☠️Pee Kay See Ess 7

Author: @Gary#4657

What should we do?

We've given you an intercepted ciphertext from our enemies. We also have access to their decryption validation oracle. The only other piece of information we know is that they are using something called PKCS#7 padding and the oracle will tell us whether the ciphertext we give them decrypts to a proper padding by AES PKCS#7 standards.

user@pc:~/Desktop$ nc challenge.nahamcon.com <port>

Добро пожаловать! This is an AES-CBC decryption validation oracle. Send us a ciphertext and we'll let you know if it's valid or not.


/------------------------\
| AES-CBC Oracle MENU:   |
| (0) Validate my ct     | 
| (1) Exit               |
\------------------------/

Choice: 0
Send your ct (hex): f69f5206cf194380e88d084c8cb1e95f0422b6a71dc8fa3955f4379e079e0f28e83811d64abe32fdbca60d49d1112b68039d584a9298fb15e3fd750794f90b3c
valid

129B

ct.hex

What did we do!