How do I password protect a .tgz file with tar in Unix?

Use crypt or gpg on the file.

Simple examples:

cat filename | crypt > filename.crypt

gpg -c –o filename.gpg filename

You can use command:

zip -P password file.zip file

Or better:

zip -e file.zip file

man zip

Neither the tar format nor the gz format has built-in support for password-protecting files.

The Windows zip format combines several different piece of functionality: compression (e.g. gzip), archiving multiple files into one (e.g. tar), encryption (e.g. gnupg), and probably others. Unix tends to have individual tools, each of which does one thing well, and lets you combine them.

The Unix equivalent of a password-protected .zip file would probably be called something like foo.tar.gz.gpg or foo.tgz.gpg.

And there are open-source zip and unzip tools for Unix, though they may not provide all the capabilities of the Windows versions (I'm fairly sure the newer .zipx format isn't supported).