Abstract: A communication system that includes a sender computer and plurality of designated receiver computers coupled to the sender through a communication link. Each one of the receiver computers is equipped with computational resources stronger than the computational resources of an adversary computer. There is provided a method for sending a secret from the sender computer to a designated receiver computer. The sender computer defining a succession of computational tasks having respective solutions. The computational tasks are so defined such that the duration of solving each task by the receiver computer is shorter than what would have been required for the adversary computer to solve the task. Next, the sender computer sending through the link the succession of tasks encrypted by previous solutions and the receiver computer receiving the tasks and is capable of decrypting the secret faster than what would have been required for the adversary computer to decrypt the secret.

Abstract: A method and apparatus for repeated communication sessions between a sender (e.g., RFID tag) and a receiver (RFID reader) that employs a proactive information security scheme is based on the assumption that the information exchanged during at least one of every n successive communication sessions is not exposed to an adversary. The sender and the receiver maintain a vector of n entries that is repeatedly refreshed by pairwise XORING entries, with a new vector of n entries that is randomly chosen by the sender and sent to the receiver as a part of each communication session. Also, a computational secure scheme based on the information secure scheme is employed to ensure that even in the case that the adversary listens to all the information exchanges, the communication between the sender and the receiver is secure. In particular, the scheme can be used in the domain of remote controls (e.g., for cars).