  The block cipher KASUMI is widely used for security in many synchronous
wireless standards. It was proposed by ETSI SAGE for usage in 3GPP (3rd
Generation Partnership Project) ciphering algorthms in 2001. There are a great
deal of cryptanalytic results on KASUMI, however, its security evaluation
against the recent zero-correlation linear attacks is still lacking so far. In
this paper, we select some special input masks to refine the general 5-round
zero-correlation linear approximations combining with some observations on the
$FL$ functions and then propose the 6-round zero-correlation linear attack on
KASUMI. Moreover, zero-correlation linear attacks on the last 7-round KASUMI
are also introduced under some weak keys conditions. These weak keys take
$2^{-14}$ of the whole key space.
  The new zero-correlation linear attack on the 6-round needs about $2^{85}$
encryptions with $2^{62.8}$ known plaintexts. For the attack under weak keys
conditions on the last 7 round, the data complexity is about $2^{62.1}$ known
plaintexts and the time complexity $2^{110.5}$ encryptions.
