Rethinking Identification Protocols
                    from the Point of View of the GDPR

             Miroslaw Kutylowski, Lukasz Krzywiecki, Xiaofeng Chen 
                        

            Wroclaw University of Technology, Wroclaw, Poland
           Xidian University, Xi'an, People's Republic of China

Abstract. 
An identification protocol has to deliver a proof that the protocol participants are who 
they claim to be. Related to the circumstances, the proof must be sufficiently convincing
for the addressee. On the other hand, as long as the data minimality principle is concerned, 
the proof should be useless for any party that is not the intended addressee.
While the first goal has attracted a lot of attention, the second one has been rather neglected.

In this paper we discuss requirements for identification protocols from the point of view 
of privacy protection requirements of the GDPR regulation introduced in Europe. 
We concern the problem of cryptographic data created by identification protocols and misusing 
them as an evidence presented to third parties. We concern in particular the case when
it appears that a malicious participant follows the protocol, however the privacy protection 
guarantees supposedly provided by the scheme are effectively broken. We show that from the point 
of view of GDPR the classical schemes like static Diffie-Hellman, Schnorr, Wu, Stinson-Wu, and 
Di Raimondo-Gennaro fail to comply with the EU Regulation even if they are deniable.

Keywords: identification scheme, privacy protection, attack, deniability, simulatability, GDPR 

CSCML'2019,  LNCS 11527, pp. 296--315