加解密方法

字符串加密、解密算法包括：
MD5、Des、Base64三种方式，详情如下所示：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;

namespace EncryptTools
{
    /// <summary>
    /// 加解密帮助类
    /// </summary>
    public class EncryptHelpers
    {
        //定义一个用于保存静态变量的实例
        private static EncryptHelpers instance = null;
        //定义一个保证线程同步的标识
        private static readonly object locker = new object();
        //构造函数为私有，使外界不能创建该类的实例
        private EncryptHelpers() { }
        public static EncryptHelpers Instance
        {
            get
            {
                if (instance == null)
                {
                    lock (locker)
                    {
                        if (instance == null) instance = new EncryptHelpers();
                    }
                }
                return instance;
            }
        }

        private byte[] Keys = new byte[]
        {
            18, 
            52, 
            86, 
            120, 
            144, 
            171, 
            222, 
            239
        };
        private string EncryptKey = "SWGSUNWG";

        #region MD5加密
        /// <summary>
        /// MD5加密
        /// </summary>
        /// <param name="content">需要加密的字符串</param>
        /// <param name="encode">字符的编码，默认null=UTF8Encoding</param>
        /// <returns></returns>
        public string MD5Encrypt(string content, Encoding encode = null)
        {
            if (string.IsNullOrEmpty(content)) return string.Empty;
            if (encode == null) encode = new UTF8Encoding();

            MD5 md5 = new MD5CryptoServiceProvider();
            byte[] t = md5.ComputeHash(encode.GetBytes(content));
            StringBuilder sb = new StringBuilder(32);
            for (int i = 0; i < t.Length; i++)
                sb.Append(t[i].ToString("x").PadLeft(2, '0'));
            return sb.ToString();
        }

        /// <summary>
        /// MD5加密(返回16位加密串)
        /// </summary>
        /// <param name="content">需要加密的字符串</param>
        /// <param name="encode">字符的编码，默认null=UTF8Encoding</param>
        /// <returns></returns>
        public string MD5Encrypt16(string content, Encoding encode = null)
        {
            if (string.IsNullOrEmpty(content)) return string.Empty;
            if (encode == null) encode = new UTF8Encoding();
            MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
            string result = BitConverter.ToString(md5.ComputeHash(encode.GetBytes(content)), 4, 8);
            result = result.Replace("-", "");
            return result;
        }
        #endregion

        #region Des 加密、解密
        /// <summary> 
        /// 加密数据 
        /// 如秘钥为空 则返回原文
        /// </summary> 
        /// <param name="content">加密前文本</param> 
        /// <param name="desKey">密匙</param> 
        /// <returns></returns> 
        public string DesEncrypt(string content, string desKey)
        {
            try
            {
                if (string.IsNullOrEmpty(desKey)) return content;

                DESCryptoServiceProvider des = new DESCryptoServiceProvider();
                des.Mode = CipherMode.ECB;
                var keys = new byte[8];
                if (desKey.Length < 8)
                {
                    var tmpkeys = System.Text.Encoding.UTF8.GetBytes(desKey);
                    for (int i = 0; i < keys.Length; i++)
                    {
                        if (tmpkeys.Length > i)
                            keys[i] = tmpkeys[i];
                        else
                            keys[i] = 0;
                    }
                }
                else keys = System.Text.Encoding.UTF8.GetBytes(desKey.Substring(0, 8));

                des.Key = keys;
                des.IV = des.Key;
                byte[] inputByteArray = System.Text.Encoding.UTF8.GetBytes(content);
                MemoryStream ms = new MemoryStream();
                CryptoStream cs = new CryptoStream(ms, des.CreateEncryptor(), CryptoStreamMode.Write);
                cs.Write(inputByteArray, 0, inputByteArray.Length);
                cs.FlushFinalBlock();
                StringBuilder sb = new StringBuilder();
                foreach (var item in ms.ToArray())
                {
                    sb.Append(item.ToString());
                    sb.Append("_");
                }

                if (sb.Length > 0) sb = sb.Remove(sb.Length - 1, 1);
                return sb.ToString();
            }
            catch (System.Exception e)
            {
                return content;
            }
        }

        /// <summary> 
        /// 解密数据 
        /// 如秘钥为空 则返回原文
        /// </summary> 
        /// <param name="content">密文</param> 
        /// <param name="desKey">密匙</param> 
        /// <returns>解密失败返回空字符串</returns> 
        public string DesDecrypt(string content, string desKey)
        {
            try
            {
                if (string.IsNullOrEmpty(desKey)) return content;

                DESCryptoServiceProvider des = new DESCryptoServiceProvider();
                des.Mode = CipherMode.ECB;
                var keys = new byte[8];
                if (desKey.Length < 8)
                {
                    var tmpkeys = System.Text.Encoding.UTF8.GetBytes(desKey);
                    for (int i = 0; i < keys.Length; i++)
                    {
                        if (tmpkeys.Length > i)
                            keys[i] = tmpkeys[i];
                        else
                            keys[i] = 0;
                    }
                }
                else keys = System.Text.Encoding.UTF8.GetBytes(desKey.Substring(0, 8));

                des.Key = keys;
                des.IV = des.Key;
                var data = content.Split('_');
                byte[] inputByteArray = new byte[data.Length]; ;
                for (int i = 0; i < data.Length; i++)
                {
                    inputByteArray[i] = Convert.ToByte(data[i]);
                }
                MemoryStream ms = new MemoryStream();
                CryptoStream cs = new CryptoStream(ms, des.CreateDecryptor(), CryptoStreamMode.Write);
                cs.Write(inputByteArray, 0, inputByteArray.Length);
                cs.FlushFinalBlock();
                System.Text.Encoding encoding = new System.Text.UTF8Encoding();
                return encoding.GetString(ms.ToArray());
            }
            catch (System.Exception e)
            {
                return "";
            }
        }

        /// <summary> 
        /// 加密数据 
        /// </summary> 
        /// <param name="encryptString">加密前文本</param> 
        /// <returns></returns> 
        public string DesEncrypt(string encryptString)
        {
            string result;
            try
            {
                byte[] bytes = Encoding.UTF8.GetBytes(EncryptKey.Substring(0, 8));
                byte[] keys = Keys;
                byte[] bytes2 = Encoding.UTF8.GetBytes(encryptString);
                DESCryptoServiceProvider dESCryptoServiceProvider = new DESCryptoServiceProvider();
                MemoryStream memoryStream = new MemoryStream();
                CryptoStream cryptoStream = new CryptoStream(memoryStream,
                    dESCryptoServiceProvider.CreateEncryptor(bytes, keys), CryptoStreamMode.Write);
                cryptoStream.Write(bytes2, 0, bytes2.Length);
                cryptoStream.FlushFinalBlock();
                result = Convert.ToBase64String(memoryStream.ToArray());
            }
            catch
            {
                result = encryptString;
            }
            return result;
        }

        /// <summary> 
        /// 解密数据 
        /// </summary> 
        /// <param name="decryptString">密文</param> 
        /// <returns>解密失败返回空字符串</returns> 
        public string DesDecrypt(string decryptString)
        {
            string result;
            try
            {
                byte[] bytes = Encoding.UTF8.GetBytes(EncryptKey);
                byte[] keys = Keys;
                byte[] array = Convert.FromBase64String(decryptString);
                DESCryptoServiceProvider dESCryptoServiceProvider = new DESCryptoServiceProvider();
                MemoryStream memoryStream = new MemoryStream();
                CryptoStream cryptoStream = new CryptoStream(memoryStream,
                    dESCryptoServiceProvider.CreateDecryptor(bytes, keys), CryptoStreamMode.Write);
                cryptoStream.Write(array, 0, array.Length);
                cryptoStream.FlushFinalBlock();
                result = Encoding.UTF8.GetString(memoryStream.ToArray());
            }
            catch
            {
                result = decryptString;
            }
            return result;
        }

        #endregion

        #region Base64加密解密
        /// <summary>
        /// Base64加密
        /// </summary>
        /// <param name="content">需要加密的字符串</param>
        /// <param name="encode">字符的编码，默认null=UTF8Encoding</param>
        /// <returns></returns>
        public string Base64Encrypt(string content, Encoding encode = null)
        {
            if (encode == null) encode = new UTF8Encoding();

            return Convert.ToBase64String(encode.GetBytes(content));
        }

        /// <summary>
        /// Base64解密
        /// </summary>
        /// <param name="content">需要解密的字符串</param>
        /// <param name="encode">字符的编码，默认null=UTF8Encoding</param>
        /// <returns></returns>
        public string Base64Decrypt(string content, Encoding encode = null)
        {
            if (encode == null) encode = new UTF8Encoding();

            return encode.GetString(Convert.FromBase64String(content));
        }
        #endregion



    }
}

测试代码：
 private void MD5Encrypt_Click(object sender, EventArgs e)
        {
            this.txtMd5Value.Text=EncryptHelpers.Instance.MD5Encrypt(this.txtMd5Key.Text.Trim());
        }

        private void MD5Encrypt16_Click(object sender, EventArgs e)
        {
            this.txtMd5Value.Text = EncryptHelpers.Instance.MD5Encrypt16(this.txtMd5Key.Text.Trim());
        }

        private void DesEncrypt_Click(object sender, EventArgs e)
        {
            this.txtDesValue.Text = EncryptHelpers.Instance.DesEncrypt(this.txtDesKey.Text.Trim(),"医技预约平台");
        }

        private void DesDecrypt_Click(object sender, EventArgs e)
        {
            this.txtDesValue.Text = EncryptHelpers.Instance.DesDecrypt(this.txtDesValue.Text.Trim(), "医技预约平台");
        }

        private void Base64Encrypt_Click(object sender, EventArgs e)
        {
            this.txtBaseValue.Text = EncryptHelpers.Instance.Base64Encrypt(this.txtBaseKey.Text.Trim());
        }

        private void Base64Decrypt_Click(object sender, EventArgs e)
        {
            this.txtBaseValue.Text = EncryptHelpers.Instance.Base64Decrypt(this.txtBaseValue.Text.Trim());
        }

        private void DesEncrypt2_Click(object sender, EventArgs e)
        {
            this.txtDesValue2.Text = EncryptHelpers.Instance.DesEncrypt(this.txtDesKey2.Text.Trim());
        }

        private void DesDecrypt2_Click(object sender, EventArgs e)
        {
            this.txtDesValue2.Text = EncryptHelpers.Instance.DesDecrypt(this.txtDesValue2.Text.Trim());
        }