1. Introduction

In the world of web applications, password security is paramount. Storing user passwords directly in a database is an absolute no-go. If your database is ever compromised, those passwords become immediately available to attackers, leading to widespread account takeovers. This is where password hashing comes in, and among the strongest and most widely recommended algorithms is Bcrypt.

This tutorial will guide you through understanding Bcrypt, why it’s superior for password hashing, and how to implement it effectively in your applications.

2. What is Bcrypt?

Bcrypt is a password hashing function designed by Niels Provos and David Mazières in 1999. It’s based on the Blowfish cipher and, crucially, is an adaptive hash function. This “adaptivity” is its superpower for password security.

3. Why Bcrypt is Superior for Password Hashing

3.1 Cost Factor (Work Factor/Rounds)

Unlike simple hash functions (like MD5 or SHA-256) which are very fast, Bcrypt is intentionally slow.

It has a “cost factor” (also known as “work factor” or “rounds”) that you can configure. This factor determines how many times the hashing algorithm is executed.

The key benefit: As computing power increases over time, you can simply increase the cost factor to keep the hashing process computationally expensive for attackers. This makes brute-force attacks and rainbow table attacks exponentially harder.

For a legitimate user, a few hundred milliseconds delay for login is imperceptible. For an attacker trying billions of passwords, a few hundred milliseconds per hash becomes years.

3.2 Salting Built-In

Bcrypt inherently incorporates a salt into its hashing process. A salt is a unique, randomly generated string added to each password before hashing.

Purpose of Salting:

• Prevents Rainbow Table Attacks: Without salting, identical passwords would produce identical hashes, allowing attackers to use pre-computed “rainbow tables” to quickly reverse hashes. Salting ensures that even if two users have the same password, their hashes will be different.
• Prevents Attacks on Multiple Accounts: It prevents an attacker from hashing one password and then using that hash to compromise multiple accounts if they happen to share the same password.

3.3 Adaptive and Future-Proof

Its adaptive nature means it can evolve with hardware advancements. You don’t need to switch to a completely new algorithm every few years; you just adjust the cost factor.

4. How Bcrypt Works (Simplified)

• A unique, random salt is generated for each password.
• The password and the salt are fed into the Bcrypt algorithm.
• The algorithm performs a number of rounds (determined by the cost factor) of a complex cryptographic operation.
• The final output is a hash string that includes the cost factor and the salt itself, making the hash self-contained.

5. Common Bcrypt Implementations

Most modern programming languages and frameworks have robust Bcrypt libraries. You should always use a well-vetted, mature library rather than attempting to implement Bcrypt yourself.

Here are examples for common languages:

• Java: Spring Security’s BCryptPasswordEncoder
• Python: bcrypt library
• Node.js: bcryptjs (Pure JavaScript, good for browsers) or bcrypt (Native C++ binding, faster)
• PHP: password_hash() (using PASSWORD_BCRYPT algorithm)
• Ruby: bcrypt gem
• C#: BCrypt.Net-Core