# __Sharif CTF 8__ ## _DES_
## Information**Category:** | **Points:** | **Writeup Author**--- | --- | ---Crypto | 50 | MiKHalyCH
**Description:** 
> See [known_plaintexts.txt](known_plaintexts.txt). There is a single unknown DES key K.All plain texts are encrypted under K, resulting in the corresponding cipher text.Can you find K?flag is SharifCTF{K},where K is a 64-bit hexadecimal value, without the 0x prefix. (K includes the parity bits.)
## Solution
There are just 2 interesting lines in [known_plaintexts.txt](known_plaintexts.txt):```ef17ae3946ebae4c -> f084cae61e607b05f084cae61e607b05 -> ef17ae3946ebae4c```Like ![img](images/img.jpg). It means, that K is [weak](https://en.wikipedia.org/wiki/Weak_key#Weak_keys_in_DES).There are just 4 weak keys in DES. One of them is our answer.