SMIME Decryption

Hi folks !
I am working on an application in dotnet 2.0; receiving a smime message

which reads something like
========================================
MIME-Version: 1.0
Content-type: application/x-pkcs7-mime; smime-type=enveloped-data;
name="smime.p7m"
Content-Transfer-Encoding: base64
MIIcdsfefej [.....] (lots of chars)
========================================

What can i programatically do with the lot of chars, to get to the
original message ? I know in the content is the simmetric key of the
DES3 algorithm but it is encrypted with my public message, so i need to

decrypt it with my private and apply the des3.
but i do not how to do it !!?!!?
i know only the theory so far
but how to achieve this using C# is a mistery


best regards, thanks in advance


Michel Gallant, help me out in this one :D

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