Password encoding with BCrypt in Spring Boot - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a BCrypt password encoder bean.

Spring Boot

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;

@Configuration
public class SecurityConfig {

    @Bean
    public BCryptPasswordEncoder passwordEncoder() {
        return new [1]();
    }
}

Drag options to blanks, or click blank then click option'

ABCryptPasswordEncoder

BPasswordEncoder

CEncoder

DBCryptEncoder

Attempts:

3 left

💡 Hint

Common Mistakes

Using a generic interface name instead of the concrete BCryptPasswordEncoder class.

Misspelling the class name.

The BCryptPasswordEncoder class is used to create a password encoder bean for BCrypt hashing.

2fill in blank

medium

Complete the code to encode a raw password using BCryptPasswordEncoder.

Spring Boot

BCryptPasswordEncoder encoder = new BCryptPasswordEncoder();
String rawPassword = "mySecret123";
String encodedPassword = encoder.[1](rawPassword);

Drag options to blanks, or click blank then click option'

Ahash

Bencrypt

Cencode

Ddigest

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'hash' or 'encrypt' which are not method names in this class.

Confusing encoding with encryption.

The encode method of BCryptPasswordEncoder hashes the raw password securely.

3fill in blank

hard

Fix the error in the code to verify a raw password against an encoded password.

Spring Boot

BCryptPasswordEncoder encoder = new BCryptPasswordEncoder();
String rawPassword = "password123";
String encodedPassword = "$2a$10$7QJH1...";
boolean matches = encoder.[1](rawPassword, encodedPassword);

Drag options to blanks, or click blank then click option'

Acompare

Bverify

Ccheck

Dmatches

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect method names like 'check' or 'verify'.

Swapping the order of parameters.

The matches method takes the raw password first, then the encoded password to verify if they match.

4fill in blank

hard

Fill both blanks to correctly verify a password using BCryptPasswordEncoder.

Spring Boot

BCryptPasswordEncoder encoder = new BCryptPasswordEncoder();
boolean isValid = encoder.[1]([2], encodedPassword);

Drag options to blanks, or click blank then click option'

Amatches

BrawPassword

CencodedPassword

Dencode

Attempts:

3 left

💡 Hint

Common Mistakes

Using the encoded password as the first argument.

Using 'encode' instead of 'matches' method.

The matches method checks if the rawPassword matches the encodedPassword.

5fill in blank

hard

Fill all three blanks to create a Spring service that encodes a password and verifies it.

Spring Boot

import org.springframework.stereotype.Service;
import org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder;

@Service
public class PasswordService {

    private final BCryptPasswordEncoder encoder = new [1]();

    public String encodePassword(String [2]) {
        return encoder.[3]([2]);
    }

    public boolean verifyPassword(String rawPassword, String encodedPassword) {
        return encoder.matches(rawPassword, encodedPassword);
    }
}

Drag options to blanks, or click blank then click option'

ABCryptPasswordEncoder

Bpassword

Cencode

DPasswordEncoder

Attempts:

3 left

💡 Hint

Common Mistakes

Using interface name instead of concrete class for encoder.

Using wrong parameter name in method.

Calling a non-existent method instead of 'encode'.

The service uses BCryptPasswordEncoder to encode the password by calling the encode method.

Practice

1. What is the main purpose of using BCryptPasswordEncoder in Spring Boot?

easy

A. To validate email addresses

B. To decode passwords back to plain text

C. To generate random passwords for users

D. To securely encode passwords before storing them

Solution

1. Step 1: Understand BCryptPasswordEncoder role

   BCryptPasswordEncoder is used to convert plain passwords into a secure encoded form.

2. Step 2: Identify correct purpose

   It does not decode or generate passwords, only encodes them securely.

3. Final Answer:

   To securely encode passwords before storing them -> Option D

4. Quick Check:

   Password encoding = Secure storage [OK]

Hint: BCrypt encodes, never decodes passwords [OK]

Common Mistakes:

• Thinking BCrypt can decode passwords
• Confusing encoding with password generation
• Using it for unrelated tasks like email validation

2. Which of the following is the correct way to create a BCryptPasswordEncoder instance in Spring Boot?

easy

A. BCryptPasswordEncoder encoder = BCryptPasswordEncoder();

B. BCryptPasswordEncoder encoder = new BCryptPasswordEncoder();

C. BCryptPasswordEncoder encoder = new BCryptPasswordEncoder.encode();

D. BCryptPasswordEncoder encoder = encode(new BCryptPasswordEncoder());

Solution

1. Step 1: Recall Java object creation syntax

   In Java, to create an object, use the new keyword followed by the constructor.

2. Step 2: Match correct syntax

   BCryptPasswordEncoder encoder = new BCryptPasswordEncoder(); correctly uses new BCryptPasswordEncoder(); to create an instance.

3. Final Answer:

   BCryptPasswordEncoder encoder = new BCryptPasswordEncoder(); -> Option B

4. Quick Check:

   Object creation = new + constructor [OK]

Hint: Use 'new' keyword to create objects in Java [OK]

Common Mistakes:

• Omitting 'new' keyword when creating objects
• Calling methods instead of constructors
• Incorrect method chaining in object creation

3. Given the following code snippet, what will be the output of matches method?

BCryptPasswordEncoder encoder = new BCryptPasswordEncoder();
String rawPassword = "mypassword";
String encodedPassword = encoder.encode(rawPassword);
boolean result = encoder.matches("mypassword", encodedPassword);
System.out.println(result);

medium

A. true

B. false

C. Compilation error

D. Runtime exception

Solution

1. Step 1: Understand encode and matches methods

   The encode method creates a hashed password. The matches method checks if the raw password matches the encoded hash.

2. Step 2: Analyze the code flow

   The raw password "mypassword" is encoded, then matches compares the same raw password with the encoded one, so it returns true.

3. Final Answer:

   true -> Option A

4. Quick Check:

   matches(raw, encoded) = true if same password [OK]

Hint: matches() returns true if raw matches encoded password [OK]

Common Mistakes:

• Assuming encode returns plain text
• Thinking matches compares encoded strings directly
• Expecting false because encoded password looks different

4. Identify the error in the following Spring Boot code snippet for password encoding:

BCryptPasswordEncoder encoder;
String encoded = encoder.encode("secret");

medium

A. String type cannot hold encoded password

B. encode method does not exist in BCryptPasswordEncoder

C. encoder is not initialized before use

D. Missing import statement for BCryptPasswordEncoder

Solution

1. Step 1: Check variable initialization

   The variable encoder is declared but not assigned an instance before calling encode.

2. Step 2: Understand consequences

   Using an uninitialized object causes a NullPointerException at runtime.

3. Final Answer:

   encoder is not initialized before use -> Option C

4. Quick Check:

   Uninitialized objects cause runtime errors [OK]

Hint: Always initialize objects before calling methods [OK]

Common Mistakes:

• Forgetting to create new instance with 'new'
• Assuming declaration equals initialization
• Ignoring runtime NullPointerException

5. You want to store user passwords securely in your Spring Boot application. Which approach correctly uses BCryptPasswordEncoder to encode and verify passwords during login?

hard

A. Encode password on registration, store encoded; on login, use matches(rawPassword, storedEncodedPassword)

B. Store plain password; on login, encode input and compare with stored plain password

C. Encode password on registration, store encoded; on login, encode input and compare encoded strings directly

D. Encode password on registration, store encoded; on login, decode stored password and compare with input

Solution

1. Step 1: Understand secure password storage

   Passwords must be encoded before storing; plain text storage is insecure.

2. Step 2: Verify password correctly on login

   Use matches(rawPassword, storedEncodedPassword) to check if input matches stored hash without decoding.

3. Final Answer:

   Encode password on registration, store encoded; on login, use matches(rawPassword, storedEncodedPassword) -> Option A

4. Quick Check:

   Use matches() to verify passwords securely [OK]

Hint: Use matches() to check raw vs encoded passwords [OK]

Common Mistakes:

• Comparing encoded strings directly (they differ each time)
• Storing plain text passwords
• Trying to decode encoded passwords (not possible)