How it works

QRTalk implements end-to-end message encryption, information time-to-live and client-server secure communications.

End-to-end encryption

All exchanged contents are protected by end-to-end encryption: no one but the sender and recipient can access them.

Devices generate RSA key pairs for encryption. The private key is saved in the device private storage and the public key is sent to the QRTalk server, where it is associated with a anonymous random user ID.

Outgoing messages are individually encrypted using AES (in CBC mode) with secure random initialization vector and key. The random key is encrypted using the corresponding public key for each of the recipient devices and then dispatched to the server for delivery. Additional routing information (i.e. user IDs and TTL) is not encrypted since it must be accessible to the server.

Communications with server are encrypted using AES (in CBC mode) with short-lived SRP6 negotiated keys and random initialisation vectors.

Users’ public keys are downloaded from server and can be accessed only by authenticated users.

Identity and public key of other users can be verified using fingerprints.

Messages can be signed with sender’s private key.

Public key verification together with message signing makes message-forging and man-in-the-middle attacks totally impossible.

Information Time-to-Live

Messages and media are stored on servers only if recipient is temporarily off-line, else they are not stored at all but simply forwarded to destination.

User selects message’s time-to-live at send time: 5 minutes, 1 hour, 1 day, 1 week.

If message recipient is off-line at send time, encrypted message is temporarily stored on server and deleted either when it get delivered to its final destination or when associated time-to-live expires.

From a server perspective, chat messages and tracking events are totally opaque objects and must be delivered to destination devices in order to be of any use.

Client application stores encrypted messages on device, in the private storage space. When time-to-live expires messages are deleted from device local storage too.

Secure network connections

Client/server connections are protected with symmetric encryption (AES) using one-time, per-connection large random keys.

✓ Each connection uses SRP6 to negotiate a new one-time large random encryption key.

✓ All connections are short lived and transport only AES encrypted information.

✓ SRP6 authentication passwords are generated on clients; new large random passwords are generated every 24 hours.