1:MD5

以前在asp时代常用的MD5算法好象是从动网流出来的，后来大家都用它，基本上有两种 ,区别在md5.asp的结尾部分

MD5 = LCase(WordToHex(a) & WordToHex(b) & WordToHex(c) & WordToHex(d))
 
MD5=LCase(WordToHex(b) & WordToHex(c)) 

分别对应32位和16位加密方式

在C#中对应的实现为

/// <summary>
       /// 16位MD5加密方法,以前的DVBBS所使用
       /// </summary>
       /// <param name="strSource">待加密字串</param>
        /// <returns>加密后的字串</returns>
        public string MD5Encrypt(string strSource)
        {
            return MD5Encrypt(strSource, 16);
        }
        /// <summary>
        /// MD5加密,和动网上的16/32位MD5加密结果相同
        /// </summary>
        /// <param name="strSource">待加密字串</param>
        /// <param name="length">16或32值之一,其它则采用.net默认MD5加密算法</param>
        /// <returns>加密后的字串</returns>
        public string MD5Encrypt(string strSource, int length)
        {
            byte[] bytes = Encoding.ASCII.GetBytes(strSource);
            byte[] hashValue = ((System.Security.Cryptography.HashAlgorithm)System.Security.Cryptography.CryptoConfig.CreateFromName("MD5")).ComputeHash(bytes);
            StringBuilder sb = new StringBuilder();
            switch (length)
            {
                case 16:
                    for (int i = 4; i < 12; i++)
                        sb.Append(hashValue[i].ToString("x2"));
                    break;
                case 32:
                    for (int i = 0; i < 16; i++)
                    {
                        sb.Append(hashValue[i].ToString("x2"));
                    }
                    break;
                default:
                    for (int i = 0; i < hashValue.Length; i++)
                    {
                        sb.Append(hashValue[i].ToString("x2"));
                    }
                    break;
            }

同样的其它语言都实现了DES加密与.net framework的des基础实现也不一样，比较郁闷的是我刚开始使用.net framework时还真的改写过perl版的des,后面才发现其实有更简单的办法，因为网上流传的perl/c/java版的des算法都是块加密的，设置CipherMode为ECB就好了，郁闷ing.

源代码如下

        public static byte[] DESKey = new byte[] {0x82, 0xBC, 0xA1, 0x6A, 0xF5, 0x87, 0x3B, 0xE6, 0x59, 0x6A, 0x32, 0x64, 0x7F, 0x3A, 0x2A, 0xBB, 0x2B, 0x68, 0xE2, 0x5F, 0x06, 0xFB, 0xB8, 0x2D, 0x67, 0xB3, 0x55, 0x19, 0x4E, 0xB8, 0xBF, 0xDD };
        /// <summary>
        /// DES加密
        /// </summary>
        /// <param name="strSource">待加密字串</param>
        /// <param name="key">32位Key值</param>
        /// <returns>加密后的字符串</returns>
        public string DESEncrypt(string strSource) {
            return DESEncrypt(strSource, DESKey);
        }
        public string DESEncrypt(string strSource,byte[] key)
        {
            SymmetricAlgorithm sa = Rijndael.Create();
            sa.Key = key;
            sa.Mode= CipherMode.ECB;
            sa.Padding = PaddingMode.Zeros;
            MemoryStream ms = new MemoryStream();
            CryptoStream cs = new CryptoStream(ms, sa.CreateEncryptor(), CryptoStreamMode.Write);
            byte[] byt = Encoding.Unicode.GetBytes(strSource);
            cs.Write(byt, 0, byt.Length);
            cs.FlushFinalBlock();
            cs.Close();
            return Convert.ToBase64String(ms.ToArray());
        }
        /// <summary>
        /// DES解密
        /// </summary>
        /// <param name="strSource">待解密的字串</param>
        /// <param name="key">32位Key值</param>
        /// <returns>解密后的字符串</returns>
        public string DESDecrypt(string strSource) {
            return DESDecrypt(strSource, DESKey);
        }
        public string DESDecrypt(string strSource,byte[] key)
        {
            SymmetricAlgorithm sa = Rijndael.Create();
            sa.Key = key;
            sa.Mode = CipherMode.ECB;
            sa.Padding = PaddingMode.Zeros;
            ICryptoTransform ct = sa.CreateDecryptor();
            byte[] byt = Convert.FromBase64String(strSource);
            MemoryStream ms = new MemoryStream(byt);
            CryptoStream cs = new CryptoStream(ms, ct, CryptoStreamMode.Read);
            StreamReader sr = new StreamReader(cs, Encoding.Unicode);
            return sr.ReadToEnd();
        }