OpenSSL::Random.random_bytes

static VALUE
ossl_rand_bytes(VALUE self, VALUE len)
{
    VALUE str;
    int n = NUM2INT(len);
    int ret;

    str = rb_str_new(0, n);
    ret = RAND_bytes((unsigned char *)RSTRING_PTR(str), n);
    if (ret == 0) {
        ossl_raise(eRandomError, "RAND_bytes");
    } else if (ret == -1) {
        ossl_raise(eRandomError, "RAND_bytes is not supported");
    }

    return str;
}