FEAL-8 has been expanded to FEAL-N (N round FEAL with 64-bit key), where FEAL-N with N=4/8 is identical to FEAL-4/-8 which have been previously published respectively. N is a user defined parameter (N≥4, N:even, N=2^x, 2 ≥2 is recommended). FEAL-N has also been expanded to FEAL-NX (X: expansion, N round FEAL with 12-bit key) that accepts 128-bit keys. When the right half of the 128-bit key is all zeros, FEAL-NX works as FEAL-N. Upward compatibility is an important concept of the FEAL cipher family [1].