A hardware random number generator is designed with the help of digital clock manager. The number is evenly distributed in a random manner. Each number in the series is individualistic. The generated random number is unpredictable. Therefore they are used in key generation. Such keys are used to secure the transferred information. Built-in self test is an application of TRNG. Built-in self testing enables the circuit to test for any faults. BIST is a procedure where a circuit is designed so that it tests itself and describes whether it is faulty or fault free. A true random number which is generated using DCM is put in the circuit which is under testing. The corresponding circuit is vedic multiplier. The faults in the circuit under test are detected using built-in self test process. The software tool used for programming part is Xilinx suite 14.3.