On security against the server in designated tester public key encryption with keyword search

• The security of dPEKS against KG attacks is redefined with the attacker being the server.
• The IND-KGA-SERVER security model is proposed to describe security against the server.
• A dPEKS scheme secure against the server's KG attacks is proposed.
• The solution can be seen as a bootstrap from IND-KGA security to IND-KGA-SERVER security.

The offline keyword guessing attack (KG attack) is a new security threat to the designated tester public key encryption with keyword search (dPEKS). Many techniques have been proposed to resist such an attack. However, all the schemes which are secure against KG attacks have not solved the problem that the KG attacker is the server. We redefine the security of dPEKS against KG attacks and propose IND-KGA-SERVER security. Then based on the existence of the Certificate Authority of the Public Key Infrastructure and the deterministic digital signature, we demonstrate how to construct secure dPEKS when the KG attacker is the server. Our solution is a bootstrap from IND-KGA secure dPEKS to the one of IND-KGA-SERVER security.