Wrap-up and resources

Key Takeaways

1. Linux and the command line for defenders: On Linux everything is a file, and logs are text you read with small commands joined by pipes. Know where the important logs live, read permissions at a glance, and always ask: who? when? from where? how many times?
2. Cryptography: how secrets stay secret: Encryption protects confidentiality and is undone with a key; hashing is a one-way fingerprint that protects integrity; a signature proves the sender. TLS combines them all, and the world is now moving to post-quantum algorithms.
3. Web application security: the OWASP Top 10:2025: Check permission on the server for every request, keep commands apart from data, know your components, and fail safe. Those four cover most of the list.
4. Systems and network security: hardening, segmentation and Zero Trust: Patch what is actually exploited first, close what you do not need, segment the network so attackers cannot roam, trust no request just because it comes from inside, and keep an offline copy.

Term	Definition	Part
/var/log/auth.log	The sign-in, SSH and sudo log on Debian and Ubuntu.	1
rwx	Read 4, write 2, execute 1; for owner, then group, then others.	1
sudo	Run a command as root; every use is logged.	1
Hash and salt	A fixed-length fingerprint that cannot be reversed, and a random value added before hashing.	2
Symmetric and asymmetric	Encryption with one shared key, and with a public and private key pair.	2
PQC	Cryptography that resists quantum computers, such as ML-KEM and ML-DSA.	2
Injection	Commands slipped inside data that the system runs as commands.	3
Number one in OWASP 2025	Broken Access Control: reaching data or functions without permission.	3
Stopping SQL injection	Parameterised queries, input validation, and least privilege for the database account.	3
Zero Trust	No automatic trust; verify every request every time.	4
EDR	Endpoint protection by watching behaviour and responding.	4
The 3-2-1 rule	Three copies, on two kinds of media, one off-site or offline.	4

Grouped by type. Start with the official docs for precision, or an article or video for the explanation.