Hiding conceals where a message is; encryption turns its contents into ciphertext that requires a matching key to read. Coo combines both by carrying encrypted private words inside an ordinary visible sentence as one copyable message.
Coo / iOS & AndroidHide encrypted words in ordinary text
Get Coo for a visible sentence with encrypted private words inside.
Hiding and encryption answer different questions
Hiding answers “What does someone see?” Encryption answers “What is needed to read the private content?” A message can use either approach or both.
| Approach | What the reader encounters | What opens the content |
|---|---|---|
| Hiding alone | A carrier with concealed content | A compatible reveal method |
| Encryption | Ciphertext instead of readable private words | The matching decryption key |
| Hiding with encryption | A carrier containing encrypted content | The reveal method and matching key |
Finding hidden content and decrypting it are different operations. A reveal tool can extract concealed data without providing encryption. Hopi explicitly describes its method as hiding, not encryption, and advises encrypting sensitive content first. StegZero states that without a passphrase, it only hides the message.
The word “hidden” therefore does not tell you whether a tool protects the content with encryption. Equally, encryption alone does not supply an ordinary cover sentence.
A puzzle and a private note have different needs
For a harmless puzzle, hiding “Look under the blue cup” gives your friend something to discover. An agreed reveal tool can be enough because discovering the answer is the goal.
A personal note has another requirement: extracting the hidden data should still leave encrypted content that needs the matching key. For example, you might want to acknowledge a friend’s message while keeping a more personal request inside it:
Example visible sentence: “Thanks for checking in.”
Private words: “I had a difficult day. Could we talk tonight?”
In Coo, these go into separate input fields but become one combined message to copy. The visible sentence is the cover; the private words are encrypted inside it. The recipient copies the full received message into Coo to open those words.
Coo keeps private text on the device and gives it a cover
Private text messages are not uploaded to or stored on Coo message servers. The matching connection key opens the private text for the sender and connected recipient, while the chosen messenger carries the visible sentence and ciphertext. Coo’s usage overview describes this combined-message design.
Three technical facts explain how the two protections work together:
- On-device AES-256-GCM: Coo encrypts and decrypts the private text on the device. The combined message contains ciphertext rather than the private wording in readable form.
- Random 256-bit connection keys: A new connection uses a randomly generated symmetric key. The matching connection key decrypts messages created for that connection.
- Cover-text authentication: Coo includes the visible sentence as additional authenticated data and authenticates it together with the ciphertext before opening the private content.
That last mechanism links the ordinary cover to the encrypted words. NIST’s definition of authenticated encryption explains that GCM generates an authentication tag over the additional authenticated data and ciphertext.
Coo / iOS & AndroidPrivate text, encrypted on your device
Coo combines your cover sentence and encrypted words without uploading private text to Coo message servers.
Choose according to what needs protecting
Use the recipient’s intended experience to make the decision:
- A playful answer to discover: Hiding alone can suit a puzzle whose answer does not need confidentiality.
- Private wording that requires a key: Choose encryption. Concealment alone does not provide this protection.
- An ordinary sentence carrying encrypted private words: Choose a method that combines hiding and encryption, such as Coo.
For Coo, both people install the app and connect before the sender creates the message. If a message was made before connecting, create a new one afterward; adding a connection does not make the earlier message open for that recipient.
Use the existing illustrated guide to hiding a private message inside ordinary text for the sender and recipient demonstration. Test a short message through the messenger you intend to use and check that the received copy opens in Coo, rather than assuming every app preserves the combined message.
How it works
Coo / iOS & AndroidTry one note with two meanings
Get Coo and try “Thanks for checking in” with your own private words, then open the combined message with your connected recipient.