Bcrypt Password Hash Generator

What is Bcrypt?

Bcrypt is a password-hashing function designed specifically for securely storing passwords. Created in 1999 by Niels Provos and David Mazières, bcrypt remains one of the most recommended methods for password hashing today, despite its age.

How Bcrypt Works

Bcrypt is based on the Blowfish cipher and incorporates several security features that make it ideal for password hashing:

1. Cost Factor (Work Factor)

Bcrypt uses a cost parameter that determines how computationally intensive the hashing process will be. This parameter allows you to make hashing slower as computers get faster, maintaining security over time. The cost is expressed as a power of 2, so each increment doubles the required work.

2. Salt Generation

Bcrypt automatically generates a random salt for each password hash. This 128-bit (22 character) salt ensures that identical passwords will produce different hash outputs, thwarting rainbow table attacks and ensuring each hash is unique.

3. Slow Key Setup Phase

Bcrypt uses an expensive key setup phase derived from the Blowfish cipher. This makes it significantly slower than algorithms like MD5 or SHA-1, which is beneficial for password hashing where slowness is a security feature.

Understanding Bcrypt Hash Format

A bcrypt hash string consists of several parts:

$2a$10$N9qo8uLOickgx2ZMRZoMyeIjZAgcfl7p92ldGxad68LJZdL17lhWy
|_||_||____________________||______________________________|
 | |        |                        |
 | |        |                        +-- Hash (Base64-encoded)
 | |        +-- Salt (Base64-encoded, 22 chars)
 | +-- Cost parameter (10)
 +-- Algorithm version (2a)

Algorithm Version

The algorithm version identifier has several variations:

• $2$ - Original version (now deprecated)
• $2a$ - Most widely used format
• $2y$ - PHP's implementation (functionally identical to $2a$ in modern PHP)
• $2b$ - Fixed implementation handling non-ASCII passwords correctly

Cost Parameter

The cost parameter (10 in the example) indicates the work factor - 2^10 iterations. Higher values increase security but also increase computation time. As hardware improves, this value should be increased to maintain security.

Bcrypt vs. Other Password Hashing Algorithms

Implementing Bcrypt in Different Languages

PHP

// Generate a hash (PHP 5.5+)
$hash = password_hash('user_password', PASSWORD_BCRYPT, ['cost' => 12]);

// Verify a password against a hash
if (password_verify('user_password', $hash)) {
    echo "Password is valid!";
} else {
    echo "Password is invalid!";
}

Node.js

const bcrypt = require('bcrypt');
const saltRounds = 12;

// Generate a hash
async function hashPassword(password) {
    const hash = await bcrypt.hash(password, saltRounds);
    return hash;
}

// Verify a password
async function verifyPassword(password, hash) {
    const match = await bcrypt.compare(password, hash);
    return match;
}

Python

import bcrypt

# Generate a hash
def hash_password(password):
    password_bytes = password.encode('utf-8')
    salt = bcrypt.gensalt(12)  # rounds=12
    hash = bcrypt.hashpw(password_bytes, salt)
    return hash

# Verify a password
def verify_password(password, hashed):
    password_bytes = password.encode('utf-8')
    return bcrypt.checkpw(password_bytes, hashed)

Bcrypt Best Practices

1. Choose the Right Cost Factor

Select a cost factor that makes hashing take about 250ms on your server. This balances security with performance. Periodically review and increase this value as hardware improves.

2. Handle Long Passwords Correctly

Bcrypt has a 72-byte limit for passwords. For extremely long passwords, consider pre-hashing with SHA-256 before passing to bcrypt, but be careful to maintain salt uniqueness.

3. Keep Hashes Private

Even though bcrypt hashes are designed to be resistant to cracking, you should still protect your hash database as if it contained plaintext passwords. Treat hash leaks as serious security incidents.

4. Update Legacy Hashes

If you're migrating from a weaker algorithm, rehash passwords with bcrypt the next time users log in successfully.

5. Consider Newer Algorithms for New Projects

While bcrypt is still secure, consider Argon2 for new projects, especially where memory-hardness is a concern. Argon2 won the Password Hashing Competition in 2015 and provides additional protection against certain types of attacks.

Common Bcrypt Questions

Is Bcrypt Still Secure in 2023?

Yes, bcrypt remains secure when used with an appropriate cost factor. No practical attacks have been demonstrated against properly implemented bcrypt. Its adaptable work factor allows it to remain secure as hardware improves.

How Often Should I Update the Cost Factor?

A good rule of thumb is to reevaluate your cost factor every 1-2 years, or whenever you significantly upgrade your hardware. The goal is to maintain the same time cost (around 250ms) as hardware gets faster.

How Do I Migrate from MD5/SHA1 to Bcrypt?

When a user logs in, verify their password against your old hash system. If correct, create a new bcrypt hash of their password and replace the old hash. This gradual migration approach doesn't require users to reset passwords.

For example:

if (old_hash_verify(password, stored_old_hash)) {
    // Login successful, update to bcrypt
    $new_bcrypt_hash = password_hash(password, PASSWORD_BCRYPT, ['cost' => 12]);
    // Store $new_bcrypt_hash in database, replacing old hash
}

What Are the Bcrypt Version Differences ($2a$, $2y$, $2b$)?

These prefix identifiers represent different implementations or fixes in bcrypt:

• $2$ - Original bcrypt (obsolete and rarely seen)
• $2a$ - The most common format, with some implementation variations
• $2y$ - PHP's implementation to fix the non-ASCII character handling issue
• $2b$ - OpenBSD's fixed implementation addressing the same issues

For modern applications, these differences rarely matter as current libraries handle them correctly.

Conclusion

Despite being over two decades old, bcrypt remains one of the most reliable ways to hash passwords. Its adaptive nature, built-in salting, and deliberate slowness provide excellent protection against brute force attacks and rainbow tables.

While newer algorithms like Argon2 offer additional benefits (particularly better memory-hardness), bcrypt continues to be a solid choice that's widely supported across languages and platforms. By selecting an appropriate cost factor and following best practices, you can ensure your users' passwords remain secure against attackers.