c - 4 个字符破解速度很快，但添加第 5 个循环会减慢整个程序的速度

Question

我正在为一个类编写一个程序，该程序通过在命令提示符处收集散列密码并将该散列与 crypt() 函数生成的散列进行匹配来破解 5 个字符 (aA-zZ) 密码。我的问题是添加第五个循环来破解 5 个字符的密码会减慢程序的停止速度，即使对于 1-4 个字符的密码也是如此，我必须取消。删除第 5 个循环可在一分钟内破解 1-4 个字符的密码。

我们只介绍了类中的基础知识，这在我的代码中进行了演示。因此解决方案必须符合此编码级别。

#include <cs50.h>
#include <stdio.h>
#include <crypt.h>
#include <string.h>

void printpass (string fst, string hsh1, string hsh);
/* prompt user for 1 cmd line argument */
int main(int argc, string argv[])

{    
    /* only allow 1 cmd line argument and return cmd line error
    and exit if false */    
    if (argc != 2)
    {
        printf("Invalid request!\n");
            return 1;
    }
    string hash = argv[1];
    char slt1 = hash[0];
    char slt2 = hash[1];
    char salt[3] = {slt1, slt2, '\0'};
    char alpha[52] = "QWERTYUIOPASDFGHJKLZXCVBNMqwertyuiopasdfghjklzxcvbnm";//upper & lowercase passwords only

    for (int d = 0; d < 52; d++) //search for one character pw
    {
        char s1 = alpha[d];
        char first1[2] = {s1, '\0'};
        string hash0 = crypt(first1, salt);
        printpass (first1, hash0, hash);

        if (strcmp(hash0, hash) != 0) 
        for (int f = 0; f < 52; f++) //search for two character pw
        {
            char s2 = alpha[f];
            char first2[3] = {s1, s2, '\0'};
            string hash1 = crypt(first2, salt);
            printpass (first2, hash1, hash);

            if (strcmp(hash1, hash) != 0 || strcmp(hash0, hash) != 0)
            for (int h = 0; h < 52; h++) //search for two character pw
                {
                    char s3 = alpha[h];
                    char first3[4] = {s1, s2, s3, '\0'};
                    string hash2 = crypt(first3, salt);
                    printpass (first3, hash2, hash);

                    if (strcmp(hash2, hash) != 0 || strcmp(hash1, hash) != 0 || strcmp(hash0, hash) != 0)
                    for (int j = 0; j < 52; j++) //search for two character pw
                        {
                            char s4 = alpha[j];
                            char first4[5] = {s1, s2, s3, s4, '\0'};
                            string hash3 = crypt(first4, salt);
                            printpass (first4, hash3, hash);

                            if (strcmp(hash3, hash) != 0 || strcmp(hash2, hash) != 0 || strcmp(hash1, hash) != 0 || strcmp(hash0, hash) != 0)
                            for (int l = 0; l < 52; l++) //search for two character pw
                                {
                                    char s5 = alpha[l];
                                    char first5[6] = {s1, s2, s3, s4, s5, '\0'};
                                    string hash4 = crypt(first5, salt);
                                    printpass (first5, hash4, hash);

                                }
                            }
                }
        }
    }
}

void printpass (string fst, string hsh1, string hsh) //compare hashes and print if true
{
    if (strcmp(hsh1, hsh) == 0)
    {
        printf("%s", fst);
    }
}

随着代码中的第五次循环，1-4 个字符的密码应在一分钟内完成。

Answer 1

4 个字符长的密码最多需要 7311616 (or 52^4)迭代破解，5个字符长的密码最多需要380204032 (or 52^5)迭代。