1- Public-key cryptography can be used for encryption and key exchange. Furthermore, it has some properties (such as nonrepudiation) which are not offered by symmetric key cryptography. So why do we still use symmetric cryptography in current applications?

2- Assume a fast public-key library such as OpenSSL that can decrypt data at a rate of 100 Kbit/sec using the RSA algorithm on a modern PC. On the same machine, AES can decrypt at a rate of 17 Mbit/sec. Assume we want to decrypt a movie stored on a DVD. The movie requires 1 GByte of storage. How long does decryption take with either algorithm?