Danny and the Square Difference

Danny gets a long string of length $N$ comprising only of numerals. He is very fond of mathematics and tries experimenting on it but cannot think of anything. His brother Manny helps him out by giving him a question. He asks Danny to identify all the contiguous segments of size $K$ from the sub string beginning at $A$ and ending at $B$ both inclusive that can be represented in the form of $a^2 - b