OpenSSL is a software library that provides cryptographic functions and tools for creating and managing SSL/TLS certificates. One of the tools included in OpenSSL is the command-line utility openssl, which can be used to generate various types of cryptographic objects, such as private keys, public keys, certificate signing requests (CSRs), and certificates. A CSR is a file that contains the information needed by a certificate authority (CA) to issue a digital certificate for a web server. A CSR includes the public key of the web server, the domain name or names that the certificate will cover, and some identifying information about the organization or individual requesting the certificate. To generate a CSR for serving HTTPS with Apache HTTPD, the openssl command can be used with the req option, which stands for request. The req option takes several parameters, such as -new, -newkey, -nodes, -keyout, and -out, to specify the details of the CSR generation process. For example, the following command will generate a new private key and a new CSR for the domain example.com, using a 2048-bit RSA algorithm, and saving the files as example.key and example.csr respectively:

openssl req -new -newkey rsa:2048 -nodes -keyout example.key -out example.csr

The command will also prompt the user to enter some information for the CSR, such as the country code, state or province name, locality name, organization name, organizational unit name, common name, and email address. The common name is the most important field, as it should match the domain name or names that the certificate will cover. For example, if the certificate is for example.com, the common name should be example.com. If the certificate is for multiple domains, such as example.com and www.example.com, the common name should be one of them, and the rest should be specified as subject alternative names (SANs) in a configuration file. After the CSR is generated, it can be sent to a CA for signing and obtaining a certificate, which can then be installed and configured on the Apache HTTPD server to enable HTTPS.

References :

OpenSSL : The official website of the OpenSSL project, which provides documentation, downloads, and support for the OpenSSL software.

Apache: CSR & SSL Installation (OpenSSL) - DigiCert : A guide from DigiCert on how to create a CSR and install an SSL certificate on an Apache server using OpenSSL.

How to Generate a Certificate Signing Request (CSR) for Apache Web Server Using OpenSSL - The SSL Store™ : A tutorial from The SSL Store on how to generate a CSR for an Apache web server using OpenSSL.

GoDaddy - Apache: Generate CSR (Certificate Signing Request) : A step-by-step instruction from GoDaddy on how to generate a CSR for Apache 2.x using OpenSSL.

The sshd configuration file is used to customize the behavior of the SSH server daemon. Some of the lines in the file can affect the security of the server and should be modified accordingly. The following are two examples of such lines:

Protocol 2, 1: This line specifies the SSH protocol versions that are supported by the server. The possible values are 1 and 2, where 1 is the older and less secure version and 2 is the newer and more secure version. The recommended value is 2, as it provides stronger encryption, authentication, and integrity mechanisms. Allowing protocol 1 can expose the server to various attacks, such as man-in-the-middle, replay, and insertion attacks. Therefore, this line should be changed to Protocol 2 or commented out (as protocol 2 is the default value).

PermitRootLogin yes: This line determines whether root login is allowed on the server. The possible values are yes, no, prohibit-password, and without-password. The value yes allows root login with any authentication method, including password. This can pose a serious security risk, as root is the most privileged user on the system and can perform any action. If an attacker manages to guess or obtain the root password, they can gain full control over the server. Therefore, this line should be changed to no or prohibit-password (which allows root login only with public key authentication) or commented out (as no is the default value).

References :  LPIC-2 202 exam objectives ,  LPIC-2 202-450 Exam Prep: Network Configuration ,  The Best Ways to Secure Your SSH Server ,  Configure the /etc/ssh/sshd_config file

Linux SSH Server (sshd) Configuration and Security Options With ... 1

The Best Ways to Secure Your SSH Server - How-To Geek

 The Apache HTTPD directive that enables HTTPS protocol support is SSLEngine on. This directive activates the SSL/TLS protocol engine for the current virtual host. HTTPS is a secure version of HTTP that uses SSL/TLS to encrypt the communication between the client and the server.  To enable HTTPS, the server must have a valid SSL certificate and a corresponding private key, and configure them using the SSLCertificateFile and SSLCertificateKeyFile directives 1 2 3   References :

LPIC-2 Overview

LPIC-2 202-450

SSL/TLS Strong Encryption: How-To - Apache HTTP Server Version 2.4

The /etc/sysct1.conf file is used to configure kernel parameters at runtime. The net.ipv4.ip_forward parameter controls whether IP packet forwarding is enabled for IPv4. Setting it to 1 enables packet forwarding, while setting it to 0 disables it. This setting is applied at boot time and persists across system restarts. The other options are either incorrect or temporary solutions that do not survive a reboot.  References :  LPIC-2 201 exam objectives ,  LPIC-2 201-450 Exam Prep: Network Configuration

The TransferLog and CustomLog directives are both used to specify the location and format of the access log file in Apache HTTPD. The access log file records information about each request received by the server, such as the client IP address, the request method, the requested URL, the response status code, and the bytes sent.

The TransferLog directive is a simple way to enable access logging, without any customization. It takes one argument, which is the name of the log file or a pipe to a program that will handle the log data. For example:

TransferLog logs/access_log

The CustomLog directive is a more flexible way to enable access logging, with the ability to customize the log format and conditionally log requests based on environment variables. It takes two or three arguments, which are the name of the log file or a pipe to a program, the log format string or a nickname defined by the LogFormat directive, and optionally an expression that evaluates to true or false for each request. For example:

CustomLog logs/access_log common CustomLog “|/usr/bin/rotatelogs logs/access_log.%Y-%m-%d 86400” combined CustomLog logs/ssl_access_log “%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x " %r " %b” env=HTTPS

The ErrorLog directive is another logging directive in Apache HTTPD, but it is used to specify the location and format of the error log file, which records any errors or warnings encountered by the server. For example:

ErrorLog logs/error_log

The ServerLog and VHostLog directives are not valid logging directives in Apache HTTPD. They may be confused with the ServerSignature and VirtualHost directives, which are used for other purposes.

References :

Log Files - Apache HTTP Server Version 2.4

Directive Index - Apache HTTP Server Version 2.4

Apache Logging Basics - The Ultimate Guide To Logging

The tool dig, which stands for domain information groper, is a command-line utility that provides the most information when performing DNS queries, without any options. Dig can query any type of DNS record and display the full response from the DNS server, including the header, question, answer, authority, and additional sections. Dig can also show the query time, server address, response code, flags, and statistics.  Dig is a versatile and powerful tool that can be used for troubleshooting, testing, and debugging DNS issues 1 2 3   References :

dig(1) - Linux manual page

How to Use the Dig Command on Linux

How to use the dig command for DNS queries on Linux

 To log into a remote SSH server using SSH keys, the client needs to generate a public and private key pair using the ssh-keygen utility. The private key (~/.ssh/id_rsa) should be kept secret and protected by a passphrase, while the public key (~/.ssh/id_rsa.pub) should be copied to the remote server’s authorized_keys file (~/.ssh/authorized_keys) using the ssh-copy-id utility or manually. The authorized_keys file contains the public keys of the clients that are allowed to log into the server using SSH keys. The client can then use the ssh command with the -i option to specify the private key file to authenticate to the server without entering a password.  References :

LPIC-2 Exam 202 Objectives , Topic 212: System Security, 212.3 Secure shell (SSH) (weight: 4)

How To Configure SSH Key-Based Authentication on a Linux Server

How To Configure SSH Key-Based Authentication on a Linux Server