Migrating notes from Notion - Initial stage

content/notes/https-ssl-certs.md

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+---
+tags:
+  - networking
+  - notes
+  - web
+author: TrudeEH
+draft: false
+showToc: true
+title: HTTPS and SSL Certificates
+---
+
+## HTTP(s)
+
+The `http` protocol sends data as plaintext, which is an issue when sharing sensitive data such as messages and passwords.  
+`https` uses `TLS` to encrypt sensitive traffic between the client and server, creating a secure connection between the two.
+
+## TLS
+
+TLS is a form of [[encryption]], used to secure HTTPS connections.  
+TLS replaces SSL (a deprecated protocol), however, the term SSL is still used often.
+
+### Handshake
+
+To establish a secure connection, a 'handshake' is performed between the client and the server.
+1. The client send a message with browser and OS info, and all supported encryption algorithms.
+2. The server selects the strongest supported algorithm, and responds with some server info, the selected algorithm, and an SSL Certificate (contains the domain name, certificate authority and public key).
+3. The client checks the certificate to ensure that it is valid and signed by a valid certificate authority.
+4. If the certificate is valid, the client generates a random session key, and encrypts it with the server's public key.
+5. The session key is sent to the server.
+6. The server decrypts the session key, using its own private key. If the key is valid, the server sends a finish message back to the client.
+7. The client sends its own finish message, and a secure connection is established.
+
+### SSL Certificates
+
+SSL Certificates are needed because without them, a malicious actor could intercept the client's first handshake message, and establish a secure connection with the client, obtaining its secrets.  
+A trusted third party is needed to validate that the public key sent to the client matches the server's actual public key.  
+[Let’s Encrypt](https://letsencrypt.org) is a non-profit organization that signs certificates for free.
+
+#### Certbot
+
+The easiest way to generate a *Let's Encrypt* certificate is through `certbot`, which is available as a snap package.
+
+```Shell
+sudo apt install snapd
+sudo snap install core && sudo snap refresh core
+sudo snap install --classic certbot
+sudo ln -s /snap/bin/certbot /usr/bin/certbot
+```
+
+> If you use a firewall, open port 80, as it is required for `certbot` to verify your domain information.  
+> Once `certbot` is installed, you can either generate a standalone certificate (for example, to use for IRC), or follow the [official instructions](https://certbot.eff.org/instructions) for any web service that you already own.
+
+For example, for an IRC server, run the following command:
+
+```Shell
+sudo certbot certonly --standalone --preferred-challenges http -d irc.example.com
+```
+
+Replace `irc.example.com` with your actual domain.  
+The certificate will be stored as two files …
+- `/etc/letsencrypt/live/irc.example.com/fullchain.pem`
+- `/etc/letsencrypt/live/irc.example.com/privkey.pem`  
+… which you can copy to any location you need.  
+These files will be renewed every 90 days, so remember to either update them manually, or add a `crontab` entry to automate the process.