For a prime number p, Bergman (1974) established that End(Z p × Z p 2 ) is a semilocal ring with p 5 elements that cannot be embedded in matrices over any commutative ring. We identify the elements of End(Z p × Z p 2 ) with elements in a new set, denoted by E p , of matrices of size 2 × 2, whose elements in the rst row belong to Z p and the elements in the second row belong to Z p 2 ; also, using the arithmetic in Z p and Z p 2 , we introduce the arithmetic in that ring and prove that the ring End(Z p × Z p 2 ) is isomorphic to the ring E p . Finally, we present a Di e-Hellman key interchange protocol using some polynomial functions over E p de ned by polynomial in Z [X].