Secure storage for credentials in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Securely storing and retrieving a password

Given the Flutter code below using flutter_secure_storage, what will be the output when retrieving the stored password after saving it?

Flutter

final storage = FlutterSecureStorage();
await storage.write(key: 'password', value: 'mySecret123');
String? pwd = await storage.read(key: 'password');
print(pwd);

A null

B mySecret123

C Throws a runtime error

D Empty string

💡 Hint

Think about what the read method returns after a successful write.

The write method stores the value securely. The read method returns the stored value as a string if it exists, so it prints 'mySecret123'.

❓ lifecycle

intermediate

When to clear secure storage on logout?

In a Flutter app using flutter_secure_storage for credentials, when is the best time to clear stored credentials to keep the app secure?

A When the user logs out

B When the app starts

C Only when the app is uninstalled

D Never clear stored credentials

💡 Hint

Think about user privacy and security after ending a session.

Clearing credentials on logout ensures no sensitive data remains accessible if someone else uses the device.

📝 Syntax

advanced

Correct syntax for writing to secure storage

Which option shows the correct syntax to write a username 'user123' to flutter_secure_storage with key 'username'?

Flutter

final storage = FlutterSecureStorage();

A await storage.write(key: 'username', value: 'user123');

B storage.write('username', 'user123');

C storage.write(key='username', value='user123')

D await storage.set('username', 'user123');

💡 Hint

Check the method name and parameter names carefully.

The write method requires named parameters key and value and returns a Future, so await is needed.

🔧 Debug

advanced

Why does reading from secure storage return null?

A developer writes this code but reading the key 'token' returns null. What is the most likely cause?

Flutter

final storage = FlutterSecureStorage();
await storage.write(key: 'Token', value: 'abc123');
String? token = await storage.read(key: 'token');
print(token);

A The write method failed silently

B flutter_secure_storage does not support string values

C The read method requires a callback

D Key names are case-sensitive, so 'Token' and 'token' differ

💡 Hint

Check the exact spelling and casing of keys used.

flutter_secure_storage treats keys as case-sensitive strings, so 'Token' and 'token' are different keys.

🧠 Conceptual

expert

Why use flutter_secure_storage over SharedPreferences for credentials?

Which reason best explains why flutter_secure_storage is preferred for storing user credentials instead of SharedPreferences?

A flutter_secure_storage stores data in plain text for easy access

B SharedPreferences is faster and more secure

C flutter_secure_storage encrypts data and stores it securely on device hardware

D SharedPreferences automatically clears data on app close

💡 Hint

Think about data encryption and protection on mobile devices.

flutter_secure_storage uses platform-specific secure storage mechanisms with encryption, unlike SharedPreferences which stores plain text.