Hindu-muslim marriage under sma

Dear Sir, 

I am a Hindu girl  to marry a Muslim boy, with whom I've been in a relationship for 6 years. Both of our families will not allow us to do the same. We want to register our marriage legally. We do not want any conversion of religion or such acts and are very liberal to these verticals. We both are working as engineers in MNCs and are well established. Please advice us where and how to register our marriage legally, without any notice to our respective families. 

Regards,

Anamika Shetty