  Authenticated Key Exchange (AKE) protocols represent an important
cryptographic mechanism that enables several parties to communicate securely
over an open network. Elashry, Mu and Susilo proposed in 2015 an Identity Based
Authenticated Key Exchange (IBAKE) protocol where different parties establish
secure communication by means of their public identities. The authors also
introduced a new security notion for IBAKE protocols called resiliency, that
is, if a shared secret between a group of parties is compromised or leaked,
they can generate another completely new shared secret without the need to set
up a new key exchange session. They then proved that their IBAKE protocol
satisfies this security notion.
  We analyze the security of their protocol and prove that it has a major
security flaw which renders it insecure against an impersonation attack. We
also disprove the resiliency property of their scheme by proposing an attack
where an adversary can compute any share secret key if just one secret bit is
leaked.
