Design of LOKI97  Dr Lawrie Brown   This paper describes the
design of LOKI97, a private key block cipher with 128-bit data
and a 256-bit key schedule, which can be initialised by 128,
192, or 256-bit keys. The data computation uses 16 rounds of a
balanced feistel network with a complex function f which
incorporates two S-P layers. The 256-bit key schedule uses 48
rounds of an unbalanced feistel network using the same complex
function f to generate the subkeys.   LOKI97 is a new 16 round
Feistel cipher on 128-bit data using a complex non-linear
function f(A,B), with a 256-bit key schedule which can be
initialised using 128, 192, or 256-bit keys.  LOKI97 has evolved
from the earlier LOKI89 [BrPS90], and LOKI91 [BKPS91] 64-bit
block ciphers. Whilst LOKI91 is currently considered secure
against known attacks such as differential and linear
cryptanalysis, its effective key size of about 260 will be
inadequate in future, as demonstrated by the recent brute force
searches of 56-bit keyspaces [RSAD97]).  It was thus