What type of certificate is this?

I have been reading papers about authentication in VANETS and some of them mention a certificate that a trusted authority generates for a vehicle and has the following form: $${C_{V_i}}=S_{TA}+H(PID_{V_i}|PID_{TA}|P_{TA}|P_{V_I})*x_i$$
Here $S_{TA}$ is a secret that belongs to Trusted Authority.
$H()$ is a hash function.
$PID_{V_i}$ is the pseudo-identity of vehicle $V_i$.
$PID_{TA}$ is the pseudo-identity of $TA$.
$P_{TA}$ is the public key of $TA$.
$P_{V_i}$ is the public of of vehicle $V_i$.
and $x_i$ is a random secret generated by the $TA$.
the form is TA's secret plus some hash value times another random secret. They also mention that they are working with elliptic curve cryptography for their works.