Question

I’m having trouble understanding the difference between

A) return strcmp($digest, $signature) == 0;

and

B) return strcmp($digest, $signature);

Answer 1

Normally strcmp() returns -1, 0, or 1 if the first string is less than, equal to, or greater than the second respectively. By comparing the result of that to 0 in

return strcmp($digest, $signature) == 0;

the result of strcmp() is turned to a boolean that only tests for equality rather than greater than/less than by comparison. The function will return TRUE if the two strings are equal (strcmp() == 0), and FALSE otherwise, discarding the other greater/less than information.