計算機安全之密碼安全從 Hash 到 MD5

時間 2019-12-10

原文原文鏈接

字符串哈希就是把一個字符串變成 long long 存起來, 而後對 1e9 + 7 取模, $b[i] = s[i]*{131}^{s.length() - 1 - i}$ ,sum[i] 存的是 b[i] 的前綴和 c++

若是出現哈希衝突的話咱們須要採起的措施是算出這個字符串的兩個哈希值而後進行比較若是說 131 是 base1 那麼須要定義 base2 值爲 313算法

如下是實現代碼app

#include <bits/stdc++.h>
using namespace std;

long long mod = 1e9 + 7;
long long base1 = 131LL, base2 = 313LL;
const int maxn = 1e5 + 10;
char s[maxn];

int main() {
    scanf("%s", s);
    int len = strlen(s);

    long long hash1 = 0, hash2 = 0;
    for(int i = 0; i < len; i ++) {
        hash1 = hash1 * base1 % mod;
        hash1 = (hash1 + s[i]) % mod;

        hash2 = hash2 * base2 % mod;
        hash2 = (hash2 + s[i]) % mod;
    }

    printf("%lld %lld\n", hash1, hash2);

    return 0;
}

可是這種哈希的辦法仍是很容易被破解由於哈希出來的值的種類有限因此很容易被破解那麼這個時候咱們能夠選擇一種更爲複雜的算法對咱們的密碼進行加密因而就有了 MD5 算法函數

string password；oop

算法思想：要使得 password.length() % 512 == 448 因此在長度不夠的時候要對字符串進行填充注意是在字符串後面進行填充第一位填充爲 1 其他用 0 填充在填充以後再在填充好的字符串後加上原密碼串若是此時消息長度大於 $2^64$ 取低位的 64 位的值加密

數據處理：須要用到的四個常數 A:0x67452301 B:0x0EFCDAB89 C:0x98BADCFE D:0x10325476spa

須要用到的四個函數：① F(X, Y, Z) = (X & Y) | ((~X) & Z)3d

　　　　　　　　　　② G(X,Y,Z)=(X & Z) | (Y & (~Z))blog

　　　　　　　　　　③ H(X,Y,Z)=X ^ Y ^ Zci

　　　　　　　　　　④ I(X,Y,Z)=Y ^ (X | (~Z))

把消息分以 512 位爲一分組進行處理，每個分組進行 4 輪變換，以上面所說 4 個常數爲起始變量進行計算，從新輸出 4 個變量，以這 4 個變量再進行下一分組的運算，若是已是最後一個分組，則這 4 個變量爲最後的結果，即MD5值。

代碼實現：

#include <bits/stdc++.h>
using namespace std;

#define shift(x, n) (((x) << (n)) | ((x) >> (32-(n))))
#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)))
#define A 0x67452301
#define B 0xefcdab89
#define C 0x98badcfe
#define D 0x10325476

unsigned int strlength;
unsigned int atemp;
unsigned int btemp;
unsigned int ctemp;
unsigned int dtemp;

const unsigned int k[]={
        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};

const unsigned int s[]={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};
const char str16[] = "0123456789abcdef";

void mainLoop(unsigned int M[]) {
    unsigned int f, g;
    unsigned int a = atemp;
    unsigned int b = btemp;
    unsigned int c = ctemp;
    unsigned int d = dtemp;
    for(unsigned int i = 0; i < 64; i ++) {
        if(i < 16) {
            f = F(b, c, d);
            g = i;
        } else if (i < 32) {
            f = G(b, c, d);
            g = (5 * i + 1) % 16;
        } else if(i < 48) {
            f = H(b, c, d);
            g = (3 * i + 5) % 16;
        } else {
            f = I(b, c, d);
            g = (7 * i) % 16;
        }
        unsigned int tmp = d;
        d = c;
        c = b;
        b = b + shift((a + f + k[i] + M[g]), s[i]);
        a = tmp;
    }
    atemp = a + atemp;
    btemp = b + btemp;
    ctemp = c + ctemp;
    dtemp = d + dtemp;
}

unsigned int* add(string str) {
    unsigned int num = ((str.length() + 8) / 64) + 1;
    unsigned int *strByte = new unsigned int[num * 16];
    strlength = num * 16;
    for (unsigned int i = 0; i < num * 16; i ++)
        strByte[i] = 0;
    for (unsigned int i = 0; i < str.length(); i ++) {
        strByte[i >> 2] |= (str[i]) << ((i % 4) * 8);
    }
    strByte[str.length() >> 2] |= 0x80 << (((str.length() % 4)) * 8);

    strByte[num * 16 - 2] = str.length() * 8;
    return strByte;
}
string changeHex(int a) {
    int b;
    string str1;
    string str = "";
    for(int i = 0; i < 4; i ++) {
        str1 = "";
        b = ((a >> i * 8) % (1 << 8)) & 0xff;
        for (int j = 0; j < 2; j ++) {
            str1.insert(0, 1, str16[b % 16]);
            b = b / 16;
        }
        str += str1;
    }
    return str;
}

string getMD5(string source) {
    atemp = A;
    btemp = B;
    ctemp = C;
    dtemp = D;
    unsigned int *strByte = add(source);
    for(unsigned int i = 0; i < strlength / 16; i ++) {
        unsigned int num[16];
        for(unsigned int j = 0; j < 16; j ++)
            num[j] = strByte[i * 16 + j];
        mainLoop(num);
    }
    return changeHex(atemp).append(changeHex(btemp)).append(changeHex(ctemp)).append(changeHex(dtemp));
}

int main() {
    string ss;
    cin >> ss;
    string s = getMD5(ss);
    cout << s << endl << endl << endl;
    return 0;
}

　　　　　　　　　　　　　　　　　That's All