MD5，SHA1，SHA256，SHA512等經常使用加密算法

using System;
using System.IO;
using System.Data;
using System.Text;
using System.Diagnostics;
using System.Security;
using System.Security.Cryptography;

/* 
 * .Net框架因爲擁有CLR提供的豐富庫支持，只需不多的代碼便可實現先前使用C等舊式語言很難實現的加密算法。本類實現一些經常使用機密算法，供參考。其中MD5算法返回Int的ToString字串。返回數字字母型結果的算法參見以前Blog文章
 */
namespace 檔案數字化加工
{
    /// <summary>
    /// 類名：HashEncrypt
    /// 做用：對傳入的字符串進行Hash運算，返回經過Hash算法加密過的字串。
    /// 屬性：［無］
    /// 構造函數額參數：
    /// IsReturnNum:是否返回爲加密後字符的Byte代碼
    /// IsCaseSensitive：是否區分大小寫。
    /// 方法：此類提供MD5，SHA1，SHA256，SHA512等四種算法，加密字串的長度依次增大。
    /// </summary>
    public class HashEncrypt
    {
        //private string strIN;
        private bool isReturnNum;
        private bool isCaseSensitive;

        /// <summary>
        /// 類初始化，此類提供MD5，SHA1，SHA256，SHA512等四種算法，加密字串的長度依次增大。
        /// </summary>
        /// <param name="IsCaseSensitive">是否區分大小寫</param>
        /// <param name="IsReturnNum">是否返回爲加密後字符的Byte代碼</param>
        public HashEncrypt(bool IsCaseSensitive, bool IsReturnNum)
        {
            this.isReturnNum = IsReturnNum;
            this.isCaseSensitive = IsCaseSensitive;
        }

        private string getstrIN(string strIN)
        {
            //string strIN = strIN;
            if (strIN.Length == 0)
            {
                strIN = "~NULL~";
            }
            if (isCaseSensitive == false)
            {
                strIN = strIN.ToUpper();
            }
            return strIN;
        }

        public string MD5Encrypt(string strIN)
        {
            //string strIN = getstrIN(strIN);
            byte[] tmpByte;
            MD5 md5 = new MD5CryptoServiceProvider();
            tmpByte = md5.ComputeHash(GetKeyByteArray(getstrIN(strIN)));
            md5.Clear();

            return GetStringValue(tmpByte);

        }

        public string SHA1Encrypt(string strIN)
        {
            //string strIN = getstrIN(strIN);
            byte[] tmpByte;
            SHA1 sha1 = new SHA1CryptoServiceProvider();

            tmpByte = sha1.ComputeHash(GetKeyByteArray(strIN));
            sha1.Clear();

            return GetStringValue(tmpByte);

        }

        public string SHA256Encrypt(string strIN)
        {
            //string strIN = getstrIN(strIN);
            byte[] tmpByte;
            SHA256 sha256 = new SHA256Managed();

            tmpByte = sha256.ComputeHash(GetKeyByteArray(strIN));
            sha256.Clear();

            return GetStringValue(tmpByte);

        }

        public string SHA512Encrypt(string strIN)
        {
            //string strIN = getstrIN(strIN);
            byte[] tmpByte;
            SHA512 sha512 = new SHA512Managed();

            tmpByte = sha512.ComputeHash(GetKeyByteArray(strIN));
            sha512.Clear();

            return GetStringValue(tmpByte);

        }

        /// <summary>
        /// 使用DES加密（Added by niehl 2005-4-6）
        /// </summary>
        /// <param name="originalValue">待加密的字符串</param>
        /// <param name="key">密鑰(最大長度8)</param>
        /// <param name="IV">初始化向量(最大長度8)</param>
        /// <returns>加密後的字符串</returns>
        public string DESEncrypt(string originalValue, string key, string IV)
        {
            //將key和IV處理成8個字符
            key += "12345678";
            IV += "12345678";
            key = key.Substring(0, 8);
            IV = IV.Substring(0, 8);

            SymmetricAlgorithm sa;
            ICryptoTransform ct;
            MemoryStream ms;
            CryptoStream cs;
            byte[] byt;

            sa = new DESCryptoServiceProvider();
            sa.Key = Encoding.UTF8.GetBytes(key);
            sa.IV = Encoding.UTF8.GetBytes(IV);
            ct = sa.CreateEncryptor();

            byt = Encoding.UTF8.GetBytes(originalValue);

            ms = new MemoryStream();
            cs = new CryptoStream(ms, ct, CryptoStreamMode.Write);
            cs.Write(byt, 0, byt.Length);
            cs.FlushFinalBlock();

            cs.Close();

            return Convert.ToBase64String(ms.ToArray());
        }

        public string DESEncrypt(string originalValue, string key)
        {
            return DESEncrypt(originalValue, key, key);
        }

        /// <summary>
        /// 使用DES解密（Added by niehl 2005-4-6）
        /// </summary>
        /// <param name="encryptedValue">待解密的字符串</param>
        /// <param name="key">密鑰(最大長度8)</param>
        /// <param name="IV">m初始化向量(最大長度8)</param>
        /// <returns>解密後的字符串</returns>
        public string DESDecrypt(string encryptedValue, string key, string IV)
        {
            //將key和IV處理成8個字符
            key += "12345678";
            IV += "12345678";
            key = key.Substring(0, 8);
            IV = IV.Substring(0, 8);

            SymmetricAlgorithm sa;
            ICryptoTransform ct;
            MemoryStream ms;
            CryptoStream cs;
            byte[] byt;

            sa = new DESCryptoServiceProvider();
            sa.Key = Encoding.UTF8.GetBytes(key);
            sa.IV = Encoding.UTF8.GetBytes(IV);
            ct = sa.CreateDecryptor();

            byt = Convert.FromBase64String(encryptedValue);

            ms = new MemoryStream();
            cs = new CryptoStream(ms, ct, CryptoStreamMode.Write);
            cs.Write(byt, 0, byt.Length);
            cs.FlushFinalBlock();

            cs.Close();

            return Encoding.UTF8.GetString(ms.ToArray());

        }

        public string DESDecrypt(string encryptedValue, string key)
        {
            return DESDecrypt(encryptedValue, key, key);
        }

        private string GetStringValue(byte[] Byte)
        {
            string tmpString = "";
            if (this.isReturnNum == false)
            {
                ASCIIEncoding Asc = new ASCIIEncoding();
                tmpString = Asc.GetString(Byte);
            }
            else
            {
                int iCounter;
                for (iCounter = 0; iCounter < Byte.Length; iCounter++)
                {
                    tmpString = tmpString + Byte[iCounter].ToString();
                }
            }
            return tmpString;
        }

        private byte[] GetKeyByteArray(string strKey)
        {

            ASCIIEncoding Asc = new ASCIIEncoding();

            int tmpStrLen = strKey.Length;
            byte[] tmpByte = new byte[tmpStrLen - 1];

            tmpByte = Asc.GetBytes(strKey);

            return tmpByte;

        }

    }
}