Common key exchanging method and communication device

摘要

Upon receipt of a public value X from a device A, a device B estimates a time to be taken for calculation of a public value Y and a time to be taken for calculation of a common key K, and then calculates a required operation time Tb required at the device B for a key exchanging process for transmission to the device A to report a response delay time (S306 and S307). Then, the device B actually calculates the public value Y and the common key K (S309 and S310). Upon receipt of the required operation time Tb, the device A extends a waiting limit (timeout time) for a response from the device B to a time when the required operation time Tb elapses from the reception (S311). <IMAGE>