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Everything is in the title: I'm aiming to download a big file, and I don't want to waste time downloading it because I don't know if it's password protected or not, especially with my slow internet connexion.
So my question is how could I check whether this file is protected or not before downloading, or at least downloading just a small amount of the file.
ps: I'm using Free Download Manager.
Thanks in advance for your answers.

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Depending on the compression mechanism and how it was encrypted, you might be able to download the first N bytes and then, 1) check for the compression "signature" (telling you the compressed file is not encrypted), and 2) read the compression signature to see if it says it's encrypted internally. However, zip files, eg, have their "directory" containing encryption info at the very end of the zip file, so this only works for some cases.

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Thanks for your answer. So, for a zip file there is no way. What about a rar file? – zagoku Apr 3 '14 at 14:19
I'm not familiar with the structure of a rar. You can probably find it in Wikipedia, though, and figure it out for yourself. – Daniel R Hicks Apr 3 '14 at 15:43
According to this website… , it's possible to check if a zip file is password-protected by downloading only the 7th Byte of the file (or the first 7 bytes if the server doesn't support resuming downloads). – zagoku Mar 27 at 20:19

No, there is no way to tell if a file is password protected before you download it. Either the location you are downloading from needs to tell you before you download or you will have to download the file first in order to determine--either manually or programmatically--that the file is password protected.

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