Password Protect a zip file

You have a folder arbitrarily named TestZip. You place your file NAMEOFFILE.txt in that folder. Now, you can apply a password to that TestZip container that Windows 10 will respect, and open a dialog for that password during the extraction:

zip -er TestZip.zip ./TestZip

This will prompt you for a password, which it will not echo, and a verify challenge to re-enter that password. On the Windows 10 side, there will be a password challenge before the folder and its file contents can be extracted:

You can not set a zip password on an individual file, but rather the enclosing folder that you zip.

If you pass in an existing .zip file as the file to be zipped/encrypted, you will end up with an encrypted zip file containing a zip file, and the recipient will have to decompress it twice.

Therefore you should start with your standard, non-encrypted, non-zipped file - let's call that NameOfFile.txt

Then the command:

 zip -e my.zip NameOfFile.txt

should prompt you for a password, then use that password to encrypt the txt file into the resulting my.zip file.

From your description, you say "...but my file is not a txt file", but you are passing a text file into the zip command, so that may be where the problem lies.

I just finished testing both approaches. Only the file placed in a folder and then that folder encrypted causes the Windows 10 (2H20) extract process to prompt for a password. Just applying the encryption to the zip compressed file results in Windows 10 extracting the file with no password challenge.

Wow. That seems like a significant bug in ZIP.

If Windows is decrypting the file without prompting for a password then either zip never applied the encryption (in which case it should have warned you), or the encryption is so weakly applied that the content is readable anyway (e.g. it doesn't actually encrypt the data, just stores a flag about the password).

The man page for zip indicates that encryption is supported at the zip file level, not related to its contents (folders vs. files), A quick test here does show binary-level differences between the same file zipped with and without a password.

I just successfully applied an encryption password to a single file in this form, and unzip provided the password challenge:

zip -e file.zip file.png

I didn't bother with the Windows 10 (2H20) booting to test, as I believe this time, the encryption worked.