Patent ID: 7747014

Claim:
An information transmission method comprising the steps of: transmitting specified information between an information sending apparatus and an information receiving apparatus to enable the information sending apparatus and the information receiving apparatus to hold in common an encryption key used to encrypt original main information and decrypt encryption-resultant main information; generating a first random number in the information receiving apparatus; sending the generated first random number from the information receiving apparatus to the information sending apparatus; in the information sending apparatus, generating a sync signal in response to the first random number sent from the information receiving apparatus; in the information sending apparatus, generating key information relating to the encryption key; adding the generated key information to a position immediately following the generated sync signal to generate a set of the sync signal and the key information, wherein the sync signal indicates a position of the key information; generating a second random number in the information sending apparatus; embedding the generated set of the sync signal and the key information in the generated second random number to generate a composite signal; sending the generated composite signal from the information sending apparatus to the information receiving apparatus; in the information sending apparatus, generating the encryption key in response to the generated key information; in the information sending apparatus, encrypting the original main information in response to the generated encryption key to generate the encryption-resultant main information; sending the generated encryption-resultant main information from the information sending apparatus to the information receiving apparatus; in the information receiving apparatus, detecting the sync signal in the composite signal sent from the information sending apparatus; in the information receiving apparatus, extracting the key information from the composite signal in response to the detected sync signal; in the information receiving apparatus, generating the encryption key in response to the extracted key information; and in the information receiving apparatus, decrypting the encryption-resultant main information sent from the information sending apparatus in response to the generated encryption key.