zip file encryption on Windows and Mac (or another solution)

Paul McCabe
Paul McCabe used Ask the Experts™

I regularly need to send files (usually MS Office, PDF or images) with sensitive information to clients via email and am looking for a good way to protect these documents. The main aim is having a safeguard in case of inadvertently emailing to the wrong recipient (which can happen all too easily with autocomplete etc).
The solution needs to be very user-friendly: it should be cross-platform (i.e. work for both Windows and Mac users), and it is not an option to require clients to install software.

Possible solution
One solution I have considered is to use an encrypted .zip folder into which the files could be placed. This would be pretty convenient, as individual files don’t need to be protected one by one, and files can be freely used once outside the .zip folder.
This approach would work well for clients on Windows, as long as the .zip folder encryption method is ZipCrypto. I know ZipCrypto is not the most secure of encryption methods, but it is sufficient for our purposes. So that leaves Mac users, but I cannot seem to find any information online as to whether Mac OS can open ZipCrypto-encrypted .zip folders.

1)      Does anyone know if Mac OS can open ZipCrypto-encrypted .zip folders ?
2)      Or, is there a better solution that I am unaware of ?
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1. Yes OSX can open ZIP files that use ZipCrypto as it is a fairly basic form of encryption. Similar to Windows - OSX has built-in support for decrypting ZIP files and there are plenty of apps too.

2. You might want to consider an encrypted cloud service like this one  - .. this means you never attach any files to emails but instead share links to the file or folder and if you use public key encryption you can ensure that only the chosen individual can open a specific file/folder in a trusted end-to-end transaction.


1. Great ! So I can use ZipCrypto for OSX users too. Do you happen to know of any stronger .zip encryption method that is natively compatible with both Windows and OSX ?

2. Absolutely, I agree that is another good solution and one I had considered (I already use a similar solution for large files that cannot be sent by email). Unfortunately however, my clients are on the conservative side / a little behind the times, and prefer traditional email....

If you want OS-level support (i.e. no additional software to install in Windows or OSX) then ZIP is the best option with the default ZIPCrypto but relatively insecure.  You're dealing with lowest common denominator here.  OSX can support AES but not by default .. it requires either freeware like Keka (which is a great little app for OSX) - or installing a small OSX update via terminal to support it.

OSX also supports TAR but that's not on Windows.

Personally I prefer TAR and 7Z and there are free clients for OSX and Windows but thats probably outside your requirements.


Hi Eoin,

OK, that is very clear. Many thanks for the valuable information and your suggestions, they are very much appreciated.


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