MD5算法具有以下特点：

1、压缩性：任意长度的数据，算出的MD5值长度都是固定的。

2、容易计算：从原数据计算出MD5值很容易。

3、抗修改性：对原数据进行任何改动，哪怕只修改1个字节，所得到的MD5值都有很大区别。

4、弱抗碰撞：已知原数据和其MD5值，想找到一个具有相同MD5值的数据（即伪造数据）是非常困难的。

5、强抗碰撞：想找到两个不同的数据，使它们具有相同的MD5值，是非常困难的。

然后我就在想，如果把一个字符串用MD5加密过以后再不停的进行MD5加密，会得到什么样的结果呢？遂有了以下代码：

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

namespace MD5puzzle
{
    class Program
    {
        static void Main(string[] args)
        {
            Int64 i = 0, j = 0;
            Int64 max = 10000000;

            string niconiconi = "niconiconi";
            string niconi, nico=niconiconi;

            StreamWriter swOut = new StreamWriter(@"E:\md5.txt", false, Encoding.Default);

            for (i = 0; (i < max) && (j == 0); i++)
            {
                niconi = does.MD5(nico);

                if (niconi == niconiconi)
                {
                    j = 1;
                }

                swOut.WriteLine(niconi + " " + i);
                nico = niconi;
            }

 
            System.Console.WriteLine("Finish");
            System.Console.Read();

        }

 
        public void domd5p()
        {

            Int64 i = 0, j = 0;
            Int64 max = 100000000;

            string nico = does.MD5("niconiconi");
            string niconi;

            for (i = 0; (i < max) && (j == 0); i++)
            {
                niconi = does.MD5(nico);

                if (niconi == nico)
                {
                    j = 1;
                }

                System.Console.WriteLine("NO." + i + "_" + niconi);
                nico = niconi;
            }

            System.Console.Read();
        }
    }



    class does
    {
        public static string MD5(string Sourcein)
        {
            MD5CryptoServiceProvider MD5CSP = new MD5CryptoServiceProvider();

            byte[] MD5Source = System.Text.Encoding.UTF8.GetBytes(Sourcein);

            byte[] MD5Out = MD5CSP.ComputeHash(MD5Source);

            return Convert.ToBase64String(MD5Out);
        }
    }
}

这里我把数据写到了md5.txt里。

当中改动过上限。括号里面的是上限，大家可以感受一下

没错，那个只有5百万次的已经有160MB了。我家的电脑实在比较无能。我玩到5百万就玩不下去了，有兴趣的同学可以下下来去试试。下面贴出前100个md5码

rRIpUGNjjelWrYVo1BInLA== 0

UrjRsTpLZN0WL72SDuid4w== 1

6MICH12/VVlQPlcqAyy3Aw== 2

3dOqdPJsUmBXwLAQaDGGHQ== 3

T+DsqpgWx5k/uZMtY5V1ig== 4

nMD0ewc/sG4F48SFyapgyA== 5

yYQi6mMUkxq8Hrf096EkKw== 6

+UzysWlAHkxNs33qK5BLCw== 7

h/9vU01bY5OQvCzgFiPzKA== 8

iUg4RSM4dc+C42bA7tddVQ== 9

MauXvC2lY72PuvNJUEO0pg== 10

sE75QOo3pLLz6p6WGA4gHA== 11

5Dpk6YBnDklIi/hpodU2sQ== 12

htzQz2LvmXEkq/ZC+KLJCQ== 13

aRX22z67lAsOqtTH+Tw8cQ== 14

lDklDi/l3/evDZxpPMgueQ== 15

FwaH5M0IfUFI8JxSGhhXhw== 16

Fl/Nn0ndML7kAzVy7eBz2Q== 17

721lIGZeXmLWUJFLoVKnzw== 18

rkeOoYGytxnNd5IbCjmXkg== 19

Ka8JEiL243jL3Af6sEPFvg== 20

A/IjZkj0a9HuHeTbOOiVsw== 21

P+AUgz4lMx2zyIwV1cE1+w== 22

T0Y7bPSx3e1Ihly2vaOK2w== 23

GmYdOwKhkQK9q+qQP8YweA== 24

coMC8O6Y/nMXj/800kZK3w== 25

bvCqEuLmSoHXgRfPhLy1uw== 26

n9jqVhYvunn8RPNeqA8z9g== 27

J3roDv2oLFdx5kd5+I6Fsw== 28

EtihsewoZlvcv7otGqTZ6w== 29

cub9APkZUzsvDAaV0Wmuog== 30

Fx3sYg0FkmEodUDJ9+e9hw== 31

IqrobIoalFbAF1Ien1/zAg== 32

Pb/fqpq2WEatKNnXEUx8Tw== 33

DJL8TLWnUvPndt5zTZaEcw== 34

BsUzuXzY07VTX/7f6TrVMQ== 35

OukV8qcNJPMd2tpAIaNYew== 36

jHbVc69HjE6fxSdyQKOOSA== 37

u5U6EFealDnTtVNYr6JMrQ== 38

dfTeboDPc0Zs8AE7y7Ryog== 39

THZ7l6lgnsah40pt1CIemA== 40

fOCcL2r2evM2QrwZnQeBPg== 41

byRrkNKG6erMWIA7uTqYxw== 42

e5qvFWng2siIbBiqCtWzxw== 43

6o6PosWy4h8nB+N/Ll9Wfg== 44

aI4xMxmdOLGr50p8PfXwKA== 45

sTtqsdyqgQYeHeziUwcXqQ== 46

mHEkXO/CSkdkJGUJ+9zfbg== 47

u8FTFCqdDE9BemXf6S5+iw== 48

vSkD5Loe4tWoVMSP5+zg7Q== 49

pyILkblGKZTcPs7iYRvcjw== 50

7f8iNhqqqJ9Jrs38lxtzhg== 51

3J8FT6WJCn/L1S3DHgXaSg== 52

f+aU3Kzm9CEqa02hBwlh9A== 53

gUPwk0TORS0MAZih0ksPUA== 54

mWIy2fhoA6b000+0ikpWTQ== 55

eQfD0zcukAwp37L6vJj6iQ== 56

U2wE534uWJTe5UAnAAu6gw== 57

VoL6uzLMskTCmil+C49Cpg== 58

1nEmQmBACaL0XVbUiSxv0Q== 59

BJxt/vpHsDVfizCvl5uRBg== 60

P/9excuqnyAxugIY4SLGgA== 61

O2qqoVKGa2RcW9b516d6Ww== 62

4Y3ULLcU+sOvKBjN8lEBvA== 63

hgWxbnIiZwXIYQ4FBSXTGg== 64

O7cxBcVgMD3ayM1H83cOhA== 65

x2xN7L/jccWH32bzzhk9ag== 66

setWXmUwVLncbIVZbnrVrg== 67

PgKpptzklLuLySSwU+zrJg== 68

fcHiicljN4dxG14Mer3ZAQ== 69

XG/9yosdOJ5NeeyP6JSG9A== 70

ETG8Fold3DHsmXiNvMxiFQ== 71

0RCECvl47EJaiYvNp7GHYA== 72

UQzRsVFXDbMPrO/cWeDj8g== 73

ogfGyPme4UxBEl6l/eWsPA== 74

z/C5G8525jGcvi5eYrWuTg== 75

Og7XbR6gzKji2WA2R2JnHQ== 76

/ZlcPNR70j+eVkPmim8v2Q== 77

pzspFErbLd8IPfoduULddA== 78

wYMqORQQ6XjQtwo4ewRD9Q== 79

UOhZzCdeUKplKV9J1TKJ0A== 80

0tVvT87rDcofgnud4mihbQ== 81

OKr/3PJN6FOO6xnhFAzW9w== 82

q0x6G834+fE6rbKBDORX9Q== 83

7/u3D3au9aixMKDpizP43Q== 84

9fa3y05Ao5kH8GQIIDiqqg== 85

VDhlIKghoLSbK3GJI3iREg== 86

S203+Ud/EhpNlvruXTNv3w== 87

NkyVsm2M/UcCGHX0ne1i3Q== 88

u+6SeE2UTAbe2IicGx7XUQ== 89

CPiFazZNP6LHpOIK86vkzg== 90

CgttspQziSWrq4H7QqshlA== 91

MT/YfWKSquFvkRBLYLyciA== 92

e3okGK6a2xqlqojhAI/y1Q== 93

KkJq1mGfoiJXjrQXvt3QSQ== 94

fuBEgx4H2U0Oy89TI4VgMQ== 95

Pb8U1wlvgJ8RaSn1KC/y6A== 96

uSy3xXweQiQRTwOMcA2RJA== 97

lc7RHW8ew5KWJcZoJg1wuw== 98

s+kWyYo+xGfgjZ4FI8IuaA== 99

老笔记整理六：MD5的小作死