Passphrase-Gated Access
The sender defines a secret code at send time. Without this code, the message content is completely inaccessible — even to someone holding the recipient's device.
Unlock Content
Passphrase-ProtectedMessages.
Add a secret unlock code to any message. Recipients must enter the correct passphrase to decrypt and read. Double-layer encryption — even if someone has the device, they still need the code.
In the App
Set the Unlock Code
Compose your message, set a passphrase, and send. The recipient sees a locked message that requires the code to reveal its contents.
Core Capabilities
Two Keys Are Better Than One
Unlock Content adds a human-controlled passphrase layer on top of standard end-to-end encryption.
Double-Layer Encryption
Messages are first encrypted with standard E2E keys, then wrapped in a second layer derived from the passphrase. Two independent encryption barriers protect every message.
No Hints or Recovery
There are no password hints, no recovery options, and no brute-force workarounds. If you don't know the code, the message stays locked forever.
Works with Everything
Lock text messages, file attachments, images, or any content type. Unlock Content works seamlessly with all City of Hats message formats.
Process
How Unlock Content Works
Four steps from composition to passphrase-gated decryption.
Compose Message
Write your message and add any attachments as usual. Text, files, images — everything can be passphrase-locked.
Set Passphrase
Choose a secret unlock code. This passphrase is used to derive a second encryption key. Share it with the recipient through a separate channel.
Send Locked
The message is double-encrypted and sent. The recipient receives a locked message with no content preview — just a prompt to enter the code.
Enter Code & Read
The recipient enters the passphrase. If correct, both encryption layers are removed and the message appears instantly. Wrong code? Nothing happens.
Applications
When to Use Unlock Content
Any time you need an extra layer of security beyond standard encryption.
Confidential Business
Send contracts, financials, or trade secrets with a passphrase shared in person or over a call. Even a compromised device reveals nothing.
Legal Documents
Attorneys can lock privileged communications behind a code shared only with the client. No unauthorized access, no accidental exposure.
Medical Records
Healthcare providers can share patient data locked with a code known only to the patient. HIPAA-grade access control at the message level.
Financial Information
Account numbers, credentials, and financial details protected by a passphrase. Even if the chat is accessed, the sensitive content stays locked.
Journalism & Sources
Lock sensitive information behind a code agreed upon in advance. If the journalist's device is seized, the locked messages reveal nothing.
Personal Secrets
Share passwords, surprise plans, or private information with an extra lock. Only someone who knows both you and the code can read it.
🛡 Threat Model
What We Enforce
Unlock Content is built on zero-knowledge passphrase handling and double-layer encryption.
Enforced by Architecture
- Passphrase-derived key generated on sender's device only
- Double-layer E2E + passphrase encryption
- No content preview or metadata leakage when locked
- Instant decryption with correct passphrase
- Works with all message and attachment types
- Passphrase never transmitted to servers
Never Allowed
- No server-side passphrase storage
- No password hints or recovery options
- No brute-force or bypass mechanisms
- No content preview before unlocking
- No third-party access to passphrase-derived keys
No system is invulnerable. Stating what we defend against — and where our boundaries are — is more credible than claiming absolute security. Learn More →
Platform
Learn More
Passphrase-ProtectedMessages.
Add a secret unlock code to any message. Recipients must enter the correct passphrase to decrypt and read. Double-layer encryption — even if someone has the device, they still need the code.