An ordinary message in chat.
Private words between you.
Sounds good. See you tomorrow.
I wish tomorrow were tonight. I miss you. 💜
Your recipient pastes the message into Coo to open the private words.
Choose how to hide your message
Browser tools and Coo use different formats. Choose one method with your recipient.
| Tool | How it works |
|---|---|
| Hopi ↗ | Hides and reveals text; no encryption. |
| StegZero ↗ | Optional passphrase encryption, according to its documentation. |
| Coo | AES-256-GCM Private message encryption · 256-bit random connection keys |
An ordinary sentence. 256-bit encryption inside.
AES-256-GCM
Coo encrypts your private words on your device with AES-256-GCM. The visible sentence and ciphertext travel through your chat.
256-bit random connection keys
Coo generates a random 256-bit key when you connect. The matching connection key opens the private words in Coo.
Cover text and ciphertext authentication
The visible sentence is included in authentication. Coo verifies both the cover text and ciphertext before opening the content.
Coo / iOS & AndroidWant to exchange hidden messages with your person?
Copy the message and paste it into your usual chat.
Make a private connection.
Connect with your person in the app.
Write what they see—and what you mean.
Write the visible sentence and your private words. Coo encrypts the private words.
Paste it into the chat you already use.
Copy the message and paste it into your usual chat.
Copy. Paste. Open the meaning beneath.
Your recipient pastes the message into Coo to open the private words.
Coo / iOS & AndroidTry creating and opening a message
Write the visible sentence and your private words. Coo encrypts the private words.