prepare signature using private key and certificate in C#.Net

Dear sir,
I have been developing an application in to integrate with Webmethod. My company (Insurance firm) need to connect to Bank (bank using webMethod ),Here bank provided https service (URL with parameter)
There are two requiment.
1 Account statement Module–for generating bank statement in MT940 format, I succeeded to generate ,it’s over
2 Payment module, everything working fine, but bank request me to add signature along with payment xml file. I need to prepare signature using private key and certificate.
but unforutnaly I don’t know to create a signature.

So kindly help me to provide the solution, I am looking for some source code in . Net or documentation.

Hoping you will consider my request

Shafeeque vc

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