MD5的全称是message-digest algorithm 5(信息-摘要算法，在90年代初由mit laboratory for computer science和rsa data security inc的ronald l. rivest开发出来， 经md2、md3和md4发展而来。

MD5具有很好的安全性(因为它具有不可逆的特征,加过密的密文经过解密后和加密前的东东相同的可能性极小)

sharp demo

using System;
using System.Security.Cryptography;
using System.Text;
namespace CSharpTest1
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
            Console.WriteLine(GetMd5Str1("hello"));//BC4B2A76B9719D91 
            Console.WriteLine(UserMd5("hello"));
        }

        /**//// <summary>
            /// MD5 16位加密 加密后密码为大写
            /// </summary>
            /// <param name="ConvertString"></param>
            /// <returns></returns>
        public static string GetMd5Str1(string ConvertString)
        {
            MD5CryptoServiceProvider md5 = new MD5CryptoServiceProvider();
            string t2 = BitConverter.ToString(md5.ComputeHash(Encoding.UTF8.GetBytes(ConvertString)), 4, 8);
            t2 = t2.Replace("-", "");
            return t2;
        }

        /**//// <summary>
            /// MD5  32位加密
            /// </summary>
            /// <param name="str"></param>
            /// <returns></returns>
        static string UserMd5(string str)
        {
            string cl = str;
            StringBuilder pwd = new StringBuilder();
            MD5 md5 = MD5.Create();//实例化一个md5对像
                                   // 加密后是一个字节类型的数组，这里要注意编码UTF8/Unicode等的选择　
            byte[] s = md5.ComputeHash(Encoding.UTF8.GetBytes(cl));
            // 通过使用循环，将字节类型的数组转换为字符串，此字符串是常规字符格式化所得
            for (int i = 0; i < s.Length; i++)
            {
                // 将得到的字符串使用十六进制类型格式。格式后的字符是小写的字母，如果使用大写（X）则格式后的字符是大写字符
                pwd.Append(s[i].ToString("X2"));
                //pwd = pwd + s[i].ToString("X");

            }
            return pwd.ToString();
        }
    }
}

unity demo

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Md5Test : MonoBehaviour {

    public string fileName="1.txt";//streamingAssets 文件夹下面的文件名称
    public string testSting = "this is test string";


    /// <summary>
    /// 将一个文件转换为md5字符串，并保存
    /// </summary>
    /// <param name="fileName">File name.</param>
    void PaseFile(string fileName){
        string filePath = System.IO.Path.Combine (Application.streamingAssetsPath, fileName);//文件路径
        string fileMd5Path=System.IO.Path.Combine (Application.streamingAssetsPath, "md5_"+fileName);//md5 存储路径
        if(System.IO.File.Exists(filePath)){
            using(System.IO.FileStream stream=System.IO.File.Open(filePath,System.IO.FileMode.Open)){
                stream.Position = 0;//从文件首部开始
                string md5 = GetMd5FromStream (stream);//获取文件对应的md5数据
                System.IO.FileStream fs = new System.IO.FileStream (fileMd5Path,System.IO.FileMode.Create,System.IO.FileAccess.Write,System.IO.FileShare.Write);
                byte[] buff = System.Text.Encoding.UTF8.GetBytes (md5);
                fs.Write (buff,0,buff.Length);//保存生成的md5信息
                fs.Close ();
                Debug.Log ("<color=#ff0000> change over</color>");
            }

        }


    }
    /// <summary>
    /// 
    /// 通过数据流获取对应的md5文件
    /// </summary>
    /// <returns>The md5.</returns>
    /// <param name="stream">Stream.</param>
    string GetMd5FromStream(System.IO.FileStream stream){
        byte[] buff;
        using(System.Security.Cryptography.MD5 md5=new System.Security.Cryptography.MD5CryptoServiceProvider()){
            buff = md5.ComputeHash (stream);

        }
        System.Text.StringBuilder builder = new System.Text.StringBuilder ();
        foreach (var item in buff) {
            builder.Append (item.ToString ("x2").ToLower());//把二进制的字节，转换为16进制的数字形式的字符串
        }
        string res = builder.ToString ();
        Debug.Log (res);
        return res;
    }


    /// <summary>
    /// 通过字节数组获取md5字符串
    /// </summary>
    /// <returns>The md5 from bytes.</returns>
    /// <param name="data">Data.</param>
    string GetMd5FromBytes(byte[] data){
        byte[] buff;
        using(System.Security.Cryptography.MD5 md5=new System.Security.Cryptography.MD5CryptoServiceProvider()){
            buff = md5.ComputeHash (data);
        }
        System.Text.StringBuilder builder = new System.Text.StringBuilder ();
        foreach (var item in buff) {
            builder.Append (item.ToString ("x2").ToLower());//把二进制的字节，转换为16进制的数字形式的字符串
        }
        string res = builder.ToString ();
        Debug.Log (res);
        return res;

    }

    void  OnGUI(){
        if(GUI.Button(new Rect(30,30,100,30),"file md5")){
            PaseFile (fileName); //将一个文件转换为md5字符串，并保存
        }

        if(GUI.Button(new Rect(30,80,100,30),"string md5")){

            byte[] data = System.Text.Encoding.UTF8.GetBytes (testSting);//将字符串转换为字节数组
            string md5=GetMd5FromBytes (data);//通过字节数组获取对应的md5字符串

            Debug.Log ("<color=#ff0000> change over</color>");
        }

    }
}