關於MD5值的原理本文不在介紹，本文主要介紹MD5值的兩種編碼的相互轉換(32位和BASE64編碼的24位)，實際應用過程中經常會涉及到兩種編碼的相互轉換。快熟使用工具tomeko.net。

C#示例程序：

using System;
using System.Text;

namespace test
{
    class Program
    {
        static void Main(string[] args)
        {
            string original = "123456";

            Console.WriteLine("original: " + original);

            var md5Hex = BitConverter.ToString(new System.Security.Cryptography.MD5CryptoServiceProvider().ComputeHash(Encoding.Default.GetBytes(original))).Replace("-", "").ToLower();
            Console.WriteLine("md5Hex: " + md5Hex);

            //b64是以=結尾的長度為24位的密文
            var b64 = Convert.ToBase64String(new System.Security.Cryptography.MD5CryptoServiceProvider().ComputeHash(Encoding.Default.GetBytes(original)));
            Console.WriteLine("b64: " + b64);

            //b64Tomd5Hex
            var b64Tomd5Hex = BitConverter.ToString(new System.Security.Cryptography.FromBase64Transform().TransformFinalBlock(Encoding.Default.GetBytes(b64), 0, Encoding.Default.GetBytes(b64).Length)).Replace("-", "").ToLower();
            Console.WriteLine("b64Tomd5Hex: " + b64Tomd5Hex);

            //md5HexToBase64
            string md5HexToBase64 = HexString2B64String(md5Hex);
            Console.WriteLine("md5HexToBase64: " + md5HexToBase64);

            Console.ReadKey(true);
        }

        /// <summary>
        /// 32位md5轉24位base64
        /// </summary>
        /// <param name="input"></param>
        /// <returns></returns>
        public static string HexString2B64String(string input)
        {
            return Convert.ToBase64String(HexStringToHex(input));
        }

        public static byte[] HexStringToHex(string inputHex)

        {
            var resultantArray = new byte[inputHex.Length / 2];
            for (var i = 0; i < resultantArray.Length; i++)
            {
                resultantArray[i] = Convert.ToByte(inputHex.Substring(i * 2, 2), 16);
            }
            return resultantArray;
        }
    }
}
 

測試結果：

original: 123456
md5Hex: e10adc3949ba59abbe56e057f20f883e
b64: 4QrcOUm6Wau+VuBX8g+IPg==
b64Tomd5Hex: e10adc3949ba59abbe56e057f20f883e
md5HexToBase64: 4QrcOUm6Wau+VuBX8g+IPg==

MD5值轉換(Hex 32位 <-> base64 24位)