What need to be done for calling web-methods that requires digital signature

I am working on this application that will call a web service developed by Company ABC. Here are few requirements that they have described.

The data passed to web service methods & the data returned in response is digitaly signed. It is client application responsibility to digitaly sign request data & also verify the digital signatures on responses coming back from our system.

I have only used calls to web servcies without any d开发者_C百科igital signing requirements. Typically I will just add a web-reference to web-service in my project, instantiate the object and call web-methods.

Now that I have to digitally sign request and verify digital signature on response, what extra measures will I have to take? Will I need any more information regarding digital signatures (certificates or PKI type stuff) from Company ABC before I can actually start calling their web-methods?

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I have not used Digital signatures myself, but I just search MSDN and this is what I found: http://msdn.microsoft.com/en-us/library/aa529260.aspx