在C#中，對token進行加密通常使用的是對稱加密算法，如AES（Advanced Encryption Standard）。以下是一個使用AES加密和解密token的示例：

首先，需要引入System.Security.Cryptography命名空間。

using System.Security.Cryptography;

接下來，創建一個加密和解密的方法：

public static class AesEncryption
{
    private const int KeySize = 256;
    private const int BlockSize = 128;

    public static string Encrypt(string plainText, string key)
    {
        using (var aes = new AesManaged())
        {
            aes.KeySize = KeySize;
            aes.BlockSize = BlockSize;
            aes.Mode = CipherMode.CBC;
            aes.Padding = PaddingMode.PKCS7;

            var keyBytes = Encoding.UTF8.GetBytes(key);
            var iv = new byte[aes.BlockSize / 8];
            Array.Copy(keyBytes, iv, iv.Length);

            aes.Key = keyBytes;
            aes.IV = iv;

            using (var encryptor = aes.CreateEncryptor())
            {
                var inputData = Encoding.UTF8.GetBytes(plainText);
                var encryptedData = encryptor.TransformFinalBlock(inputData, 0, inputData.Length);
                return Convert.ToBase64String(encryptedData);
            }
        }
    }

    public static string Decrypt(string cipherText, string key)
    {
        using (var aes = new AesManaged())
        {
            aes.KeySize = KeySize;
            aes.BlockSize = BlockSize;
            aes.Mode = CipherMode.CBC;
            aes.Padding = PaddingMode.PKCS7;

            var keyBytes = Encoding.UTF8.GetBytes(key);
            var iv = new byte[aes.BlockSize / 8];
            Array.Copy(keyBytes, iv, iv.Length);

            aes.Key = keyBytes;
            aes.IV = iv;

            using (var decryptor = aes.CreateDecryptor())
            {
                var inputData = Convert.FromBase64String(cipherText);
                var decryptedData = decryptor.TransformFinalBlock(inputData, 0, inputData.Length);
                return Encoding.UTF8.GetString(decryptedData);
            }
        }
    }
}

現在，你可以使用這些方法對token進行加密和解密：

string token = "your_token_here";
string key = "your_key_here"; // 請確保密鑰長度至少為16個字符

// 加密token
string encryptedToken = AesEncryption.Encrypt(token, key);
Console.WriteLine("Encrypted token: " + encryptedToken);

// 解密token
string decryptedToken = AesEncryption.Decrypt(encryptedToken, key);
Console.WriteLine("Decrypted token: " + decryptedToken);

請注意，密鑰（key）應該是足夠復雜且安全的，并且在加密和解密過程中保持不變。在實際應用中，密鑰應該從安全的配置源獲取，而不是硬編碼在代碼中。