A right-to-left binary modular exponentiation algorithm in java i.e. calculating a^b mod n

ModExp.java

public class ModExp {

  public static void main(String[] args) {
		System.out.println(modExp(4,13,497));
	}
	
	public static int modExp(int a, int b, int n){
		int d = 1;
		String k = Integer.toBinaryString(b);
		for(int i = 1; i <= k.length(); i++){
			if(k.charAt(k.length()-i) == '1'){
				d = (d*a) % n;
			}
			a = (a*a) % n;
		}
		return d;
	}
}