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Dropbox Knows when You Share Copyrighted Files Without Sneaking in Your Account

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A tweet went trending on Sunday, pointing to how the user received a DMCA notice that a file has been blocked from being shared on Dropbox. The tweet got more than 3, 000 retweets within a few days, but the system has been in place for years. It allows Dropbox to screen and block pre ? selected files from circulating without the system knowing what the user?s files are. This anti ? infringement system saves Dropbox from being raided by the Feds.

How it Works


Hashing is a common word in the world of computer science, where it allows Web services to screen passwords without storing your original password. It is also used to confirm that a file remained unchanged as it traveled from one user to another. In this scenario, the hash function was used to detect a unique identifier based on what is fed into it.

Simply put, this identifier could tell you if a file has a duplicate version somewhere. The process is a one way street as the hash could not determine what the original file is without owning a copy of the file for comparison.

Like a Fingerprint

The hash is like a fingerprint: the print is unique, but you can never tell who owns it unless you have a record to identify its ownership. The DMCA is a hash ? based system that cannot tell what the file is, but knows when an exact same file has been reported to be taken down. When you upload a file to Dropbox, the hash is generated and your file gets encrypted to prevent unauthorized users from opening it.

The Dropbox legal team verifies the DMCA complaint, and then adds the file?s hash to the company?s hash blacklist. All hashes included in the list are legally not allowed to be shared. If the file you shared is exactly the same as what the copyright holder complained about, then it will be blocked by DMCA from being shared with other users.

Dropbox Statement

Dropbox released a statement defending itself from the accusations, saying that they receive DMCA notices to take down copyrighted links. They follow a fair process based on the law and then decide to disable the link. Dropbox insisted that they use hashes to determine the files that must be blocked and does not check private folders for security reasons.

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