackers depend on clients reporting their true upload and download statistics. Programmers are increasingly exploiting this vulnerability by developing software which falsifies upload and download reports to the tracker.

The exploit was first widely publicized over a year ago, but no solution has yet been found. Only standard code is sent to the tracker, which is impossible to verify using the current BitTorrent protocol.

As ratio cheating software is becoming easier to use and more readily available, the pressure is on Bram Cohen and BitTorrent Inc. to update the protocol to catch ratio “cheats”.

However, Bram Cohen has told Zeropaid that he stands by the comments he made in 2005, arguing that ratio monitoring is destructive to sharing.

“[Leechers are] engaging in perfectly reasonable and non-destructive behavior and the site is trying to punish him for it, thus fostering the creation of clients which lie about their statistics. This is the site’s fault, and the result could do serious damage to the value of BitTorrent statistics generally. Sites which do this are being extremely destructive, and the way they grandstand about how they’re fostering sharing really ticks me off,” he said.

Bram argues that the tit-for-tat nature of protocol is sufficient enough to stop destructive leeching. The BitTorrent protocol is robust enough to handle file sharers who limit their upload and do not seed after the file has finished downloading.

“Even if almost everyone quit the instant their download was completed you’d still have decent download rates, they’d just be closer to everyone’s upload rates,” he explains.

By definition this means download speeds will be slower, which could easily be classed as “destructive”.

Still, according to Cohen, the alternative of monitoring ratios is worse.

“What typically happens in a single torrent is that at the beginning upload and download ratios are reasonably correlated, then over time people finish downloading, and some of them leave, but a significant number of seeds remain. After a while there’s a period of time where there are many more seeders than downloaders. Anyone who joins the torrent at this late time will be generally get a download rate limited by their download capacity, and anyone who tries to upload to them will only be able to do so at a low rate. Such people will have very out of whack upload/download ratios, but they’re downloading from otherwise unutilized upload resources, and hence not being anywhere near the drain on the system that their total upload/download ratio indicates,” he explains.

“Just a little bit of threatening to ban people can get the overall balance to be very heavily weighted on the side of uploading, making it difficult for people to accomplish a reasonable amount of upload even if they try.”

To encourage sharing beyond the tit-for-tat system, Cohen suggests that user ratios should not be monitored at the peak of each swarm, or if a torrent is heavily seeded. Alternatively, he suggests adapting an alternative method for calculating the ratio, which takes into consideration the health of a torrent:

“When a client reports new downloads to the tracker, the tracker can multiply the amount by (number of current peers total – number of current seeds) / (number of current peers total) and add that to the ‘total downloaded’. This results in most people having a ‘ratio’ of more than 1, but that isn’t actually a problem unless you’re more interested in mathematical purity than practical behavior.”

So far, the BitTorrent world has not been turned on its head by ratio cheating software, but there is no accounting for the future. Without support from BitTorrent Inc. to upgrade the protocol, private tracker administrators who want to keep ratio monitoring may be forced to develop a new protocol.

*Editor’s Note: This story is a follow up to a previous article

BitTorrent Ratio Exploit Software on the Increase

He can solve two Sudoko brainteasers during his 30-minute commute on the ferry between Marin and San Francisco. And he has earned a high score of 320 on Tringo, a combination of Tetris and Bingo.

Other puzzles aren’t so easy to crack.

Relating to people can be difficult for Cohen, who has Asperger’s syndrome, a form of autism that affects social skills. Unlike Sudoko or a Rubik’s Cube, people don’t always follow the same patterns. But Cohen has learned to read subtle body language and facial expressions. He practices making eye contact, detecting sarcasm and not taking it literally, and understanding other cues that are natural and automatic to most people.