Symmetric Ciphers on Aditya Telange

Cryptohack - Keyed Permutations [5 pts]

Fri, 20 May 2022 00:00:00 +0530

The Solution is shared considering CAN I SHARE MY SOLUTIONS?

Problem

AES, like all good block ciphers, performs a “keyed permutation”. This means that it maps every possible input block to a unique output block, with a key determining which permutation to perform.

A “block” just refers to a fixed number of bits or bytes, which may represent any kind of data. AES processes a block and outputs another block. We’ll be specifically talking the variant of AES which works on 128 bit (16 byte) blocks and a 128 bit key, known as AES-128.

Cryptohack - Resisting Bruteforce [10 pts]

Fri, 20 May 2022 00:00:00 +0530

The Solution is shared considering CAN I SHARE MY SOLUTIONS?

Problem

If a block cipher is secure, there should be no way for an attacker to distinguish the output of AES from a random permutation of bits. Furthermore, there should be no better way to undo the permutation than simply bruteforcing every possible key. That’s why academics consider a cipher theoretically “broken” if they can find an attack that takes fewer steps to perform than bruteforcing the key, even if that attack is practically infeasible.