RFB auth phase

[Poieana Cosmin]

Hi, I'm trying to test some data exchange using RFB protocol (a small low level app in py) but it something wrong with the encryption of the challenge.
In major versions like 3.7/3.8 I simply mirror the bits in each byte of the key then I send the encrypted form of the received challenge and all is fine. But when I do the same with 3.3/3.5 versions the received ResultMessage is 0x01 -> Fail. I can't understand, I studied closely the documentation from site and tried many other methods, but why isn't working as expected ?
Thanks in advance, is just for my homework.