How to know you are sharing a tort file

Dropbox a class of networked storage tools how do you know that you have shared the infringing documents? Are they constantly prying into the privacy of users? No, no, actually they didn't do anything bad.

If you know what "file hash matching blacklist" means, you can skip the rest of this article. Dropbox checks whether the hash value of the shared file matches to the prohibited list, and if it matches, blocks the sharing of the file.

If these words make you sound confused, please continue to understand.

Operation Principle:

In computer science, there is a very popular concept called "hash value" (hashing).

It's very common--from allowing Web services to view but not storing your passwords--to determine that a file has not changed during user transfer.

In this case, the hash function is an algorithm that presents a unique identifier based on what you enter.

A hash value is usually just a string of digits and characters. The hash value of a file may be 4F2900F2FDFAF, while the hash of the B file may be dba7b12a19fe9. The hash value of the Dropbox may be much longer than this example (which allows for more hash values), but we all know what it means.

If you execute the hash function correctly, you will get the same identifier 2 times against the same file--but even a slight change to the file will completely change the hash value.

This identifier can be used to tell you if the file is identical to another file--but this is a one-way channel. Hash value but tell you what the original file is, unless you already know or copy the file for comparison.

This may make you think of hash values like fingerprints. Everyone's fingerprints are unique, but they can't be used to identify someone unless you have a fingerprint of that person to match. Similarly, a DMCA compliance system based on a hash value cannot say what this file is unless it is identical to the file that has received the revocation request.

When you upload a file to Dropbox, you do two things: the hash value is generated, and then the file is encrypted so that any unauthorized user (hacker or Dropbox employee) cannot open the file through the Dropbox server.

(For encryption: Dropbox master the encrypted key, so if you receive a legitimate request, they can open your file.) Their system has established a monitoring mechanism so that employees cannot peek at your files. )

After the Dropbox legal team verified the DMCA complaint, Dropbox added the hash value of the file to a large blacklist containing all known hash values of files that could not be legally shared. If you share a link to the file, Dropbox checks to see that the file's hash value falls within the blacklist range.

If you share a document that is the copyright holder's complaint, the document will be banned from sharing with others. If this is another file-a new file or even a modified version of the same file-a hash based anti-infringement system will not know what the file is.

In other words, the company does not actively scan users ' files to search for copyrighted material, at least based on Dropbox's public statements. There is no artificial (or robotic) eavesdropping on your MP3 or trying to find your files, or reading your Harry Potter collection of novels. They just have a big ban on sharing file lists, and they just identify these files in a way that deliberately does not know what the specific content of any non-blacklist file is.

Now, this is not to say that a system based on hashing is not a security concern. For example, in the case of government requirements, theoretically Dropbox will identify any user who stores a particular file on the account. But for any cloud based storage system, it is the same, in which the user does not process all of the cryptographic programs.

Here is Dropbox's official comment on the Twitter message:

"There have always been questions about how we deal with copyright notices," he said. We sometimes receive DMCA notices that require a partial link to be removed for copyright reasons. Upon receipt of these notices, we deal with these requirements in accordance with the law and disable the identified links. We have an automated system that avoids users using Dropbox links to share exactly the same material. This is done by comparing the file hash value. We do not view the files of the user's private folders and we are committed to keeping the user's files secure. ”