Patent ID: 7702102

Claim:
A method for transmitting data, comprising: providing each of a plurality of users of a public communication network with a secret encryption program and a secret algorithm for generating an encryption key; by a first user of the public communication network: receiving a first random value originating from useful data produced in a first stochastic process; generating a first symmetrical encryption key based on the first random value using the secret algorithm; transmitting the first random value to a second user remote from the first user over the public communication network; by the second user: receiving the first random value from the first user; and generating the first symmetrical encryption key based on the received random value using the secret algorithm; the first and second users then encrypting and communicating the useful data over the public communication network using the secret encryption program and the first symmetrical encryption key; and wherein the first random value comprises a digital value derived from the useful data; wherein the first user comprises a remote maintenance device; the second and remaining users comprise respective automation devices connected to each other by a bus; each of the respective automation devices obtaining plural random values of stochastic data; combining two different subsets of the plural random values, producing two different data words; communicating the two different data words to the respective automation devices and to the remote maintenance device; inputting the two different data words into two different encryption programs that are identical in each of the respective automation devices and the remote maintenance device; generating two different symmetrical encryption keys from the two different data words via the two different encryption programs in each of the respective automation devices and the remote maintenance device; and communicating encrypted data using one or the other of the two different symmetrical encryption keys at a given time among the respective automation devices and the remote maintenance device; and switching between the two different symmetrical encryption keys at a predetermined time among all of the respective automation devices and the remote maintenance device at once.