How it works

Mark needs to send personal text to Sarah, and wants only Sarah to be able to read it.
Mark writes the text in the Input field.
A password is automatically created. Or Mark and Sarah can establish a password for their messages over a secure channel (by voice, for example).
Mark can send the encrypted field OR the sharing URL field over an insecure channel (for example a chat, mail, Skype, Facebook, etc.) where Sarah can read it.
Sarah opens the sharing URL (or opens this page and pastes the encrypted text), enters the password and can read the original message in the decrypted field.

Note: Neither MyWhisper.net nor anyone else on the network can see the original text or the password, or the encrypted text unless the sharing URL is used. Everything stays in Mark's and Sarah's browsers, and encryption and decryption run there in JavaScript.