The smart card has been suggested for personal security in public key cryptosystems. As the size of the keys in public key cryptosystems is increased, the design of crypto-controllers in smart cards becomes more complicated. This paper proposes a secure device in a terminal, “Secure Module”, which can support precomputation technique for Schnorr-type cryptosystems such as Schnorr [7], DSA [1], KCDSA [5]. This gives a simple method to implement secure public key cryptosystems without technical efforts to redesign a cryptographic controller in 25mm ² smart card ICs.