This is the third post in a three-part series that I’m writing as a way to introduce Cryptographic Hashes from an Offensive Security perspective. The first post explained what hashes are, the second post explained how you would go about figuring out what kind of hash you’re working with, and this post is about trying to figure out how to crack the hash. Cracking hashes is the process of reverse-engineering or brute-forcing the hash to recover the original data, such as passwords. This final post in our offensive security series will walk you through how to crack hashes, with a focus on using John the Ripper, but we’ll also touch on other tools like Hashcat.

What Does It Mean to Crack a Hash?

Cracking a hash means finding the original data (like a password) that was transformed into the hash. Since cryptographic hash functions are designed to be one-way, cracking usually involves one of these approaches:

• Brute Force: Trying every possible combination of characters until a match is found.
• Dictionary Attack: Using a precompiled list of possible passwords (a dictionary) and hashing each one to see if it matches the target hash.
• Rainbow Tables: Precomputed tables of common hashes and their corresponding plaintext values, used to crack hashes more quickly.
• Hybrid Attack: A combination of dictionary and brute force methods, where slight variations of known words are tried.

John the Ripper

John the Ripper is one of the most popular and powerful tools for cracking hashes. It’s a highly versatile password cracker that supports a wide range of hash formats and is available on many platforms. Its community has developed numerous plug-ins and wordlists to extend its functionality, making it the go-to tool for many security professionals.

Let’s take a look at how to use John the Ripper to crack different types of hashes.

Step-by-Step Guide: Cracking Hashes with John the Ripper

1. Identify the Hash Type
Before starting the cracking process, you need to identify the hash type. In previous blog posts, we discussed how to identify a hash based on its format and length. If you know the type of hash, you can optimize your cracking efforts.

2. Install John the Ripper
If you don’t already have John the Ripper installed, you can install it on most Linux systems using:

sudo apt-get install john

For other systems, you can download the latest version from the official John the Ripper website.

3. Prepare the Hashes for Cracking
Create a text file containing the hashes you want to crack. Ensure that each hash is on a new line. Save the file as something like ‘hashes.txt’. Here are the contents of a hashes.txt file that I set up for easy cracking.

5f4dcc3b5aa765d61d8327deb882cf99
098f6bcd4621d373cade4e832627b4f6

4. Run John the Ripper

To start cracking, run the following basic command where –wordlist represents the wordlist you want to use. Cultivating and collecting good wordlists is an important skill and hobby in offensive security. Lists like the leak from the RockYou breach (with its 14 million+ passwords) are very common to use in Capture the Flag (CTF) and training boxes. There are lists that are much bigger and better that you can find online. Also, if you do decent Open Source Intelligence (OSINT) on your targets, you may very well create targeted/curated lists to use. Things like variations on your target’s pets’ names, kids’ names, favorite teams, etc. For example, “Spot, Sp0t, $p0t, Steelers, $teelers, $teeler$, $t33ler$” and so on. There are many tools (including John) to help you take a word and generate all of those permutations for you.

// --wordlist: This option tells John to use a dictionary file (wordlist) of potential passwords.
john --wordlist=/path/to/wordlist.txt hashes.txt

John will attempt to match the hashes in your file against the passwords in your wordlist. If a match is found, John will output the cracked password.

5. Use Predefined Hash Formats
Sometimes, John may not automatically recognize the hash format. If you know the hash type, you can specify it explicitly with the –format option.

For example, to crack an MD5 hash, try the following. Since our hashes.txt file contains MD5 hashes, I’ll show the actual output. This was almost instantaneous:

$ john --format=raw-md5 --wordlist=/usr/share/wordlists/rockyou.txt hashes.txt
Using default input encoding: UTF-8
Loaded 2 password hashes with no different salts (Raw-MD5 [MD5 256/256 AVX2 8x3])
Warning: no OpenMP support for this hash type, consider --fork=12
Press 'q' or Ctrl-C to abort, almost any other key for status
password         (?)
test             (?)
2g 0:00:00:00 DONE (2024-11-18 14:00) 100.0g/s 8313Kp/s 8313Kc/s 8332KC/s tyson4..tauruz
Use the "--show --format=Raw-MD5" options to display all of the cracked passwords reliably
Session completed.

For NTLM hashes (commonly used in Windows systems):

john --format=nt hashes.txt

Common Formats:

• MD5: –format=raw-md5
• SHA-1: –format=raw-sha1
• NTLM: –format=nt
• bcrypt: –format=bcrypt

6. Brute Force Cracking
If a dictionary attack fails or you don’t have a good wordlist, you can use brute force. This method tries all possible combinations of characters, but it can take a long time depending on the complexity of the password.

Example command:

// --incremental: This option tells John to perform a brute force attack.
john --incremental hashes.txt

7. Checking Cracked Passwords
Once the cracking process is complete (or if you want to check progress), you can use the following command to display the cracked passwords. Since we already cracked these above, this is my output when I run this command:

// --show tells John to show the passwords, 
// --format is usually needed to reliably see the results.
$ john hashes.txt --show --format=raw-md5
?:password
?:test

2 password hashes cracked, 0 left

// This is what I get with --show only, leaving off the format.  
// You'll note when I actually cracked these the first time, 
// John had suggested --show with --format and that definitely 
// works better.  I mean, this doesn't even show the right
// number of hashes corresponding with the file.
$ john hashes.txt --show
0 password hashes cracked, 4 left

This will list all the hashes that have been successfully cracked and their corresponding plaintext passwords.

Advanced John the Ripper Techniques

Hybrid Attacks: You can combine dictionary and brute force attacks using rules. This allows John to try slight variations on the words in your dictionary (e.g., adding numbers, changing case).

john --wordlist=/path/to/wordlist.txt --rules hashes.txt

Custom Mask Attacks: If you know part of the password format (e.g., passwords are always 8 characters and include numbers), you can customize John’s brute force method with masks.

Other Tools for Cracking Hashes

While John the Ripper is one of the most popular tools, there are other tools worth mentioning:

Hashcat is another powerful hash-cracking tool known for its speed and GPU support. Hashcat can perform various types of attacks, including brute force, dictionary, and hybrid attacks.

Example Hashcat command for MD5 cracking using our example hashes.txt file

// -m 0: Specifies the hash type (MD5).
// -a 0: Specifies the attack mode (dictionary).
// -o cracked.txt: The output file for cracked passwords.

$ hashcat -m 0 -a 0 -o cracked.txt hashes.txt /usr/share/wordlists/rockyou.txt
hashcat (v6.2.6) starting

OpenCL API (OpenCL 3.0 PoCL 6.0+debian  Linux, None+Asserts, RELOC, LLVM 17.0.6, SLEEF, DISTRO, POCL_DEBUG) - Platform #1 [The pocl project]
============================================================================================================================================
* Device #1: cpu-haswell-13th Gen Intel(R) Core(TM) i7-1355U, 2802/5669 MB (1024 MB allocatable), 12MCU

Minimum password length supported by kernel: 0
Maximum password length supported by kernel: 256

Hashes: 2 digests; 2 unique digests, 1 unique salts
Bitmaps: 16 bits, 65536 entries, 0x0000ffff mask, 262144 bytes, 5/13 rotates
Rules: 1

Optimizers applied:
* Zero-Byte
* Early-Skip
* Not-Salted
* Not-Iterated
* Single-Salt
* Raw-Hash

ATTENTION! Pure (unoptimized) backend kernels selected.
Pure kernels can crack longer passwords, but drastically reduce performance.
If you want to switch to optimized kernels, append -O to your commandline.
See the above message to find out about the exact limits.

Watchdog: Hardware monitoring interface not found on your system.
Watchdog: Temperature abort trigger disabled.

Host memory required for this attack: 3 MB

Dictionary cache built:
* Filename..: /usr/share/wordlists/rockyou.txt
* Passwords.: 14344392
* Bytes.....: 139921507
* Keyspace..: 14344385
* Runtime...: 1 sec


Session..........: hashcat
Status...........: Cracked
Hash.Mode........: 0 (MD5)
Hash.Target......: hashes.txt
Time.Started.....: Mon Nov 18 14:08:32 2024 (0 secs)
Time.Estimated...: Mon Nov 18 14:08:32 2024 (0 secs)
Kernel.Feature...: Pure Kernel
Guess.Base.......: File (/usr/share/wordlists/rockyou.txt)
Guess.Queue......: 1/1 (100.00%)
Speed.#1.........:  2446.1 kH/s (0.31ms) @ Accel:512 Loops:1 Thr:1 Vec:8
Recovered........: 2/2 (100.00%) Digests (total), 2/2 (100.00%) Digests (new)
Progress.........: 172032/14344385 (1.20%)
Rejected.........: 0/172032 (0.00%)
Restore.Point....: 165888/14344385 (1.16%)
Restore.Sub.#1...: Salt:0 Amplifier:0-1 Iteration:0-1
Candidate.Engine.: Device Generator
Candidates.#1....: tyson4 -> floryna

Started: Mon Nov 18 14:08:19 2024
Stopped: Mon Nov 18 14:08:33 2024

$ cat cracked.txt
5f4dcc3b5aa765d61d8327deb882cf99:password
098f6bcd4621d373cade4e832627b4f6:test

Online Hash Cracking Services
There are also online hash-cracking services that can speed up the process, such as:

CrackStation: Free online service for cracking MD5, SHA-1, and other hash types using large dictionaries. For instance, both of my hashes from above would have been instantly cracked via the CrackStation website. Here was the output when I put them in:

Hashes.com: In their own words, “Hashes.com is a site dedicated to hash recovery”. They are home to many different tools (free and paid) and they also instantly cracked my example hashes with this output:

Proceeded!
2 hashes were checked: 2 found 0 not found

Found:
5f4dcc3b5aa765d61d8327deb882cf99:password
098f6bcd4621d373cade4e832627b4f6:test

Best Practices for Hash Cracking

• Use Strong Wordlists: A good wordlist is essential for dictionary attacks. The RockYou.txt wordlist is one of the most popular, containing millions of common passwords.
• Leverage GPU Power: If possible, use Hashcat or John the Ripper with GPU acceleration to speed up the cracking process.
• Automate Your Workflow: Use scripts to automate the process of identifying and cracking hashes in large datasets.
• Understand Legal Boundaries: Cracking hashes should only be done in legal and ethical contexts, such as penetration tests, security audits, or in scenarios where you have permission.

Cracking hashes is a critical skill in offensive security, allowing you to recover passwords and understand security vulnerabilities in systems. While John the Ripper is a versatile and powerful tool, others like Hashcat, CrackStation, and Hashes.com can complement your efforts depending on the task at hand. With the right tools, techniques, and wordlists, you’ll be able to crack a wide variety of hash types in the course of your security audits or penetration tests.

Okay, that’s it. Hopefully, over the course of this series you’ve gotten a good basic overview of hashes, how to identify them, and how to begin to think about cracking them.

This post is the second of three posts that I have planned in a little mini-series. Last time, we looked at What are Cryptographic Hashes? and this time, we’re going to talk about how to identify cryptographic hashes that you might find in the wild.

In offensive security and during security audits, you’ll often encounter cryptographic hashes. These may be part of password dumps, logs, malware signatures, or other files. However, not all hashes are labeled clearly, and determining the type of hash used is essential for further analysis, especially when cracking or reversing it. Let’s dive into how you can identify cryptographic hashes in the wild and the tools that make the process easier.

This is important for a few reasons, but from an Offensive Security perspective, the biggest reason is that you often need to identify the type of hash you’re dealing with is to be able to crack it correctly. If you’re just using a huge, pre-computed rainbow table like I assume CrackStation uses, identifying them is less important because it just finds them as they are and returns the stored initial plain text value that was used to make the digest. In the case of other tools that you want to run specific wordlists against where you “hash on demand”, you have to know what you’re trying for before you start. So how do we do it?

Over time, you may develop some kind of sixth sense about it and be able to look at them and be pretty sure what you’re seeing. But, if you’re new or want to know the process that is going on behind the scenes, here’s a decision process. First, look at the length of the hash. Here are some lengths of some very popular hash types you’re likely to encounter. Length alone doesn’t always give you a definitive answer, but it helps rule out many possibilities.

• MD5: 32 hexadecimal characters (128 bits).
• SHA-1: 40 hexadecimal characters (160 bits).
• SHA-256: 64 hexadecimal characters (256 bits).
• SHA-512: 128 hexadecimal characters (512 bits).
• bcrypt: Typically around 60 characters (includes a salt).

Next thing you want to do is look for special formatting of the hash itself that might be unique to the hash’s “signature”.

• bcrypt hashes often start with $2a$, $2b$, or $2y$.
• MD5 is typically a straightforward 32-character hexadecimal string.
• NTLM (used in Windows environments) often has a 32-character hexadecimal format similar to MD5 but is distinct in purpose.

The next thing you want to do (honestly, maybe this should kind of be step 0 even) is consider the context of where the hash came from. It isn’t super likely that you just “found a hash on the ground”, you usually have some context with it and that context can give us some hints.

• Password Databases: If you’re analyzing a password database, it’s common to find hashes like bcrypt, PBKDF2, or even older ones like MD5.
• File Integrity Checks: If the hash is related to file integrity checks (e.g., software downloads), SHA-256 or SHA-512 is often used.
• Certificates and Signatures: Digital certificates or signatures may use SHA-256 or SHA-1, although SHA-1 has been largely deprecated.

Another thing to do is to look for evidence and distinctive markers at specific points in the hash. Some hash functions, particularly those used for passwords (like bcrypt, PBKDF2, and Argon2), employ salting and iterations to increase security. The salt is a random value added to the input to ensure the same passwords don’t produce identical hashes. Hashes with salts often have longer lengths and may include markers or delimiters in the format, like the way you might find a Bcrypt hash that starts with ‘$2a$10$…’ where ’10’ is the cost factor.

So if you found a hash like $2y$12$EXRkfkdmXn2gzds2SSituJWMqp3hPFO4lH/vqFhD8aJL.lfwBby4a during a penetration test and you figure out that $2y$ indicates the algorithm is bcrypt and 12 indicates the number of iterations (also called the cost factor). You can then use a tool like John the Ripper or Hashcat with your favorite wordlists, specifying bcrypt as the algorithm.

The next step (maybe it might be your first step) is to try using some tools to help you. The truth is that these tools apply some of the heuristics that I’ve already outlined (and many more that I haven’t) in order to figure out what you’re dealing with. One of the most popular is called hashID (which replaced hash-identifier), a Python tool that you can install with pip and then call from the command line. Here is an example of me using it to identify some hashes.

$ hashid '5d41402abc4b2a76b9719d911017c592'
Analyzing '5d41402abc4b2a76b9719d911017c592'
[+] MD2
[+] MD5
[+] MD4
[+] Double MD5
[+] LM
[+] RIPEMD-128
[+] Haval-128
[+] Tiger-128
[+] Skein-256(128)
[+] Skein-512(128)
[+] Lotus Notes/Domino 5
[+] Skype
[+] Snefru-128
[+] NTLM
[+] Domain Cached Credentials
[+] Domain Cached Credentials 2
[+] DNSSEC(NSEC3)
[+] RAdmin v2.x

$ hashid '$2y$12$EXRkfkdmXn2gzds2SSituJWMqp3hPFO4lH/vqFhD8aJL.lfwBby4a'
Analyzing '$2y$12$EXRkfkdmXn2gzds2SSituJWMqp3hPFO4lH/vqFhD8aJL.lfwBby4a'
[+] Blowfish(OpenBSD)
[+] Woltlab Burning Board 4.x
[+] bcrypt

You’ll notice that sometimes, you get a LOT of possible results. That’s why I personally put the tools a little lower on the list. You will want to use context to try to figure out which of those suggestions is most likely. From there, you may have to try a few different times to crack the hash, but you should have some kind of logic to the order. Consider the context, the technology stack, when it was written, what you know about the development team, etc. You may see some people suggest tools like OnlineHashCrack (use the menu to go to Free Tools, then Hash Identification). The direct link is here, but that can change. Unless you can’t install hashID on your system for some reason, I’d just use hashID. Online Hash Crack literally seems to be using something like hash-identifier under the hood, as the results are the very similar.

Hash Identifier

+-$ hash-identifier 5d41402abc4b2a76b9719d911017c592
   #########################################################################
   #     __  __                     __           ______    _____           #
   #    /\ \/\ \                   /\ \         /\__  _\  /\  _ `\         #
   #    \ \ \_\ \     __      ____ \ \ \___     \/_/\ \/  \ \ \/\ \        #
   #     \ \  _  \  /'__`\   / ,__\ \ \  _ `\      \ \ \   \ \ \ \ \       #
   #      \ \ \ \ \/\ \_\ \_/\__, `\ \ \ \ \ \      \_\ \__ \ \ \_\ \      #
   #       \ \_\ \_\ \___ \_\/\____/  \ \_\ \_\     /\_____\ \ \____/      #
   #        \/_/\/_/\/__/\/_/\/___/    \/_/\/_/     \/_____/  \/___/  v1.2 #
   #                                                             By Zion3R #
   #                                                    www.Blackploit.com #
   #                                                   Root@Blackploit.com #
   #########################################################################
--------------------------------------------------

Possible Hashs:
[+] MD5
[+] Domain Cached Credentials - MD4(MD4(($pass)).(strtolower($username)))

Least Possible Hashs:
[+] RAdmin v2.x
[+] NTLM
[+] MD4
[+] MD2
[+] MD5(HMAC)
[+] MD4(HMAC)
[+] MD2(HMAC)
[+] MD5(HMAC(WordPress))
[+] Haval-128
[+] Haval-128(HMAC)
[+] RipeMD-128
[+] RipeMD-128(HMAC)
[+] SNEFRU-128
[+] SNEFRU-128(HMAC)
[+] Tiger-128
[+] Tiger-128(HMAC)
[+] md5($pass.$salt)
[+] md5($salt.$pass)
[+] md5($salt.$pass.$salt)
[+] md5($salt.$pass.$username)
[+] md5($salt.md5($pass))
[+] md5($salt.md5($pass))
[+] md5($salt.md5($pass.$salt))
[+] md5($salt.md5($pass.$salt))
[+] md5($salt.md5($salt.$pass))
[+] md5($salt.md5(md5($pass).$salt))
[+] md5($username.0.$pass)
[+] md5($username.LF.$pass)
[+] md5($username.md5($pass).$salt)
[+] md5(md5($pass))
[+] md5(md5($pass).$salt)
[+] md5(md5($pass).md5($salt))
[+] md5(md5($salt).$pass)
[+] md5(md5($salt).md5($pass))
[+] md5(md5($username.$pass).$salt)
[+] md5(md5(md5($pass)))
[+] md5(md5(md5(md5($pass))))
[+] md5(md5(md5(md5(md5($pass)))))
[+] md5(sha1($pass))
[+] md5(sha1(md5($pass)))
[+] md5(sha1(md5(sha1($pass))))
[+] md5(strtoupper(md5($pass)))
--------------------------------------------------

OnlineHashCrack

Input: 5d41402abc4b2a76b9719d911017c592

Results: 
Your hash may be one of the following:
- MD2
- MD5
- MD4
- Double MD5
- LM
- RIPEMD-128
- Haval-128
- Tiger-128
- Skein-256(128)
- Skein-512(128)
- Lotus Notes/Domino 5
- Skype
- ZipMonster
- PrestaShop
- md5(md5(md5($pass)))
- md5(strtoupper(md5($pass)))
- md5(sha1($pass))
- md5($pass.$salt)
- md5($salt.$pass)
- md5(unicode($pass).$salt)
- md5($salt.unicode($pass))
- HMAC-MD5 (key = $pass)
- HMAC-MD5 (key = $salt)
- md5(md5($salt).$pass)
- md5($salt.md5($pass))
- md5($pass.md5($salt))
- md5($salt.$pass.$salt)
- md5(md5($pass).md5($salt))
- md5($salt.md5($salt.$pass))
- md5($salt.md5($pass.$salt))
- md5($username.0.$pass)
- Snefru-128
- NTLM
- Domain Cached Credentials
- Domain Cached Credentials 2
- DNSSEC(NSEC3)
- RAdmin v2.x
- Cisco Type 7

It is possible that some tools that you use to crack the hashes have some built-in identifiers (like John the Ripper), but they don’t work independently.

Identifying cryptographic hashes is a critical skill during security audits or penetration tests. With so many different algorithms in use, the ability to quickly pinpoint the hash type allows you to assess security, crack passwords, and verify data integrity. By leveraging online tools, command-line utilities like hashID, and your understanding of hash lengths and formats, you can efficiently identify the most commonly used hashes.

In the next post, we’ll explore how to crack these hashes, using both brute force and other techniques.

This post is the first of three posts that I have planned in a little mini-series. I want to post about What are Cryptographic Hashes?, then Identifying Hashes, and finally Cracking Hashes.

So, what is a Cryptographic Hash? At its core, a cryptographic hash function is a mathematical algorithm that takes an input and returns a fixed-size string of characters, which is typically a hexadecimal number. The output is called a hash or digest. Cryptographic hash functions are designed to be secure and resistant to tampering, which makes them highly useful in a variety of security-related contexts. The key features of cryptographic hashes are:

1. Deterministic: The same input will always produce the same hash.
2. Fixed Length: Regardless of the size of the input, the hash produced will always be of a fixed size (e.g., SHA-256 always produces a 256-bit hash).
3. Efficient: Computing the hash for any input is relatively fast.
4. Pre-image Resistance: It should be computationally infeasible to reverse the process and determine the original input from the hash.
5. Collision Resistance: Two different inputs should not produce the same hash.
6. Avalanche Effect: Even a small change to the input should drastically change the output hash.

That Avalanche Effect part is actually really important and easier to understand with a demonstration. If a hashing of similar words resulted in similar hashes, you could actually figure out the original message very easily as you got closer and closer. Instead, abcd, abcdd, abcdD, and abcde actually hash to wildly different SHA256 Hashes, for example. Pretty smart, I think.

$ echo "abcd" | sha256sum
fc4b5fd6816f75a7c81fc8eaa9499d6a299bd803397166e8c4cf9280b801d62c

$ echo "abcdd" | sha256sum
2fc0920b01e12a239cac49f999c641dafaa841da88428c08632ec1fa9860920f

$ echo "abcdD" | sha256sum
f71367ae3183ad102b186748aba1a2132c73168b79a3e2612199f2d74ae9d9b0

$ echo "abcde" | sha256sum
0283da60063abfb3a87f1aed845d17fe2d9ba8c780b478dc4ae048f5ee97a6d5

Where do we use Cryptographic Hashes? Well, I’m writing about this under the banner of Offensive Security, so some logical guesses could be made. One thing they are used for is for storing passwords. Instead of storing the passwords directly in a database or even storing an encrypted version that can be decrypted, it is a good practice to store a Cryptographic Hash. Then when someone tries to log in, you hash the input and then compare the hashes. That way, the passwords are harder to determine from the hash alone. Another use is for data integrity. If a hash is taken of a file or a message and that hash is published, you can confirm that you have the exact same file or message by calculating the hash yourself and comparing.

What are the dangers here? Why are there so many kinds of hashes? Well – like a lot of things – this is actually a hard problem. If the hash algorithm isn’t very good, it could have collisions. That means two or more messages hash to the same value, so if apple and orange both hash to ABCDEF and ABCDEF is stored in the database as the password hash, then providing either a password of apple or orange at login would let you in. That’s not great. Also, if it is possible for multiple inputs to have the same output, then a file with a hash of AAABBBCCC is published, but someone also makes a version of a file full of viruses that also hashes out to AAABBBCCC, then we’ve lost trust in the process.

Here are just four examples of hash algorithms that had been trusted, but aren’t anymore.

MD4 (Message Digest Algorithm 4)
Discovered Collisions: Yes (1995)
Details: MD4 is an earlier version of MD5 and was found to be insecure in the mid-1990s. Collisions were discovered in MD4 as early as 1995, and since then, the hash function has been considered broken and insecure. MD4 was eventually replaced by more secure algorithms like SHA and MD5, though MD5 also suffered from its own weaknesses.
Examples: MD4 is largely obsolete but might still be found in legacy systems.

MD5 (Message Digest Algorithm 5)
Discovered Collisions: Yes (2004)
Details: MD5 is one of the most famous cryptographic hash functions with widely known collisions. It produces a 128-bit hash value. In 2004, researchers demonstrated a practical method to find collisions in MD5. Since then, the hash function has been considered broken and unsuitable for security purposes like digital signatures and certificates.
Examples: In 2008, an attack was demonstrated that allowed attackers to create a rogue Certificate Authority (CA) certificate, which undermined the trust model of SSL certificates.

SHA-0 (Secure Hash Algorithm 0)
Discovered Collisions: Yes (2004)
Details: SHA-0 is the predecessor of SHA-1 and was withdrawn from use due to its vulnerability to collisions. Researchers found theoretical weaknesses, and in 2004, they were able to demonstrate actual collisions in the function. As a result, SHA-0 was deprecated early in its life.
Examples: SHA-0 is no longer used in any modern cryptographic system due to these vulnerabilities.

SHA-1 (Secure Hash Algorithm 1)
Discovered Collisions: Yes (2017)
Details: SHA-1, which produces a 160-bit hash value, was long considered secure but began to show theoretical weaknesses in the early 2000s. In 2017, Google and the CWI Institute in Amsterdam successfully generated a practical collision using the “SHAttered” attack. This discovery showed that SHA-1 was vulnerable to collision attacks and should no longer be used in critical security applications.
Examples: SHA-1 has been deprecated for use in SSL certificates, and major browsers no longer accept SHA-1-signed certificates.

Understanding these foundational concepts is critical as we move forward in our offensive security series. In our next post, we will dive into how to identify a hash you find in the wild—whether it’s from a password dump, a malware sample, or part of an intercepted communication.