What Is Bcrypt?

Updated on April 22, 2025

Passwords are an important but vulnerable part of IT security. Whether it’s managing databases, authenticating users, or securing web applications, hashing and storing passwords correctly is crucial. Bcrypt is a popular choice in enterprise security because of its strong and reliable design. This article will explain how Bcrypt works and why it’s such an essential tool.

Defining Bcrypt and Its Role in Security

Bcrypt is an adaptive password hashing function designed to secure passwords by transforming them into unreadable hashes. It is based on the Blowfish cipher, which is a symmetric-key encryption algorithm. Created by Niels Provos and David Mazières in 1999, Bcrypt is engineered to resist brute-force attacks and enhance password protection.

The Problem Bcrypt Solves

Storing passwords securely is a persistent challenge in IT. Weak hashing algorithms like MD5 or SHA-1, once considered secure, are now outdated and susceptible to attacks such as rainbow tables and brute-forcing. These vulnerabilities can result in catastrophic data breaches that expose sensitive user information. Bcrypt addresses these issues with core features like salting, adjustable work factors, and iterative hashing, making it a preferred choice for modern applications.

Core Concepts Behind Bcrypt

To fully appreciate Bcrypt, it’s important to understand its key components and concepts:

Key Derivation Function (KDF)

A Key Derivation Function takes a password and converts it into a secure cryptographic key. Bcrypt functions as a KDF by hashing passwords and making the output computationally intensive enough to deter brute-force attacks, even on advanced hardware.

Hashing

Hashing is the process of converting input data (such as a password) into a fixed-size, unique string of characters known as a hash. Unlike encryption, hashing is a one-way process, meaning it cannot be reversed to recover the original input. This makes it ideal for storing passwords securely.

Salt

Salting adds an essential layer of security to the hashing process. A salt is a random string that is combined with the password before hashing. This ensures that even if two users have the same password, their hashed values will be unique. Salting effectively neutralizes attacks like rainbow tables.

Work Factor (Cost)

Bcrypt introduces an adjustable parameter called the work factor or cost. This parameter dictates how computationally expensive the hashing process will be. A higher cost factor increases the time required to compute the hash, making brute-force attacks significantly more difficult.

Blowfish Cipher

Bcrypt is built upon the Blowfish block cipher, an encryption algorithm designed by Bruce Schneier. Blowfish’s specific key setup and adaptable functionality make it an ideal foundation for Bcrypt’s password hashing mechanism.

How Bcrypt Works

Bcrypt employs a series of steps to securely hash passwords, creating a robust defense against common attack vectors.

Salting Process

When a password is hashed using Bcrypt, the system generates a random salt. This salt is added to the password before the hashing process begins. The unique salt ensures that even identical passwords produce distinct hashes.

Iterative Hashing

The heart of Bcrypt’s security lies in its iterative hashing mechanism. It performs multiple rounds of hashing using the Blowfish cipher, with the number of iterations determined by the work factor. This iterative process significantly slows down attempts to compute hashes, increasing system security as hardware improves.

Output Format

Bcrypt’s output is a standardized string that includes the following:

• The algorithm identifier ($2b$)
• The work factor
• The salt
• The resulting hash

Here’s an example of a Bcrypt hash:

$2b$12$abcdefghijABCDEFGHIjklmnop12345612345abcde1234567890uvwxyz

The inclusion of the salt in the output ensures that no two hashes will look identical, even with the same input password.

Key Features and Components of Bcrypt

Bcrypt offers several distinctive features that make it stand out as a secure password hashing function:

• Salt Generation: Automatically generates a unique salt for each password to counteract precomputed attacks like rainbow tables.
• Adjustable Work Factor: Enables the computational cost of hashing to be increased as hardware capabilities improve, ensuring long-term resistance to brute-force attacks.
• Rainbow Table Resistance: Salting prevents attackers from using precomputed lookup tables to crack hashes.
• Wide Adoption: Bcrypt is supported by numerous programming languages, libraries, and frameworks, making it easily accessible across platforms.

Use Cases and Applications

Bcrypt plays a critical role in various security-focused applications. Some of its common use cases include:

Password Storage

Bcrypt is predominantly used for securely hashing and storing user passwords in databases, ensuring they remain protected even if the database is compromised.

Authentication Systems

During the login process, Bcrypt verifies user credentials by comparing the hashed input password with the stored hash, ensuring a secure match.

Web Applications

Web applications use Bcrypt to protect user accounts by safeguarding passwords from being exposed to attackers.

Operating System Security

Some operating systems leverage Bcrypt to hash user passwords, securing local and remote access.

Advantages of Bcrypt (And Trade-offs)

Bcrypt is celebrated for its strong security, but like any tool, it comes with its own set of trade-offs.

Advantages

• Strong Security: Adaptive salting and iterative hashing protect against brute-force and rainbow table attacks.
• Configurable Security: The adjustable work factor allows systems to strengthen hashing as processing power grows.
• Proven Standard: Bcrypt has been vetted over decades, making it a trusted choice in sensitive environments.

Trade-offs

• Computational Cost: Bcrypt’s design is intentionally resource-intensive, which can burden systems with high-volume password hashing requirements.
• Risk of Misuse: Improper implementation or mismanagement of the work factor could inadvertently weaken security or impact system performance.

Key Terms Appendix

• Bcrypt: A password hashing function based on the Blowfish cipher, designed for secure password storage and verification.
• Key Derivation Function (KDF): Converts passwords into secure cryptographic keys using hashing and other mechanisms to bolster security.
• Hashing: A one-way process that generates a unique, fixed-size string for an input, such as a password.
• Salt: A random value added to data (e.g., passwords) before hashing to create unique hashes and resist precomputed attacks.
• Work Factor (Cost): An adjustable setting in Bcrypt that determines the computational difficulty of hashing.
• Blowfish Cipher: A symmetric-key block cipher that forms the technical foundation of Bcrypt.
• Rainbow Table: A precomputed table of hash values used in cracking password hashes.