Patent ID: 7970140
Filing Date: 2011-06-28
Classification: H04L

Abstract:
1. A method for transmitting a multilevel optical signal from a transmitting node to a receiving node, comprising the steps of: generating in the transmitting node a running key based on an input of an encryption key K; generating in the transmitting node synchronization data used to confirm synchronization of the running key between the transmitting node and the receiving node; inserting in the transmitting node the synchronization data into transmission data; generating in the transmitting node the multilevel optical signal based on the value of the running key for synchronization data and the transmission data; transmitting the multilevel optical signal to the receiving node; storing in a first storage unit of the transmitting node each of the synchronization data that has been inserted into the transmission data and the running key in association with each other; monitoring in the transmitting node whether the synchronization of the running key used is established between the transmitting node and the receiving node; receiving in the receiving node the multilevel optical signal and converting the multilevel optical signal into an electric signal; generating in the receiving node a running key that is the same as and synchronized with the running key generated in the transmitting node in accordance with the input of the encryption key K; controlling in the receiving node a receiving threshold value used to determine the multilevel optical signal in accordance with the running key generated in the receiving node so as to convert the multilevel optical signal received into binary data and to output the binary data; storing in a second storage unit of the receiving node each of the synchronization data divided from the transmission data and the running key generated in the receiving node in association with each other; confirming in the receiving node a status of reception of the synchronization data so as to monitor whether the synchronization of the running key is established between the receiving node and the transmitting node; generating a synchronization confirmation signal in the receiving node and transmitting the synchronization confirmation signal to the transmitting node when the receiving node legitimately receives the synchronization data; generating in the transmitting node a status confirmation signal used to confirm the status of the receiving node and transmitting the status confirmation signal to the receiving node when the transmitting node does not legitimately receive the synchronization data under a predetermined condition; and determining according to a response to the status confirmation signal whether the synchronization of the running key is shifted and perform re-synchronization of the running key between the transmitting node and the receiving node, wherein the transmitting and receiving nodes each determine the position of the running key for the encryption and decryption based on the information on the position of the running key associated with the synchronization data stored in the first and the second storage unit when the re-synchronization of the running key is performed, and wherein the transmitting and receiving node each generate a new running key at a position that is ahead of the position of the running key associated with the synchronization data with which the synchronization has been confirmed while referencing the synchronization data and information on a position of the corresponding running key stored in the first and second storage unit.