在C#中，可以使用加密算法來加密和解密byte數組。以下是一個示例代碼，演示如何使用AES算法對byte數組進行加密和解密。

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

class Program
{
    static void Main()
    {
        string plaintext = "Hello, world!";
        byte[] plainBytes = Encoding.UTF8.GetBytes(plaintext);

        byte[] key = Encoding.UTF8.GetBytes("0123456789abcdef");
        byte[] iv = Encoding.UTF8.GetBytes("fedcba9876543210");

        byte[] encryptedBytes = Encrypt(plainBytes, key, iv);
        Console.WriteLine("Encrypted: " + BitConverter.ToString(encryptedBytes).Replace("-", ""));

        byte[] decryptedBytes = Decrypt(encryptedBytes, key, iv);
        string decryptedText = Encoding.UTF8.GetString(decryptedBytes);
        Console.WriteLine("Decrypted: " + decryptedText);
    }

    static byte[] Encrypt(byte[] plainBytes, byte[] key, byte[] iv)
    {
        using (Aes aes = Aes.Create())
        {
            aes.Key = key;
            aes.IV = iv;

            using (MemoryStream ms = new MemoryStream())
            {
                using (CryptoStream cs = new CryptoStream(ms, aes.CreateEncryptor(), CryptoStreamMode.Write))
                {
                    cs.Write(plainBytes, 0, plainBytes.Length);
                    cs.FlushFinalBlock();
                    return ms.ToArray();
                }
            }
        }
    }

    static byte[] Decrypt(byte[] encryptedBytes, byte[] key, byte[] iv)
    {
        using (Aes aes = Aes.Create())
        {
            aes.Key = key;
            aes.IV = iv;

            using (MemoryStream ms = new MemoryStream())
            {
                using (CryptoStream cs = new CryptoStream(ms, aes.CreateDecryptor(), CryptoStreamMode.Write))
                {
                    cs.Write(encryptedBytes, 0, encryptedBytes.Length);
                    cs.FlushFinalBlock();
                    return ms.ToArray();
                }
            }
        }
    }
}

在上面的示例中，我們使用AES算法對字符串"Hello, world!"進行加密和解密。首先將明文字符串轉換為byte數組，然后使用Encrypt方法對其進行加密，再使用Decrypt方法對加密后的數據進行解密。最后我們將解密后的byte數組轉換為字符串輸出。