static void main()
{
    //读取pfx证书
    X509Certificate2 x509 = new X509Certificate2(@"mycert.pfx", "654321", X509KeyStorageFlags.Exportable);
    
    String plaintext = "hello,world!";
    //利用证书中的公钥加密
    String enc = RSAEncrypt(x509.PublicKey.Key.ToXmlString(false), plaintext);
    Console.WriteLine(enc);
    //利用证书中的私钥解密
    String plain = RSADecrypt(x509.PrivateKey.ToXmlString(true), enc);
    Console.WriteLine(plain);
}

//string xmlPublicKey : xml 格式的公钥字符串
//string m_strEncryptString: 明文字符串
public static string RSAEncrypt(string xmlPublicKey, string plainText)
{
    RSACryptoServiceProvider provider = new RSACryptoServiceProvider();
    provider.FromXmlString(xmlPublicKey);
    byte[] bytes = new UnicodeEncoding().GetBytes(plainText);
    return Convert.ToBase64String(provider.Encrypt(bytes, false));
}

//string xmlPrivateKey ：xml 格式的私钥字符串
//string encryptedText : 先加密然后经过Base64编码的字符串
public static string RSADecrypt(string xmlPrivateKey, string encryptedText)
{
    RSACryptoServiceProvider provider = new RSACryptoServiceProvider();
    provider.FromXmlString(xmlPrivateKey);
    byte[] rgb = Convert.FromBase64String(m_strDecryptString);
    byte[] bytes = provider.Decrypt(rgb, false);
    return new UnicodeEncoding().GetString(bytes);
}