Digital portable communications systems (PCS) use cryptographic security techniques to provide privacy to traffic and to prevent fraudulent use of the system resources. Both secret-key and public-key cryptographic protocols are available to provide security to PCS. We present a new protocol, which combines secret-key and public-key techniques. This hybrid protocol has the advantages over the other conventional protocols of not having to maintain a database of secret keys in the PCS networks, and not having to perform the complex and time consuming calculations at the time of authentication in the portables.