What Is Kali Linux, and Do You Need It?
If you’ve heard a 13-year-old would-be hacker talking about how 1337 they are, chances are, Kali Linux came up. Despite it’s script kiddie reputation, Kali is actually a real tool (or set of tools) for security professionals.
Kali is a Linux distribution based on Debian. Its goal is simple; include as many penetration and security audit tools as possible in one convenient package. Kali delivers, too. Many of the best open-source tools for conducting security tests are collected and ready to use.
Also read: 
4 Great Linux Distros Designed for Privacy and Security
Why Kali?
Kali is developed and maintained by Offensive Security. They’re a well-known and trusted presence in the security world, even certifying security professionals with some of the most highly respected certifications available.
It’s a convenient solution, too. Kali doesn’t require that you maintain a Linux install or collect your own software and dependencies. It’s turn-key. All the work is out of the way, so you can focus on the real work of auditing whichever system you’ve set out to test.
How Do You Use It?
Kali is a Linux distribution. Like any other, you can install it permanently on a hard drive. That works fine, but you don’t want to use Kali as a daily driver operating system. Its purposely built for penetration testing, and that’s about all that you should use it for.
Kali is best as a live distribution. You can burn Kali to a DVD or run it off of a USB drive. You don’t ever need to install anything on Kali or save any files, so spinning it up on the occasion where you need to test a system is great. It also affords the flexibility to get a Kali machine running anywhere on whichever network you’re looking to test.
What Does Kali Have?
Kali has security tools and not a whole lot else. It does, however, have a lot of security tools.
It has classic information gathering tools like NMap and Wireshark.
Kali also has WiFi-centered tools like Aircrack-ng, Kismet, and Pixie.
For attacking passwords, there are tools like Hydra, Crunch, Hashcat, and John the Ripper.
Then there are more complete suites of tools, including Metasploit and Burp Suite.
That’s only a small percentage of the security tools available by default with Kali. It would take a long time to go through all of them, but you can clearly see that many of the more popular tools are represented.
Is Kali For You?
Kali is not for everyone. It’s not a regular Linux distribution to run on your laptop and think that you’re cool for running a “hacker OS.” If you do so, you’re running a potentially insecure system. Kali is designed to run as root. It’s not secured and configured like a regular Linux distribution. It’s an offensive tool, not a defensive one.
Kali isn’t a joke either. You can do some real damage with the tools that it comes bundled with, and you can get yourself into real trouble. It’s all too easy for an uneducated user to do something seriously illegal and find themselves in a situation no one wants to be in.
With all that having been said, Kali is a great tool for professional use. If you’re a network admin and want to conduct real-world tests on your network, Kali might be just what you need. Kali also has some excellent tools for developers (especially web devs) to audit their applications before they go live.
Of course, if you’re interested in learning about security the right way, you can certainly use Kali in a controlled environment to teach yourself or follow any number of great courses.
Kali Linux is a bundle of many of the best security tools. It’s an incredible asset for professionals, but it can also be a big problem in the hands of the uninitiated. Use Kali with care and take advantage of its awesome potential. If you don’t, you’re going to end up having a really bad time.
Nick is a freelance tech. journalist, Linux enthusiast, and a long time PC gamer.
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What does kali linux do
Kali Linux (formerly known as BackTrack Linux) is an open-source, Debian-based Linux distribution aimed at advanced Penetration Testing and Security Auditing. Kali Linux contains several hundred tools targeted towards various information security tasks, such as Penetration Testing, Security Research, Computer Forensics and Reverse Engineering. Kali Linux is a multi platform solution, accessible and freely available to information security professionals and hobbyists.
Kali Linux was released on the 13th March 2013 as a complete, top-to-bottom rebuild of BackTrack Linux, adhering completely to Debian development standards.
Kali Linux Features
- More than 600 penetration testing tools included: After reviewing every tool that was included in BackTrack, we eliminated a great number of tools that either simply did not work or which duplicated other tools that provided the same or similar functionality. Details on what’s included are on the Kali Tools site.
- Free (as in beer) and always will be: Kali Linux, like BackTrack, is completely free of charge and always will be. You will never, ever have to pay for Kali Linux.
- Open source Git tree: We are committed to the open source development model and our development tree is available for all to see. All of the source code which goes into Kali Linux is available for anyone who wants to tweak or rebuild packages to suit their specific needs.
- FHS compliant: Kali adheres to the Filesystem Hierarchy Standard, allowing Linux users to easily locate binaries, support files, libraries, etc.
- Wide-ranging wireless device support: A regular sticking point with Linux distributions has been support for wireless interfaces. We have built Kali Linux to support as many wireless devices as we possibly can, allowing it to run properly on a wide variety of hardware and making it compatible with numerous USB and other wireless devices.
- Custom kernel, patched for injection: As penetration testers, the development team often needs to do wireless assessments, so our kernel has the latest injection patches included.
- Developed in a secure environment: The Kali Linux team is made up of a small group of individuals who are the only ones trusted to commit packages and interact with the repositories, all of which is done using multiple secure protocols.
- GPG signed packages and repositories: Every package in Kali Linux is signed by each individual developer who built and committed it, and the repositories subsequently sign the packages as well.
- Multi-language support: Although penetration tools tend to be written in English, we have ensured that Kali includes true multilingual support, allowing more users to operate in their native language and locate the tools they need for the job.
- Completely customizable: We thoroughly understand that not everyone will agree with our design decisions, so we have made it as easy as possible for our more adventurous users to customize Kali Linux to their liking, all the way down to the kernel.
- ARMEL and ARMHF support: Since ARM-based single-board systems like the Raspberry Pi and BeagleBone Black, among others, are becoming more and more prevalent and inexpensive, we knew that Kali’s ARM support would need to be as robust as we could manage, with fully working installations for both ARMEL and ARMHF systems. Kali Linux is available on a wide range of ARM devices and has ARM repositories integrated with the mainline distribution so tools for ARM are updated in conjunction with the rest of the distribution.
- For more features of Kali Linux, please see the following page: Kali Linux Overview.
Kali Linux is specifically tailored to the needs of penetration testing professionals, and therefore all documentation on this site assumes prior knowledge of, and familiarity with, the Linux operating system in general. Please see Should I Use Kali Linux? for more details on what makes Kali unique.
Updated on: 2021-Sep-27
Author: g0tmi1k
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What does kali linux do
IMPORTANT! Never download Kali Linux images from anywhere other than the official sources.
Always be sure to verify the SHA256 checksums of the file you’ve downloaded against our official values.
It would be easy for a malicious entity to modify a Kali installation to contain exploits or malware and host it unofficially.
Where to Get Official Kali Linux Images
ISO Files for Intel-based PCs
In order to run Kali “Live” from a USB drive on standard Windows and Apple PCs, you’ll need a Kali Linux bootable ISO image, in either 32-bit or 64-bit format.
If you’re not sure of the architecture of the system you want to run Kali on, on Linux or macOS, you can run the command uname -m at the command line. If you get the response, “x86_64”, use the 64-bit ISO image (the one containing “amd64” in the file name); if you get “i386”, use the 32-bit image (the one containing “i386” in the file name). If you’re on a Windows system, the procedure for determining whether your architecture is detailed on Microsoft’s website.
The Kali Linux images are available both as directly downloadable “.iso/.img” files or via “.torrent” files.
Building your own Kali Linux ISO, standard or customized, is a very simple process.
Virtual Machines Images
If you want to run Kali Linux as a “guest” under VMware or VirtualBox, Kali Linux is available as a pre-built virtual machines with any guest tools already installed. These image are available in a 64-bit (amd64), and 32-bit PAE (i*86) formats.
ARM Images
The hardware architectures of ARM-based devices vary considerably, so it is not possible to have a single image that will work across all of them. Pre-built Kali Linux images for the ARM architecture are available for a wide range of devices.
Scripts for building your own ARM images locally are also available on GitLab. For more details, see the articles on setting up an ARM cross-compilation environment and building a custom Kali Linux ARM chroot.
Verifying Your Downloaded Kali Image
Why do I need to do this?
Before you run Kali Linux Live, or install it to your hard disk, you want to be very sure that what you’ve got actually is Kali Linux, and not an imposter. Kali Linux is a professional penetration testing and forensics toolkit. As a professional penetration tester, having absolute confidence in the integrity of your tools is critical: if your tools are not trustworthy, your investigations will not be trustworthy, either.
Moreover, as the leading penetration testing distribution, Kali’s strengths mean that a bogus version of Kali Linux could do a tremendous amount of damage if it were deployed unwittingly. There are plenty of people with plenty of reason to want to stick very sketchy stuff into something that looks like Kali, and you absolutely do not want to find yourself running something like that.
Avoiding this is simple:
- Only download Kali Linux via the official download pages at kali.org/downloads/ or offensive-security.com/kali-linux-vmware-arm-image-download/ — you will not be able to browse to these pages without SSL; encrypting the connection makes it much harder for an attacker to use a “man-in-the-middle” attack to modify your download. There are a few potential weaknesses to even these sources — see the sections on verifying the download with the SHA256SUMS file and its signature against the official Kali Development team private key for something much closer to absolute assurance.
- Once you’ve downloaded an image, and before you run it, always validate that it really is what it’s supposed to be by verifying its checksum using one of the procedures detailed below.
There are several methods for verifying your download. Each provides a certain level of assurance, and involves a corresponding level of effort on your part.
- You can download an ISO image from an official Kali Linux “Downloads” mirror, calculate the ISO’s SHA256 hash and compare it by inspection with the value listed on the Kali Linux site. This is quick and easy, but potentially susceptible to subversion via a DNS poisoning: it assumes that the site to which, for example, the domain “kali.org” resolves is in fact the actual Kali Linux site. If it somehow were not, an attacker could present a “loaded” image and a matching SHA256 signature on the fake web page. See the section “Manually Verify the Signature on the ISO (Direct Download)”, below.
- You can download an ISO image through the torrents, and it will also pull down a file — unsigned — containing the calculated SHA256 signature. You can then use the shasum command (on Linux and macOS) or a utility (on Windows) to automatically verify that the file’s computed signature matches the signature in the secondary file. This is even easier than the “manual” method, but suffers from the same weakness: if the torrent you pulled down is not really Kali Linux, it could still have a good signature. See the section “Verify the Signature on the ISO Using the Included Signature File (Torrent Download)”, below.
- To be as close to absolutely certain as possible that the Kali Linux download you’ve obtained is the real thing, you can download both a cleartext signature file and and version of the same file that has been signed with the official Kali Linux private key and use GNU Privacy Guard (GPG) to first, verify that the computed SHA256 signature and the signature in the cleartext file match and second, verify that the signed version of the file containing the SHA256 hash has been correctly signed with the official key.
If you use this more complicated process and successfully validate your downloaded ISO, you can proceed with pretty complete assurance that what you’ve got is the official image and that it has not been tampered with in any way. This method, while the most complex, has the advantage of providing independent assurance of the integrity of the image. The only way this method can fail is if the official Kali Linux private key is not only subverted by an attacker, but also not subsequently revoked by the Kali Linux development team. For this method, see the section on verification using the SHA256SUMS file.
What do I need to do this?
If you’re running on Linux, you probably already have GPG (GNU Privacy Guard) installed. If you’re on Windows or macOS, you’ll need to install the appropriate version for your platform.
- If you’re on a PC running Windows, download and install GPG4Win from here. Certain versions of Windows do not have the native ability to calculate SHA256 checksums. To check this, you can open the command prompt and run certutil -? . If you do have this installed, you can run certutil -hashfile kali-linux-2021.3-live-amd64.iso sha256 to verify your download. If you do not have certutil installed, you will also need a utility such as Microsoft File Checksum Integrity Verifier or Hashtab to verify your download.
- If you’re on a Macintosh running macOS, download and install GPGTools from here. Alternatively, if you have Homebrew installed, just run brew install gnupg
Once you’ve installed GPG, you’ll need to download and import a copy of the Kali Linux official key. Do this with the following command:
Your output should look like this:
Verify that the key is properly installed with the command:
The output will look like this:
You’re now set up to validate your Kali Linux download.
How Do I Verify My Downloaded Image?
Manually Verify the Signature on the ISO (Direct Download)
If you downloaded the ISO directly from the downloads page, verify it using the following procedure.
On Linux, or macOS, you can generate the SHA256 checksum from the ISO image you’ve downloaded with the following command (assuming that the ISO image is named “kali-linux-2021.3-live-amd64.iso”, and is in your current directory):
The output should look like this:
The resulting SHA256 signature, “e316b27025922e9f6bca0cacee6dde83dbfd4a549ad18026526f5824af639fc1”, can be seen to match the signature displayed in the “sha256sum” column on the official download page for the 64-bit Intel architecture Kali Linux 2021.3 ISO image:
Verify the Signature on the ISO Using the Included Signature File (Torrent Download)
If you downloaded your copy of the Kali Linux ISO image via the torrents, in addition to the ISO file (e.g. kali-linux-2021.3-live-amd64.iso), there will be a second file containing the computed SHA256 signature for the ISO, with the extension “.txt.sha256sum” (e.g. kali-linux-2021.3-live-amd64.txt.sha256sum). You can use this file to verify the authenticity of your download on Linux or macOS with the following command:
If the image is successfully authenticated, the response will look like this:
IMPORTANT! If you are unable to verify the authenticity of the Kali Linux image you have downloaded as described in the preceding section, do NOT use it! Using it could endanger not only your own system, but any network you connect to as well as the other systems on that network. Stop, and ensure that you have downloaded the images from a legitimate Kali Linux mirror.
Verify the ISO Using the SHA256SUMS File
This is a more complex procedure, but offers a much higher level of validation: it does not rely on the integrity of the web site you downloaded the image from, only the official Kali Linux development team key that you install independently. To verify your image this way for an Intel architecture version of Kali, you will need to download three files from the Kali “Live CD Image” site for the current release (v2021.3, as of this writing):
- The ISO image itself (e.g. kali-linux-2021.3-live-amd64.iso)
- The file containing the calculated SHA256 hash for the ISO, SHA256SUMS
- The signed version of that file, SHA256SUMS.gpg
Before verifying the checksums of the image, you must ensure that the SHA256SUMS file is the one generated by Kali Linux. That’s why the file is signed by Kali’s official key with a detached signature in SHA256SUMS.gpg. If you have not already done so, Kali’s official key can be downloaded and imported into your keychain with this command:
or this command
Your output should look like this:
You should verify that the key is properly installed with the command:
The output will look like this:
Once you have downloaded both SHA256SUMS and SHA256SUMS.gpg, you can verify the signature as follows:
If you do not get that “Good signature” message or if the key ID does not match, then you should stop and review whether you downloaded the images from a legitimate Kali Linux mirror. The failed verification strongly suggests that the image you have may have been tampered with.
If you did get the “Good signature” response, you can now be assured that the checksum in the SHA256SUMS file was actually provided by the Kali Linux development team. All that remains to be done to complete the verification is to validate that the signature you compute from the ISO you’ve downloaded matches the one in the SHA256SUMS file. You can do that on Linux or macOS with the following command (assuming that the ISO is named “kali-linux-2021.3-live-amd64.iso” and is in your working directory):
If the image is successfully authenticated, the response will look like this:
If you do not get “OK” in response, then stop and review what’s happened: the Kali image you have has apparently been tampered with. Do NOT use it.
Once you’ve downloaded and verified your image, you can proceed to create a bootable “Kali Linux Live” USB drive.
Updated on: 2021-Sep-27
Authors: g0tmi1k , gamb1t
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