Patent ID: 7471795
Filing Date: 2008-12-30
Classification: H04L

Abstract:
1. An information transmission system comprising: a sending apparatus for sending a composite signal including a first sync signal, a second sync signal, a first initial value, and encryption-resultant information, the first sync signal repetitively occurring at a first predetermined period, the second sync signal repetitively occurring at a second predetermined period shorter than the first predetermined period, wherein a plurality of the second sync signals are present in one period of the first sync signal in the composite signal; a receiving apparatus for receiving the composite signal from the sending signal in the received apparatus, for detecting the first sync signal and the second sync composite signal, and for decrypting the encryption-resultant information in the received composite signal; wherein the sending apparatus comprises: first means for implementing a first shifting action synchronously with the second sync signal to generate a first pseudo random number signal, and for suspending the first shifting action synchronously with the first sync signal during a first prescribed time interval; second means for generating the first initial value in response to the first pseudo random number signal generated by the first means; third means separate from the second means for generating a second initial value in response to the first pseudo random number signal generated by the first means; fourth means for generating a first encryption key in response to the first pseudo random number signal generated by the first means, the first encryption key being updated synchronously with the second sync signal; fifth means for encrypting original information into the encryption-resultant information in response to the first encryption key generated by the fourth means and the second initial value generated by the third means; sixth means for generating a combination-resultant signal inclusive of the first sync signal, the second sync signal, and the encryption-resultant information; seventh means for adding the first initial value generated by the second means to the combination-resultant signal during the first prescribed time interval for which the first shifting action of the first means is suspended to get the composite signal; wherein the receiving apparatus comprises: eighth means for implementing a second shifting action, equal to the first shifting action, synchronously with the detected second sync signal to generate a second pseudo random number signal equal to the first pseudo random number signal, and for suspending the second shifting action synchronously with the detected first sync signal during a second prescribed time interval corresponding to the first prescribed time interval; ninth means for generating a third initial value normally equal to the first initial value in response to the second pseudo random number signal generated by the eighth means; tenth means separate from the ninth means for generating a fourth initial value equal to the second initial value in response to the second pseudo random number signal generated by the eighth means; eleventh means for generating a second encryption key equal to the first encryption key in response to the second pseudo random number signal generated by the eighth means, the second encryption key being updated synchronously with the detected second sync signal; twelfth means for detecting the first initial value in the received composite signal; thirteenth means for comparing the first initial value detected by the twelfth means and the third initial value generated by the ninth means to check a synchronization between the sending apparatus and the receiving apparatus; and fourteenth means for decrypting the encryption-resultant information in the received composite signal in response to the second encryption key generated by the eleventh means and the fourth initial value generated by the tenth means.