Security system using RSA algorithm and method thereof

A security system comprising:

• a key input section for receiving a secret key and a public key used in encryption or decryption of a message;
• a random coefficient generating section for generating a random coefficient value having a predetermined bit size;
• a first calculation section for dividing the secret key into a first secret key and a second secret key by using the generated random coefficient value, and performing an exponentiation of an RSA algorithm by using the respective first and second secret keys and the public key;
• and
• a second calculation section for performing the encryption or the decryption by combining the results of the exponentiation calculated by using the first and second secret keys, respectively,
• wherein the first calculation sets a lower bit of the secret key corresponding to the bit size of the random coefficient as the second secret key, and a value of shifting bitwise right the secret key by the bit size of the random coefficient as the first secret key.