Busting the padding oracle with PadBuster

Secure cryptosystems shouldn't reveal any plaintext-relevant information about encrypted messages. Oracle attacks are powerful demonstrations of how you don't need much seemingly meaningless information to end up with a full decrypted message. Our CryptOMG web app provides a challenge that can be defeated by exploiting a padding oracle: a system that gives us information about the validity of padding in a decryption process without revealing the key or message.

Interrogating the padding oracle

I load up the CryptOMG main page and select the first challenge (like last time, we're out to get /etc/passwd). On the test page, I see nothing of interest in the actual content...