des-guess.c

// gcc -Wall -Wextra -O2 guess.c -lcrypto -o guess

#include <openssl/des.h>
#include <stdint.h>
#include <string.h>

int main() {
    DES_cblock key_data;
    if (!DES_random_key(&key_data)) {
        printf("couldn't generate random key");
        return 1;
    }

    for (uint64_t t = 0; t < 100 * 1000 * 1000; ++t) {
        memcpy(key_data, &t, 8);
        DES_key_schedule ks;
        DES_set_key(&key_data, &ks);

        const_DES_cblock in = {};
        DES_cblock out;
        DES_ecb_encrypt(&in, &out, &ks, DES_ENCRYPT);
    }
}