Last Saturday, a designer named Darrell Whitelaw posted on Twitter a picture showing one of your folders in Dropbox blocked for alleged copyright infringement. The tweet had as much impact – certainly more than expected Whitelaw – many people assumed that the blockage is in a new or even service staff scour accounts looking for illegal material resource. But it is not so.
As with most online services based in the United States, Dropbox needs to be subject to the laws of the DMCA (Digital Millenium Copyright Act) which, among other rules, determines which content is irregular indisponibilizado if the rights holder so requests.
To TechCrunch , the company explained that every time it receives a notification of copyright infringement, denounced the link is blocked, but the file remains intact on the user account. It happened in the case of Darrell Whitelaw. This is the way the company found to prevent the file from being shared and bring you trouble with the law.
The most interesting part comes now: to prevent users generate new links to blocked material sharing, Dropbox implemented a verification system that calculates the hash of the file. Hashes associated with files protected by law are then recorded in a kind of “blacklist”.
Thus, if the user attempts to share a material not previously available, the system will automatically lock your and immediately, because the computation of hash of a file that has not changed, even when it is a copy, will always result in the same code.
In summary, the system of protection of Dropbox works like this: every time you upload a file to share it, its respective hash is calculated, if the code is equal to any of the existing block list, the sharing is prevented at the same time.
It may seem an exaggeration, but this way Dropbox can avoid legal problems and has one gun to prevent links to content stored on their servers to be shared on forums or download pages, for example.
Ultimately, it is an interesting system and indicating that no employee is at any moment by checking what is valid or not in other user accounts (although this is possible). Nor do we face a new idea: Dropbox uses hashes for years, not only to check illegal content but also to prevent there being two or more files are exactly alike in their servers , saving storage resources.