http://ssd.iykpqm7jiradoeezzkhj7c4b33g4hbgfwelht2evxxeicbpjy44c7ead.onion/ps/module/deep-dive-end-end-encryption-how-do-public-key-encryption-systems-work
The bad actor could decide to change the contents of the file before passing it along to César. For example, they could change "Meet me in the garden," to "Meet me in the cafeteria." But most of the time, the bad actor decides to leave the contents unmodified. So, the bad actor forwards Julia’s message to César as though nothing happened, César knows to meet Julia in the garden, and gasp , to their surprise, the bad actor is there too!