Experience Certificate Valid Or Not

I am working in a sole proprietorship firm(that is not registered in mca) in bangalore as a software developer from almost been 2 years.
I am getting salary by cash. so at releasing time , firm will not provide me salary slip.so how to tell interviewr that i am getting this salary.
I want to know that
if the experience certificate given by this proprietorship firm will be valid / countable for CMM level companies?
Thank you.

Dear Jaising,
For proof of salary, you may ask to your employer for salary certificate. its normal letter, which declare about your salary details.
But, i doubt whether will they provide you or not..? as they are very smart, so, they didn't give you any letter or salary slip infact, they even use to pay salary in cash, as they don't wanted to get it in to any controversy.
But, you may try..