static ASN1_INTEGER *x509_load_serial(char *CAfile, char *serialfile,
                                      int create)
{
    char *buf = NULL, *p;
    ASN1_INTEGER *bs = NULL;
    BIGNUM *serial = NULL;
    size_t len;

    len = ((serialfile == NULL)
           ? (strlen(CAfile) + strlen(POSTFIX) + 1)
           : (strlen(serialfile))) + 1;
    buf = app_malloc(len, "serial# buffer");
    if (serialfile == NULL) {
        OPENSSL_strlcpy(buf, CAfile, len);
        for (p = buf; *p; p++)
            if (*p == '.') {
                *p = '\0';
                break;
            }
        OPENSSL_strlcat(buf, POSTFIX, len);
    } else
        OPENSSL_strlcpy(buf, serialfile, len);

    serial = load_serial(buf, create, NULL);
    if (serial == NULL)
        goto end;

    if (!BN_add_word(serial, 1)) {
        BIO_printf(bio_err, "add_word failure\n");
        goto end;
    }

    if (!save_serial(buf, NULL, serial, &bs))
        goto end;

 end:
    OPENSSL_free(buf);
    BN_free(serial);
    return bs;
}