5. Public-key encryption can be used for encryption and key exchange. It also has some desireable properties (such as nonrepudiation) which are not offered by symmetric/private key encryption. Why do we still use symmetric cryptography in current applications? 6. Assume a company has 120 employees. A new security policy requires that encrypted messages be encrypted using a symmetric cipher. How many keys will be necessary, if you are to ensure that every possible pair of communicating parties can communicate in secret?