MD5加密

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一、MD5概念

MD5，全名Message Digest Algorithm 5 ，中文名为消息摘要算法第五版，
为计算机安全领域广泛使用的一种散列函数，用以提供消息的完整性保护。
上面这段话话引用自百度百科，我的理解MD5是一种信息摘要算法，主要是通过特定的hash散列方法将文本信息转换成简短的信息摘要，
压缩+加密+hash算法的结合体，是绝对不可逆的。

二、MD5计算步骤

MD5以512位分组来处理输入的信息，且每一分组又被划分为16个32位子分组，
经过了一系列的处理后，算法的输出由四个32位分组组成，将这四个32位分组级联后将生成一个128位散列值。

第一步、填充

如果输入信息的长度(bit)对512求余的结果不等于448，就需要填充使得对512求余的结果等于448。
填充的方法是填充一个1和n个0。填充完后，信息的长度就为N*512+448(bit)；

第二步、记录信息长度

用64位来存储填充前信息长度。这64位加在第一步结果的后面，这样信息长度就变为N*512+448+64=(N+1)*512位。

第三步、装入标准的幻数（四个整数）

标准的幻数（物理顺序）是（A=(01234567)16，B=(89ABCDEF)16，C=(FEDCBA98)16，D=(76543210)16）。如果在程序中定义应该是（A=0X67452301L，B=0XEFCDAB89L，C=0X98BADCFEL，D=0X10325476L）。有点晕哈，其实想一想就明白了。

第四步、四轮循环运算

循环的次数是分组的个数（N+1）

1）将每一512字节细分成16个小组，每个小组64位（8个字节）
2）先认识四个线性函数(&是与,|是或,~是非,^是异或)

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FF(a,b,c,d,Mj,s,ti)表示a=b+((a+F(b,c,d)+Mj+ti)<<<s) < span="" style="word-wrap: break-word;">
GG(a,b,c,d,Mj,s,ti)表示a=b+((a+G(b,c,d)+Mj+ti)<<<s) < span="" style="word-wrap: break-word;">
HH(a,b,c,d,Mj,s,ti)表示a=b+((a+H(b,c,d)+Mj+ti)<<<s) < span="" style="word-wrap: break-word;">
II(a,b,c,d,Mj,s,ti)表示a=b+((a+I(b,c,d)+Mj+ti)<<<s) < span="" style="word-wrap: break-word;">

4）四轮运算

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//MessageDigestAlgorithm5.h
#pragma once
#include
#include
#include
using namespace std;
typedef unsigned char Byte;
class CMessageDigestAlgorithm5
{
public:
CMessageDigestAlgorithm5(void);
~CMessageDigestAlgorithm5(void);
//MD5算法主函数,对str加密
string Encode(string &str);
string Encode(ifstream& infile);
private:
unsigned int F(unsigned int x, unsigned int y,unsigned int z);
unsigned int G(unsigned int x, unsigned int y,unsigned int z);
unsigned int H(unsigned int x, unsigned int y,unsigned int z);
unsigned int I(unsigned int x, unsigned int y,unsigned int z);
void Initialize();
unsigned int LeftRotate(unsigned int opNumber,unsigned int opBit);
void FF(unsigned int &a, unsigned int b,unsigned int c,unsigned int d, unsigned int Mj,unsigned int s,unsigned int Ti);
void GG(unsigned int &a, unsigned int b,unsigned int c,unsigned int d, unsigned int Mj,unsigned int s,unsigned int Ti);
void HH(unsigned int &a, unsigned int b,unsigned int c,unsigned int d, unsigned int Mj,unsigned int s,unsigned int Ti);
void II(unsigned int &a, unsigned int b,unsigned int c,unsigned int d, unsigned int Mj,unsigned int s,unsigned int Ti);
void ByteToUnsignedInt(const Byte* input, unsigned int* output, size_t length);
string ByteToHexString(const Byte* input, size_t length);
void UnsignedIntToByte(const unsigned int * input, Byte* output, size_t length);
void ProcessOfMDA5(const Byte block[64]);
void EncodeByte(const Byte* input, size_t length);
void Final();
private:
unsigned int m_ChainingVariable[4];
unsigned int m_Count[2];
Byte m_Result[16];
Byte m_Buffer[64];
enum
{
S11 = 7,
S12 = 12,
S13 = 17,
S14 = 22,
S21 = 5,
S22 = 9,
S23 = 14,
S24 = 20,
S31 = 4,
S32 = 11,
S33 = 16,
S34 = 23,
S41 = 6,
S42 = 10,
S43 = 15,
S44 = 21,
};
static const Byte g_Padding[64];
};

view plain <a href="http://blog.csdn.net/xiaofengcanyuexj/article/details/37698801#" class="CopyToClipboard" title="copy" background-position:left="" top;background-size:initial;background-repeat:no-repeat;background-attachment:initial;background-origin:initial;background-clip:initial;background-color:inherit;border:none;padding:1px;margin:0px="" 10px="" 0px="" 0px;font-size:9px;display:inline-block;width:16px;height:16px;text-indent:-2000px;"="" style="word-wrap: break-word; text-decoration: none; color: rgb(160, 160, 160); background-image: url("");">copy

//MessageDigestAlgorithm5.cpp
#include "stdafx.h"
#include "MessageDigestAlgorithm5.h"
const Byte CMessageDigestAlgorithm5::g_Padding[64] = { 0x80 };//第一位补1，其他补0
CMessageDigestAlgorithm5::CMessageDigestAlgorithm5(void)
{
}
CMessageDigestAlgorithm5::~CMessageDigestAlgorithm5(void)
{
}
unsigned int CMessageDigestAlgorithm5::F(unsigned int x, unsigned int y,unsigned int z)
{
return (x & y) | ((~ x) & z);
}
unsigned int CMessageDigestAlgorithm5::G(unsigned int x, unsigned int y,unsigned int z)
{
return (x & z) | (y & (~ z));
}
unsigned int CMessageDigestAlgorithm5::H(unsigned int x, unsigned int y,unsigned int z)
{
return x ^ y ^ z;
}
unsigned int CMessageDigestAlgorithm5::I(unsigned int x, unsigned int y,unsigned int z)
{
return y ^ (x | (~ z));
}
/***************************************************
*参数：空
*功能：初始化链接变量
*返回值：空
****************************************************/
void CMessageDigestAlgorithm5::Initialize()
{
m_Count[0] = m_Count[1] = 0;
m_ChainingVariable[0] = 0x67452301;
m_ChainingVariable[1] = 0xefcdab89;
m_ChainingVariable[2] = 0x98badcfe;
m_ChainingVariable[3] = 0x10325476;
}
/***************************************************
*参数：opNumber表示待左移的数
opBit表示左移的位数
*功能：完成循环左移操作
*返回值：循环左移后值
****************************************************/
unsigned int CMessageDigestAlgorithm5::LeftRotate(unsigned int opNumber,unsigned int opBit)
{
unsigned int left = opNumber;
unsigned int right = opNumber;
return (left << opBit) | (right >> (32 - opBit));
}
void CMessageDigestAlgorithm5::FF(unsigned int &a, unsigned int b,unsigned int c,unsigned int d, unsigned int Mj,unsigned int s,unsigned int Ti)
{
unsigned int temp = a + F(b,c,d) + Mj + Ti;
a = b + LeftRotate(temp,s);
}
void CMessageDigestAlgorithm5::GG(unsigned int &a, unsigned int b,unsigned int c,unsigned int d,unsigned int Mj,unsigned int s,unsigned int Ti)
{
unsigned int temp = a + G(b,c,d) + Mj + Ti;
a = b + LeftRotate(temp,s);
}
void CMessageDigestAlgorithm5::HH(unsigned int &a, unsigned int b,unsigned int c,unsigned int d, unsigned int Mj,unsigned int s,unsigned int Ti)
{
unsigned int temp = a + H(b,c,d) + Mj + Ti;
a = b + LeftRotate(temp,s);
}
void CMessageDigestAlgorithm5::II(unsigned int &a, unsigned int b,unsigned int c,unsigned int d, unsigned int Mj,unsigned int s,unsigned int Ti)
{
unsigned int temp = a + I(b,c,d) + Mj + Ti;
a = b + LeftRotate(temp,s);
}
/***************************************************
*参数：input表示输入字节数组
output表示输出unsigned int数组
length表示输入字节长度
*功能：byte转unsigned int（左低右高）
*返回值：空
****************************************************/
void CMessageDigestAlgorithm5::ByteToUnsignedInt(const Byte* input, unsigned int* output, size_t length)
{
for(size_t i = 0,j = 0;j < length;++ i, j += 4)
{
output[i] = ((static_cast<unsigned < span="" style="word-wrap: break-word;">int>(input[j]))
|((static_cast<unsigned < span="" style="word-wrap: break-word;">int>(input[j + 1])) << 8)
|((static_cast<unsigned < span="" style="word-wrap: break-word;">int>(input[j + 2])) << 16)
|((static_cast<unsigned < span="" style="word-wrap: break-word;">int>(input[j + 3])) << 24));
}
}
/***************************************************
*参数：input表示输入unsigned int数组
output表示输出字节数组
length表示输入字节长度
*功能：unsigned int转byte
*返回值：空
****************************************************/
void CMessageDigestAlgorithm5::UnsignedIntToByte(const unsigned int * input, Byte* output, size_t length)
{
for (size_t i = 0, j = 0; j < length; ++i, j += 4)
{
output[j] = static_cast(input[i] & 0xff);
output[j + 1] = static_cast((input[i] >> 8) & 0xff);
output[j + 2] = static_cast((input[i] >> 16) & 0xff);
output[j + 3] = static_cast((input[i] >> 24) & 0xff);
}
}
/***************************************************
*参数：groups[]表示一个512位（64字节）分组
*功能：四轮主要操作
*返回值：空
****************************************************/
void CMessageDigestAlgorithm5::ProcessOfMDA5(const Byte groups[64])
{
unsigned int a = m_ChainingVariable[0], b = m_ChainingVariable[1], c = m_ChainingVariable[2], d = m_ChainingVariable[3];
unsigned int M[16];
ByteToUnsignedInt( groups, M, 64);
FF(a, b, c, d, M[ 0], S11, 0xd76aa478);
FF(d, a, b, c, M[ 1], S12, 0xe8c7b756);
FF(c, d, a, b, M[ 2], S13, 0x242070db);
FF(b, c, d, a, M[ 3], S14, 0xc1bdceee);
FF(a, b, c, d, M[ 4], S11, 0xf57c0faf);
FF(d, a, b, c, M[ 5], S12, 0x4787c62a);
FF(c, d, a, b, M[ 6], S13, 0xa8304613);
FF(b, c, d, a, M[ 7], S14, 0xfd469501);
FF(a, b, c, d, M[ 8], S11, 0x698098d8);
FF(d, a, b, c, M[ 9], S12, 0x8b44f7af);
FF(c, d, a, b, M[10], S13, 0xffff5bb1);
FF(b, c, d, a, M[11], S14, 0x895cd7be);
FF(a, b, c, d, M[12], S11, 0x6b901122);
FF(d, a, b, c, M[13], S12, 0xfd987193);
FF(c, d, a, b, M[14], S13, 0xa679438e);
FF(b, c, d, a, M[15], S14, 0x49b40821);
GG(a, b, c, d, M[ 1], S21, 0xf61e2562);
GG(d, a, b, c, M[ 6], S22, 0xc040b340);
GG(c, d, a, b, M[11], S23, 0x265e5a51);
GG(b, c, d, a, M[ 0], S24, 0xe9b6c7aa);
GG(a, b, c, d, M[ 5], S21, 0xd62f105d);
GG(d, a, b, c, M[10], S22, 0x2441453);
GG(c, d, a, b, M[15], S23, 0xd8a1e681);
GG(b, c, d, a, M[ 4], S24, 0xe7d3fbc8);
GG(a, b, c, d, M[ 9], S21, 0x21e1cde6);
GG(d, a, b, c, M[14], S22, 0xc33707d6);
GG(c, d, a, b, M[ 3], S23, 0xf4d50d87);
GG(b, c, d, a, M[ 8], S24, 0x455a14ed);
GG(a, b, c, d, M[13], S21, 0xa9e3e905);
GG(d, a, b, c, M[ 2], S22, 0xfcefa3f8);
GG(c, d, a, b, M[ 7], S23, 0x676f02d9);
GG(b, c, d, a, M[12], S24, 0x8d2a4c8a);
HH(a, b, c, d, M[ 5], S31, 0xfffa3942);
HH(d, a, b, c, M[ 8], S32, 0x8771f681);
HH(c, d, a, b, M[11], S33, 0x6d9d6122);
HH(b, c, d, a, M[14], S34, 0xfde5380c);
HH(a, b, c, d, M[ 1], S31, 0xa4beea44);
HH(d, a, b, c, M[ 4], S32, 0x4bdecfa9);
HH(c, d, a, b, M[ 7], S33, 0xf6bb4b60);
HH(b, c, d, a, M[10], S34, 0xbebfbc70);
HH(a, b, c, d, M[13], S31, 0x289b7ec6);
HH(d, a, b, c, M[ 0], S32, 0xeaa127fa);
HH(c, d, a, b, M[ 3], S33, 0xd4ef3085);
HH(b, c, d, a, M[ 6], S34, 0x4881d05);
HH(a, b, c, d, M[ 9], S31, 0xd9d4d039);
HH(d, a, b, c, M[12], S32, 0xe6db99e5);
HH(c, d, a, b, M[15], S33, 0x1fa27cf8);
HH(b, c, d, a, M[ 2], S34, 0xc4ac5665);
II(a, b, c, d, M[ 0], S41, 0xf4292244);
II(d, a, b, c, M[ 7], S42, 0x432aff97);
II(c, d, a, b, M[14], S43, 0xab9423a7);
II(b, c, d, a, M[ 5], S44, 0xfc93a039);
II(a, b, c, d, M[12], S41, 0x655b59c3);
II(d, a, b, c, M[ 3], S42, 0x8f0ccc92);
II(c, d, a, b, M[10], S43, 0xffeff47d);
II(b, c, d, a, M[ 1], S44, 0x85845dd1);
II(a, b, c, d, M[ 8], S41, 0x6fa87e4f);
II(d, a, b, c, M[15], S42, 0xfe2ce6e0);
II(c, d, a, b, M[ 6], S43, 0xa3014314);
II(b, c, d, a, M[13], S44, 0x4e0811a1);
II(a, b, c, d, M[ 4], S41, 0xf7537e82);
II(d, a, b, c, M[11], S42, 0xbd3af235);
II(c, d, a, b, M[ 2], S43, 0x2ad7d2bb);
II(b, c, d, a, M[ 9], S44, 0xeb86d391);
m_ChainingVariable[0] += a;
m_ChainingVariable[1] += b;
m_ChainingVariable[2] += c;
m_ChainingVariable[3] += d;
}
/***************************************************
*参数：input表示输入字节数组
length表示输入字节长度=16（8*16=128位输出）
*功能：byte转16进制
*返回值：16进制字符串
****************************************************/
string CMessageDigestAlgorithm5::ByteToHexString(const Byte* input, size_t length)
{
const char MapByteToHex[16] =
{
'0', '1', '2', '3',
'4', '5', '6', '7',
'8', '9', 'A', 'B',
'C', 'D', 'E', 'F'
};
string str;
for (size_t i = 0; i < length; ++ i)
{
unsigned int temp = static_cast<unsigned < span="" style="word-wrap: break-word;">int>(input[i]);
unsigned int a = temp / 16;
unsigned int b = temp % 16;
str.append(1, MapByteToHex[a]);
str.append(1, MapByteToHex[b]);
}
return str;
}
/***************************************************
*参数：str表示待加密文本
*功能：MD5算法主函数
*返回值：MD5加密后算列值
****************************************************/
string CMessageDigestAlgorithm5::Encode(string &str)
{
Initialize();
EncodeByte((const Byte * )(str.c_str()), str.length());
Final();
string strMD5 = ByteToHexString(m_Result,16);
return strMD5;
}
/***************************************************
*参数：infile表示待加密文件
*功能：MD5算法主函数
*返回值：MD5加密后算列值
****************************************************/
string CMessageDigestAlgorithm5::Encode(ifstream & infile)
{
if (!infile)
{
return "";
}
Initialize();
streamsize length;
string str;
char buffer[1024];
while (! infile.eof())
{
infile.read(buffer, 1024);
length = infile.gcount();
if (length > 0)
{
EncodeByte((const Byte* )buffer,length);
Final();
}
}
infile.close();
string strMD5 = ByteToHexString(m_Result,16);
return strMD5;
}
void CMessageDigestAlgorithm5::EncodeByte(const Byte* input, size_t length)
{
unsigned int index, partLen;
size_t i;
index = static_cast<unsigned < span="" style="word-wrap: break-word;">int>((m_Count[0] >> 3) & 0x3f);//转换成字节mod64
m_Count[0] += (static_cast<unsigned < span="" style="word-wrap: break-word;">int>(length) << 3);//bit数
if (m_Count[0] < (static_cast<unsigned < span="" style="word-wrap: break-word;">int>(length) << 3))
{
++m_Count[1];
}
m_Count[1] += (static_cast<unsigned < span="" style="word-wrap: break-word;">int>(length) >> 29);//
partLen = 64 - index;
if (length >= partLen)
{
memcpy(&m_Buffer[index], input, partLen);
ProcessOfMDA5(m_Buffer);
for (i = partLen; i + 63 < length; i += 64)
{
ProcessOfMDA5(&input[i]);
}
index = 0;
}
else
{
i = 0;
}
memcpy(&m_Buffer[index], &input[i], length - i);
}
void CMessageDigestAlgorithm5::Final()
{
Byte bits[8];
unsigned int tempChainingVariable[4],tempCount[2];
unsigned int index, padLen;
memcpy(tempChainingVariable, m_ChainingVariable, 16);
memcpy(tempCount, m_Count, 8);
UnsignedIntToByte(m_Count, bits, 8);
index = static_cast<unsigned < span="" style="word-wrap: break-word;">int>((m_Count[0] >> 3) & 0x3f);
padLen = (index < 56) ? (56 - index) : (120 - index);
EncodeByte(g_Padding, padLen);
EncodeByte(bits, 8);
UnsignedIntToByte(m_ChainingVariable,m_Result, 16);
memcpy(m_ChainingVariable, tempChainingVariable, 16);
memcpy(m_Count,tempCount, 8);
}

五、说明

对于MD5算法，不同的读取格式产生的字节流是不一样的，而且涉及计算可能需要数据格式转换，如把bit转换成一定的整型数据方便计算，
因此，不同MD5算法实现版本算出的结果可能有很大不一样。
因此，我觉得最好多次计算的MD5算法版本一致。关于MD5算法，有一个比较好的在线计算工具，点击MD5在线计算器。
MD5算法是不可逆的，但是，基于键值对的字典关系原理，有一些收集海量MD5信息与摘要的数据库，采用枚举法能够从MD5值找到原文本信息，
提供一个类似的工具，点击MD5在线破解。此外，在此提供MD5的讨论社区，点击MD5讨论社区。

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