Man-in-the-middle (MITM) Attacks

What is MITM Attack

A MITM attack is a form of cyber-attack where a user is introduced with some kind of meeting between the two parties by a malicious individual, manipulates both parties and achieves access to the data that the two people were trying to deliver to each other. A man-in-the-middle attack also helps a malicious attacker, without any kind of participant recognizing till it's too late, to hack the transmission of data intended for someone else and not supposed to be sent at all. In certain aspects, like MITM, MitM, MiM or MIM, MITM attacks can be referred.

Blowfish Algorithm in Cryptography

 Blowfish is a symmetric, 64-bit block cipher with changeable length. As a "general-purpose algorithm," it was created by Bruce Schneier in 1993 as a quick, cost-free replacement for the venerable Data Encryption Standard (DES) and International Data Encryption Algorithm (IDEA) encryption techniques.

Types of Cyber Attacks

 A cyber-attack is an exploitation of computer systems and networks. It uses malicious code to alter computer code, logic or data and lead to cybercrimes, such as information and identity theft.

We are living in a digital era. Now a day, most of the people use computer and internet. Due to the dependency on digital things, the illegal computer activity is growing and changing like any type of crime.

Cyber-attacks can be classified into the following categories:

Public Key Encryption

 

Public key cryptography provides a secure way to exchange information and authenticate users by using pairs of keys. The public key is used for encryption and signature verification, while the private key is used for decryption and signing. When the two parties communicate with each other to transfer the intelligible or sensible message, referred to as plaintext, is converted into apparently random unreadable for security purposes referred to as ciphertext. 

Block Cipher Design Principles

 Block ciphers are built in the Feistel cipher structure. Block cipher has a specific number of rounds and keys for generating ciphertext.Block cipher is a type of encryption algorithm that processes fixed-size blocks of data, usually 64 or 128 bits, to produce ciphertext. The design of a block cipher involves several important principles to ensure the security and efficiency of the algorithm. Some of these principles are:

What is Proxy Server?

 A proxy server refers to a server that acts as an intermediary between the request made by clients, and a particular server for some services or requests for some resources. There are different types of proxy servers available that are put into use according to the purpose of a request made by the clients to the servers. The basic purpose of Proxy servers is to protect the direct connection of Internet clients and Internet resources. There are many Proxy providers in the market that provide services to both individuals and businesses.

Cyber Security Firewalls

 

Firewalls

Firewalls are a central architectural element to any network. They are designed to keep out all network traffic, except traffic which we allow. Firewalls operate on Layer 4, typically controlling TCP and UDP access to internal assets. Next-Generation Firewalls operate on all the layers of the OSI model, including Layer 7.

Traffic entering a network, e.g. through a Firewall, is called ingress traffic. Traffic leaving is called egress.

Cyber Security Wi-Fi Attacks

 A potent and important area to computer security is WIFI. Devices and systems are no longer required to be interconnected via physical cables, but can instead be reached by anyone within signal radius. WIFI enables many new devices to be capable of networking.

Penetration Testing & Social Engineering

 

Penetration Testing & Social Engineering

Penetration testing serves as a pro-active measure to try identify vulnerabilities in services and organizations before other attackers can.

Cyber Security Network Mapping & Port Scanning

 If we are to defend, we first need to know what to defend. Asset Management often relies on Network Mapping to identify which systems are live on a network.

Asset management and knowing what you expose on the network, including which services are hosted is very important for anyone looking to defend their network.

Cyber Security - Risk Analysis

 Now that we have already studied the principles, policies and standards of cybersecurity systems, we move forward to Risk Analysis in cybersecurity. With increasing number of attacks and crimes against computer systems and networks, there is also an urgent need for firms to perform regular Risk Analysis of their cybersecurity systems for better coverage and long-term solutions to cybercrimes.

VPN in Cyber Security

 Virtual Private Network, more commonly known as VPN, describes a software application that provides a secure route for a network node to connect to the internet. In this chapter, we will discuss in detail the functioning and characteristics of VPN services. So, let’s start our chapter on this note.

Cyber Security - Dark Web

 The Dark Web, also known as Darknet, is a part of the world wide web where most of the illegal activities take place on the internet. From phishing to scams and much more, these attacks are very harmful, and most cyber experts are trying to figure out a way to solve this problem.

Types of Cyberattacks

 Cyberattacks are growing in numbers, and there is an urgent need of more robust cybersecurity measures to counter these attacks. We as programmers and IT professionals must be aware of the most common types of cyberattacks that occur in top organizations over the course.

Basics of Cyber Technology

 The rise of cyber technology and the invention of the Internet are very important incidents in the modern technology era. With the rise of these entities, there is also an increase in cybercrimes and attacks.

Before we reach these subjects on a wider scale, we must discuss the background concepts which form the basic structure of Cyber Technology. These include topics like networking, the OSI Model, Internet, Networking protocols and some other concepts.

History of Cyber Security

 Today, cyber security finds a place in almost all major companies and stakeholders’ hindsight. But in the early days, the concept of cyber security was very vague.

It was not until many years later that the development of cyber security was taken seriously due to the frequent occurrence of cyber-attacks and threats from dangerous entities. The development of these measures became the evolution of cyber security.

Cyber Security Tutorial

Cybersecurity is one of the most sought-after skills in the modern era. With such a large information pool, and an even larger network of nodes, Cybersecurity has gained a lot of importance nowadays.

This cybersecurity tutorial is designed for beginners as well as professionals. In this tutorial, you will learn all essential skills, tools, and strategies regarding cybersecurity. This cybersecurity tutorial covers the topics from basic concepts to advanced techniques.

Linux Admin - Backup and Recovery

 Before exploring methods particular to CentOS for deploying a standard backup plan, let's first discuss typical considerations for a standard level backup policy. The first thing we want to get accustomed to is the 3-2-1 backup rule.

Linux Admin - Shell Scripting

 

Introduction to Bash Shell

Like flavors of GNU Linux, shells come in many varieties and vary in compatibility. The default shell in CentOS is known as the Bash or Bourne Again Shell. The Bash shell is a modern day, modified version of Bourne Shell developed by Stephen Bourne. Bash was the direct replacement to the original Thompson Shell on the Unix operating system developed at Bell Labs by Ken Thompson and Dennis Ritchie (Stephen Bourne was also employed by Bell Labs)

JavaScript - Comments

 

JavaScript Comments

JavaScript comments are used to explain the purpose of the code. The comments are not executed as a part of program and these are solely meant for human developers to understand the code better.

JavaScript Tutorial

 

JavaScript Tutorial

JavaScript is a lightweight, interpreted programming language. It is commonly used to create dynamic and interactive elements in web applications. JavaScript is very easy to implement because it is integrated with HTML. It is open and cross-platform.

Linux Admin - Traffic Monitoring in CentOS

 There are several third party tools that can add enhanced capabilities for CentOS traffic monitoring. In this tutorial, we will focus on those that are packaged in the main CentOS distribution repositories and the Fedora EPEL repository.

There will always be situations where an Administrator (for one reason or another) is left with only tools in the main CentOS repositories. Most utilities discussed are designed to be used by an Administrator with the shell of physical access. When traffic monitoring with an accessible web-gui, using third party utilities such as ntop-ng or Nagios is the best choice (versus re-creating such facilities from scratch).

Linux Admin - Install Anonymous FTP

 Before delving into installing FTP on CentOS, we need to learn a little about its use and security. FTP is a really efficient and well-refined protocol for transferring files between the computer systems. FTP has been used and refined for a few decades now. For transferring files efficiently over a network with latency or for sheer speed, FTP is a great choice. More so than either SAMBA or SMB.

Systemd Services Start and Stop

 systemd is the new way of running services on Linux. systemd has a superceded sysvinit. systemd brings faster boot-times to Linux and is now, a standard way to manage Linux services. While stable, systemd is still evolving.

systemd as an init system, is used to manage both services and daemons that need status changes after the Linux kernel has been booted. By status change starting, stopping, reloading, and adjusting service state is applied.

First, let's check the version of systemd currently running on our server.

Linux Admin - Quota Management

 

CentOS disk quotas can be enabled both; alerting the system administrator and denying further disk-storage-access to a user before disk capacity is exceeded. When a disk is full, depending on what resides on the disk, an entire system can come to a screeching halt until recovered.

Enabling Quota Management in CentOS Linux is basically a 4 step process −

• Step 1 − Enable quota management for groups and users in /etc/fstab.

• Step 2 − Remount the filesystem.

• Step 3 − Create Quota database and generate disk usage table.

• Step 4 − Assign quota policies.

Enable Quota Management in /etc/fstab

First, we want to backup our /etc/fstab filen −

[root@centosLocal centos]# cp -r /etc/fstab ./

We now have a copy of our known working /etc/fstab in the current working directory.

# 
# /etc/fstab 
# Created by anaconda on Sat Dec 17 02:44:51 2016 
# 
# Accessible filesystems, by reference, are maintained under '/dev/disk' 
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
# 
/dev/mapper/cl-root        /         xfs     defaults                      0 0
UUID = 4b9a40bc-9480-4     /boot     xfs     defaults                      0 0

/dev/mapper/cl-home        /home     xfs     defaults,usrquota,grpquota    0 0

/dev/mapper/cl-swap        swap      swap    defaults                      0 0

We made the following changes in the options section of /etc/fstab for the volume or Label to where quotas are to be applied for users and groups.

• usrquota
• grpquota

As you can see, we are using the xfs filesystem. When using xfs there are extra manual steps involved. /home is on the same disk as /. Further investigation shows / is set for noquota, which is a kernel level mounting option. We must re-configure our kernel boot options.

root@localhost rdc]# mount | grep ' / ' 
/dev/mapper/cl-root on / type xfs (rw,relatime,seclabel,attr2,inode64,noquota)

[root@localhost rdc]#

Reconfiguring Kernel Boot Options for XFS File Systems

This step is only necessary under two conditions −

• When the disk/partition we are enabling quotas on, is using the xfs file system
• When the kernel is passing noquota parameter to /etc/fstab at boot time

Step 1 − Make a backup of /etc/default/grub.

cp /etc/default/grub ~/

Step 2 − Modify /etc/default/grub.

Here is the default file.

GRUB_TIMEOUT=5 
GRUB_DISTRIBUTOR="$(sed 's, release .*$,,g' /etc/system-release)" 
GRUB_DEFAULT=saved 
GRUB_DISABLE_SUBMENU=true 
GRUB_TERMINAL_OUTPUT="console" 
GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=cl/root rd.lvm.lv=cl/swap rhgb quiet" 
GRUB_DISABLE_RECOVERY="true"

We want to modify the following line −

GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=cl/root rd.lvm.lv=cl/swap rhgb quiet" 

to

GRUB_CMDLINE_LINUX="crashkernel=auto rd.lvm.lv=cl/root rd.lvm.lv 
=cl/swap rhgb quiet rootflags=usrquota,grpquota"

Note − It is important we copy these changes verbatim. After we reconfigure grub.cfg, our system will fail to boot if any errors were made in the configuration. Please, try this part of the tutorial on a non-production system.

Step 3 − Backup your working grub.cfg

cp /boot/grub2/grub.cfg /boot/grub2/grub.cfg.bak

Make a new grub.cfg

[root@localhost rdc]# grub2-mkconfig -o /boot/grub2/grub.cfg 
Generating grub configuration file ... 
Found linux image: /boot/vmlinuz-3.10.0-514.el7.x86_64 
Found initrd image: /boot/initramfs-3.10.0-514.el7.x86_64.img 
Found linux image: /boot/vmlinuz-0-rescue-dbba7fa47f73457b96628ba8f3959bfd 
Found initrd image: /boot/initramfs-0-rescuedbba7fa47f73457b96628ba8f3959bfd.img 
done

[root@localhost rdc]#

Reboot

[root@localhost rdc]#reboot

If all modifications were precise, we should not have the availability to add quotas to the xfs file system.

[rdc@localhost ~]$ mount | grep ' / ' 
/dev/mapper/cl-root on / type xfs (rw,relatime,seclabel,attr2,inode64,usrquota,grpquota)
 
[rdc@localhost ~]$

We have passed the usrquota and grpquota parameters via grub.

Now, again edit /etc/fstab to include / since /homeon the same physical disk.

/dev/mapper/cl-root/xfs
defaults,usrquota,grpquota        0 0

Now let's enable the quota databases.

[root@localhost rdc]# quotacheck -acfvugM

Make sure Quotas are enabled.

[root@localhost rdc]# quotaon -ap 
group quota on / (/dev/mapper/cl-root) is on 
user quota on / (/dev/mapper/cl-root) is on 
group quota on /home (/dev/mapper/cl-home) is on 
user quota on /home (/dev/mapper/cl-home) is on 
[root@localhost rdc]#

Remount the File System

If the partition or disk is separate from the actively booted partition, we can remount without rebooting. If the quota was configured on a disk/partition booted in the root directory /, we may need to reboot the operating system. Forcing the remount and applying changes, the need to remount the filesystem may vary.

[rdc@localhost ~]$ df 
Filesystem              1K-blocks     Used      Available      Use%     Mounted on
/dev/mapper/cl-root     22447404      4081860   18365544       19%         /
devtmpfs                903448        0         903448         0%          /dev
tmpfs                   919308        100       919208         1%          /dev/shm
tmpfs                   919308        9180      910128         1%          /run
tmpfs                   919308        0         919308         0%          /sys/fs/cgroup
/dev/sda2               1268736       176612    1092124        14%         /boot
/dev/mapper/cl-var      4872192       158024    4714168        4%          /var
/dev/mapper/cl-home     18475008      37284     18437724       1%          /home
tmpfs                   183864        8         183856         1%          /run/user/1000

[rdc@localhost ~]$

As we can see, LVM volumes are in use. So it's simple to just reboot. This will remount /home and load the /etc/fstab configuration changes into active configuration.

Learn Linux/Unix in-depth with real-world projects through our Linux/Unix certification course. Enroll and become a certified expert to boost your career.

Create Quota Database Files

CentOS is now capable of working with disk quotas on /home. To enable full quota supprt, we must run the quotacheck command.

quotacheck will create two files −

• aquota.user
• aquota.group

These are used to store quota information for the quota enabled disks/partitions.

Following are the common quotacheck switches.

Switch	Action
-u	Checks for user quotas
-g	Checks for group quotas
-c	Quotas should be enabled for each file system with enables quotas
-v	Displays verbose output

Add Quota Limits Per User

For this, we will use the edquota command, followed by the username −

[root@localhost rdc]# edquota centos

Disk quotas for user centos (uid 1000):  
Filesystem                   blocks       soft       hard     inodes     soft     hard 
/dev/mapper/cl-root              12          0          0         13        0        0  
/dev/mapper/cl-home            4084          0          0        140        0        0

Let's look at each column.

• Filesystem − It is the filesystem quotas for the user applied to

• blocks − How many blocks the user is currently using on each filesystem

• soft − Set blocks for a soft limit. Soft limit allows the user to carry quota for a given time period

• hard − Set blocks for a hard limit. Hard limit is total allowable quota

• inodes − How many inodes the user is currently using

• soft − Soft inode limit

• hard − Hard inode limit

To check our current quota as a user −

[centos@localhost ~]$ quota 
Disk quotas for user centos (uid 1000):  
Filesystem             blocks     quota      limit grace    files   quota   limit   grace 
/dev/mapper/cl-home    6052604    56123456   61234568       475     0       0       [centos@localhost ~]$

Following is an error given to a user when the hard quota limit has exceeded.

[centos@localhost Downloads]$ cp CentOS-7-x86_64-LiveKDE-1611.iso.part ../Desktop/

cp: cannot create regular file ‘../Desktop/CentOS-7-x86_64-LiveKDE-
1611.iso.part’: Disk quota exceeded

[centos@localhost Downloads]$

As we can see, we are closely within this user's disk quota. Let's set a soft limit warning. This way, the user will have advance notice before quota limits expire. From experience, you will get end-user complaints when they come into work and need to spend 45 minutes clearing files to actually get to work.

As an Administrator, we can check quota usage with the repquota command.

[root@localhost Downloads]# repquota  /home  
                    Block limits                            File limits  
User            used     soft     hard     grace       used     soft     hard     grace 
----------------------------------------------------------------------------------------
root      --       0         0        0                   3        0        0        
centos    -+ 6189824  56123456 61234568                 541      520      540      6days 

[root@localhost Downloads]#

As we can see, the user centos has exceeded their hard block quota and can no longer use any more disk space on /home.

-+denotes a hard quota has been exceeded on the filesystem.

When planning quotas, it is necessary to do a little math. What an Administrator needs to know is:How many users are on the system? How much free space to allocate amongst users/groups? How many bytes make up a block on the file system?

Define quotas in terms of blocks as related to free disk-space.It is recommended to leave a "safe" buffer of free-space on the file system that will remain in worst case scenario: all quotas are simultaneously exceeded. This is especially on a partition that is used by the system for writing logs.

Linux Admin - User Management

 When discussing user management, we have three important terms to understand −

• Users
• Groups
• Permissions

We have already discussed in-depth permissions as applied to files and folders. In this chapter, let's discuss about users and groups.

Linux Admin - File / Folder Management

 To introduce permissions as they apply to both directories and files in CentOS Linux, let's look at the following command output.

Linux Admin - Basic CentOS Linux Commands

 Before learning the tools of a CentOS Linux Administrator, it is important to note the philosophy behind the Linux administration command line.

Linux was designed based on the Unix philosophy of “small, precise tools chained together simplifying larger tasks”. Linux, at its root, does not have large single-purpose applications for one specific use a lot of the time. Instead, there are hundreds of basic utilities that when combined offer great power to accomplish big tasks with efficiency.

Linux Admin - CentOS Overview

Unique among business class Linux distributions, CentOS stays true to the open-source nature that Linux was founded on. The first Linux kernel was developed by a college student at the University of Helsinki (Linus Torvalds) and combined with the GNU utilities founded and promoted by Richard Stallman. CentOS has a proven, open-source licensing that can power today’s business world.

CentOS has quickly become one of the most prolific server platforms in the world. Any Linux Administrator, when seeking employment, is bound to come across the words: “CentOS Linux Experience Preferred”. From startups to Fortune 10 tech titans, CentOS has placed itself amongst the higher echelons of server operating systems worldwide.

What makes CentOS stand out from other Linux distributions is a great combination of −

• Open source licensing

• Dedicated user-base of Linux professionals

• Good hardware support

• Rock-solid stability and reliability

• Focus on security and updates

• Strict adherence to software packaging standards needed in a corporate environment

Before starting the lessons, we assume that the readers have a basic knowledge of Linux and Administration fundamentals such as −

• What is the root user?

• The power of the root user

• Basic concept of security groups and users

• Experience using a Linux terminal emulator

• Fundamental networking concepts

• Fundamental understanding of interpreted programming languages (Perl, Python, Ruby)

• Networking protocols such as HTTP, LDAP, FTP, IMAP, SMTP

• Cores that compose a computer operating system: file system, drivers, and the kerne