Play Nice

Problem

Not all ancient ciphers were so bad... The flag is not in standard format. nc mercury.picoctf.net 6057 playfair.py

Solution

  1. 1.
    Look at the source code and at the bottom it links to the Wikipedia page for a Playfair cipher
  2. 2.
    Find a Playfair cipher decoder, such as DCode. Paste in the ciphertext y7bcvefqecwfste224508y1ufb21ld and the alphabet/key meiktp6yh4wxruavj9no13fb8d027c5glzsq. Make sure to increase the grid size to 6x6 so the entire alphabet fits.
  3. 3.
    Click "Decrypt" to get WD9BUKBSPDTJ7SKD3KL8D6OA3F03G0 convert this to lowercase with python -c "print('WD9BUKBSPDTJ7SKD3KL8D6OA3F03G0'.lower())" to get wd9bukbspdtj7skd3kl8d6oa3f03g0.
  4. 4.
    Paste the decrypted text into the program on the server to get the flag: Congratulations! Here's the flag: 2e71b99fd3d07af3808f8dff2652ae0e.

Flag

2e71b99fd3d07af3808f8dff2652ae0e