When designing a system that involves user authentication, one important aspect is the storage of hashed passwords. The Bcrypt hashing algorithm is widely recommended for password hashing due to its adaptive nature and resistance to brute-force attacks. However, a crucial question arises: what column type and length should be used to store these Bcrypt hashed passwords in a database?

Understanding Bcrypt

Bcrypt is a sophisticated and time-tested hashing algorithm. It offers several advantages:

• Salt Generation: Automatically integrates a unique salt for each password, enhancing security.
• Adaptive Hashing: Allows adjustment of its computational cost (aka work factor), keeping pace with advancing hardware capabilities.
• Fixed-Length Output: Regardless of the input length, Bcrypt produces a fixed-length hash.

Bcrypt generates a 60-character string (including parts like the algorithm version, cost factor, and salt value). It can extend up to 72 bytes if the input string uses 8-bit characters. This fixed length is crucial when considering the column specifications in your database.

Choosing the Right Column Type

Storage Requirements

When choosing a column type for storing Bcrypt hashed passwords, you should consider the following requirements:

1. Character Storage: Since Bcrypt outputs a text-based string, a character-based column type is required.
2. Consistent Length: Bcrypt provides a consistently sized output, which simplifies storage decisions.

Recommended Column Types

In SQL Databases

In typical SQL databases like MySQL or PostgreSQL, the following column types are suitable:

• VARCHAR(60): This is the simplest option, given Bcrypt's fixed 60-character length. It's both efficient and straightforward since this type is specifically optimized for variable-length strings.

1  CREATE TABLE users (
2      id INT PRIMARY KEY,
3      username VARCHAR(255) NOT NULL,
4      password_hash VARCHAR(60) NOT NULL -- Bcrypt hashed password
5  );

• CHAR(60): If your database frequently queries the hashed password field, consider using CHAR(60). This can sometimes improve performance because it employs fixed-length storage, though the benefits are generally marginal.

In NoSQL Databases

For NoSQL databases, such as MongoDB, character string storage is inherently flexible:

• String: Utilize a simple string data type, which naturally accommodates Bcrypt's fixed output size.

1  {
2      "username": "john_doe",
3      "password_hash": "$2b$12$e4FmaP.dZj56HBy.Ifs0ieuCeqE1ET8KkPjT5i3UPASmXTA9y63eG"
4  }

Additional Considerations

Cost Factor

The cost factor (or work factor) determines the computational complexity of the Bcrypt algorithm. Higher values increase security but also require more processing time. It's important to note that the cost factor does not affect the hash length; hence, it does not influence column size.

Future-Proofing

Although Bcrypt hashes are currently limited to 60 characters, considering slight updates to the algorithm in the future could mean minor increases in size. As such, opting for a VARCHAR(255) or similar type might facilitate future expansions without the need for a structural change.

Bcrypt Column Storage Summary

Using Bcrypt to hash passwords is a vital part of securing your application's user data. Selecting an appropriate database column type and length ensures that your system is both secure and efficient. With consistent handling of hashed password sizes, you can focus more on other security practices, knowing your password infrastructure is solid.