How to accept the format of .cer file for validation

How to accept the format of .cer file for validation

Hi,

I want to validate the file of .cer file format .
i tried with the blow code but not working 


rules:{
            myfile: {
                  required: true,
                  accept: 'application/pkix-cert/*'
                },
                sr1: "required"
           
        },
    messages: {
         myfile:{
            required:"Upload Certificate",
            accept:"File must be Cer | Pem"
         },
         sr1: " Enter SerialNumber"
       
    }
















Please help me that how to solve the above problem

Regards
G.Lenin