Abstract: The invention is a method for broadcast encryption that allows a broadcaster to send encrypted data to a set of users such that only a subset of authorized users can decrypt said data. The method comprises modifications to the four stages of the basic Cipher-text Policy Attribute-Based Encryption techniques. The method can be adapted to transform any Attribute-Based Encryption scheme that supports only temporary revocation into a scheme that supports the permanent revocation of users.

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 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.