CS 145 Lecture 19 – Passwords, stack vs. heap
Agenda
- brute force password generation
- Java is copy-by-value
- primitives hold values
- objects are references, which hold addresses (http://xkcd.com/138/)
- Pointer Fun with Binky
- stack vs. heap
- == vs. equals
Code
Account.java
package preexam2;
public class Account {
public static boolean authenticate(String password) {
return password.equals("horsieso");
}
}
Cracker.java
package preexam2;
import java.util.Arrays;
public class Cracker {
public static void test(int[] foo) {
foo[0] = 17;
}
public static long getPasswordCount(int nsymbols,
int nchars) {
nsymbols = 0;
return (long) Math.pow(nsymbols, nchars);
}
public static void main(String[] args) {
int a = 26;
System.out.println(getPasswordCount(a, 5));
System.out.println(getPasswordCount(52, 5));
System.out.println(getPasswordCount(62, 5));
System.out.println(getPasswordCount(26, 8));
int[] bigHeavyStuff = new int[1];
System.out.println(Arrays.toString(bigHeavyStuff));
test(bigHeavyStuff);
System.out.println(Arrays.toString(bigHeavyStuff));
String symbols = "abcdefghijklmnopqrstuvwxyz";
char[] guess = new char[8];
for (int i = 0; i < symbols.length(); ++i) {
guess[0] = symbols.charAt(i);
for (int j = 0; j < symbols.length(); ++j) {
guess[1] = symbols.charAt(j);
for (int k = 0; k < symbols.length(); ++k) {
guess[2] = symbols.charAt(k);
for (int l = 0; l < symbols.length(); ++l) {
guess[3] = symbols.charAt(l);
for (int m = 0; m < symbols.length(); ++m) {
guess[4] = symbols.charAt(m);
for (int n = 0; n < symbols.length(); ++n) {
guess[5] = symbols.charAt(n);
for (int o = 0; o < symbols.length(); ++o) {
guess[6] = symbols.charAt(o);
for (int p = 0; p < symbols.length(); ++p) {
guess[7] = symbols.charAt(p);
String aGuess = new String(guess);
// System.out.println(aGuess);
boolean isCracked = Account.authenticate(aGuess);
if (isCracked) {
System.out.println(aGuess);
}
}
}
}
}
}
}
}
}
}
}
Haiku
Heap: refs cheap,
Stack: vars tack on, whacked on back.
Don’t ignore your store.
news keep.Stack: vars tack on, whacked on back.
Don’t ignore your store.