phpBB CMS Hashing: A Deep Dive into Its Security Mechanisms


The phpBB forum software, a popular open-source Content Management System (CMS), uses a specialized hashing algorithm for securing user passwords. This algorithm is identified by hashes starting with "$2a$", indicating its reliance on the Blowfish cipher in the bcrypt hashing function. Originating in the late 1990s, bcrypt was designed to enhance security and resist brute-force attacks, making it a preferred choice for password hashing in various applications, including phpBB.

Example Hash

An example of a phpBB hash might look like this:
This string encapsulates the algorithm identifier ($2a$), the cost parameter (10), a 22-character salt, and the 31-character hash of the password.


In phpBB, this hashing mechanism is employed to securely store user passwords. When a user creates or updates their password, it is hashed using this method before being stored in the database. This ensures that even if the database is compromised, the passwords remain secure against straightforward decryption attempts.


The development of bcrypt and its integration into systems like phpBB reflects the ongoing effort to enhance password security in the digital age. As computational power increased, older hashing algorithms became more vulnerable, necessitating the development of more secure methods like bcrypt to safeguard sensitive data effectively.

How it Works

Bcrypt works by first generating a salt, a random string used to hash the password. This salt, along with the password, is processed through several iterations of the Blowfish cipher. The number of iterations is determined by the cost parameter, with a higher value indicating more rounds and thus increased security but also more processing time.


The use of a unique salt for each password is a crucial aspect of bcrypt's security. It prevents attackers from using precomputed tables (like rainbow tables) to crack passwords and ensures that two identical passwords will have different hashes, making pattern detection and password cracking significantly more challenging.


While bcrypt is highly secure, it's not without limitations. Its computational intensity can strain system resources, especially with higher cost parameters. Also, being designed for general-purpose CPUs, it is more vulnerable to hardware-based attacks using specialized devices like GPUs or ASICs.

Particularities Compared to Other Algorithms

Compared to other hashing algorithms like MD5 or SHA-1, bcrypt is significantly more secure due to its adaptive nature. The ability to adjust the cost parameter allows it to remain resilient against brute-force attacks even as computational power increases. Furthermore, the inclusion of a salt in every hash greatly mitigates the risk of rainbow table attacks.

Computational Power/Cost

The computational power required for bcrypt is adjustable, making it a versatile choice. However, this can be a double-edged sword. While higher cost parameters mean better security, they also require more processing power and time, potentially impacting system performance and user experience.

Resistance to Attacks

Bcrypt's resistance to attacks, especially brute-force and rainbow table attacks, is robust. Its adaptive nature and the inclusion of salts make it a formidable choice for password hashing. However, it's less resistant to hardware-accelerated attacks due to its CPU-centric design.


Despite its strengths, bcrypt is not immune to becoming obsolete. As technology evolves, so do hacking techniques and hardware capabilities. This evolution demands continuous assessment and potential upgrades to more advanced hashing algorithms or additional security measures.

Modern Alternatives

Modern alternatives to bcrypt include Argon2, which won the Password Hashing Competition in 2015. Argon2 is designed to be resistant to both GPU and ASIC attacks, making it a strong candidate for replacing bcrypt in applications where such attacks are a significant concern.


Bcrypt's compatibility is generally good across various systems and programming languages, making it a versatile option. Its implementation in phpBB is a testament to its adaptability and effectiveness in a widely-used CMS platform.


In conclusion, the bcrypt hashing mechanism employed by phpBB, identified by hashes starting with "$2a$", remains a secure and reliable method for password protection. While it has limitations, particularly in terms of computational intensity and vulnerability to hardware-accelerated attacks, its strengths in resistance to common cracking methods make it a solid choice. However, administrators and developers should remain vigilant and consider modern alternatives like Argon2 as the technological landscape evolves to ensure the highest level of security in their applications.

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