The core to understand padding oracle attack is understanding the method that is in use. The method includes cryptographic padding using certain block ciphers. Usage of cryptographic block ciphers however leads to the conclusion that 'a text which has undergone a cryptographic block cipher encoding, must be a multiple of the block size that was decided upon, before enforcing the encoding algorithm'.
Please read the attached document to learn more about Padding Oracle Attack.
Authored By - Binayak Banerjee
TCS Cyber Security Community