Tags: crypto
Rating:
# Tyrannosaurus Rex
Author: [roerohan](https://github.com/roerohan)
# Requirements
- Python
# Source
```python
#!/usr/bin/env python
import base64
import binascii
h = binascii.hexlify
b = base64.b64encode
c = b'37151032694744553d12220a0f584315517477520e2b3c226b5b1e150f5549120e5540230202360f0d20220a376c0067'
def enc(f):
e = b(f)
print(e)
z = []
i = 0
while i < len(e):
z += [ e[i] ^ e[((i + 1) % len(e))]]
i = i + 1
print(z)
print(bytearray(z))
c = h(bytearray(z))
return c
```
```
We found this fossil. Can you reverse time and bring this back to life?
```
# Exploitation
In this challenge, you have to reverse the steps to get back the original flag from the ciphertext `c`. Make a function `dec(x)` which takes in the ciphertexts and spits out the original text.
```python
#!/usr/bin/env python
import base64
import binascii
h = binascii.hexlify
b = base64.b64encode
c = b'37151032694744553d12220a0f584315517477520e2b3c226b5b1e150f5549120e5540230202360f0d20220a376c0067'
def enc(f):
e = b(f)
print(e)
z = []
i = 0
while i < len(e):
z += [ e[i] ^ e[((i + 1) % len(e))]]
i = i + 1
print(z)
print(bytearray(z))
c = h(bytearray(z))
return c
def dec(x):
x = list(bytes.fromhex(x.decode()))
z = ord('Z')
for i in range(len(x)):
print(chr(z), end='')
z = x[i] ^ z
dec(c)
```
Now, just run this with python, and pipe the output to `base64 -d`.
```bash
$ python fossil | base64 -d
flag{tyrannosauras_xor_in_reverse}
```
The flag is:
```
flag{tyrannosauras_xor_in_reverse}
```
