As stated from the doc: "Returns 1 if the signature is correct, 0 if it is incorrect, and -1 or false on error. "
In the second example as a well as in Stiv's note, following condition will match for both 0 or false, which have different meaning:
elseif ($ok == 0) {
echo "bad";
}
On should do an identical test here (===) instead of an equal test (==):
elseif ($ok === 0) {
echo "bad";
}
---
var_dump(0==false); //==> true
var_dump(0===false);//==> false