Discuss symmetric and asymmetric key encryption- Computer Network Security
Question 1:
An important service provided by any system is the ability to run a process on a predetermined schedulewithout human intertention. The “automation” of tasks can reduce the workload of the system administrator significantly. Unfortunately Linux currently offers not one service but potentially three-cron, anacron, and systemd timer units.
In about a page compare and contrast all three systems. Illustrate your discussion by using the systemfiles /etc/anacron and /etc/crontab
and by constructing equivalent systemd service and timer files.
Question 2:
The web administrator of your organisation needs to login remotely to the machine that is running the organisation’s public web site. You tell her that the only way to login is via The Secure Shell-which she knows nothing about! Assuming she is logging in via a Linux box write a help document for her containing the following
a. A short introduction to SSH, explaining why it is the preferredway of logging into a remotemachine-this explanation will need to discuss symmetric and asymmetric key encryption.
b. A discussion of the contents of the file ~/.ssh/known_hosts.
Your discussion should include (but not be limitted to):
– how the file is populated,
– how the keys in the file are used by SSH,
– a discussion of “man-in-the-middle” attacks,
– why the hostnames in the file are “hashed”, and
– how individual keys can be deleted by ssh-keygen.
c. A description how to configure access so that no passwords are needed-that is by using user asymmetric keys. This will require a discussion (with examples) of the command sshkeygen, the file ~/.ssh/authorized_keys, passphrase protected keys and the commands ssh-agent and ssh-add.
Question 3:
A user comes to you requesting that you create and implement a backup policy for his desktop machine. What he wants, is to be able to place a blank DVD in his Single-Sided DVD-burner at the end of the working day on a Friday and have all the files he has been working on for the week backed up automatically that evening to the DVD!
After a bit more questioning you find out that:
– He frequently creates/deletes and changes files on a daily basis.
– He wants to be able to recover files for any given day.
– He only wants his home directory backed up.
– His home directory contains about 2Gbytes of data.
– His desktop machine has a spare disk (mounted as /spare) that has plenty of free space for temporary storage.
Tasks that need to be done:
a. Using the information above design a backup policy.
Give a detailed description and justification of your backup-policy.
b. Using tar, a shell script or scripts and systemd timer and service files to implement your backup policy.
