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我正在尝试在 C++ 中实现一个基本的 MD5 算法。我主要关注维基页面的算法，这看起来很简单。然而，我真的已经战斗了一段时间了。我没有得到空字符串所需的哈希值。我什至去看看 64 轮中的每一轮都发生了什么，但无济于事。这是我到目前为止所做的。代码没有优化或写得特别好，但我只是把它拼凑在一起，所以看看我是否走在正确的轨道上。

#include "md5.h"
#include <iostream>
#include <iomanip>
#include <windows.h>

using namespace std;

unsigned int rotateL(unsigned int x, int n)
{
    return ((x) << n) | ((x) >> (32 - n));

}

int main()
{
//The required hash value using existing md5 algorithm

MD5 md5 ;
cout << "empty str is:" << endl;
puts( md5.digestString( "" ) ) ;


//Initialize Vars
unsigned int a = 0x67452301;
unsigned int b = 0xefcdab89;
unsigned int c = 0x98badcfe;
unsigned int d = 0x10325476;

//Make a copy of above
unsigned int A = a;
unsigned int B = b;
unsigned int C = c;
unsigned int D = d;


//Assuming an empty string ""
//The message would be appended with 1 and then padded with 0's
//so m = 10000....until 512 bits
//is this true?
unsigned int m[16] = {0x80000000, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
    , 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};

int r[64] =  {7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22, 7, 12, 17, 22
    ,5,  9, 14, 20, 5,  9, 14, 20, 5,  9, 14, 20, 5,  9, 14, 20
        ,4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23, 4, 11, 16, 23
        ,6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21, 6, 10, 15, 21};

unsigned int k[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 };


// Do an ititial Round just for testing...
unsigned int f = 0;
cout << "Doing round " << dec << 1 << endl;
f = (b & c) | ((~b) & d);   //round 1
cout << "f is " << hex << f << endl;
unsigned int temp = d;
d = c;
c = b;
int i = 0;
int g = 0;
cout << "k is " << hex << k[0] << endl;
cout << "r is " << dec << r[0] << endl;
b = b^(rotateL( a ^ f ^ k[0] ^ m[0] ,r[0]));
a = temp;

cout << "a is " << hex << a << endl;
cout << "b is " << hex << b << endl;
cout << "c is " << hex << c << endl;
cout << "d is " << hex << d << endl;

for (int i=1;i<16;i++){
    cout << "Doing round " << dec << i+1 << endl;
    f = (b & c) | ((~b) & d);   //round 1
    g = i;
    cout << "f is " << hex << f << endl;
    //res = d & b | ~d & c; //round 2

    unsigned int temp = d;
    d = c;
    c = b;
    cout << "k is " << hex << k[i] << endl;
    cout << "r is " << dec << r[i] << endl;
    b = b^(rotateL( a ^ f ^ k[i] ^ m[g] ,r[i]));
    a = temp;

    cout << "a is " << hex << a << endl;
    cout << "b is " << hex << b << endl;
    cout << "c is " << hex << c << endl;
    cout << "d is " << hex << d << endl;
    system("PAUSE");
}

for (int i=16;i<32;i++){
    cout << "Doing round " << dec << i+1 << endl;
    f = d & b | ~d & c; //round 2
    cout << "f is " << hex << f << endl;

    g = ((5*i)+1)%16;

    unsigned int temp = d;
    d = c;
    c = b;
    cout << "k is " << hex << k[i] << endl;
    cout << "r is " << dec << r[i] << endl;
    b = b^(rotateL( a ^ f ^ k[i] ^ m[g] ,r[i]));
    a = temp;

    cout << "a is " << hex << a << endl;
    cout << "b is " << hex << b << endl;
    cout << "c is " << hex << c << endl;
    cout << "d is " << hex << d << endl;
    system("PAUSE");
}


for (int i=32;i<48;i++){
    cout << "Doing round " << dec << i+1 << endl;
    f = b ^ c ^ d;
    cout << "f is " << hex << f << endl;

    g = ((3*i)+5)%16;

    unsigned int temp = d;
    d = c;
    c = b;
    cout << "k is " << hex << k[i] << endl;
    cout << "r is " << dec << r[i] << endl;
    b = b^(rotateL( a ^ f ^ k[i] ^ m[g] ,r[i]));
    a = temp;

    cout << "a is " << hex << a << endl;
    cout << "b is " << hex << b << endl;
    cout << "c is " << hex << c << endl;
    cout << "d is " << hex << d << endl;
    system("PAUSE");
}

for (int i=48;i<64;i++){
    cout << "Doing round " << dec << i+1 << endl;
    f = c ^ (b | ~ d);
    cout << "f is " << hex << f << endl;

    g = ((7*i))%16;

    unsigned int temp = d;
    d = c;
    c = b;
    cout << "k is " << hex << k[i] << endl;
    cout << "r is " << dec << r[i] << endl;
    b = b^(rotateL( a ^ f ^ k[i] ^ m[g] ,r[i]));
    a = temp;

    cout << "a is " << hex << a << endl;
    cout << "b is " << hex << b << endl;
    cout << "c is " << hex << c << endl;
    cout << "d is " << hex << d << endl;
    system("PAUSE");
}

A = A ^ a;
B = B ^ b;
C = C ^ c;
D = D ^ d;

cout << "Finally: " << endl;
cout << "A is " << hex << A << endl;
cout << "B is " << hex << B << endl;
cout << "D is " << hex << C << endl;
cout << "D is " << hex << D << endl;

//The above would now be appended but they 
//do not equal to the required hash! 
//So clearly it is wrong??


return 0;

}

我有一种感觉，也许我在填充阶段做错了什么，但我无法弄清楚。任何帮助将不胜感激！

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1 回答 1

3

这可能是您的问题之一：

for (int i=1;i<16;i++){

我认为“i”需要初始化为0，而不是1。因为维基百科代码显示它是这样的：

//Main loop:
    for i from 0 to 63
        if 0 ≤ i ≤ 15 then
            f := (b and c) or ((not b) and d)
            g := i

此外，当您在每一轮更新“b”时，您可以按如下方式实现它：

b = b^(rotateL( a ^ f ^ k[i] ^ m[g] ,r[i]));

但是维基百科页面上的参考代码是这样实现的：

b := b + leftrotate((a + f + k[i] + w[g]) , r[i])

请注意，参考代码只是将所有这些值相加，您使用的是 xor (^) 运算符。

我怀疑还有其他问题，因此您可能需要使用参考代码仔细检查您的实现。

于 2012-04-28T16:55:54.697 回答