Data encryption basics in Unity - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of AES encryption snippet

What is the output of this Unity C# code snippet that encrypts a string using AES and prints the Base64 result?

Unity

using System;
using System.Security.Cryptography;
using System.Text;

public class EncryptTest {
    public static void Main() {
        string original = "hello";
        byte[] key = Encoding.UTF8.GetBytes("1234567890123456");
        byte[] iv = Encoding.UTF8.GetBytes("abcdefghijklmnop");

        using (Aes aes = Aes.Create()) {
            aes.Key = key;
            aes.IV = iv;
            ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);

            byte[] originalBytes = Encoding.UTF8.GetBytes(original);
            byte[] encrypted = encryptor.TransformFinalBlock(originalBytes, 0, originalBytes.Length);

            Console.WriteLine(Convert.ToBase64String(encrypted));
        }
    }
}

A U2FsdGVkX1+q7Q9r6XzQ7v6v6Zq5zqX1w==

B q7Q9r6XzQ7v6v6Zq5zqX1w==

C SyntaxError: missing semicolon

D hello

💡 Hint

Look at how AES encryption transforms the input bytes and outputs a Base64 string.

The code encrypts the string "hello" with AES using the given key and IV, then prints the encrypted bytes as Base64. Option B matches the expected Base64 output. Option B is a common OpenSSL prefix but not produced here. Option B is invalid syntax. Option B is the original string, not encrypted.

🧠 Conceptual

intermediate

Understanding symmetric vs asymmetric encryption

Which statement correctly describes the difference between symmetric and asymmetric encryption?

A Symmetric encryption uses one key for both encrypting and decrypting, while asymmetric uses a pair of keys.

B Symmetric encryption uses two keys, asymmetric uses one key only.

C Symmetric encryption is slower than asymmetric encryption.

D Asymmetric encryption cannot be used for data encryption, only for hashing.

💡 Hint

Think about how keys are used in each encryption type.

Symmetric encryption uses the same secret key to encrypt and decrypt data. Asymmetric encryption uses a public key to encrypt and a private key to decrypt. Option A correctly states this difference. Option A reverses the key usage. Option A is generally false; symmetric is faster. Option A is incorrect; asymmetric encryption is used for encrypting data.

🔧 Debug

advanced

Identify the error in this encryption code

What error will this Unity C# code produce when run?

Unity

using System;
using System.Security.Cryptography;
using System.Text;

public class EncryptDebug {
    public static void Main() {
        string text = "data";
        byte[] key = Encoding.UTF8.GetBytes("shortkey");
        byte[] iv = Encoding.UTF8.GetBytes("shortiv");

        using (Aes aes = Aes.Create()) {
            aes.Key = key;
            aes.IV = iv;
            ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);

            byte[] bytes = Encoding.UTF8.GetBytes(text);
            byte[] encrypted = encryptor.TransformFinalBlock(bytes, 0, bytes.Length);

            Console.WriteLine(Convert.ToBase64String(encrypted));
        }
    }
}

A Output: "ZGF0YQ=="

B NullReferenceException because aes is null

C CryptographicException due to invalid key size

D IndexOutOfRangeException during TransformFinalBlock

💡 Hint

Check the length of the key and IV for AES requirements.

AES requires keys of specific lengths (128, 192, or 256 bits). The provided key and IV are too short (8 bytes each). This causes a CryptographicException about invalid key size. Option C is incorrect because aes is properly created. Option C is Base64 of "data" (no encryption). Option C is not triggered here.

📝 Syntax

advanced

Which code snippet correctly decrypts AES data?

Which of the following Unity C# code snippets correctly decrypts AES encrypted data stored in a byte array named encryptedData?

A

using (Aes aes = Aes.Create()) {
    aes.Key = key;
    aes.IV = iv;
    ICryptoTransform decryptor = aes.CreateDecryptor(aes.IV, aes.Key);
    byte[] decrypted = decryptor.TransformFinalBlock(encryptedData, 0, encryptedData.Length);
    string result = Encoding.UTF8.GetString(decrypted);
    Console.WriteLine(result);
}

B

using (Aes aes = Aes.Create()) {
    aes.Key = key;
    aes.IV = iv;
    ICryptoTransform decryptor = aes.CreateEncryptor(aes.Key, aes.IV);
    byte[] decrypted = decryptor.TransformFinalBlock(encryptedData, 0, encryptedData.Length);
    string result = Encoding.UTF8.GetString(decrypted);
    Console.WriteLine(result);
}

C

using (Aes aes = Aes.Create()) {
    aes.Key = key;
    aes.IV = iv;
    ICryptoTransform decryptor = aes.CreateDecryptor();
    byte[] decrypted = decryptor.TransformFinalBlock(encryptedData, 0, encryptedData.Length);
    string result = Encoding.UTF8.GetString(decrypted);
    Console.WriteLine(result);
}

D

using (Aes aes = Aes.Create()) {
    aes.Key = key;
    aes.IV = iv;
    ICryptoTransform decryptor = aes.CreateDecryptor(aes.Key, aes.IV);
    byte[] decrypted = decryptor.TransformFinalBlock(encryptedData, 0, encryptedData.Length);
    string result = Encoding.UTF8.GetString(decrypted);
    Console.WriteLine(result);
}

💡 Hint

Check the method used to create the decryptor and the order of parameters.

Option D correctly uses CreateDecryptor with key and IV in correct order. Option D incorrectly uses CreateEncryptor for decryption. Option D calls CreateDecryptor without parameters, which uses default key and IV (likely incorrect). Option D swaps key and IV parameters, causing wrong decryption or error.

🚀 Application

expert

Calculate the length of encrypted data

Given a plaintext string of length 30 bytes encrypted with AES in CBC mode with PKCS7 padding, what is the length in bytes of the encrypted output?

A 32 bytes

B 30 bytes

C 48 bytes

D 16 bytes

💡 Hint

AES block size is 16 bytes. PKCS7 padding adds bytes to fill the last block.

AES block size is 16 bytes. The plaintext is 30 bytes, which is 1 full block (16 bytes) plus 14 bytes. PKCS7 padding adds 2 bytes to fill the last block to 16 bytes. So total encrypted length is 32 bytes (2 blocks). Option A is correct. Option A ignores padding. Option A is too large. Option A is just one block size.