In command line, execute Make crack followed by ./crack 50cI2vYkF0YU2

crack.c

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

int check_inputs(string argv[]);
bool check_salt(string input_string);
bool check_is_alphanumeric(char input_char);
bool check_is_alpha(char input_char);
char * retrieve_salt(string input_string);
void test_salt(string hashed);

int main(int argc, string argv[])
{
    int check_inputs_result = check_inputs(argv);

    if (check_inputs_result == 0)
    {
        test_salt(argv[1]);
    }
    else
    {
        printf("Usage: %s hash\n", argv[0]);
        return 1;
    }
}

int check_inputs(string argv[])
{
    string program_name = argv[0];
    string attempted_input = argv[1];
    string potential_extra_input = argv[2];

    // If no/invalid key is entered or if too many inputs are detected, fail test
    if (attempted_input[1] == '\0' || potential_extra_input != '\0')
    {
        return 1;
    }
    else if (!check_salt(attempted_input))
    {
        return 1;
    }

    // Pass test if not returned a fail already
    return 0;
}

bool check_salt(string input_string)
{
    for (int i = 0; i < 2; i++)
            if (!check_is_alphanumeric(input_string[i]))
            {
                // Fail if the first two digits are not alphanumeric
                return false;
            }

    return true;
}

bool check_is_alphanumeric(char input_char)
{
    bool check = (
                    check_is_alpha(input_char)
                    ||
                    (input_char >= '0' && input_char <= '9')
                 );
    return check;
}

bool check_is_alpha(char input_char)
{
    bool check = (
                    (input_char >= 'A' && input_char <= 'Z')
                    ||
                    (input_char >= 'a' && input_char <= 'z')
                 );
    return check;
}

void test_salt(string hashed)
{
    char* salt_automated = retrieve_salt(hashed);

    // Hard coding salt for comparison
    char salt_hardcoded_chars[3] = {'5', '0', '\0'};
    char *salt_hardcoded = salt_hardcoded_chars;

    printf("Calculated salt string of length %lu: |%c%c%c|\n", strlen(salt_automated), salt_automated[0], salt_automated[1], salt_automated[2]);
    printf("Hardcoded salt string of length %lu: |%c%c%c|\n", strlen(salt_hardcoded), salt_hardcoded[0], salt_hardcoded[1], salt_hardcoded[2]);

    printf("Salt_automated |%s| compared to salt_hardcoded |%s|?\n", salt_automated, salt_hardcoded);

    char *automated_salt_crpyt_output = crypt("LOL", salt_automated);
    printf("Test - Automated: %s\n", automated_salt_crpyt_output);

    char *hardcoded_salt_crpyt_output = crypt("LOL", salt_hardcoded);
    printf("Test - Hardcoded: %s\n", hardcoded_salt_crpyt_output);

}

char * retrieve_salt(char * input_string)
{
    char salt[3];
    memcpy(salt, input_string, 2);
    salt[2] = '\0';

    // Convert the array into a string and return
    char *return_salt = salt;

    printf("Retrieved salt: %s\n", return_salt);

    return return_salt;

}