Patent ID: 7010127

Claim:
A cryptographic communication method, comprising: individually authenticating, in each transmission side, a common communication key and an individual transmission side only key that is different from the common communication key, thereby using both keys to encipher or decode in each transmission side, determining, in each transmission side, whether a target file is enciphered by the individual transmission side only key, decoding the target file using the individual transmission side only key, if determined that the target file is enciphered, and not decode processing the target file as an unprocessed target file, if determined that the target file is not enciphered; and enciphering for transmission, in each transmission side, the decoded target file or the unprocessed target file that is not enciphered, using the common communication key, wherein in each transmission side, the decoding using the individual transmission side only key and the enciphering using the common communication key are performed continuously, if the decoding is performed.