Take the 2-minute tour ×
Super User is a question and answer site for computer enthusiasts and power users. It's 100% free, no registration required.

When I drag files from a .ZIP file my friend sent me, it barks:

Do you want to copy this folder without encryption?`

A problem is preventing that folder from being encrypted.

enter image description here

What's causing the error?

(When I use 7Zip or WinRar to unzip that same folder, there's no warnings/errors whatsoever.)

share|improve this question

3 Answers 3

up vote 1 down vote accepted

Appears to be a bug in how Windows handles zip files created on a Mac, as explained by http://blogs.msdn.com/b/asklar/archive/2012/05/03/why-do-zip-files-from-mac-os-show-up-as-green-encrypted.aspx

The problem happens when Windows gets confused about how to interpret file/folder attributes. In FAT/NTFS, these values are stored according to this definition of File Attribute Constants. You’ll see that FILE_ATTRIBUTE_ENCRYPTED has a value of 0x4000.

The interesting part is how Mac OS is storing its file attributes in the zip archive. Mac OS, being a UNIX based OS, uses the UNIX file/folder attributes system (and permissions, but that’s a topic for another time…).. Well, it just so happens that in POSIX, the flag to describe a directory/folder (S_IFDIR) coincidentally also has the value 0x4000. So it turns out the zip decompression code wasn’t aware that there might be other operating systems out there that might create zip archives…

Bonus question: can you change this behavior. Answer: No; but you can clear the encryption flag from the extracted files/folders easily.

share|improve this answer

For what it's worth (and the OP's screenshot helps confirm), this seems to pop up when a file is compressed on a Mac using its context menu/built-in Compress function and then unzipped on Windows. (Sorry, not enough cred to comment, but figured worth mentioning.)

Seems harmless in my experience to say Yes for all. Note that (again, in my experience) the files weren't encrypted on the Mac either.

enter image description here

share|improve this answer

The inital files probably had their NTFS encryption set. I wouldn't worry too much about it. Unless it doesn't open. Then you need to tell your friend to send the files to you unencrypted :)

share|improve this answer
    
what do you mean by NTFS encryption set ? –  Pacerier Jul 23 '11 at 5:51
    
It's essentially an attribute flag, like system and read only. technet.microsoft.com/en-us/library/bb457065.aspx –  surfasb Jul 23 '11 at 18:55
    
This blog post explains why it occurs: blogs.msdn.com/b/asklar/archive/2012/05/03/… –  shthed Mar 10 at 16:37

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.