Private File
In 1996, Aladdin Systems came out with a cool piece of security software called "Private File." This software allowed users to encrypt any file and send it securely.
From their documentation:
Why is the product called Private File?
That's just our way of letting you know that when you make your files private (by way of a simple drag and drop action), they will be protected with strong encryption as well as bring compressed -- using the award-winning Stuffit compression technology. The private files you create can be sent anywhere in the world, thanks to our cross-platform versions for Mac and Windows and because we also have a legally exportable (outside the US) version!
Private File used industry standard algorithm called MD5. The International version would use 40-bit encryption while the domestic version used 128-bit encryption.
Private File was available for Macintosh System 7.0.1 and Windows 95 and NT 4.0.
Easy to Encrypt and Decrypt
Private File works by Drag-Drop. You take any file or folder, drop it on the "PF Encrypt" icon, type in a secure password, and it will compress and encrypt very quickly.
Encrypted StuffIt archives created with the Private File utility will have .pf extensions.
To Decrypt, simply drag the file with the .pf extension to the "PF Decrypt" application, enter the password and it will decrypt the file.
Private File was discontinued sometime in 1999. Smith Micro Software acquired Aladdin Systems in 2005. (Note Aladdin Systems had to change the company name in 2004 as part of a trademark settlement from Aladdin Knowledge Systems.)
Today's Solution
If you're looking for the same functionality in Macintosh OS X world, Stuffit 16 is a good solution. You have the same drag-drop flexibility as Private File with today's compression technology. Stuffit 16 offers 512-bit encryption.
We come a long way in software. When Private File came out it cost $49.95. Today a digital copy of Stuffit 16 only cost $9.99