Write the full, unabridged version of your letter below. None of what you write will be sent over the network until you've had a chance to mark which parts you want to protect. Provide all relevant information for the recipient to follow up with you, just as you would in a typical private email.

When you've finished, click the button below to continue to the protect phase (you will still be able to come back and make changes if necessary.)

Note: This website is a demonstration sandbox for using the blackhighlighter jQuery plugin. The database is regularly erased—which means your post might not be here tomorrow! If you want a more persistent service, then install the software yourself, or get in touch with brian@hostilefork.com about joining forces to build blackhighlighter.com

Now it's time to pull out your "black highlighter" and protect any information you don't want posted to the public. You'll be sending these protected contents to the recipient with a certificate. To make edits to what you've written, go back to the "Compose" tab.

Click on a protected section to un-protect it. Anything marked in orange is a suggestion you can protect with a single click (email addresses, etc.)

View the low-level redacted data that will be sent to the server

The marked out text of your letter won't be published. Instead, what will be published are digital signatures that can be used to verify what you entered, without actually containing the hidden text. You will be given certificates for these missing parts, that you may share privately with who you wish.

go back and edit -or-

Legal note: By posting your letter, you are agreeing to publish it under the Creative Commons No Derivative Works license. This gives others the right to present copies for commentary (or for any other purpose)—as long as those copies and digital signatures are not modified.

You MUST send the following information to the recipient (and save a copy yourself). It contains the verifiable proof of what was written in the hidden parts of the letter. The server has only enough information to do that verification — but it cannot guess the information without the certificate.

Remember: none of this was sent to the server! So if you lose this information, then evidence of what you have written will be lost!

Keep that safe, because both the missing information AND the proof to verify it are contained in that certificate. You can test the certificate by visiting the following URL:

Running on Node.js v5.11.1 and Heroku : (project page, source, credits)