Password hashing is the process of transforming a plaintext password into a fixed-size string of characters, which appears random. This transformation uses a cryptographic hash function, making it computationally infeasible to reverse the process and retrieve the original password. Hashing is a one-way function: even if an attacker obtains the hash, they cannot easily derive the original password.

Unlike encryption, which is reversible with a key, hashing is designed to be irreversible. This property is crucial for storing passwords securely, as it ensures that even if a database is breached, the attacker cannot immediately access user credentials.

Storing passwords in plaintext is a critical security risk. If attackers gain access to such data, they can compromise user accounts and potentially other systems where users reuse passwords. Password hashing mitigates this risk by ensuring that even if hashes are stolen, cracking them requires significant computational effort.

According to the OWASP Top Ten, improper password storage is a leading cause of data breaches. Using strong, modern hashing algorithms like Argon2 is recommended by organizations such as NIST and ENISA.

Argon2 was introduced in 2015 as the winner of the Password Hashing Competition (PHC). Developed by Alex Biryukov, Daniel Dinu, and Dmitry Khovratovich, Argon2 was designed to address the shortcomings of earlier algorithms like bcrypt and PBKDF2, particularly their vulnerability to GPU and ASIC attacks.

The algorithm is now widely recognized as the state-of-the-art in password hashing and is recommended by leading cybersecurity authorities, including OWASP. If you're interested in an in-depth analysis of Argon2's strengths and future in secure hashing, see Unlocking the Strength of Argon2: The Future of Secure Hashing.

• Memory-hardness: Argon2 requires a configurable amount of memory, making it resistant to attacks using specialized hardware.
• Configurable time cost: The number of iterations can be adjusted to increase computational effort.
• Parallelism: Supports multi-core processing for efficiency and enhanced security.
• Flexibility: Multiple variants (Argon2d, Argon2i, Argon2id) for different use cases.
• Modern cryptographic design: Incorporates the latest research in password security.

These features make Argon2 password hashing highly effective against brute-force, dictionary, and side-channel attacks.

• Argon2d: Optimized for resistance against GPU and ASIC attacks; uses data-dependent memory access. Best for applications where side-channel attacks are not a concern.
• Argon2i: Uses data-independent memory access, making it suitable for environments where side-channel attacks are a risk.
• Argon2id: A hybrid of Argon2d and Argon2i, offering a balance between resistance to side-channel and GPU attacks. Recommended for most password hashing scenarios.

For password hashing, Argon2id is generally recommended by NIST and OWASP.

Before implementing Argon2 password hashing, ensure you have:

• Basic knowledge of Python or your preferred programming language.
• Access to a development environment (e.g., Visual Studio Code, PyCharm).
• Administrative privileges to install libraries.

This guide uses Python for demonstration, but Argon2 libraries are available for most major languages.

For Python, the recommended library is argon2-cffi, which provides bindings to the official Argon2 C implementation.

pip install argon2-cffi

For other languages:

• Java: argon2-jvm
• Go: alexedwards/argon2id
• Node.js: node-argon2

Choosing the right parameters is crucial for Argon2 password hashing security and performance. The main parameters are memory cost, time cost, parallelism, and salt.

Memory cost determines how much RAM (in kilobytes) Argon2 will use during hashing. Higher memory usage increases resistance to parallel attacks using GPUs or ASICs. For most applications, a minimum of 64MB (65536 KB) is recommended, but values up to 256MB or more are common for high-security environments. Adjust based on your server's available resources.

Time cost specifies the number of iterations (or passes) over the memory. Increasing this value slows down hashing, making brute-force attacks more expensive. A typical starting value is 2 or 3, but higher values can be used for increased security.

Parallelism sets the number of threads used for hashing. This should match the number of CPU cores available to optimize performance. For most systems, a value between 2 and 8 is suitable.

A salt is a unique, random value added to each password before hashing. It ensures that identical passwords produce different hashes, preventing attackers from using precomputed tables (rainbow tables). Salts should be at least 16 bytes and generated using a secure random number generator.

For more on salts, see OWASP Password Storage Cheat Sheet or review Salting Passwords Properly: 2025 Best Practices for a comprehensive look at modern salting techniques.

Let's walk through hashing a password using argon2-cffi in Python.

from argon2 import PasswordHasher

# Initialize the PasswordHasher with secure parameters
ph = PasswordHasher(
    time_cost=3,      # Number of iterations
    memory_cost=65536, # Memory in KB (64 MB)
    parallelism=4,    # Number of parallel threads
    hash_len=32,      # Length of the hash
    salt_len=16       # Length of the salt
)

# Hash a password
password = "SuperSecurePassword123!"
hash = ph.hash(password)
print("Argon2 hash:", hash)

The resulting hash contains all necessary parameters and the salt, making verification straightforward.

To verify a password, use the verify() method. This checks if the provided password matches the stored hash.

try:
    ph.verify(hash, "SuperSecurePassword123!")
    print("Password is correct!")
except:
    print("Password is incorrect!")

If the password matches, verification succeeds; otherwise, an exception is raised.

Proper error handling is essential for robust Argon2 password hashing implementations. Common exceptions include:

• argon2.exceptions.VerifyMismatchError: Raised when the password does not match the hash.
• argon2.exceptions.VerificationError: General verification failure.
• argon2.exceptions.InvalidHash: The hash format is invalid or corrupted.

from argon2 import exceptions

try:
    ph.verify(hash, user_input)
except exceptions.VerifyMismatchError:
    print("Incorrect password.")
except exceptions.InvalidHash:
    print("Stored hash is invalid.")
except Exception as e:
    print("An error occurred:", str(e))

Always handle exceptions gracefully to avoid leaking information about password validity or system configuration.

Select parameters that balance security and performance. Argon2 password hashing should be slow enough to deter attackers but fast enough for legitimate users. Regularly review and update parameters based on hardware advancements and NIST or OWASP recommendations. You can estimate how long a cracking attempt might take with tools such as the Bruteforce Attack Limits: Calculate Time Needed calculator.

• Memory cost: At least 64MB (65536 KB), higher if possible.
• Time cost: Minimum of 2, ideally 3 or more.
• Parallelism: Match your server's CPU cores.
• Salt: At least 16 bytes, generated securely.

Store only the hash (which includes the salt and parameters) in your database. Never store plaintext passwords or salts separately. Ensure your database is secured with encryption, access controls, and regular audits. For more on secure storage, see CIS Controls. If you want to understand how password recovery and storage are handled in practice, check out How password recovering works at Online Hash Crack.

Stay informed about updates to Argon2 and password hashing best practices. Subscribe to security advisories from CISA, SANS Institute, and OWASP. Regularly update your libraries to patch vulnerabilities and benefit from performance improvements.

• Using weak or default parameters: Always configure Argon2 with strong, application-specific parameters.
• Reusing salts: Generate a unique salt for each password.
• Storing salts insecurely: Let the hash string contain the salt; do not store it separately.
• Ignoring library updates: Outdated libraries may have vulnerabilities. Update regularly.
• Not handling exceptions: Always catch and handle errors to prevent information leakage.
• Failing to migrate old hashes: When upgrading from weaker algorithms, provide a migration path for existing users. For a guide to modern cracking techniques and pitfalls, see Password Cracking Guide 2025: 5 Latest Techniques.

Avoiding these mistakes is essential for robust Argon2 password hashing security.

bcrypt has been a standard for password hashing since the late 1990s. It is widely supported and easy to implement. However, bcrypt's memory usage is fixed and relatively low, making it more susceptible to attacks using modern GPUs and ASICs. Argon2 offers configurable memory hardness, providing stronger resistance to parallel attacks.

For a detailed comparison, see OWASP Password Storage Cheat Sheet: bcrypt or review Understanding bcrypt: A Deep Dive into Its Mechanics and Usage in Cryptography.

PBKDF2 is another widely used algorithm, recommended by NIST for key derivation. While PBKDF2 allows for configurable iterations, its resistance to hardware attacks is limited due to low memory requirements. Argon2 provides better security through its memory-hard design and is generally preferred for new applications.

For more on PBKDF2, see RFC 8018.

Argon2 password hashing represents the current best practice for securing user credentials. Its memory-hard design, configurable parameters, and robust security features make it superior to older algorithms like bcrypt and PBKDF2. By following the implementation steps and best practices outlined in this guide, you can significantly enhance your application's defense against password cracking attacks. Stay vigilant, keep your libraries updated, and always prioritize security in your development process.

• Password Hashing Competition (PHC)
• OWASP Password Storage Cheat Sheet
• NIST SP 800-63B: Digital Identity Guidelines
• ENISA Password Guidelines
• SANS Institute: Password Security
• CIS Controls: Secure Configuration for Databases
• Argon2 Reference Implementation (GitHub)
• OWASP Cheat Sheet Series: Password Storage

For ongoing updates and community discussions, follow OWASP, CISA, and SANS Institute.