SHA256是一个Hash算法，跟MD5的作用是一样一样的

RSA 就是传说中著名的非对称加密算法，因为RSA加密算法有长度限制，所以一般做签名是先用SHA256算法提取固定长度的字符串，再加密Hash字符串

C# RSA算法用公钥加密数据，然后用私钥解密。不支持私钥加密，公钥解密。但是可以用私钥加密，再用私钥解密（脑壳有问题才会这么搞）

二话不说贴代码

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

namespace Utility
{
    /// <summary>
    /// 数据加密器
    /// </summary>
    public class DataEncryptor
    {
        /*
         RSA 加密算法
         */

        /// <summary>
        /// 获取RSA 密钥
        /// 下标 0 为 私钥
        /// 下标 1 为 公钥
        /// </summary>
        /// <returns></returns>
        public static string[] GetRSAKey()
        {
            RSACryptoServiceProvider provider = new RSACryptoServiceProvider();
            string privatekey = provider.ToXmlString(true);
            string publickey = provider.ToXmlString(false);
            return new string[] { privatekey, publickey };
        }

        /// <summary>
        /// RSA 加密
        /// </summary>
        /// <param name="plainText"></param>
        /// <param name="publicKey"></param>
        /// <returns></returns>
        public static string RSAEncrypt(string plainText, string publicKey)
        {
            byte[] buffer = Encoding.UTF8.GetBytes(plainText);
            RSACryptoServiceProvider provider = new RSACryptoServiceProvider();
            provider.FromXmlString(publicKey);
            byte[] output = provider.Encrypt(buffer, false);
            return Convert.ToBase64String(output);
        }

        /// <summary>
        /// RSA 解密
        /// </summary>
        /// <param name="encryptedText"></param>
        /// <param name="privateKey"></param>
        /// <returns></returns>
        public static string RSADecrypt(string encryptedText, string privateKey)
        {
            byte[] buffer = Convert.FromBase64String(encryptedText);
            RSACryptoServiceProvider provider = new RSACryptoServiceProvider();
            provider.FromXmlString(privateKey);
            byte[] output = provider.Decrypt(buffer, false);
            return Encoding.UTF8.GetString(output);
        }

        /// <summary>
        /// SHA256 提取字符串Hash
        /// </summary>
        /// <returns></returns>
        public static string SHA256Encryptor(string message)
        {
            byte[] bytes = Encoding.UTF8.GetBytes(message);
            byte[] hash = SHA256.Create().ComputeHash(bytes);

            StringBuilder builder = new StringBuilder();
            for (int i = 0; i < hash.Length; i++)
            {
                builder.Append(hash[i].ToString("x2"));
            }
            return builder.ToString();
        }
    }
}