Key schedule

In cryptography, the so-called product ciphers are a certain kind of ciphers, where the decryption of data is done in "rounds". The general setup of each "round" is the same, except for some hard-coded parameters and a part of the cipher key, called a subkey. A key schedule is an algorithm that, given the key, calculates the subkeys for these "rounds". 
Notes.
Knudsen and Mathiassen (2004) give some experimental evidence that indicate that the key schedule plays a part in providing strength against linear and differential cryptanalysis. For toy Feistel ciphers, it was observed that those with complex and well-designed key schedules can reach a uniform distribution for the probabilities of differentials and linear hulls faster than those with poorly-designed key schedules.