### Nebula 01

Let's start another challenge from Nebula machine and see what's our target this time.

### Nebula 00

Finally, exams are over so it's time to get back to security topics. Today I'm going to start documenting journey through Nebula machine from Exploit Exercises.

### File Permissions

A little break in the exams, so we have some time to discover another topic - which is file permissions on Linux. Let's fully understand how they work.

### Frequency Analysis

**Frequency analysis** is the study of the frequency of letters or groups of letters occuring next to each other. The most ancient description for what we know was made by Al-Kindi, dating back to the IXth century. This attack is used to break **monoalphabetic ciphers**, which work by simple and fixed substitution of letters. We now, that if the **a** in plaintext is encrypted to **x** letter, everytime in the ciphertext that **x** will convert to **a**.