Method and system for controlling access to a restricted location

The present disclosure describes techniques for controlling access a restricted location (114) as well as a system (100) for doing so. According to various implementations, a potential entrant to the restricted location needs to transmit two values to an access authorization device (108) located at the perimeter (112) of the restricted location in order to gain access. In one implementation, the system provides an authentication code to a first device (116) (e.g., a smartphone) via wireless communication link (120) (e.g., over a cellular network) and displays a visual image (127) with an embedded access code at a display device (104). The second device (118), which is securely paired with the first device, captures the image and sends the image data to the first device. Using the authentication code and the access code, the first device derives the two values to gain access to the restricted location.