I'm writing an article in English (not mother tongue), and I named a chapter: Other classes of ciphers. Is it ok if in this case I use the expression Further classes of ciphers?
Either is acceptable. But the meaning is slightly different. "Other" indicates difference but not lesser or greater, not better or worse. "Further" indicates difference all in one direction. So, you might choose "further" if the chapter is to indicate something like more complicated ciphers.
Alternatively, you could choose different words. You could use "Additional Classes of Ciphers" if you mean that these are more classes but do not want to indicate they have more of any particular characteristic. So for example, they won't be harder to break.
If you do want to indicate they have more of some characteristic, then you could say "More Sophisticated Classes of Ciphers" or possibly "More Complex Classes of Ciphers" or similar.