1. Key Replacement Attack on a Certificateless Signature Scheme Zhenfeng Zhang and Dengguo Feng Presenter: Yu-Chi Chen

2. Outline Yap-Heng-Goi Certificateless Signature Scheme Public Key Replacement Attack on the Yap- Heng-Goi Scheme Remark 2015/12/162

3. CL-PKC CL-PKC is better than PKC and ID-PKC. – CL-PKC does not need the certificate for identity and the management about certificate. – CL-PKC solves the key escrow problem in ID- PKC. – KGC only generates the user’s partial-private-key. 2015/12/163

4. 4 Yap-Heng-Goi scheme Sign: Verify:

5. An Attack on the Yap-Heng-Goi Scheme Replacement attack: An attacker uses public key replacement to generate a forged signature without knowing the master-key. The forged signature is valid via the verification. 2015/12/165

6. An Attack on the GS Scheme The attacker chooses a random and replaces A's public key with the value It is able to generate a signature This signature (U,V) can be valid via Verify. 2015/12/166

7. Remark. For example for signature, Remarks of the public key replacement attack. 2015/12/167