Chuck Rock and Choplifter 3 store the passwords in the ROM as plaintext. Some non standard ones.

Chuck Rock
BBBBB: Unknown/invalid(password for round 1?)

2FLAF: Invincibility and press start to skip to next level. Far more useful. :3

Choplifter 3
Last valid password is Sector 5 lvl 3: CPKCXMN

ZZZZZZB: nothing

RTDFKLN: nothing

0xFFFFFFFFFFFFFFFF: removed completely

LTSFBMB: nothing