Password hashing is the process of transforming a plaintext password into a fixed-length, irreversible string using a mathematical function called a hash function. Unlike encryption, hashing is a one-way operation: you cannot retrieve the original password from its hash. When a user logs in, the system hashes the entered password and compares it to the stored hash.

Hashing is fundamental to secure authentication systems. If an attacker steals a database of password hashes, they cannot immediately recover the actual passwords—unless the hashes are weak or improperly implemented. For an in-depth look at how different algorithms affect security, see Hash Algorithms Explained: Secure Password Storage.

The importance of secure password hashing cannot be overstated. According to CISA, weak or outdated hashing algorithms have contributed to major breaches, exposing millions of user credentials. Attackers use techniques like brute force, dictionary attacks, and rainbow tables to crack poorly hashed passwords.

Modern password hashing algorithms like Bcrypt and Argon2 are designed to slow down attackers, making large-scale password cracking computationally expensive and time-consuming. This is especially important for password-recovery scenarios, where the security of stored hashes is paramount. To explore the latest techniques used in password attacks, review the Password Cracking Guide 2025: 5 Latest Techniques.

Bcrypt is a password hashing function based on the Blowfish cipher. It was designed in 1999 to address the shortcomings of earlier hash functions like MD5 and SHA-1, which are now considered insecure for password storage (OWASP).

Bcrypt incorporates a work factor (also known as cost), which determines how computationally intensive the hashing process is. The higher the cost, the longer it takes to compute the hash, thereby increasing resistance to brute force attacks.

$2b$12$KIXIDkP6w5b8Wc1Q6rG8guZQzv2mR6fT8wZy2b1Vv0WQ1n8w3E9yK

This is an example of a Bcrypt hash. The prefix indicates the algorithm, the cost parameter, and the salt, followed by the hashed password.

• Strengths:
  • Adaptive cost: The work factor can be increased as hardware improves, maintaining resistance to attacks.
  • Built-in salt: Each hash includes a unique salt, preventing identical passwords from producing the same hash.
  • Proven track record: Bcrypt has been widely used and reviewed for over two decades.
• Limitations:
  • Limited memory hardness: Bcrypt is CPU-intensive but not memory-intensive, making it more vulnerable to attacks using specialized hardware like GPUs and FPGAs. For a comparison of how GPUs impact password recovery, check the GPU Password Cracking Benchmarks 2025: RTX vs CPUs.
  • Output length: Bcrypt hashes are limited to 184 bits, which may not be sufficient for some modern applications.
  • Password length truncation: Bcrypt only uses the first 72 bytes of the input password, potentially weakening security for longer passphrases (OWASP Password Storage Cheat Sheet).

Argon2 is the winner of the Password Hashing Competition (PHC) in 2015 and is considered the state-of-the-art in password hashing. It was designed to address the evolving landscape of hardware attacks by being both CPU and memory intensive.

Argon2 allows fine-grained control over three key parameters:

• Time cost: Number of iterations (computational effort).
• Memory cost: Amount of RAM used during hashing (memory hardness).
• Parallelism: Number of threads used (resistance to parallel attacks).

This configurability makes Argon2 highly resistant to both traditional and modern attacks, including those leveraging GPUs and ASICs.

Argon2 comes in three variants, each optimized for different threat models:

• Argon2d: Maximizes resistance to GPU cracking by using data-dependent memory access. Best for applications where side-channel attacks are not a concern.
• Argon2i: Uses data-independent memory access, making it safer against side-channel attacks. Recommended for password hashing and password-recovery scenarios.
• Argon2id: A hybrid approach combining both data-dependent and data-independent access. Argon2id is recommended by NIST for password hashing as it balances security against both attack types.

• Strengths:
  • Memory hardness: Significantly increases the cost of large-scale attacks using specialized hardware.
  • Configurable parameters: Fine-tune time, memory, and parallelism for your threat model and hardware.
  • Modern design: Built to address current and future attack vectors.
  • Strong academic backing: Extensively analyzed by the cryptographic community (University of Luxembourg).
• Limitations:
  • Newer algorithm: Less battle-tested than Bcrypt, though adoption is rapidly increasing.
  • Implementation complexity: More parameters mean more room for misconfiguration.
  • Library support: Not all platforms or languages have mature Argon2 libraries, though this is improving.

Bcrypt is highly effective against traditional brute-force attacks due to its adjustable cost factor. However, its lack of memory hardness makes it vulnerable to attackers using GPUs or FPGAs, which can compute many hashes in parallel.

Argon2, especially Argon2id, is designed to be both CPU and memory intensive. This means that even with massive parallelization, attackers face significant cost and complexity. According to ENISA, memory-hard algorithms like Argon2 provide superior defense against modern password cracking techniques.

Bcrypt’s memory usage is relatively low, which makes it fast and efficient for authentication systems but less effective against attackers with specialized hardware.

Argon2 allows you to specify the amount of memory used during hashing. By increasing memory requirements, you can dramatically slow down attackers without significantly impacting user experience. However, setting memory too high can affect server performance, so careful tuning is essential.

Bcrypt offers a single tunable parameter: the cost factor. While simple, this limits flexibility.

Argon2’s three parameters—time, memory, and parallelism—offer granular control over security and performance. This flexibility allows organizations to adapt to evolving threats and hardware capabilities.

Bcrypt is widely supported across virtually all programming languages and frameworks. Mature libraries exist for Python (bcrypt), Node.js (bcrypt), Java, PHP, and more.

Argon2 support is growing rapidly. Libraries are available for Python (argon2-cffi), Node.js (argon2), Go, Rust, and others. However, some legacy systems may lack native Argon2 support, requiring additional dependencies or custom implementations. For a practical guide on implementing Argon2, see Hashing Passwords: Argon2 Implementation Walkthrough.

Migrating from Bcrypt to Argon2 is a strategic decision for organizations seeking stronger password security. The recommended approach is to use a progressive migration:

• Continue verifying existing passwords with Bcrypt.
• When a user logs in, re-hash their password with Argon2 and update the stored hash.
• Over time, all active user passwords will be protected by Argon2.

This approach avoids forcing users to reset passwords and ensures a smooth transition. For more details, see OWASP’s migration guidance.

• Always use a unique, cryptographically secure salt for each password.
• Set the cost factor (Bcrypt) or time/memory/parallelism (Argon2) as high as your system can tolerate without degrading user experience.
• Never use outdated algorithms like MD5, SHA-1, or unsalted hashes (CIS Password Policy Guide). For further reading on MD5's weaknesses, see MD5: Understanding Its Mechanics, Limitations, and Modern Alternatives.
• Regularly review and update your password hashing parameters as hardware capabilities evolve.
• Monitor authoritative sources like NIST and OWASP for updated recommendations.

• Using weak or outdated algorithms: MD5, SHA-1, and even unsalted SHA-256 are not suitable for password storage.
• Improper salt usage: Reusing salts or using predictable values undermines security.
• Low cost factors: Setting Bcrypt or Argon2 parameters too low makes hashes easier to crack.
• Truncating passwords: Bcrypt’s 72-byte limit can silently weaken security if not handled properly.
• Ignoring library updates: Outdated libraries may contain vulnerabilities or lack support for secure defaults.
• Storing plaintext passwords: Never store or log plaintext passwords, even temporarily.

For more on common mistakes, see SANS Institute: Secure Password Storage.

When deciding between Bcrypt vs Argon2 for password-recovery and secure storage, consider the following:

• Security requirements: For maximum resistance to modern attacks, Argon2id is recommended by NIST and OWASP.
• Compatibility: If you require broad compatibility or are working with legacy systems, Bcrypt remains a strong choice.
• Performance: Tune parameters to balance security and user experience. Test on your production hardware.
• Migration: If currently using Bcrypt, plan a phased migration to Argon2id for future-proof security.
• Library support: Choose well-maintained, reputable libraries and keep them updated.

Ultimately, both Bcrypt and Argon2 are vastly superior to outdated options. However, Argon2id offers the best protection against current and emerging threats, making it the preferred choice for new systems. For more details on how professional password audit, testing, and recovery services handle secure hashing, visit Professional Password Audit, Testing & Recovery.

The Bcrypt vs Argon2 debate reflects the ongoing evolution of password security. While Bcrypt has served as a reliable standard for years, Argon2—especially Argon2id—sets a new benchmark for defending against sophisticated attacks. For organizations prioritizing robust password-recovery and future-proof security, Argon2id is the clear winner. However, any secure, well-implemented password hashing algorithm is vastly preferable to weak or outdated alternatives.

Stay informed, follow best practices, and regularly review your password hashing strategy to keep pace with the changing threat landscape.

• NIST Special Publication 800-63B: Digital Identity Guidelines
• OWASP Top 10: Broken Authentication
• ENISA: Passwords in the Wild
• OWASP Password Storage Cheat Sheet
• CISA: Understanding Password Security
• University of Luxembourg: Argon2
• SANS Institute: Secure Password Storage
• Password Hashing Competition (PHC)
• CIS Password Policy Guide