An embodiment includes an apparatus comprising: a display module; at least one memory coupled to the display module; at least one processor, coupled to the at least one memory, to perform operations comprising: (a) encoding first content, which is based on a first value, in a first bar code, (b) displaying the first bar code with the display module; (c) receiving a second bar code, which includes second content based on a second value, from a second computing node; (d) encoding third content, which is based on a third value, in a third bar code, (e) displaying the third bar code with the display module; (f) determining an encryption key based on the first and second values; and (g) exchanging a message, encrypted based on the encryption key, with the second computing node. Other embodiments are described herein.