Lai-Massey scheme

The Lai-Massey scheme is a cryptographic structure used in the design of block ciphers. It is used in IDEA and IDEA NXT.

Let ${\displaystyle \mathrm {F} }$ be the round function and ${\displaystyle \mathrm {H} }$ a half-round function and let ${\displaystyle K_{0},K_{1},\ldots ,K_{n}}$ be the sub-keys for the rounds ${\displaystyle 0,1,\ldots ,n}$ respectively.

...
Wikipedia