Patent ID: 7764789

Claim:
A device for encrypting a data stream, comprising: a key bit stream generator configured to generate a key bit stream, comprising: a feedback shift register configured to generate a bit sequence; a decimator configured to pick out, on the basis of a decimation value m, every m th bit of the bit sequence so as to obtain the key bit stream consisting of the bits picked out; and a readjuster configured to readjust the decimation value m in response to a predetermined event; and an encrypter configured to encrypt the data stream on the basis of the key bit stream, wherein the feedback shift register is a linear feedback shift register which consists of N internal bit registers and has a characteristic of generating a bit sequence of a period duration of 2 N −1, and the decimation value m is relatively prime with respect to the period duration so that during times the decimation value m remains constant between consecutive readjustments, the key bit stream is identical with a portion of an output bit sequence of a different linear feedback shift register being different from the feedback shift register of the device, also consisting of N internal bit registers, and also providing a period duration of 2N−1, but having a different characteristic.