Thumbprint of Digital ID

[Sandipan Gangopadhyay]

I used Xenroll and openssl to create a Digital ID on a Windows System. This is working fine. I can use it to sign emails.   My question is that when I view this certificate on IE or OE, Windows shows the digital ID's SHA1 Thumbprint.   This obviously is a hash, but of what ? The public key in a particular format ? The certificate in a particular format ?   If this is of the public key alone, could I calculate this myself using openssl and the PKCS10 .csr ?   Regards,   Sandipan