In today’s digital age, securing online accounts is more critical than ever. With the rise of cybersecurity threats, it’s essential to understand the importance of strong password practices. While biometric authentication systems and multi-factor authentication (MFA) are gaining popularity, passwords remain the most common form of securing online accounts. However, many users still create weak passwords, making them vulnerable to various types of cyberattacks. This article will focus on the concept of password entropy and its crucial role in resisting brute-force attacks, offering insights into how increasing password complexity can protect your online presence.
Why Passwords Still Matter
Despite advancements in cybersecurity, passwords remain the first line of defense for securing personal and organizational data. However, many people still use weak passwords, relying on simple, predictable patterns or reusing passwords across multiple platforms. This vulnerability makes it much easier for attackers to gain unauthorized access to personal information. Thus, creating strong and complex passwords is more important than ever.
The key issue lies in password predictability, which is where the concept of entropy comes in. Entropy measures the unpredictability or randomness of a password, and the higher the entropy, the more secure the password is against attacks. Higher entropy means a password is more difficult to guess, significantly enhancing security.
The Risk of Weak Passwords
This research explores the relationship between password entropy and its resistance to brute-force attacks. Brute-force attacks involve cybercriminals attempting every possible combination of characters until they crack the password. While this approach can be slow, weak passwords make the process significantly faster for attackers. To illustrate this, I simulated brute-force attacks on both an Apache-based website and an SSH service using passwords of varying entropy levels.
By utilizing tools in Kali Linux, I was able to measure key metrics such as cracking time, network load, and tool efficiency. This experiment provides valuable insights into how password complexity impacts security.
Understanding Password Complexity and Entropy
Password Complexity and Entropy
Password complexity refers to how difficult it is to guess or crack a password. One of the most important factors in determining password complexity is entropy. Entropy, introduced by Claude Shannon in 1948, measures the unpredictability or randomness of a password. A password with high entropy is extremely difficult to guess.
The formula for calculating entropy (H) of a password is:
H(X)=−∑p(x)⋅log2(p(x))
Where:
H(X) is the entropy of the password.
p(x) is the probability of each character in the password.
log2 is the base-2 logarithm.
In simpler terms, entropy is about how random and unpredictable your password is. A higher entropy value corresponds to a more complex, harder-to-crack password. However, real-world behaviors, such as using simple words or common patterns, can drastically lower effective entropy.
Online Password Attacks
Cybercriminals use various online password attacks to crack weak passwords. Some common attacks include:
Dictionary Attacks: Using a list of common words to guess the password.
Brute-Force Attacks: Trying every possible combination of characters.
Credential Stuffing: Using leaked credentials from previous breaches to attempt login.
These attacks can be mitigated by factors like rate-limiting and network speed. However, the complexity of the password itself plays a key role in defending against these attacks.
Tools for Cracking Passwords
To simulate password attacks, I used several tools available in Kali Linux:
Hydra: A fast, flexible tool for brute-force password cracking across multiple protocols.
Medusa: A high-speed password-cracking tool optimized for performance.
Ncrack: A tool focusing on network reliability and stealth, ideal for cracking network services.
How I Tested Password Entropy
Environment Setup
For this experiment, I set up the following:
Operating System: Kali Linux 2024.1
Target Services: Apache2 web server with HTTP Basic Authentication and OpenSSH server for remote login.
Authentication Setup: Used a .htpasswd file for Apache and default SSH configuration.
User Accounts: Created three users with passwords of varying entropy levels: low, medium, and high.
Password Entropy Calculation
I manually calculated the entropy of each password based on their character set and length. Below are the results:
PasswordLength (L)Character Set Size (N)Entropy
password123: Length = 11, Character Set Size = 36, Entropy = 56.5 bits
Tr4inStat10n: Length = 12, Character Set Size = 62, Entropy = 71.5 bits
V!9x*2qz#B: Length = 10, Character Set Size = 94, Entropy = 65.7 bits
Attack Simulation
I used Hydra, Medusa, and Ncrack to attack the Apache and SSH services. I ran these attacks with the following parameters:
5 concurrent threads
3 login attempts per second
30-second timeout after success or failure
I also used Wireshark to monitor network activity and track the progress of the attacks.
Data Collection
The following metrics were recorded during the attacks:
Time-to-crack for each password
Number of packets sent
Bandwidth consumed during the attack
Experimental Results: Impact of Entropy on Attack Success
Apache Authentication
Hydra: Fastest in cracking passwords but generated the most network traffic.
Medusa: Slower but more bandwidth-efficient.
Ncrack: Balanced speed and efficiency.
SSH Authentication
SSH took longer to crack due to encryption and rate-limiting protections. Among the tools:
Hydra: Fast but detected by SSH security mechanisms.
Medusa: Slower but quieter.
Ncrack: Efficient and stealthy.
I plotted the time-to-crack for each password with varying entropy. The results showed that higher entropy passwords took much longer to crack, highlighting the importance of strong passwords.
What Did I Learn?
The experiment clearly demonstrated that passwords with higher entropy are much harder to crack. Low-entropy passwords were cracked quickly, while higher-entropy passwords required exponentially more time, making them more secure.
Moreover, SSH authentication proved more resilient to attacks compared to Apache Basic Authentication due to built-in encryption and protections. Among the cracking tools, Hydra was the fastest but had higher traffic, Medusa was slower but stealthier, and Ncrack provided a balanced approach.
Conclusion: Strengthening Your Passwords
This study reinforces the critical role of password complexity in cybersecurity. Higher entropy passwords are significantly more secure against brute-force attacks. The key takeaway is straightforward: use strong, complex passwords and avoid common words or simple patterns.
While strong passwords are vital, additional security measures such as multi-factor authentication (MFA) can further enhance your protection. In today’s cyber landscape, it's essential to understand the concept of entropy and apply it to your password practices to keep your online accounts safe.
Final Thoughts
By increasing the entropy of your passwords, you make it much harder for attackers to gain unauthorized access. Cyber threats are constantly evolving, and weak passwords are no longer acceptable. It’s time to strengthen your defenses by moving away from simple, predictable passwords and adopting more complex alternatives.
Stay safe and protect your online presence by embracing better password practices today.
Ivo Pereira | Computer Science Student & Cybersecurity Enthusiast
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