Rating:
# Daheck
## Description
Unicode? ...da heck?
[DaHeck.java](DaHeck.java)
## Solution
The DaHeck class have a check_flag function which is:
```
private static boolean check_flag(String s) {
char[] cs = s.toCharArray();
char[] daheck = new char[cs.length];
int n = cs.length ^ daheck.length;
char[] heck = "001002939948347799120432047441372907443274204020958757273".toCharArray();
while (true) {
try {
if (heck[n] - cs[n % cs.length] < 0) daheck[n] = (char) (heck[n] - cs[n % cs.length] % 128);
else daheck[n] = (char) (heck[n] - cs[n % cs.length] % 255);
n++;
} catch (Throwable t) {
break;
}
}
return "\uffc8\uffbd\uffce\uffbc\uffca\uffb7\uffc5\uffcb\u0005\uffc5\uffd5\uffc1\uffff\uffc1\uffd8\uffd1\uffc4\uffcb\u0010\uffd3\uffc4\u0001\uffbf\uffbf\uffd1\uffc0\uffc5\uffbb\uffd5\uffbe\u0003\uffca\uffff\uffda\uffc3\u0007\uffc2\u0001\uffd4\uffc0\u0004\uffbe\uffff\uffbe\uffc1\ufffd\uffb5".equals(new String(daheck));
}
```
The string daheck should be identical with the int array at the end.
The while loop that generates daheck operates like this:
```
for n in range(len(cs)):
daheck[n] = (char) (heck[n] - cs[n])
```
Which is an unsigned int substraction. (-1 = \uffff)
Hence, I reversed it using numpy's uint16 in the [script](daheck.py).
```
for i in range(len(daheck)):
cs += chr(np.uint16(-daheck[i] + heck[i]))
```
And that got me the flag.
```
hsctf{th4t_w4s_fun!_l3ts_try_s0m3_m0r3_r3v3rs3}
```
