DesuDesuTalk is an userscript for 4chan and other imageboards that lets you encrypt messages into images in-browser, only to be seen by other DesuDesutalk users. Messages can be sent entirely privately, to certain groups of users or to whoever is using the script.
Installation and use:
1. install greasemonkey for firefox or tampermonkey for chrome.
1.1 other browsers might as well leave now, using javascript cryptography DDT can be quite taxing on less optimized browsers.
2. install DDT by visiting
https://github.com/desudesutalk/desudesutalk/raw/master/ddt.user.js3. after installing the script, an icon should appear on the bottom right corner of any supported imageboard. Click on it to bring up the user interface.
3. first, you'll want to 'log in'. from the log in tab. You need to choose a password and a salt to generate yourself public and private keys. All functions rely on these keys that are included in the generated message files, so your login is not kept on or send to any server. You should choose passwords and salts not used on other services.
3.1 Do not change the broadcast address passwords or the steg password.
4. You can now enter the Messages tab and click 'Get posts' to scan the thread for existing posts. First, you will only see posts that have been sent in broadcast mode.
5. You should click the [add] button next to Unknown posters to add them to your contact list. Doing this allows you to send messages only they can see. For the same reason, you should make a broadcast post to announce your identity and allow others to add you.
6. To post, open the post form on the imageboard and fill it out as you normally would minus the image, and solve the captcha if any. Then open DDT and the Messages tab, and click on the 'Write reply' button on the bottom left of the DDT interface. Select and image and address, write your hidden post and click on 'crypt and send'.
Full guide at
https://github.com/desudesutalk/desudesutalk/wiki/How-to-use-this-script 