wpa_supplicant slow to verify server certificate

[wpa at fastmail.fm]

Hi, there, 

I am using wpa_supplicant 0.4.8. on an embedded system for TTLS
authentication, but I found it takes about 2 seconds to verify a server
certificate. That is too slow for my system. I am not sure why it is
take that long to verify the server certificate. Is there any way to
reduce or optimize the speed to verify server certificate?

Thank you very much, Andrew