A system is described for exchanging encrypted short messages between computers which remain permanently isolated from any network accessible to the attacker. The main advantage is effective protection of these computers from malware which could circumvent the encryption. For transmission, the ciphertext is passed between isolated and connected computers in the form of a QR code, which is displayed on and scanned from a screen. The security of qrypt0 therefore rests on the cryptography and the computer's physical isolation rather than on the computer security of the encrypting device.