Tags: crypto
Rating:
# 1337UP LIVE CTF 2023
## Keyless
> My friend made a new encryption algorithm. Apparently it's so advanced, you don't even need a key!
>
> Author: CryptoCat
>
> [`keyless.zip`](https://raw.githubusercontent.com/D13David/ctf-writeups/main/1337uplive/crypto/keyless/keyless.zip)
Tags: _crypto_
## Solution
We get the following `python` code:
```python
def encrypt(message):
encrypted_message = ""
for char in message:
a = (ord(char) * 2) + 10
b = (a ^ 42) + 5
c = (b * 3) - 7
encrypted_char = c ^ 23
encrypted_message += chr(encrypted_char)
return encrypted_message
flag = "INTIGRITI{REDACTED}"
encrypted_flag = encrypt(flag)
with open("flag.txt.enc", "w") as file:
file.write(encrypted_flag)
```
All steps can be reversed quite easily, so we write a script to do so, and get the flag.
```python
flag = open("flag.txt.enc", "r").read()
def decrypt(message):
result = ""
for char in message:
char = ord(char) ^ 23
char = (char + 7) // 3
char = (char - 5) ^ 42
char = (char - 10) // 2
result += chr(char)
return result
print(decrypt(flag))
```
Flag `INTIGRITI{m4yb3_4_k3y_w0uld_b3_b3773r_4f73r_4ll}`
