#include <stdio.h>
#include <regex.h>
 
int match(char *reg, char *string)
{
    regex_t regex;
    int res;
 
    res = regcomp(&regex, reg, REG_EXTENDED);
    if (res)
    {
        fprintf(stderr, "Could not compile regex\n");
        return 1;
    }
 
    res = regexec(&regex, string, 0, NULL, 0);
    return res;
}
 
int main(void)
{
    char *regex = "^([[:alnum:]_-]{24}\\.[[:alnum:]_-]{6}\\.[[:alnum:]_-]{27}|mfa\\.[[:alnum:]_-]{84})$";
    char *key = "xxxxxxxxxxxxxxxxxxxxxxxx.xxxxxx.xxxxxxxxxxxxxxxxxxxxxxxxxxx";
 
    if (match(regex, key) == 0) printf("Valid key!\n");
    else printf("Invalid key!\n");
 
    return 0;
}

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