在C#中使用OpenSSL進行加密，你可以使用OpenSSL的C#綁定庫，如OpenSSL.NET。以下是一個使用OpenSSL.NET庫進行AES加密的示例：

首先，你需要安裝OpenSSL.NET庫。你可以通過NuGet包管理器來安裝：

Install-Package OpenSSL.NET

然后，你可以使用以下代碼進行AES加密：

using System;
using System.Text;
using OpenSSL.Core;
using OpenSSL.Crypto;

class Program
{
    static void Main()
    {
        string plaintext = "Hello, World!";
        string key = "abcdefghijklmnop"; // AES-128 requires 16 bytes key
        string iv = "1234567890abcdef"; // AES requires 16 bytes IV

        byte[] encrypted = Encrypt(plaintext, key, iv);
        Console.WriteLine("Encrypted: " + Convert.ToBase64String(encrypted));

        string decrypted = Decrypt(encrypted, key, iv);
        Console.WriteLine("Decrypted: " + decrypted);
    }

    static byte[] Encrypt(string plaintext, string key, string iv)
    {
        byte[] plainBytes = Encoding.UTF8.GetBytes(plaintext);
        byte[] keyBytes = Encoding.UTF8.GetBytes(key);
        byte[] ivBytes = Encoding.UTF8.GetBytes(iv);

        using (Aes aes = Aes.Create())
        {
            aes.Key = keyBytes;
            aes.IV = ivBytes;

            ICryptoTransform encryptor = aes.CreateEncryptor(aes.Key, aes.IV);

            using (MemoryStream memoryStream = new MemoryStream())
            {
                using (CryptoStream cryptoStream = new CryptoStream(memoryStream, encryptor, CryptoStreamMode.Write))
                {
                    cryptoStream.Write(plainBytes, 0, plainBytes.Length);
                    cryptoStream.Close();
                }

                return memoryStream.ToArray();
            }
        }
    }

    static string Decrypt(byte[] ciphertext, string key, string iv)
    {
        byte[] keyBytes = Encoding.UTF8.GetBytes(key);
        byte[] ivBytes = Encoding.UTF8.GetBytes(iv);

        using (Aes aes = Aes.Create())
        {
            aes.Key = keyBytes;
            aes.IV = ivBytes;

            ICryptoTransform decryptor = aes.CreateDecryptor(aes.Key, aes.IV);

            using (MemoryStream memoryStream = new MemoryStream())
            {
                using (CryptoStream cryptoStream = new CryptoStream(memoryStream, decryptor, CryptoStreamMode.Write))
                {
                    cryptoStream.Write(ciphertext, 0, ciphertext.Length);
                    cryptoStream.Close();
                }

                return Encoding.UTF8.GetString(memoryStream.ToArray());
            }
        }
    }
}

請注意，這只是一個簡單的示例，用于演示如何使用OpenSSL.NET庫進行AES加密。在實際應用中，你可能需要考慮更多的安全因素，如密鑰管理、填充方案等。此外，OpenSSL支持多種加密算法和模式，你可以根據需要選擇合適的算法和模式。在使用不同的加密模式和算法時，請確保了解相關的安全建議和最佳實踐。