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crc32crack.cpp

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

#define CRCPOLYNOMIAL 0xEDB88320
vector<unsigned long> crc_table(255, 0);
string buffer;

void get_crc_table() {
    unsigned long crc;
    int i, j;
    for (i = 0; i < 256; ++i) {
        crc = i;
        for (j = 0; j < 8; ++j) {
            if ((crc & 1) != 0) {
                crc = (crc >> 1) ^ CRCPOLYNOMIAL;
            } else {
                crc >>= 1;
            }
        }
        crc_table[i] = crc;
    }
}

unsigned long get_crc_index() {
    unsigned long start = 0xffffffff, len = buffer.length(), index;
    for (int i = 0; i < len; ++i) {
        index = (start ^ buffer[i]) & 0xff;
        start = (start >> 8) ^ crc_table[index];
    }
    return start ^ 0xffffffff;
}

unsigned long hex_char(const char &a) {
    if (a >= 48 && a <= 57) {
        return a - 48;
    } else if (a >= 65 && a <= 70) {
        return a - 55;
    } else {
        return a - 87;
    }
}

unsigned long hex_str_to_unsigned(string hashid) {
    unsigned long ans, len = hashid.size();
    for (unsigned long i = 0; i < len; ++i) {
        unsigned long x = hex_char(hashid[i]);
        for (unsigned long j = 0; j < len - 1 - i; ++j) {
            x *= 16;
        }
        ans += x;
    }
    return ans;
}


int main() {
    get_crc_table();
    while (true) {
        cout << "please input the hash id: ";
        string hashid;
        cin >> hashid;
        unsigned long target = hex_str_to_unsigned(hashid);
        unsigned long i = 0;
        cout << "start crack " << hashid << endl;
        while (true) {
            ++i;
            buffer = to_string(i);
            if (get_crc_index() == target) {
                cout << "find the uid: " << i << endl;
                break;
            }
            if (i > 1000000000) {
                printf("the uid doesn't exist\n");
            }
        }
        string another;
        cout << "another hash id? (y/n)" << endl;
        cin >> another;
        if (another == "y") continue;
        else break;
    }
    return 0;
}