前言

为了帮助同学们完成痛苦的实验课程设计，本作者将其作出的实验结果及代码贴至CSDN中，供同学们学习参考。如有不足或描述不完善之处，敬请各位指出，欢迎各位的斧正！

一、实验目的

1.掌握MD5算法的工作原理。
2.熟悉.NET Framework 4 MD5码编程
3.熟悉MD5的常规应用

二、实验环境

Microsoft Visual Studio 2019

三、实验基本方法

1.用C语言编写MD5算法，验证MD5原理；（见实验程序清单）
2.用C#编写基于.NET Framework实现字符串的MD5码计算；（见实验程序清单）
3.用C#编写基于.NET Framework文件的MD5码计算；（见实验程序清单）
4.用MD5进行文件完整性校验;（见实验结果）
5.用MD5编写Windows窗体登录界面，实验MD5在身份认证系统中的应用。（见实验结果）

四、实验程序清单

1.分析C语言编写的MD5算法实现。
2.分析程序关键原代码。
3.分析用MD5进行文件完整性校验。
4.分析在系统登录中MD5算法的应用。

源代码修改如下：

#include "stdafx.h"
#include "md5.h"
using namespace std;
/* Constants for MD5Transform routine. */
#define S11 7
#define S12 12
#define S13 17
#define S14 22
#define S21 5
#define S22 9
#define S23 14
#define S24 20
#define S31 4
#define S32 11
#define S33 16
#define S34 23
#define S41 6
#define S42 10
#define S43 15
#define S44 21
/* F, G, H and I are basic MD5 functions.
*/
#define F(x, y, z) (((x) & (y)) | ((~x) & (z)))
#define G(x, y, z) (((x) & (z)) | ((y) & (~z)))
#define H(x, y, z) ((x) ^ (y) ^ (z))
#define I(x, y, z) ((y) ^ ((x) | (~z)))
/* ROTATE_LEFT rotates x left n bits.
*/
#define ROTATE_LEFT(x, n) (((x) << (n)) | ((x) >> (32-(n))))

/* FF, GG, HH, and II transformations for rounds 1, 2, 3, and 4.
Rotation is separate from addition to prevent recomputation.
*/
#define FF(a, b, c, d, x, s, ac) { \
	(a) += F ((b), (c), (d)) + (x) + ac; \
	(a) = ROTATE_LEFT ((a), (s)); \
	(a) += (b); \
}
#define GG(a, b, c, d, x, s, ac) { \
	(a) += G ((b), (c), (d)) + (x) + ac; \
	(a) = ROTATE_LEFT ((a), (s)); \
	(a) += (b); \
}
#define HH(a, b, c, d, x, s, ac) { \
	(a) += H ((b), (c), (d)) + (x) + ac; \
	(a) = ROTATE_LEFT ((a), (s)); \
	(a) += (b); \
}
#define II(a, b, c, d, x, s, ac) { \
	(a) += I ((b), (c), (d)) + (x) + ac; \
	(a) = ROTATE_LEFT ((a), (s)); \
	(a) += (b); \
}


const byte MD5::PADDING[64] = {
    
     0x80 };
const char MD5::HEX[16] = {
    
    
	'0', '1', '2', '3',
	'4', '5', '6', '7',
	'8', '9', 'a', 'b',
	'c', 'd', 'e', 'f'
};


/* Default construct. */
MD5::MD5() {
    
    
	reset();
}

/* Construct a MD5 object with a input buffer. */
MD5::MD5(const void* input, size_t length) {
    
    
	reset();
	update(input, length);
}

/* Construct a MD5 object with a string. */
MD5::MD5(const string& str) {
    
    
	reset();
	update(str);
}

/* Construct a MD5 object with a file. */
MD5::MD5(ifstream& in) {
    
    
	reset();
	update(in);
}

/* Return the message-digest */
const byte* MD5::digest() {
    
    

	if (!_finished) {
    
    
		_finished = true;
		final();
	}
	return _digest;
}

/* Reset the calculate state */
void MD5::reset() {
    
    

	_finished = false;
	/* reset number of bits. */
	_count[0] = _count[1] = 0;
	/* Load magic initialization constants. */
	_state[0] = 0x67452301;
	_state[1] = 0xefcdab89;
	_state[2] = 0x98badcfe;
	_state[3] = 0x10325476;
}

/* Updating the context with a input buffer. */
void MD5::update(const void* input, size_t length) {
    
    
	update((const byte*)input, length);
}

/* Updating the context with a string. */
void MD5::update(const string& str) {
    
    
	update((const byte*)str.c_str(), str.length());
}

/* Updating the context with a file. */
void MD5::update(ifstream& in) {
    
    

	if (!in) {
    
    
		return;
	}

	std::streamsize length;
	char buffer[BUFFER_SIZE];
	while (!in.eof()) {
    
    
		in.read(buffer, BUFFER_SIZE);
		length = in.gcount();
		if (length > 0) {
    
    
			update(buffer, length);
		}
	}
	in.close();
}

/* MD5 block update operation. Continues an MD5 message-digest
operation, processing another message block, and updating the
context.
*/
void MD5::update(const byte* input, size_t length) {
    
    

	uint32 i, index, partLen;

	_finished = false;

	/* Compute number of bytes mod 64 */
	index = (uint32)((_count[0] >> 3) & 0x3f);

	/* update number of bits */
	if ((_count[0] += ((uint32)length << 3)) < ((uint32)length << 3)) {
    
    
		++_count[1];
	}
	_count[1] += ((uint32)length >> 29);

	partLen = 64 - index;

	/* transform as many times as possible. */
	if (length >= partLen) {
    
    

		memcpy(&_buffer[index], input, partLen);
		transform(_buffer);

		for (i = partLen; i + 63 < length; i += 64) {
    
    
			transform(&input[i]);
		}
		index = 0;

	} else {
    
    
		i = 0;
	}

	/* Buffer remaining input */
	memcpy(&_buffer[index], &input[i], length - i);
}

/* MD5 finalization. Ends an MD5 message-_digest operation, writing the
the message _digest and zeroizing the context.
*/
void MD5::final() {
    
    

	byte bits[8];
	uint32 oldState[4];
	uint32 oldCount[2];
	uint32 index, padLen;

	/* Save current state and count. */
	memcpy(oldState, _state, 16);
	memcpy(oldCount, _count, 8);

	/* Save number of bits */
	encode(_count, bits, 8);

	/* Pad out to 56 mod 64. */
	index = (uint32)((_count[0] >> 3) & 0x3f);
	padLen = (index < 56) ? (56 - index) : (120 - index);
	update(PADDING, padLen);

	/* Append length (before padding) */
	update(bits, 8);

	/* Store state in digest */
	encode(_state, _digest, 16);

	/* Restore current state and count. */
	memcpy(_state, oldState, 16);
	memcpy(_count, oldCount, 8);
}

/* MD5 basic transformation. Transforms _state based on block. */
void MD5::transform(const byte block[64]) {
    
    

	uint32 a = _state[0], b = _state[1], c = _state[2], d = _state[3], x[16];

	decode(block, x, 64);

	/* Round 1 */
	FF (a, b, c, d, x[ 0], S11, 0xd76aa478); /* 1 */
	FF (d, a, b, c, x[ 1], S12, 0xe8c7b756); /* 2 */
	FF (c, d, a, b, x[ 2], S13, 0x242070db); /* 3 */
	FF (b, c, d, a, x[ 3], S14, 0xc1bdceee); /* 4 */
	FF (a, b, c, d, x[ 4], S11, 0xf57c0faf); /* 5 */
	FF (d, a, b, c, x[ 5], S12, 0x4787c62a); /* 6 */
	FF (c, d, a, b, x[ 6], S13, 0xa8304613); /* 7 */
	FF (b, c, d, a, x[ 7], S14, 0xfd469501); /* 8 */
	FF (a, b, c, d, x[ 8], S11, 0x698098d8); /* 9 */
	FF (d, a, b, c, x[ 9], S12, 0x8b44f7af); /* 10 */
	FF (c, d, a, b, x[10], S13, 0xffff5bb1); /* 11 */
	FF (b, c, d, a, x[11], S14, 0x895cd7be); /* 12 */
	FF (a, b, c, d, x[12], S11, 0x6b901122); /* 13 */
	FF (d, a, b, c, x[13], S12, 0xfd987193); /* 14 */
	FF (c, d, a, b, x[14], S13, 0xa679438e); /* 15 */
	FF (b, c, d, a, x[15], S14, 0x49b40821); /* 16 */

	/* Round 2 */
	GG (a, b, c, d, x[ 1], S21, 0xf61e2562); /* 17 */
	GG (d, a, b, c, x[ 6], S22, 0xc040b340); /* 18 */
	GG (c, d, a, b, x[11], S23, 0x265e5a51); /* 19 */
	GG (b, c, d, a, x[ 0], S24, 0xe9b6c7aa); /* 20 */
	GG (a, b, c, d, x[ 5], S21, 0xd62f105d); /* 21 */
	GG (d, a, b, c, x[10], S22,  0x2441453); /* 22 */
	GG (c, d, a, b, x[15], S23, 0xd8a1e681); /* 23 */
	GG (b, c, d, a, x[ 4], S24, 0xe7d3fbc8); /* 24 */
	GG (a, b, c, d, x[ 9], S21, 0x21e1cde6); /* 25 */
	GG (d, a, b, c, x[14], S22, 0xc33707d6); /* 26 */
	GG (c, d, a, b, x[ 3], S23, 0xf4d50d87); /* 27 */
	GG (b, c, d, a, x[ 8], S24, 0x455a14ed); /* 28 */
	GG (a, b, c, d, x[13], S21, 0xa9e3e905); /* 29 */
	GG (d, a, b, c, x[ 2], S22, 0xfcefa3f8); /* 30 */
	GG (c, d, a, b, x[ 7], S23, 0x676f02d9); /* 31 */
	GG (b, c, d, a, x[12], S24, 0x8d2a4c8a); /* 32 */

	/* Round 3 */
	HH (a, b, c, d, x[ 5], S31, 0xfffa3942); /* 33 */
	HH (d, a, b, c, x[ 8], S32, 0x8771f681); /* 34 */
	HH (c, d, a, b, x[11], S33, 0x6d9d6122); /* 35 */
	HH (b, c, d, a, x[14], S34, 0xfde5380c); /* 36 */
	HH (a, b, c, d, x[ 1], S31, 0xa4beea44); /* 37 */
	HH (d, a, b, c, x[ 4], S32, 0x4bdecfa9); /* 38 */
	HH (c, d, a, b, x[ 7], S33, 0xf6bb4b60); /* 39 */
	HH (b, c, d, a, x[10], S34, 0xbebfbc70); /* 40 */
	HH (a, b, c, d, x[13], S31, 0x289b7ec6); /* 41 */
	HH (d, a, b, c, x[ 0], S32, 0xeaa127fa); /* 42 */
	HH (c, d, a, b, x[ 3], S33, 0xd4ef3085); /* 43 */
	HH (b, c, d, a, x[ 6], S34,  0x4881d05); /* 44 */
	HH (a, b, c, d, x[ 9], S31, 0xd9d4d039); /* 45 */
	HH (d, a, b, c, x[12], S32, 0xe6db99e5); /* 46 */
	HH (c, d, a, b, x[15], S33, 0x1fa27cf8); /* 47 */
	HH (b, c, d, a, x[ 2], S34, 0xc4ac5665); /* 48 */

	/* Round 4 */
	II (a, b, c, d, x[ 0], S41, 0xf4292244); /* 49 */
	II (d, a, b, c, x[ 7], S42, 0x432aff97); /* 50 */
	II (c, d, a, b, x[14], S43, 0xab9423a7); /* 51 */
	II (b, c, d, a, x[ 5], S44, 0xfc93a039); /* 52 */
	II (a, b, c, d, x[12], S41, 0x655b59c3); /* 53 */
	II (d, a, b, c, x[ 3], S42, 0x8f0ccc92); /* 54 */
	II (c, d, a, b, x[10], S43, 0xffeff47d); /* 55 */
	II (b, c, d, a, x[ 1], S44, 0x85845dd1); /* 56 */
	II (a, b, c, d, x[ 8], S41, 0x6fa87e4f); /* 57 */
	II (d, a, b, c, x[15], S42, 0xfe2ce6e0); /* 58 */
	II (c, d, a, b, x[ 6], S43, 0xa3014314); /* 59 */
	II (b, c, d, a, x[13], S44, 0x4e0811a1); /* 60 */
	II (a, b, c, d, x[ 4], S41, 0xf7537e82); /* 61 */
	II (d, a, b, c, x[11], S42, 0xbd3af235); /* 62 */
	II (c, d, a, b, x[ 2], S43, 0x2ad7d2bb); /* 63 */
	II (b, c, d, a, x[ 9], S44, 0xeb86d391); /* 64 */

	_state[0] += a;
	_state[1] += b;
	_state[2] += c;
	_state[3] += d;
}

/* Encodes input (ulong) into output (byte). Assumes length is
a multiple of 4.
*/
void MD5::encode(const uint32* input, byte* output, size_t length) {
    
    

	for (size_t i = 0, j = 0; j < length; ++i, j += 4) {
    
    
		output[j]= (byte)(input[i] & 0xff);
		output[j + 1] = (byte)((input[i] >> 8) & 0xff);
		output[j + 2] = (byte)((input[i] >> 16) & 0xff);
		output[j + 3] = (byte)((input[i] >> 24) & 0xff);
	}
}

/* Decodes input (byte) into output (ulong). Assumes length is
a multiple of 4.
*/
void MD5::decode(const byte* input, uint32* output, size_t length) {
    
    

	for (size_t i = 0, j = 0; j < length; ++i, j += 4) {
    
    
		output[i] = ((uint32)input[j]) | (((uint32)input[j + 1]) << 8) |
		(((uint32)input[j + 2]) << 16) | (((uint32)input[j + 3]) << 24);
	}
}

/* Convert byte array to hex string. */
string MD5::bytesToHexString(const byte* input, size_t length) {
    
    

	string str;
	str.reserve(length << 1);
	for (size_t i = 0; i < length; ++i) {
    
    
		int t = input[i];
		int a = t / 16;
		int b = t % 16;
		str.append(1, HEX[a]);
		str.append(1, HEX[b]);
	}
	return str;
}

/* Convert digest to string value */
string MD5::toString() {
    
    
	return bytesToHexString(digest(), 16);
}

编辑MFC对话框如下：

源代码修改如下：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Security.Cryptography;
using System.IO;

namespace Md5Test
{
    
    
    public partial class Form1 : Form
    {
    
    
        string fName;
        public Form1()
        {
    
    
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
    
    
            byte[] result = Encoding.Default.GetBytes(this.textBox1.Text.Trim());  
            MD5 md5 = new MD5CryptoServiceProvider();
            byte[] output = md5.ComputeHash(result);
            this.textBox3.Text = BitConverter.ToString(output).Replace("-", "");
            this.textBox4.Text = this.textBox3.Text.Substring(8,16) ;
        }

        private void button2_Click(object sender, EventArgs e)
        {
    
    
            OpenFileDialog openFileDialog = new OpenFileDialog();
            openFileDialog.InitialDirectory = "c:\\";
//            openFileDialog.Filter = "文本文件|*.*|C#文件|*.cs|所有文件|*.*";
            openFileDialog.RestoreDirectory = true;
            openFileDialog.FilterIndex = 1; if (openFileDialog.ShowDialog() == DialogResult.OK)
            {
    
    
                fName = openFileDialog.FileName;
                textBox2.Text = fName;
            }

        }

        private void button3_Click(object sender, EventArgs e)
        {
    
    
            FileStream file = new FileStream(fName, FileMode.Open);
            MD5 md5 = new MD5CryptoServiceProvider();
            byte[] retVal = md5.ComputeHash(file);
            this.textBox3.Text = BitConverter.ToString(retVal).Replace("-", ""); 
            this.textBox4.Text = this.textBox3.Text.Substring(8, 16);
            file.Close();
        }

        private void button4_Click(object sender, EventArgs e)
        {
    
    
            string Md5Str;
            FileStream file = new FileStream(fName, FileMode.Open);
            MD5 md5 = new MD5CryptoServiceProvider();
            byte[] retVal = md5.ComputeHash(file);
            Md5Str = BitConverter.ToString(retVal).Replace("-", "");
            file.Close();
            if (textBox5.Text.Trim().ToUpper().Equals(Md5Str.ToUpper()))
            {
    
    
                textBox_compare.Visible = true;
                textBox_compare.BackColor = Color.LightGreen;
                textBox_compare.Text = "MD5码 已匹配，文件未被修改！";
            }
            else
            {
    
    
                textBox_compare.Visible = true;
                textBox_compare.BackColor = Color.Red;
                textBox_compare.Text = "MD5码 不匹配，文件已被修改！";
            } 

        }

        private void label9_Click(object sender, EventArgs e)
        {
    
    

        }

        private void button5_Click(object sender, EventArgs e)
        {
    
    
            Form2 form = new Form2();
            form.ShowDialog();
        }

        private void button6_Click(object sender, EventArgs e)
        {
    
    
            Form3 form = new Form3();
            form.ShowDialog();

        }
    }
}

编辑MFC对话框如下：

五、实验结果

输入字符串：

计算：

注册：

登录：

登录成功
当字符串相同的时候，进行两代码计算MD5码的校验：

两代码计算的MD5码相同
选择文件：

计算文件MD5码：

复制粘贴MD5码并进行文件验证：

显示文件未被修改
若对本文件进行修改，再次计算MD5码并验证：

显示文件已被修改
更换登录账户：

进行文件验证：

显示文件未被修改

六、实验总结

由于MD5算法具有压缩性强、容易计算、抗修改性强、抗碰撞性强等特点，其主要用于把大容量信息在用数字签名软件签署私人密钥前被"压缩"成一种保密的格式(就是把一个任意长度的字节串变换成一定长的十六进制数字串)。换言之，只要文件被修改过，其MD5码的码值就会被修改，与原来MD5码的码值不匹配。