Play Nice

Problem

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

• Program

Solution

1. Look at the source code and at the bottom it links to the Wikipedia page for a Playfair cipher

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. Click "Decrypt" to get WD9BUKBSPDTJ7SKD3KL8D6OA3F03G0 convert this to lowercase with python -c "print('WD9BUKBSPDTJ7SKD3KL8D6OA3F03G0'.lower())" to get wd9bukbspdtj7skd3kl8d6oa3f03g0.

4. Paste the decrypted text into the program on the server to get the flag: Congratulations! Here's the flag: 2e71b99fd3d07af3808f8dff2652ae0e.

Flag

2e71b99fd3d07af3808f8dff2652ae0e