算法系列9《MD5》

MD5即Message-Digest Algorithm 5（信息-摘要算法5），用于确保信息传输完整一致。是计算机广泛使用的杂凑算法之一（又译摘要算法、哈希算法），主流编程语言普遍已有MD5实现。

将数据（如汉字）运算为另一固定长度值，是杂凑算法的基础原理，MD5的前身有MD2、MD3和MD4。

MD5的作用是让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）。

对MD5算法简要的叙述可以为：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。

在MD5算法中，首先需要对信息进行填充，使其位长对512求余的结果等于448。因此，信息的位长（Bits Length）将被扩展至N*512+448，N为一个非负整数，N可以是零。填充的方法如下，在信息的后面填充一个1和无数个0，直到满足上面的条件时才停止用0对信息的填充。然后，在这个结果后面附加一个以64位二进制表示的填充前信息长度。经过这两步的处理，信息的位长=N*512+448+64=(N+1）*512，即长度恰好是512的整数倍。这样做的原因是为满足后面处理中对信息长度的要求。总体流程如下图所示，表示第i个分组，每次的运算都由前一轮的128位结果值和第i块512bit值进行运算。初始的128位值为初试链接变量，这些参数用于第一轮的运算，以大端字节序来表示，他们分别为：A=0x01234567，B=0x89ABCDEF，C=0xFEDCBA98，D=0x76543210。

C++代码实现

1. 《MD5.h》

#pragma once

/* POINTER defines a generic pointer type */

typedef unsigned char *POINTER; 

/* UINT2 defines a two byte word */

typedef unsigned short int UINT2; 

/* UINT4 defines a four byte word */

typedef unsigned long int UINT4; 

class cMd5

{

private:

    unsigned int m_Content[16];

    unsigned int m_ContentLen;

    unsigned int m_TotalLen;

    static unsigned int m_T[64];

    unsigned int m_A, m_B, m_C, m_D;

private:

    inline void FF(unsigned int& a, unsigned int b, unsigned int c, unsigned int d, int k, int i, int s);

    inline void GG(unsigned int& a, unsigned int b, unsigned int c, unsigned int d, int k, int i, int s);

    inline void HH(unsigned int& a, unsigned int b, unsigned int c, unsigned int d, int k, int i, int s);

    inline void II(unsigned int& a, unsigned int b, unsigned int c, unsigned int d, int k, int i, int s);

    inline unsigned int roateLeft(unsigned int a, unsigned int c);

    void transform();

	/* MD5 context. */

	typedef struct _MD5_CTX{

		UINT4 state[4];                                   /* state (ABCD) */

		UINT4 count[2];						/* bit ,2^64(Low before) */

		unsigned char buffer[64];                         /* input buffer */

	} MD5_CTX; 

	void MD5Init (MD5_CTX *);

	void MD5Update (MD5_CTX *, unsigned char *, unsigned int);

	void MD5Final (unsigned char [16], MD5_CTX *);

	void MD5String(char *string, long buflen, char digest[]); 

	static void MD5Transform (UINT4 [4], unsigned char [64]);

	static void Encode (unsigned char *, UINT4 *, unsigned int);

	static void Decode (UINT4 *, unsigned char *, unsigned int);

	static void MD5_memcpy (POINTER, POINTER, unsigned int);

	static void MD5_memset (POINTER, int, unsigned int); 

public:

	cMd5();

	virtual ~cMd5();

    //initialize

    void beginCal();

    //Show that no longer input data, will add a filling

    void endCal();

    //Is initialized, input data, in endCal call before, can continue to add data

    void addData(unsigned char* data, unsigned int size);

    //End after operation, get the code

    unsigned char* getCode();

    void  clearMemoryHelper(char* p);

};

2. 《MD5.CPP》

#include "stdafx.h"

#include "Md5.h"

#include <string.h>

#include <stdio.h>

unsigned int cMd5::m_T[64] = {

          0xD76aa478, 0xE8C7B756, 0x242070DB, 0xC1BDCEEE,

          0xF57C0FAF, 0x4787C62A, 0xA8304613, 0xFD469501,

          0x698098D8, 0x8B44F7AF, 0xFFFF5BB1, 0x895CD7BE,

          0x6B901122, 0xFD987193, 0xA679438E, 0x49B40821,

          0xF61E2562, 0xC040B340, 0x265E5A51, 0xE9B6C7AA,

          0xD62F105D, 0x02441453, 0xD8A1E681, 0xE7D3FBC8,

          0x21E1CDE6, 0xC33707D6, 0xF4D50D87, 0x455A14ED,

          0xA9E3E905, 0xFCEFA3F8, 0x676F02D9, 0x8D2A4C8A,

          0xFFFA3942, 0x8771F681, 0x6D9D6122, 0xFDE5380C,

          0xA4BEEA44, 0x4BDECFA9, 0xF6BB4B60, 0xBEBFBC70,

          0x289B7EC6, 0xEAA127FA, 0xD4EF3085, 0x04881D05,

          0xD9D4D039, 0xE6DB99E5, 0x1FA27CF8, 0xC4AC5665,

          0xF4292244, 0x432AFF97, 0xAB9423A7, 0xFC93A039,

          0x655B59C3, 0x8F0CCC92, 0xFFEFF47D, 0x85845DD1,

          0x6FA87E4F, 0xFE2CE6E0, 0xA3014314, 0x4E0811A1,

          0xF7537E82, 0xBD3AF235, 0x2AD7D2BB, 0xEB86D391

          };

cMd5::cMd5()

{

}

cMd5::~cMd5()

{

}

void cMd5::FF(unsigned int& a, unsigned int b, unsigned int c, unsigned int d, int k, int i, int s)

{

    a = b  +  roateLeft(a  +  ((b & c) | ((~b) & d))  +  m_Content[k]  +  m_T[i], s);

}

void cMd5::GG(unsigned int& a, unsigned int b, unsigned int c, unsigned int d, int k, int i, int s)

{

    a = b  +  roateLeft(a  +  ((b & d) | (c & (~d)))  +  m_Content[k]  +  m_T[i], s);

}

void cMd5::HH(unsigned int& a, unsigned int b, unsigned int c, unsigned int d, int k, int i, int s)

{

    a = b  +  roateLeft(a  +  (b ^ c ^ d)  +  m_Content[k]  +  m_T[i], s);

}

void cMd5::II(unsigned int& a, unsigned int b, unsigned int c, unsigned int d, int k, int i, int s)

{

    a = b  +  roateLeft(a  +  (c ^ (b | (~d)))  +  m_Content[k]  +  m_T[i], s);

}

unsigned int cMd5::roateLeft(unsigned int a, unsigned int c)

{

    return ( (a << c) | (a >> (32-c)) );

}

void cMd5::transform()

{

    unsigned int AA, BB, CC, DD;

    AA = m_A;

    BB = m_B;

    CC = m_C;

    DD = m_D;

    //1 round

    FF(AA, BB, CC, DD, 0, 0, 7);

    FF(DD, AA, BB, CC, 1, 1, 12);

    FF(CC, DD, AA, BB, 2, 2, 17);

    FF(BB, CC, DD, AA, 3, 3, 22);

    FF(AA, BB, CC, DD, 4, 4, 7);

    FF(DD, AA, BB, CC, 5, 5, 12);

    FF(CC, DD, AA, BB, 6, 6, 17);

    FF(BB, CC, DD, AA, 7, 7, 22);

    FF(AA, BB, CC, DD, 8, 8, 7);

    FF(DD, AA, BB, CC, 9, 9, 12);

    FF(CC, DD, AA, BB, 10, 10, 17);

    FF(BB, CC, DD, AA, 11, 11, 22);

    FF(AA, BB, CC, DD, 12, 12, 7);

    FF(DD, AA, BB, CC, 13, 13, 12);

    FF(CC, DD, AA, BB, 14, 14, 17);

    FF(BB, CC, DD, AA, 15, 15, 22);

    //2 round

    GG(AA, BB, CC, DD, 1, 16, 5);

    GG(DD, AA, BB, CC, 6, 17, 9);

    GG(CC, DD, AA, BB, 11, 18, 14);

    GG(BB, CC, DD, AA, 0, 19, 20);

    GG(AA, BB, CC, DD, 5, 20, 5);

    GG(DD, AA, BB, CC, 10, 21, 9);

    GG(CC, DD, AA, BB, 15, 22, 14);

    GG(BB, CC, DD, AA, 4, 23, 20);

    GG(AA, BB, CC, DD, 9, 24, 5);

    GG(DD, AA, BB, CC, 14, 25, 9);

    GG(CC, DD, AA, BB, 3, 26, 14);

    GG(BB, CC, DD, AA, 8, 27, 20);

    GG(AA, BB, CC, DD, 13, 28, 5);

    GG(DD, AA, BB, CC, 2, 29, 9);

    GG(CC, DD, AA, BB, 7, 30, 14);

    GG(BB, CC, DD, AA, 12, 31, 20);

    //3 round

    HH(AA, BB, CC, DD, 5, 32, 4);

    HH(DD, AA, BB, CC, 8, 33, 11);

    HH(CC, DD, AA, BB, 11, 34, 16);

    HH(BB, CC, DD, AA, 14, 35, 23);

    HH(AA, BB, CC, DD, 1, 36, 4);

    HH(DD, AA, BB, CC, 4, 37, 11);

    HH(CC, DD, AA, BB, 7, 38, 16);

    HH(BB, CC, DD, AA, 10, 39, 23);

    HH(AA, BB, CC, DD, 13, 40, 4);

    HH(DD, AA, BB, CC, 0, 41, 11);

    HH(CC, DD, AA, BB, 3, 42, 16);

    HH(BB, CC, DD, AA, 6, 43, 23);

    HH(AA, BB, CC, DD, 9, 44, 4);

    HH(DD, AA, BB, CC, 12, 45, 11);

    HH(CC, DD, AA, BB, 15, 46, 16);

    HH(BB, CC, DD, AA, 2, 47, 23);

    //4 round

    II(AA, BB, CC, DD, 0, 48, 6);

    II(DD, AA, BB, CC, 7, 49, 10);

    II(CC, DD, AA, BB, 14, 50, 15);

    II(BB, CC, DD, AA, 5, 51, 21);

    II(AA, BB, CC, DD, 12, 52, 6);

    II(DD, AA, BB, CC, 3, 53, 10);

    II(CC, DD, AA, BB, 10, 54, 15);

    II(BB, CC, DD, AA, 1, 55, 21);

    II(AA, BB, CC, DD, 8, 56, 6);

    II(DD, AA, BB, CC, 15, 57, 10);

    II(CC, DD, AA, BB, 6, 58, 15);

    II(BB, CC, DD, AA, 13, 59, 21);

    II(AA, BB, CC, DD, 4, 60, 6);

    II(DD, AA, BB, CC, 11, 61, 10);

    II(CC, DD, AA, BB, 2, 62, 15);

    II(BB, CC, DD, AA, 9, 63, 21);

    m_A = m_A  +  AA;

    m_B = m_B  +  BB;

    m_C = m_C  +  CC;

    m_D = m_D  +  DD;

}

//initialize

void cMd5::beginCal()

{

    memset(m_Content, 0, 64);

    m_ContentLen = 0;

    m_TotalLen = 0;

    m_A = 0x67452301;

    m_B = 0xEFCDAB89;

    m_C = 0x98BADCFE;

    m_D = 0x10325476;

}

void cMd5::endCal()

{

    memset((char*)m_Content  +  m_ContentLen, 0x80, 1);

    if (m_ContentLen < 56){

     memset((char*)m_Content  +  m_ContentLen  +  1, 0, 55 - m_ContentLen);

    }

    else{

     memset((char*)m_Content  +  m_ContentLen  +  1, 0, 63 - m_ContentLen);

     transform();

     memset((char*)m_Content, 0, 56);

    }

    unsigned int h, l;

    h = 0;

    l = m_TotalLen;

    h |= ((l & 0x80000000) >> 31);

    h <<= 1;

    l <<= 1;

    h |= ((l & 0x80000000) >> 31);

    h <<= 1;

    l <<= 1;

    h |= ((l & 0x80000000) >> 31);

    h <<= 1;

    l <<= 1;

    memcpy(m_Content  +  14, &l, 4);

    memcpy(m_Content  +  15, &h, 4);

    transform();

}

void cMd5::addData(unsigned char* data, unsigned int size)

{

    unsigned int i = 0;

    unsigned int remain = 64 - m_ContentLen;

    if (remain > size)

		remain = size;

    memcpy(((char*)m_Content)  +  m_ContentLen, data, remain);

		i  += remain;

    m_ContentLen  += remain;

    m_TotalLen  += remain;

    if (m_ContentLen < 64)

		return;

    transform();

    while (i  +  64 <= size)

	{

		memcpy(m_Content, data  +  i, 64);

		transform();

		i  += 64;

		m_TotalLen  += 64;

    }

    m_ContentLen = size - i;

    m_TotalLen  += m_ContentLen;

    memcpy(m_Content, data  +  i, m_ContentLen);

}

unsigned char* cMd5::getCode()

{

    unsigned char * code = new unsigned char[16];

    memcpy(code, &m_A, 4);

    memcpy(code  +  4, &m_B, 4);

    memcpy(code  +  8, &m_C, 4);

    memcpy(code  +  12, &m_D, 4);

    return code;

}

void cMd5::clearMemoryHelper(char* p)

{

    delete []p;

}