If an 'attacker' tries to break a cipher by a [[brute-force attack|brute-force]], (trying all possible keys until it finds the correct key) then, key clustering willmakes resultit ineasier an easierto attack on a particular cipher text. If there are N''n'' possible keys without any key clustering then, the attacker willneeds onto averagetry needan toaverage tryof N''n''/2 keys to decrypt it and ano worstmore casethan of trying all N''n'' keys. If there are two keys that are clustered then, the average number of keys to try is reduced to N''n''/4 (worstand the casemaximum is N''n''-1 keys). If three keys cluster, thanthe average attempt is only N''n''/6 attempts.
