New answers tagged

7

The HMAC calculation is used as a KDF here. So 3 keys are derived. Let's start with the statement "In practice, if you know one, you'll know the other.". This is incorrect. The KDF construction uses a one way function so that you cannot get to the input keying material (or seed) s. This means that if an adversary gets hold of the symmetric key c that you ...


1

AES has 128, 192, and 256 bits key sizes and always 128-bit block size. They are usually written as AES128, AES192, and AES256. The block size is implicit since it is always 128. The basic function xor_128 is used to support x-or operation of CBC-MAC for the message block, ciphertext blocks, and keys. The block size is always 128 regardless of the key size. ...


-2

There is a perfect cipher – one-time pad (OTP). In many cases, it is not much practical because of the key size requirements. AES is rather some imperfect but practical cipher. Having a that allows all the permutations for 128-bit blocks would be neither perfect nor practical: The key size is obviously impractical and infeasible. Even copying such key ...


5

AES is not an ideal cipher, nor is it intended to be an ideal cipher. AES is meant to be a practical cipher that offers a strength close to the key size. That means it is computationally infeasible to find the key even if given the plaintext and the ciphertext. AES - when correctly used with a strong mode of operation - produces ciphertext is ...


Top 50 recent answers are included