Security becomes an important aspect to secure the data exchanged and to ensure that
the data is received by a legitimate user. Some aspects that must be considered while
exchanging information are authentication, confidentiality, and integrity. In the electronic
voting system, authentication is used to ensure that the voter is legitimate without knowing
his/her identity, while the vote collectors verify that the data is received from a legitimate
user without knowing the identity of the voter. An authentication scheme that fulfilled
this requirement is called a deniable authentication scheme. The deniable authentication
as advance authentication where the receiver can prove the source of the message and the
receiver cannot prove the source of the given message to another party. In 2013, Li -Takagi
et al. [15] proposed a deniable authentication scheme. The leak of Li-Takagi’s scheme
is that the receiver can prove the source of a given message to the third party when the
receiver fully cooperates with the third party, as described by Mashid et al. [20]. In the
proposed method, zero-knowledge proof is introduced to maintain the anonymity of the
deniable authentication scheme when the receiver fully cooperates with the third party. In
this case, the sender and the receiver generate a random number used to construct a shared
secret key for mutual authentication. Message integrity is used to ensure the originality
of the message. If the receiver forwards the message to the third party, the third party
only knows the receiver as the source of the given message. Based on the analysis, the
proposed scheme fulfils the requirement of the deniable authentication scheme when the
receiver fully cooperates with the third party. However, the proposed scheme has
additional computation cost for securing the shared secret key. Two attack schemes
carried out on both Li-Takagi and the proposed scheme are the MITM attack and the
impersonation attack. The probability of breaking the proposed scheme using MI TM attack
is lower than when using Li-Takagi’s scheme, but the probability of breaking the proposed
scheme using impersonation attack is the same as Li-Takagi’s scheme.
Keywords: Deniable authentication, fully cooperated, electronic voting
system, MITM attack, Impersonation attack.