The security of any cryptosystems is based on the way in which it produces different ciphertext for the same plaintext. Normally, various block cipher modes viz., CBC, OFC, etc., are used in producing different ciphertext for the same plaintext but it is a time consuming process. Instead of using block cipher, a different encoding method for the plaintext is proposed in this paper using magic rectangle. The advantage of using the encoding scheme is different numerals is used in encoding each characters of a plaintext. Thus instead of considering the ASCII encoding for a character to be encrypted, the numeral which occurs at the position which corresponds to the ASCII value of the character is taken from the magic rectangle. Further, different numerals from magic rectangles for the same character are produced by considering the magic sum, starting number and template of magic rectangle. Once the magic rectangles are created, the numerals which occur in the magic rectangles are considered for the encoding of the plaintext character which is then used for encryption in the cryptosystems like RSA, ElGamal. The proposed work provides an additional layer of security to any public key cryptosystems. As this model is acting as a wrapper to any public key cryptosystems, it ensures enhanced security. The proposed methodology is implemented with different processors 1, 2, 4, 8 and 16 in a simulated environment using Maui scheduler which employs back filling philosophy.