Everyday, I see many of my friends downloading movies off P2P networks like BitTorrent. Isn't there any way for those hardworking movie producers to save their work from being distributed like this?

As a security enthusiast, I'm interested in knowing the technical methodologies for stopping the files from spreading over BitTorrents. I know securing 100% is not possible, but how far can we really go? Or, how difficult can we make it?

PS: I've heard that there are some security companies which protect movies from being spread over internet (I guess that includes torrents too?). I wonder how they do it?

  • 9
    It's pretty easy. They must not show the movie to anyone to make sure no file exists in the first place. Oct 28, 2011 at 9:02
  • 10
    How far? How about bribing congress to pass ridiculous legislation.
    – rook
    Oct 28, 2011 at 14:10
  • 3
    Had to wonder if this was a slightly planted question especially with "hardworked movie producers" and the timing relative the ridiculous legislation :)
    – Rakkhi
    Oct 29, 2011 at 10:37
  • Perhaps a more social and educational approach would work better than a technical one.
    – Celeritas
    Jul 12, 2012 at 20:03

4 Answers 4


One tool for trying to enforce DRM is watermarking, i.e. embedding within the media itself a mark which is (almost) invisible to the human viewer, but which is resilient to copies (i.e. the copy has it). Once media copies are individually marked with the identity of their rightful owner, you can trace the origin of fraudulent copies. Do not get it wrong: it is not the watermarking which prevents copying, it is the threat of the lawyer commandos you will send to smite the guy who was at the origin of the leakage.

Watermarking is a hard problem, notably because it must rely on embedding information which is not visible, i.e. exactly the kind of thing that compression algorithms remove. Moreover, even with a digital-only media, there can be cropping or stretching or colour rebalancing or resampling or whatever, so watermarking must rely on properties which are not at the "pixel" level. The name is well chosen: watermarking is quite similar to the act of writing... on water.

Since the wannabe pirate has a vested interest in removing the watermark, this implies that the scheme must be "well hidden". There is a generic attack for that, which consists in degrading image quality until the mark has disappeared; by dichotomy, one can find the precise alteration which kills the mark, at which point it becomes easy to remove or modify the mark without visually altering the media. Therefore, the only kind of watermarking which really resists attacker is the one where the attacker has no way of testing whether the mark is there or not. So we are talking about professional investigators roaming the Torrents on your behalf, looking for the mark in shared files; and not about watermarking checks within graphics cards.

Another tool for enforcing DRM is targeted distribution: each copy of the media is encrypted with a key which is specific to a single reading device. There is a nifty tool called broadcast encryption which is what Blu-ray employs. Each single device able to read Blu-ray discs has its own secret encryption key; one can imagine a Blu-ray disc as containing:

  • the media, encrypted with a per-media key K;
  • encrypted copies of K by each device key Ki, for all existing devices in the world.

Then a media distributor may opt to not include the encryption of K with K678349 if it turns out that the owner of the device 678349 has "misbehaved". Moreover, all "normal" devices will insist of decrypting media, i.e. will reject unencrypted data. The niftiness of broadcast encryption is that is allows for doing that without having to embed billions of encrypted copies of K in each disc.

There again, the technical tool of broadcast encryption does not prevent copying; it merely allows for retaliation on wide scale illegal copying ventures, and ultimately may result in a "market split": namely, to ensure that, in order to view illegally copied contents, perpetrators must use a non-standard device such as a computer or a physically modified reader. There will be people who do that; but there will also be people who do not.

Remember that anti-piracy tools are economically justified, and economy is statistics: media distributors do not want to kill unauthorized copying per se, they just want to make more money. And they view an unauthorized copy as a loss, since the copier could have bought the genuine thing instead. Any tool which reduces the amount of copying can become a "big win" (a technical term meaning "millions of dollars").

The common point in all these tools is that they do not technically prevent data copying. Because it is not possible: if the user can see it, he can record it and then see it again. The tools are meant to support larger anti-copying process which do not happen in the computer world, but rather in the mundane real world where police forces may bash your door at 6:00 AM.

If we are to believe the major media distribution companies, anti-copying strategies like those explained above are totally inefficient and legislators MUST take immediate actions such as raising new taxes for their exclusive benefits. According to the same major media companies, anti-copying strategies are 100% effective and if you share a single movie on the Internet, they will get you and send you to Guantanamo within 48 hours. Whether in reality DRM works is anyone's guess.

  • 7
    That final paragraph is a very good point. Especially the final sentence:-)
    – Rory Alsop
    Oct 28, 2011 at 14:31


  • Offering good codecs
  • NOT Preventing DVD players from fast forwarding through FBI warnings and 15 minutes of marketing
  • Easy distribution: kindle, itunes, etc
  • Allowing fair use: CSS (DMCA), moving between devices, no region locks, etc
  • Reasonable pricing for electronic goods

If there is more value in buying the good then downloading from shadowy networks, people will buy. I remember being so pissed that the Harry potter video had 20 minutes of DVD locked previews that I wished I would have pirated it instead.

Don't treat the customer as the enemy.

  • 4
    I think this is an often overlooked response. It's our job to make things secure, but also to make them usable. If our controls are too onerous, no matter the difficulty, they will be bypassed by someone enterprising enough. If you provide content at a purchasable price, that is usable on as many platforms as possible, people will buy it. You could spend incredible amounts of time and effort to lock it down, inevitably locking your customers into certian configurations. But that will just create a greater demand for consumers to pirate the content.
    – Ori
    Oct 28, 2011 at 18:35
  • Exactly right @Ori. The most secure system in the world in in a waterproof safe at the bottom of the ocean, but it has no value because no one can use it.
    – this.josh
    Oct 28, 2011 at 23:24
  • Good answer Netflix, Itunes shows this is the only way.
    – Rakkhi
    Oct 29, 2011 at 10:38

The Digital Rights Management (DRM) question has been around for a while. The simple answer is:

No - anything which one individual has can be shared

Have a read of this question, and the others tagged for some discussion. Most of the protection that is put in place fails, on many levels:

  • Identifying files through checksums or signatures - these can be changed
  • Tagging files - tags can be removed
  • Removing all access to digital media - copiers will video screenings and make their own media
  • Monitoring sharing communities - some success, but penetrating the more secretive communities can be hard
  • etc
  • I understand what you mean, but it might be helpful to explan that physical control can defeat remote attestation. Additionally some of the methods for circumventing DRM involve the analog hole where quality of the copy suffers. The entertainment industry was unconcerned when multigeneration copy pushed quality down: VHS and casette tapes. However modern zero-defect copying has attracted their attention.
    – this.josh
    Oct 28, 2011 at 23:21
  • @this.josh Although lossless copies are available, the vast majority of the pirated media available is compressed (MP3, x264, etc.). You can get copies with great quality even if you are just exploiting the analog hole. That being said, unconcerned, you say? en.wikipedia.org/wiki/Home_Taping_Is_Killing_Music
    – Null
    Jan 17, 2013 at 16:36
  • @Null - just for amusement. fbcdn-sphotos-g-a.akamaihd.net/hphotos-ak-prn1/…
    – Rory Alsop
    Jan 17, 2013 at 16:41

Piracy is here to stay. Not to mention it is pretty much impossible to prevent torrenting.

Also look up I2P.

  • 1
    I hope that in the 4 years since the author asked this question, we've all learned a little something about digital piracy and p2p.
    – J Kimball
    Sep 17, 2015 at 16:48
  • Matters not. I2P is a darknet garlic routing protocol that is optimized for torrent traffic. End 2 end encrypted with untraceable scattering of encryption data fragments sent along random connections.
    – WAR10CK
    Sep 17, 2015 at 17:41

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