In this case, the user is “authenticated”, but without having a private key (in fact, the private key does not exist). This issue does not apply to MQVs. The second attack uses the autocommunication mode that is explicitly supported in HMQV to allow a user to communicate with themselves through the same public key certificate. This mode shows that HMQV is vulnerable to an unknown key sharing attack. To resolve the first attack, Hao offered to perform public key validations in 2) and 3) separately, as initially proposed by Menezes. However, this change would reduce HMQV`s efficiency gains compared to MQV. To resolve the second attack, Hao proposed to include additional identities to distinguish copies of oneself or disable the mode of self-communication. In 2005, Krawczyk proposed a hash variant of MQV called HMQV. .