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.)