Let's first breafly analyse the cipher. This cipher is a block cipher, following a construction called a Substitution Permutation Network. Here is some technical details :
- 128 bits of block size
- 3 parts for the encryption/decryption :
- 20 rounds of round key addition, substitution and permutation,
- A multiplication of the state at this point by the secret key in
$\mathbb{F}\_{2^{128}}$ , - Another 20 rounds of round key addition, substitution and permutation.
- No key schedule, the same key is repeated for each round