Patent ID: 8223962

Claim:
A common key generation system comprising: a first node including: a numeric string element generator configured to generate one or more numeric string elements from time interval information of a physical change in the first node; wherein the physical changes comprise at least one of changes in light, sound, wind power, temperature or humidity; a numeric string generator configured to generate a basic numeric string from the one or more numeric string elements and substitute the basic numeric string with one or more similar numeric strings; an encryption unit configured to encrypt the basic numeric string and the one or more similar numeric strings and to generate a cipher value list of the numeric strings in correspondence with their cipher values; and a match signal judgment unit configured to search a received cipher value from the cipher value list; and a second node including: a numeric string element generator configured to generate one or more numeric string elements from time interval information of a physical change in the second node; wherein the physical changes comprise at least one of changes in light, sound, wind power, temperature or humidity; a numeric string generator configured to generate a basic numeric string from the one or more numeric string elements; an encryption unit configured to encrypt the basic numeric string in accordance with the encryption rule, which is common to that for the first node; and a transmitter configured to transmit the generated cipher value to the first node, which is recognized as the received cipher value at the first node, wherein the match signal judgment unit searches for the cipher value transmitted from the transmitter of the second node, and a common key is generated based on the result of the search.