In this paper we give a short overview of the state of the art of secret key block ciphers. We focus on the main application of block ciphers, namely for encryption. The most important known attacks on block ciphers are linear cryptanalysis and differential cryptanalysis. Linear cryptanalysis makes use of so-called linear hulls i.e., the parity of a subset of ciphertext bits with a probability sufficiently far away from one half. Differential cryptanalysis makes use of so-called differentials (A, B),i.e., a pair of plaintexts with difference A, which after a certain number of rounds result in a difference B with a high probability. The hulls and differentials can be used to derive (parts of) the secret key.