1. A method for encryption of a data stream, the method comprising: providing the data stream, providing at least two first random number generators having a first cryptographic strength, wherein each of the at least two first random number generators is switchable between states comprising a clocked state and a working state, providing a second random number generator having a second cryptographic strength, wherein the second cryptographic strength is higher than the first cryptographic strength, switching states of the at least two first random number generators using an output of the second random number generator, using an XOR-function for combining the data stream with an output of one of the at least two first random number generators which is in the working state, such that a ciphered data stream is created.