A bit short can mean a lot of work!
In z/OS 2.3 some of the older encryption methods are no longer support and you will may need to change your certificate.
If you are using weak certificates, or have a weak Certificate Authority certificate , you will need to created new certificates. This may be a non trivial task, as you may have to update the certificates on many machines, organisations you communicate with.
So it you have an RSA keylength of 1023 bits – this is one bit short of the 1024.