Android bcrypt: A Guide to Secure Password Hashing in Android

When developing Android applications that involve user authentication and sensitive data, security is a top priority. One key aspect of securing user data is password hashing. One of the most commonly used and recommended algorithms for password hashing is bcrypt. In this guide, we'll explain what bcrypt is, how it works, and how you can use it in your Android applications to securely hash and verify passwords.

What is bcrypt?

bcrypt is a password hashing function designed to be computationally intensive and resistant to brute-force attacks. Unlike simple hashing algorithms like MD5 or SHA, bcrypt is specifically designed to make password cracking more difficult. It accomplishes this by introducing a work factor (also called a cost factor), which makes the hashing process slower and more resource-intensive.

Key features of bcrypt:

  • Salting: bcrypt automatically generates a salt (random data) for each password, which prevents attackers from exploiting precomputed tables (rainbow tables).
  • Adaptive: The work factor can be increased over time to make bcrypt more resistant to future advances in hardware and attack techniques.

Why Use bcrypt in Android?

  1. Security: Passwords stored using bcrypt are protected from many attacks, including dictionary attacks, brute force, and rainbow table attacks. The use of a salt with each password means attackers cannot precompute hash values for commonly used passwords.

  2. Salting: bcrypt hashes are salted automatically, ensuring that even if two users have the same password, their hashes will be different.

  3. Configurable Work Factor: The work factor (cost factor) can be adjusted to increase the time it takes to hash a password, which makes it harder for attackers to crack hashed passwords via brute force methods.

  4. Proven and Reliable: bcrypt has been extensively tested and is widely adopted for securing passwords in both server-side and mobile applications.

How bcrypt Works

bcrypt uses a key derivation function (KDF) that transforms a password into a fixed-length hash. Here's a step-by-step breakdown of how bcrypt hashes passwords:

  1. Password Input: A password is input by the user (e.g., "my_secure_password").
  2. Salt Generation: A random 128-bit salt is generated.
  3. Cost Factor: The bcrypt function applies a configurable cost factor, which determines how many iterations are used during the hashing process. A higher cost factor means the process will take longer and be more resistant to attacks.
  4. Hashing: The password and salt are combined and hashed using the Blowfish encryption algorithm.
  5. Output: The final bcrypt hash includes both the salt and the hash. The output is typically a string formatted as:
    perl
    $2a$12$z9G1O2d4OeRIzflTz2Oh9ekPr.M/NQxAo8z0mi0rQ1pU6OlgWbD4G
    Where $2a$12$ refers to the bcrypt version and cost factor (12 in this case), and the rest is the salt and the hashed password.

How to Use bcrypt in Android

To use bcrypt in Android, you'll need to integrate a library that implements the bcrypt hashing algorithm. Since Android does not include bcrypt natively, you can use third-party libraries like jBCrypt to handle password hashing and verification.

Steps to Use bcrypt with jBCrypt in Android:

  1. Add the jBCrypt Library to Your Project

    First, add the jBCrypt library to your build.gradle file.

    gradle
    dependencies {
    implementation 'org.mindrot:jbcrypt:0.4'
}

  2. Hashing a Password

    To hash a password using bcrypt, you can use the BCrypt class from the jBCrypt library. Here's an example of how to hash a password:

    java
    import org.mindrot.jbcrypt.BCrypt;

public class PasswordUtils {

    // Hash the password
    public static String hashPassword(String password) {
        // Generate a salt
        String salt = BCrypt.gensalt(12);  // 12 is the cost factor
        // Hash the password with the salt
        String hashedPassword = BCrypt.hashpw(password, salt);
        return hashedPassword;
    }
}
    • gensalt(12): The 12 represents the cost factor, which you can adjust based on the level of security you need (higher values result in stronger hashes, but they take longer to compute).
    • hashpw(password, salt): This function hashes the password using the provided salt.

  3. Verifying a Password

    When a user attempts to log in, you need to verify that the entered password matches the stored hash. Here's how you can do that:

    java
    public static boolean verifyPassword(String enteredPassword, String storedHash) {
    // Check if the entered password matches the stored hash
    return BCrypt.checkpw(enteredPassword, storedHash);
}

    The checkpw method compares the entered password against the stored bcrypt hash. It automatically extracts the salt and cost factor from the stored hash and verifies that the password matches.

  4. Example Usage

    Here's how you would use the methods to hash and verify passwords in an Android application:

    java
    public class MainActivity extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        String password = "mySecurePassword123";

        // Hash the password
        String hashedPassword = PasswordUtils.hashPassword(password);
        Log.d("HashedPassword", hashedPassword);

        // Verify the password
        boolean isCorrect = PasswordUtils.verifyPassword("mySecurePassword123", hashedPassword);
        Log.d("PasswordVerification", "Password is correct: " + isCorrect);
    }
}

Best Practices for Using bcrypt in Android

  1. Use a Strong Cost Factor: While bcrypt allows you to configure the cost factor, a cost factor of 12 is generally considered a good balance between security and performance. You can increase the cost factor as computing power increases over time, making your password hashing more secure.

  2. Store the bcrypt Hash Safely: When you store the hashed passwords, ensure that they are stored securely in your app's backend or a secure database. Do not store plaintext passwords at any point.

  3. Use HTTPS for Data Transmission: When sending passwords over the network (e.g., during login), ensure that you use HTTPS to encrypt the communication and prevent eavesdropping.

  4. Salting is Automatic: bcrypt automatically generates a unique salt for each password, so you don’t need to manually handle salts. Simply hash the password and store the result.

  5. Do Not Use Deprecated Hashing Algorithms: Avoid using outdated algorithms like MD5 or SHA-1 for password hashing. bcrypt is a modern and secure choice.

Conclusion

In Android development, security is crucial, and bcrypt provides a reliable, secure method to hash and verify user passwords. Using libraries like jBCrypt enables easy implementation of bcrypt in your Android applications.

By hashing passwords with bcrypt, you are making it significantly harder for attackers to retrieve the original passwords, even if they gain access to your password database. Always follow best practices for securely storing passwords and make use of advanced hashing algorithms like bcrypt to ensure your users' data remains safe.