How To Encrypt And Decrypt Data Using AES Algorithm: A Guide For Android Developers

In today’s digital world, ensuring the security and confidentiality of data has become a fundamental concern for developers. Whether you are building a financial app or handling sensitive user data, protecting information is paramount. For Android developers, encrypting data is one of the first lines of defense. The Advanced Encryption Standard (AES) is one of the most popular and widely used algorithms to encrypt and decrypt data efficiently and securely.

In this article, we’ll walk through the process of using AES encryption and decryption in Android development using Java. By the end of this guide, you’ll understand how to implement AES encryption, securely manage encryption keys, and decrypt data when needed.

What is AES?

AES, short for Advanced Encryption Standard, is a symmetric encryption algorithm used across the globe to secure sensitive data. It is known for its robustness, speed, and security and is used in various applications, ranging from mobile apps to government systems. AES operates on fixed block sizes of 128 bits, with key sizes of 128, 192, or 256 bits. 

Since AES is symmetric, the same key is used to both encrypt and decrypt data, which makes it faster than other asymmetric encryption algorithms.

Android Password-Based Encryption (PBE) Using Advanced Encryption System (AES)

Why Use AES in Android Apps?

In Android development, handling sensitive user data securely is critical. Whether it's storing passwords, personal information, or other confidential data, encryption ensures that even if the data is intercepted, it remains unreadable without the encryption key. Here’s why AES is particularly useful for Android developers:

- Efficiency: AES is computationally efficient, which means it can encrypt and decrypt data quickly without draining battery life.

- Security: It is highly secure and widely recognized as the standard for encrypting data.

- Simplicity: Implementing AES in Android is relatively simple, and there are libraries and frameworks that make integration even easier.

Understanding AES Encryption and Decryption

In AES encryption:

- Plaintext is the original data you want to protect.

- Ciphertext is the encrypted version of your plaintext.

- Key is the secret value used to perform the encryption and decryption.

AES encryption transforms your plaintext into ciphertext using a key, while AES decryption uses the same key to transform the ciphertext back into plaintext.

AES Modes of Operation

AES works in various modes such as:

• ECB (Electronic Codebook Mode): The simplest mode, but it’s insecure because identical plaintext blocks produce identical ciphertext blocks.

• CBC (Cipher Block Chaining Mode): Secure and widely used. It uses an initialization vector (IV) to ensure that the same plaintext block produces different ciphertext each time.

• GCM (Galois/Counter Mode):  Provides both encryption and authentication, making it highly secure.

In this tutorial, we’ll use CBC mode, which is widely regarded as secure when implemented correctly.

Step-by-Step Guide to Implement AES Encryption and Decryption in Android

Step 1: Setup Your Android Project

Ensure you are using Android Studio and create a new project with an appropriate package name.

In the build.gradle (Module: app) file, add the following dependency:

  

 

 This library simplifies cryptographic operations for Android.

Step 2: Define Constants

Before we dive into encryption, let's define some constants. These will be the key, initialization vector (IV), and other settings needed for encryption and decryption.

Step 3: AES Key Generation

A strong and random key is essential for the security of AES. You can generate a 256-bit AES key like this:

Step 4: Encrypt Data

The next step is to write a function to encrypt the data using AES:

In this code:

- We initialize the cipher with `AES/CBC/PKCS5Padding`.

- We pass the secret key and initialization vector (IV) to the cipher.

- Finally, we encrypt the plaintext and return the ciphertext.

Step 5: Decrypt Data

Decrypting the data is similar to encryption but with a different cipher mode:

This function accepts the ciphertext, key, and IV, then decrypts the ciphertext back to plaintext.

Step 6: Example Usage

Let’s now combine all the pieces into a simple example.

In this example, we:

1. Generate a random AES key.
2. Create a random IV.
3. Encrypt a message.
4. Decrypt the message back to its original form.

Step 7: Safeguarding the AES Key

Storing the AES key securely is critical. Hardcoding the key in your app is not recommended, as it can be extracted by attackers. Instead, consider using the Android Keystore System or EncryptedSharedPreferences to store keys securely.

Step 8: Check if the provider has the key

To check if the Android Keystore contains a key with a specific alias, such as "AndroidKeystore," you can use the following code in Java. This will query the KeyStore to see if the key exists:

Step 9: Retrieve the key from the provider

To retrieve a key from the Android Keystore, you can follow these steps. Here's an example in Java for retrieving a secret key (such as an AES key) from the Android Keystore:

Common Mistakes to Avoid

• Using ECB Mode: ECB mode is insecure for most applications as it produces the same output for identical inputs.

• Hardcoding the Secret Key: Never hardcode the encryption key within the source code.

• Weak Random Numbers for IV: Always use `SecureRandom` to generate random IVs for stronger security.

Conclusion

AES encryption is a powerful tool to secure data in Android applications. In this article, we’ve covered how to generate an AES key, encrypt and decrypt data using CBC mode, and securely handle the encryption key. Implementing AES in your app helps protect sensitive user data from potential attacks, ensuring that only authorized parties can access it.

Remember, encryption is only one part of a comprehensive security strategy. Ensure that you’re using best practices across your entire application, including secure storage, networking, and authentication.