Q8: Consider the following application scenario: suppose you would like to backup your birthday party video in a cloud, say Google Cloud. During the party, you and some of the friends got drunk, so you don't want anyone you don't know to see the video, moreover, the video file is about 5 Gigabytes. Google's public key is pkg and can be found easily online. We know that public key encryption is flexible, but it is computationally expensive, especially on large files. While a symmetric key encryption is simple and efficient, however, Google won't be able to share a secret key with its clients. More concretely, a public key encryption on 1Kb data might use less than one second, but if on 5 Gigabytes data, it might take two hours; on the other hand, a symmetric key encryption on 5 Gigabytes still cost only a couple of, say 10 seconds. Describe a possible mechanism with detailed algorithm description, so that you can use it to upload the 5 Gigabytes video quickly and securely to Google Cloud, taking about only 12 seconds (ignoring the network latency)? (10 points)