# Two Truths and a Fib

## Problem

Can you catch the fibber?

nc umbccd.io 6000

Author: Trashcanna

## Solution

![](https://3167364547-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MX1bWRlBzHpEPe1TYDD%2Fuploads%2Fgit-blob-f17ca81500da953428502677bd9cf3a68d33764c%2F1cab47cffb124df0bc82758f6887b9e3.png?alt=media)

```python
import math
from pwn import *

# A utility function that returns true if x is perfect square
def isPerfectSquare(x):
    s = int(math.sqrt(x))
    return s*s == x

# Returns true if n is a Fibinacci Number, else false
def isFibonacci(n):

    # n is Fibinacci if one of 5*n*n + 4 or 5*n*n - 4 or both
    # is a perferct square
    return isPerfectSquare(5*n*n + 4) or isPerfectSquare(5*n*n - 4)

conn = remote('umbccd.io', 6000)

done = False
while not done:
    print(conn.recvuntil('['))
    arr = eval('[' + conn.recvline().decode())

    print(arr)
    print(conn.recv())

    for num in arr:
        if isFibonacci(num):
            print(num)
            conn.send(str(num) + '\r\n')
            break

    print(conn.recv())

conn.close()
```

Eventually we get the flag:

![](https://3167364547-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2F-MX1bWRlBzHpEPe1TYDD%2Fuploads%2Fgit-blob-4e3bfcad898d70aa876ef63467b7afa0397bc84e%2F3e5d460ae8354d5cb973e787213f187b.png?alt=media)