Abstract: A computer authentication system is provided with a random number generator 5 for generating a random number on the basis of a noise signal generated by a noise generator and a code rewriter for creating a new encryption code on the basis of the random number generated by the random number generator 5 when the encryption code of a computer 1 corresponds to the encryption code of an authentication key 2, rewriting the encryption code recorded in a encryption recorder 19 of the computer 1 to the new encryption code and rewriting the encryption code recorded in an encryption recorder 10 of the authentication key 2 to the new encryption code.

Abstract: A random number generator having a simple construction which generates physical random numbers necessary for encryption. The random number generator has an amplifier to amplify noise signals generated from a noise source and digitizer to digitize the amplified noise signals. The digitizer includes a serial register.

Abstract: A power supply line on the earthed side of an AC power supply is detected in order to prevent the leakage of an electromagnetic wave. A detection apparatus detects the AC line on the earthed side of the AC power supply. A power supply terminal is provided to be connected to the AC power supply. Ground terminals are provided to be connected to ground of an electric equipment. A switching unit selectively connects either of AC lines connected with the AC power supply to ground of the detection apparatus, the selective connection being changed-over. An antenna unit detects an electromagnetic wave leaking out of the electric or electronic equipment. And, a discrimination unit discriminates an earthed side and a non-earthed side of the AC lines on the basis of a level of the electromagnetic wave and based on which of the AC lines is connected to the ground of the detection apparatus.