Confidentiality of "partial private keys" in certificateless public key crypto I'm looking at alternatives to PKI and I'm having trouble understanding exactly how certificateless public key algorithms (e.g. Al-Riyami and Paterson, Liu et al) work in practice.  It seems like the "partial private key" generated by the KGC in these systems is not actually confidential information (which would be awfully convenient for practical use of the system), but if it isn't, then I don't understand why the KGC and its master secret are necessary.

(I hope this isn't too "practical" a question for this site.)
The best way to answer this is to look at the security model in that paper.  If the adversary is allowed to request the partial private key for the target identity (i.e. the one it uses in the left-right query during the attack), then partial-private-keys are not meant to be kept secret.  If the adversary is not allowed to do so, then they must remain confidential.

After scanning their model, it seems that all partial private keys are readily supplied to adversary via Extract-Partial-Private-Key-of-A queries. This means they don't need to be kept secret.

I've got to run now, but I'll edit later if I've gotten this wrong.