  Recently, two certificateless three-party authenticated key agreement
protocols were proposed, and both protocols were claimed they can meet the
desirable security properties including forward security, key compromise
impersonation resistance and so on. Through cryptanalysis, we show that one
neither meets forward security and key compromise impersonation resistance nor
resists an attack by an adversary who knows all users' secret values, and the
other cannot resist key compromise impersonation attack. Finally, we propose
improved protocols to make up two original protocols' security weaknesses,
respectively. Further security analysis shows that our improved protocols can
remove such security weaknesses.
