Lecture 09. Security and Cryptography

Entropy

Suppose a password is chosen as a concatenation of four lower-case dictionary words, where each word is selected uniformly at random from a dictionary of size 100,000. An example of such a password is correcthorsebatterystaple. How many bits of entropy does this have?

In order to calculate the bits of entropy, we need to know how many possibilites there.

We can easily know the combinations count are $100000^4$ and the bits of entropy are $log_2 (100000^4)\approx 66\ bit$ 🤗

Lecture 08. Metaprogramming

Most makefiles provide a target called clean. This isn’t intended to produce a file called clean, but instead to clean up any files that can be re-built by make. Think of it as a way to “undo” all of the build steps. Implement a clean target for the paper.pdf Makefile above. You will have to make the target phony. You may find the git ls-filessubcommand useful. A number of other very common make targets are listed here.

Intro

Recently I was fine-tuning my deep learning model, and I habitually started to use print to print some key information on the terminal. So my workflow is like:

1. I type some hyperparameters to train my model.
2. I manually opened an Excel to record the hyperparameters used and the model evaluation results. And I will go back to step 1. If I am not satisfied with results.

Soon, I became bored with this workflow (In fact, I kept this for quite a long time.). However, I suddenly forgot to record key information manually. As a result, I had to navigate in the history output of the the terminal slowly.

debugging

Use journalctl on Linux or log show on macOS to get the super user accesses and commands in the last day. If there aren’t any you can execute some harmless commands such as sudo ls and check again.

When I run log show --last 1d, it keeps running for along time. I don’t know how long it make take, so I will just execute harmless sudo ls to check the log.

Lecture05. Command-line Environment

Job control

From what we have seen, we can use some ps aux | grep commands to get our jobs’ pids and then kill them, but there are better ways to do it. Start a sleep 10000 job in a terminal, background it with Ctrl-Z and continue its execution with bg. Now use pgrep to find its pid and pkill to kill it without ever typing the pid itself. (Hint: use the -af flags).

Lecture 03. Editors (Vim)

Complete vimtutor. Note: it looks best in a 80x24 (80 columns by 24 lines) terminal window.

It is a tutorial for beginners of vim. I will just put some notes which are not mentioned in course here.

• U command: When we press u in normal mode, we can undo the last command. What U does is fixing a whole line.

• Ctrl + G: show your location in the file and the file status. Type the linenumber you want to go, then press G, then you are there.

Intro

The process of drawing a simple relation graph in python can be broken down into 2 steps.

1. Define a graph.
2. Draw a graph.

Step 1. Define a graph

In this step, we will use the networkx package.

Install tutorial

If you are using conda, you can just type conda install networkx

If you are using pip, you can just type pip install networkx

Nodes

First of all, you need to create a graph.

Lecture 01. Shell

Create a new directory called missing under /tmp