Abstract: Frames of data are encrypted by combining each of the frames with a mask that varies from frame to frame. The mask is obtained by using a frame counter as the seed for a pseudo random number generator, generating n pseudo random numbers, where n is the number of bytes to be encrypted in each frame, and concatenating the most significant bytes of each of the n pseudo random numbers to form the mask. The encrypted frames are transmitted, received and decrypted by combining them with the mask, which is independently generated at the receiver. The frame counter is aperiodically reset to a new initial value that is a substantially random number with respect to a previous initial value.

Abstract: Synchronized communication is provided between a first station and a second station. The first station sets a frame counter to a stored initial value, receives a frame including an identifier uniquely identifying a communication channel designated for communication between the first station and the second station, and increments the frame counter. The frame counter is aperiodically reset to a new initial value, the new initial value being a substantially random number with respect to a previous initial value. When wireless communication is employed, the identifier may be a color code. If the value of the identifier is an expected value, the first station transmits to the second station a return frame including an expected value as a return frame identifier. If the value of the identifier is other than the expected value, the first station resets the frame counter and transmits to the second station a return frame including a selected value other than an expected value as a return frame identifier.