I'm working on an old CTF challenge where AES-128 was used on a 16 byte block. I have the round 10 key and the ciphertext. What techniques exist for obtaining the plaintext?
Since this is CTF, I'll give you some detailed hints.
- Normally by using only a ciphertext, you cannot determine the plaintext, since for every key the deciphered ciphertext is a valid plaintext and some of them are perfect in English or any other language. So, some other information must be given to you for verification.
- 16-Byte just means one block for AES.
- There is a difference in key schedules between AES-128 and AES-182,AES-256.
- Your CTF is not possible with the key schedules of AES-192 and AES-256
- You have given only, one round key. The different key schedule of AES -128 will enable this.
- Search for AES master key Round Keys ( in this site)