Secure storage for credentials in Flutter - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is secure storage in mobile apps?

Secure storage is a safe place on a device where sensitive data like passwords or tokens are saved so others can't easily access them.

beginner

Which Flutter package is commonly used for secure storage?

The flutter_secure_storage package is commonly used to store sensitive data securely on both Android and iOS devices.

intermediate

How does flutter_secure_storage protect data on Android?

It uses the Android Keystore system to encrypt data, making it accessible only to your app and protected by the device's security.

beginner

Why should you avoid storing passwords in plain text in mobile apps?

Storing passwords in plain text risks exposing them if the device is lost or hacked. Secure storage encrypts data to keep it safe.

beginner

What is a simple Flutter code snippet to save a token securely?

Using flutter_secure_storage: final storage = FlutterSecureStorage(); await storage.write(key: 'token', value: 'abc123');

Which Flutter package helps store credentials securely?

A flutter_secure_storage

B shared_preferences

C http

D path_provider

flutter_secure_storage encrypts data and stores it securely, unlike shared_preferences which is not encrypted.

What does flutter_secure_storage use on iOS to protect data?

A Keychain

B SQLite

C UserDefaults

D File system

On iOS, flutter_secure_storage uses the Keychain service to securely store data.

Why is it important to encrypt credentials on a device?

A To improve app speed

B To save storage space

C To prevent unauthorized access

D To reduce battery usage

Encryption protects sensitive data from unauthorized access if the device is lost or compromised.

Which of these is NOT a secure way to store passwords in Flutter?

A Using flutter_secure_storage

B Saving in plain text in shared_preferences

C Using Keychain on iOS

D Using Android Keystore

shared_preferences stores data unencrypted and is not safe for passwords.

What is the first step to use flutter_secure_storage in your Flutter app?

A Create a database

B Import dart:io

C Use setState()

D Add flutter_secure_storage to pubspec.yaml

You must add the flutter_secure_storage package to your pubspec.yaml file before using it.

Explain how flutter_secure_storage helps keep user credentials safe on mobile devices.

Think about how data is protected differently on Android and iOS.

Describe the steps to securely save and retrieve a password using flutter_secure_storage in a Flutter app.

Focus on the main methods used to store and get data.

Practice

1. What is the main purpose of using FlutterSecureStorage in a Flutter app?

easy

A. To improve app performance by caching data

B. To securely store sensitive data like passwords on the device

C. To create UI animations

D. To manage app navigation between screens

Solution

1. Step 1: Understand the role of secure storage

   Secure storage is designed to keep sensitive information safe on the device, such as passwords or tokens.

2. Step 2: Identify what FlutterSecureStorage does

   This package provides a way to write, read, and delete data securely, protecting it from unauthorized access.

3. Final Answer:

   To securely store sensitive data like passwords on the device -> Option B

4. Quick Check:

   Secure storage = safe data storage [OK]

Hint: Secure storage is for sensitive info, not UI or navigation [OK]

Common Mistakes:

• Confusing secure storage with caching
• Thinking it manages UI or navigation
• Assuming it speeds up app performance

2. Which of the following is the correct way to write a value using FlutterSecureStorage?

easy

A. storage.writeValue('token', 'abc123');

B. storage.write('token', 'abc123');

C. await storage.write(key: 'token', value: 'abc123');

D. await storage.save(key: 'token', value: 'abc123');

Solution

1. Step 1: Recall the method signature for writing data

   The correct method is write with named parameters key and value, and it returns a Future, so it should be awaited.

2. Step 2: Check each option for syntax correctness

   await storage.write(key: 'token', value: 'abc123'); uses await storage.write(key: 'token', value: 'abc123'); which is correct. Others either miss await, use wrong method names, or wrong parameter style.

3. Final Answer:

   await storage.write(key: 'token', value: 'abc123'); -> Option C

4. Quick Check:

   Write method with await and named params = await storage.write(key: 'token', value: 'abc123'); [OK]

Hint: Use await and named parameters key and value [OK]

Common Mistakes:

• Omitting await for async calls
• Using wrong method names like save or writeValue
• Passing parameters without names

3. Given this code snippet, what will be printed?

final storage = FlutterSecureStorage();
await storage.write(key: 'user', value: 'Alice');
String? name = await storage.read(key: 'user');
print(name);

medium

A. Alice

B. Error: key not found

C. FlutterSecureStorage instance

D. null

Solution

1. Step 1: Analyze the write operation

   The code writes the value 'Alice' with the key 'user' into secure storage.

2. Step 2: Analyze the read operation and print

   Reading the key 'user' returns the stored value 'Alice', which is then printed.

3. Final Answer:

   Alice -> Option A

4. Quick Check:

   Write then read same key returns stored value [OK]

Hint: Read returns stored value if key exists [OK]

Common Mistakes:

• Assuming read returns null without checking
• Confusing instance print with value print
• Expecting error if key was just written

4. What is wrong with this code snippet?

final storage = FlutterSecureStorage();
storage.write(key: 'pass', value: '1234');
String pass = storage.read(key: 'pass');
print(pass);

medium

A. Wrong method name for writing

B. Cannot print a String variable

C. Key 'pass' is invalid

D. Missing await for async calls

Solution

1. Step 1: Identify async methods usage

   Both write and read are asynchronous and return Futures, so they must be awaited.

2. Step 2: Check variable assignment and print

   Assigning String pass = storage.read(...) without await causes a type mismatch and print will show Future instance, not the value.

3. Final Answer:

   Missing await for async calls -> Option D

4. Quick Check:

   Async methods need await to get actual values [OK]

Hint: Always await async storage methods [OK]

Common Mistakes:

• Not awaiting async calls
• Assigning Future to String directly
• Ignoring async nature of storage methods

5. You want to securely store a user's credentials and then delete them when they log out. Which sequence of FlutterSecureStorage calls is correct?

hard

A. await storage.write(key: 'user', value: 'Bob'); await storage.delete(key: 'user');

B. storage.write(key: 'user', value: 'Bob'); storage.remove(key: 'user');

C. await storage.save(key: 'user', value: 'Bob'); await storage.deleteValue(key: 'user');

D. storage.set(key: 'user', value: 'Bob'); storage.delete(key: 'user');

Solution

1. Step 1: Identify correct method names and async usage

   The correct methods are write to store and delete to remove data. Both return Futures and must be awaited.

2. Step 2: Check each option for correctness

   await storage.write(key: 'user', value: 'Bob'); await storage.delete(key: 'user'); uses correct method names and awaits both calls. Other options use wrong method names or omit await.

3. Final Answer:

   await storage.write(key: 'user', value: 'Bob'); await storage.delete(key: 'user'); -> Option A

4. Quick Check:

   Use write and delete with await for secure storage [OK]

Hint: Use write and delete methods with await [OK]

Common Mistakes:

• Using wrong method names like save or remove
• Not awaiting async calls
• Mixing synchronous and async calls