Introduction

The ubiquitous use of passwords in our everyday digital lives means that they are also a prime target for malicious hackers. This has spawned an entire sub-industry focused on password cracking. In this piece, we aim to demystify the world of password crackers and how they work.

Password Strength

Password strength is a measure of the time and difficulty it would take for an attacker to successfully guess or "crack" your password. In simple terms, it's the toughness of your lock.

A weak password is like a flimsy padlock - it can be easily broken. Typical weak passwords might include sequences like "123456" or "password", as well as easily identifiable personal information like your birthdate or your pet's name. Even if these passwords use alphanumeric characters, they're common and easy for hackers to guess.

In contrast, a strong password is like a high-security lock. It's long, complex, unique, and changed regularly. A strong password might look like "jR8z!2K%9fXg&3dQ", which includes a mix of uppercase and lowercase letters, numbers, and special characters. It's also important that a strong password is not reused across multiple sites, because if one site gets hacked, all of your accounts are potentially at risk.

Password Hashes

To understand how password crackers operate, it's important to first understand how passwords are stored. In a secure system, passwords aren't stored in their original form. Instead, they're transformed into a fixed-length piece of data called a "hash" using a mathematical function known as a "hashing algorithm". When you enter your password, the system generates a hash from your input and checks it against the stored hash for your account. If the hashes match, you're granted access.

For example, using a simple hashing algorithm, the password "apple" might be transformed into a hash like "1f3870be274f6c49b3e31a0c6728957f". Even a tiny change to the password, like "apples", results in a dramatically different hash like "07e9471ae9c07400e4f028a8c5f9db04". This is the beauty of hashing; even small changes in the input result in large changes in the output, making it difficult to reverse-engineer the original password from the hash.

Password Cracking Methods

So, how do password crackers try to defeat this system? There are several popular methods, each with its own strengths and weaknesses.

1. Reverse Engineering: This involves trying to find a weakness in the hashing algorithm that would allow the original password to be deduced from the hash. While this might sound like a promising approach, it's generally impractical due to the computational complexity involved.
2. Rainbow Table Attack: A rainbow table is a precomputed table for reversing cryptographic hash functions. It's basically a huge list of hashes for possible passwords. Instead of calculating a hash for a password on-the-fly, a hacker can check if it's in the rainbow table. The tradeoff is that rainbow tables are enormous and require a lot of storage.
3. Birthday Attacks: This technique gets its name from the birthday paradox in probability theory. In the context of password cracking, it's used to find collisions in hash functions, which occurs when two different inputs produce the same hash. If a hacker can find two different passwords that produce the same hash, they might be able to use one to access an account meant to be protected by the other.

Weak Passwords and Guessing Attacks

A weak password isn't just one that's short or easy to guess. It's also a password that's vulnerable to certain types of attacks.

One common type of attack is the password-guessing attack. In this attack, the hacker doesn't attempt to reverse-engineer the hash or find a collision. Instead, they simply guess the password. This can be done either through trying to log in with different passwords (known as a "brute force" attack), capturing network packets that might contain password information, or extracting the password database from a compromised system.

One way hackers carry out password-guessing attacks is through the use of a birthday attack, which involves creating many hashes and looking for a match. This is particularly effective when a system allows unlimited attempts to guess a password.

Countermeasures

As the old saying goes, the best defense is a good offense. When it comes to password security, the best defense is a strong, unique password.

Use a password that's long, complex, and unique. Change it regularly, and don't reuse it across different sites.

Password crackers have a harder time cracking longer and more complex passwords because they require more computing resources to crack. A password like "7#!RbU8#e$6kF" will take much longer to crack than "password123".

Another countermeasure is limiting the number of incorrect attempts to input a password. This makes brute force attacks less effective because after a certain number of attempts, the account is locked or requires additional verification.

Password-Cracking Tools

Ironically, the tools used by hackers to crack passwords are also used by security professionals to test password strength. These tools, like John the Ripper or Hashcat, generate potential passwords and their corresponding hashes, then compare these hashes with those stored in a system's database.

For example, if you're a system administrator who wants to ensure your users' passwords are strong enough, you could use a password cracker to test them. If a password is cracked, it's a signal that it should be changed to something stronger. However, to prevent potential abuse, these tools should only be used in an isolated, offline environment to ensure that sensitive credentials are not exposed to the internet.

In conclusion, the world of password crackers is a complex interplay of mathematics, computing power, and human behavior. Understanding how password crackers work helps us make better decisions about our own password habits, making us all a little bit safer in our digital lives.