DevilGod - Hacktrace (Part 2)

decrypt.c

#include <ctype.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

void *encrypt(char *str, int32_t key) {
    uint32_t length = strlen(str);
    void* result = malloc(length + 1);
    char* ptr = (char*)result;

    for (int i = 0; i < length; i++) {
        char new_char;
        if (str[i] >= 'A' && str[i] <= 'Z') {
            new_char = ((str[i] - 'A' + key) % 26) + 'A';
        } else if (str[i] >= 'a' && str[i] <= 'z') {
            new_char = ((str[i] - 'a' + key) % 26) + 'a';
        } else {
            new_char = str[i];
        }
        ptr[i] = new_char;
    }
    ptr[length] = '\0';
    return result;
}

void* decrypt(char* str, int32_t key) {
    uint32_t length = strlen(str);
    void* result = malloc(length + 1);
    char* ptr = (char*)result;

    for (int i = 0; i < length; i++) {
        char new_char;
        if (str[i] >= 'A' && str[i] <= 'Z') {
            new_char = ((str[i] - 'A' - key + 26) % 26) + 'A';
        } else if (str[i] >= 'a' && str[i] <= 'z') {
            new_char = ((str[i] - 'a' - key + 26) % 26) + 'a';
        } else {
            new_char = str[i];
        }
        ptr[i] = new_char;
    }
    ptr[length] = '\0';
    return result;
}

int32_t _Mod(int32_t dividend, int32_t divisor)
{
    int32_t quotient = dividend / divisor;
    return dividend - (quotient * divisor);
}

void* _decrypt2(char* arg1, char* arg2) {
    uint32_t len = strlen(arg2);
    void* result = malloc(strlen(arg1) + 1);
    int32_t var_14_1 = 0;
    
    for (int32_t i = 0; arg1[i] != '\0'; i++) {
        if (!isalpha(arg1[i])) {
            *((char*)result + i) = arg1[i];
            var_14_1++;
        } else {
            int32_t is_upper = isupper(arg1[i]) != 0;
            char base_char = is_upper ? 'A' : 'a';
            int32_t temp1_1 = (i - var_14_1) % len;
            int32_t converted_char = is_upper ? toupper(arg2[temp1_1]) : tolower(arg2[temp1_1]);
            *((char*)result + i) = base_char + _Mod(arg1[i] - base_char - (converted_char - base_char) + 26, 26);
        }
    }
    
    *((char*)result + strlen(arg1)) = '\0';
    return result;
}


void* _encrypt2(char* arg1, char* arg2) {
    uint32_t len = strlen(arg2);
    void* result = malloc(strlen(arg1) + 1);
    int32_t var_14_1 = 0;
    
    for (int32_t i = 0; arg1[i] != '\0'; i++) {
        if (!isalpha(arg1[i])) {
            *((char*)result + i) = arg1[i];
            var_14_1++;
        } else {
            int32_t is_upper = isupper(arg1[i]) != 0;
            char base_char = is_upper ? 'A' : 'a';
            int32_t temp1_1 = _Mod(arg1[i] - base_char + var_14_1, len);
            int32_t converted_char = is_upper ? toupper(arg2[temp1_1]) : tolower(arg2[temp1_1]);
            *((char*)result + i) = base_char + _Mod(converted_char - base_char, 26);
        }
    }
    
    *((char*)result + strlen(arg1)) = '\0';
    return result;
}


int main() {
    void *encrypted = decrypt(_decrypt2("ZnimoFwlkMhyyn", "REVOLT"), 5);
    printf("%s", (char *)encrypted);
}