▁from ▁the ▁R AND ▁tables , ▁used ▁as ▁a ▁source ▁of ▁" nothing ▁up ▁my ▁sle e ve ▁numbers ". ) ▁An ▁advantage ▁is ▁that ▁Kh af re ▁can ▁encrypt ▁a ▁small ▁amount ▁of ▁data ▁very ▁rapidly ▁— ▁it ▁has ▁good ▁key ▁ag ility . ▁However , ▁Kh af re ▁probably ▁requires ▁a ▁greater ▁number ▁of ▁r ounds ▁to ▁achieve ▁a ▁similar ▁level ▁of ▁security ▁as ▁Kh uf u , ▁making ▁it ▁slower ▁at ▁bulk ▁encryption . ▁Kh af re ▁uses ▁a ▁key ▁whose ▁size ▁is ▁a ▁multiple ▁of ▁ 6 4 ▁bits . ▁Because ▁the ▁S - box es ▁are ▁not ▁key - dependent , ▁Kh af re ▁X OR s ▁sub keys ▁every ▁eight ▁r ounds . ▁ ▁D iffer ential ▁crypt analysis ▁is ▁effective ▁against ▁Kh af re : ▁ 1 6 ▁r ounds ▁can ▁be ▁broken ▁using ▁either ▁ 1 5 0 0 ▁chosen ▁plain text s ▁or ▁ 2 3 8 ▁known ▁plain text s . ▁Similarly , ▁ 2 4 ▁r ounds ▁can ▁be ▁attacked ▁using ▁ 2 5 3 ▁chosen ▁plain text s ▁or ▁ 2 5 9 ▁known ▁plain text s . ▁ ▁References ▁ ▁General ▁▁▁▁▁▁▁▁▁▁▁▁ ▁Cit ations ▁ ▁Category : Bro ken ▁block ▁ci ph ers ▁Category : Fe ist el ▁ci ph ers ▁Category : K h af ra <0x0A> </s> ▁The ▁Ghost ▁Dr um ▁is ▁a ▁children ' s ▁fant asy ▁novel ▁by ▁Susan ▁Price , ▁published ▁by ▁Fab er ▁in ▁ 1 9 8 7 , ▁and ▁the ▁first ▁book