Tags: crypto
Rating:
# Crypto: yORs Truly <3
> Author: shlswnt
> Description: I have encrypted some text but it seems I have lost the key! Can you find it?
> Unlock Hint for 0 points: A string of text can be decrypted by merely reapplying the XOR function with the key
[yors-truly.py](https://github.com/nopedawn/CTF/blob/main/WolvCTF24/Beginner-yORs-Truly/yors-truly.py)
Given th first chall crypto beginner, this is a classic XOR encryption problem. The plaintext is XORed with a key to get the ciphertext. If we lost the key but have the plaintext and the ciphertext, we can retrieve the key by XORing the plaintext and the ciphertext.
```python {title="yors-truly.py" lineNos=true lineNoStart=1}
import base64
plaintext = "A string of text can be encrypted by applying the bitwise XOR operator to every character using a given key"
key = "" # I have lost the key!
def byte_xor(ba1, ba2):
return bytes([_a ^ _b for _a, _b in zip(ba1, ba2)])
ciphertext_b64 = base64.b64encode(byte_xor(key.encode(), plaintext.encode()))
ciphertext_decoded = base64.b64decode("NkMHEgkxXjV/BlN/ElUKMVZQEzFtGzpsVTgGDw==")
print(ciphertext_decoded)
```
Here's how we can modify the code to find the key:
```python {title="solver.py" lineNos=true lineNoStart=1}
import base64
plaintext = "A string of text can be encrypted by applying the bitwise XOR operator to every character using a given key"
def byte_xor(ba1, ba2):
return bytes([_a ^ _b for _a, _b in zip(ba1, ba2)])
ciphertext_decoded = base64.b64decode("NkMHEgkxXjV/BlN/ElUKMVZQEzFtGzpsVTgGDw==")
key = byte_xor(plaintext.encode(), ciphertext_decoded)
print(key)
```
This will print the key that was used to encrypt the plaintext.
> Flag: `wctf{X0R_i5_f0rEv3r_My_L0Ve}`
