Cryptography

What this chapter covers

Cryptography is the foundation under every secure connection that a router makes.

This chapter explains the vocabulary and the main methods. It names the algorithms that you will meet, shows how a public key infrastructure creates trust, and ends with the practical work of creating and using certificates on RouterOS.

You do not need advanced mathematics. You need to understand what each tool is for and which choices are weak or strong.

How the topics fit together

The chapter moves from ideas, to algorithms, to trust, and then to practice.

The first page gives the terms and the two big families, symmetric and asymmetric. The second page puts names to them, such as AES, RSA and Diffie Hellman, and says which ones are no longer safe.

The third page asks a new question. How do you know that a public key belongs to the right owner? The answer is a PKI, with certificate authorities and a chain of trust.

The last page turns this into console work. You create a private CA, sign a server certificate, import a free certificate and select it in a service.

How to use these pages

Each topic page has the same shape, so you can skim for what you need.

• What it is: the idea in plain words.
• How it works: the mechanism, with diagrams and console examples.
• What to remember for the exam: the facts to memorise.
• Common mistakes: the classic traps.
• Check yourself: three questions to test your understanding.

The first three pages are mostly concepts. Learn the terms and the tables, and test yourself by explaining each idea aloud.

The last page is practical. Try the certificate commands on a lab router, and then open the web interface to see the result.