Security Analysis and Improvement of Proxy Signature Scheme with Certificateless and Blind Properties

Proxy signature scheme with certificateless and blind properties is called certificateless proxy blind signature (CT-PBS) scheme which holds many security properties such as unforgeability and delegation. This paper makes a security analysis on an improved CT-PBS scheme proposed recently and shows that the improved CT-PBS scheme yet does not solve the security drawbacks existing in original scheme. Four types of forgery attacks are presented: 1) The attacker (acts as a malicious Key Generation Center (KGC)) can imitate the selected original signer to authorize a selected proxy signer to get the signer right of the original signer without being known by the original signer; 2) The malicious user can forge a proxy blind signature on any message by replacing the public key of the selected original signer and the public key the selected proxy signer; 3) The attacker can authorize a selected proxy signer to get the signer right of the original signer A by replacing A’s public key; 4) The malicious original signer can forge proxy blind signature on any message by replacing the public key of the selected proxy signer. We also give an improved method on these security problems and a security analysis.