Looking for crossplatform solution to sharing sensitive files
Create a password secured zip archive of your sensitive contents.

Create a terms of use simpletext file or optionally a pdf version with the same text as these will be easily readable on just about any system.

An overly simple example:

"if you disagree with these terms of use, close this zip/image archive and securely delete zip/image archive immediately"

or

"if you agree, use _ passcode to unlock _ zip/image archive"

Create and place the password protected zip file and the terms of use plain text and/or pdf documents into an unsecured zip file.

The user that opens the content would not be able to miss the terms of use before opening the sensitive content.

If you're scratching your head. we are leveraging nesting as a technique to ensure users have read and accepted the terms of use before accessing the contents. Here's a picture of and a link to the Wikipedia article on Matryoshka Dolls to better visualize how this works.