authentication

Question

I am way new to cryptography. I have figured out how to decrypt an mpeg file. I now need to authenticate the images. I have a certificate embedded in the decrypted image file along with an "R" and "S". What are the steps to pull the "P" (prime) out of the embedded certificate and verify the signature? I'm on a windows xp sp3 platform using Visual Studio 2008 sp1.

Thanks.