Hi,
it’s up to the network to require authentication. If the MSC doesn’t ask the authentication request, then the MS won’t get authentified.
In this case (that’s a strategy chosen by operator), the procedure will continue as if the MS was succesfully authentified.
The ciphering is done few messages after : ciphering mode command, ciphering mode confirm, where the MS and the NSS exchange cipher key.
Regards
pix