I am createing an asp.net web application in which i want to use(i want to use a digital signature certificate which is already issued to the User with my application for every registerd user) a digitalsignature to the user and using that digital signature the user can encrypt and decypt the files and data and mail using combination of private key and public key 
the user will logon using this dsc in the application and using this dsc user can save his data in encypted format in the the   he can ecrpt a file and save on server he can send encrypted email msgs and can decypt the data using same dsc from the database or decypt the file using same dsc

here DSC means Digital Signature Certificate

My Basic Question is How can i Ge the Private Key Of Digital Signature?

Please Help...

Hi

To this you need use the Asymmetric algoritham with Crytography.

To get basic idea about secure your application data  see here

http://msdn.microsoft.com/en-us/library/aa302378.aspx\

to make digital signature with .net public and private key 

http://www.codeproject.com/KB/vb/Digital_Signatures.aspx

http://www.c-sharpcorner.com/UploadFile/Gowri%20S%20Paramasivam/Cryptography211242005003308AM/Cryptography2.aspx

tnx

Thanks for the reply...
but i need not to create the Digital Signature i do have signatures issued by the issuing authority i just need to get the private key of that signature can you please help me with some code samples...


Thanks and Regards,
Meetu Choudhary

Check this one explaining basic premise public-key cryptography and how it relates to XML Digital Signatures, detail the creation of a key pair, give examples for signing and verifying an XML document, and discuss different implementations to provide reliable application licensing...
http://www.codeproject.com/KB/security/xmldsiglic.aspx
For your exact problem of using Private key you can check here for some inputs...
http://dotnetslackers.com/articles/security/Hashing_MACs_and_Digital_Signatures_in_NET.aspx
http://www.eggheadcafe.com/conversation.aspx?messageid=29236387&threadid=29236365

I have already gone through these links 
let me clarify my problem once again
I am developing a web application in asp.net 3.5 framework with C# and in that application i have a rich textbox or multi line text box which contains data of n length and i want to encrypt and decrypt the data using the digital signatures 
please consider that the user using the web application is already having the digital signatures from a Gov. recognized body and my application will not create any Digital Signature it will only use the .pfx file or the installed signature I am able to open the certificate store and it is displaying all the certificates installed on the computer.
now what i need is i want to encrypt the data using the digital signature's public key and decrypt it using the private key of the same digital signature. I may save the public key in the DB for encryption but to decrypt the data we need the digital signature.
please Help me its really very urgent. 
 

Thanks and Regards
Meetu Choudhary

this might help you in this regard...
http://www.4guysfromrolla.com/articles/022807-1.aspx
http://www.codeproject.com/KB/cpp/RsaSignatureAppendix.aspx

Sir  Thanks for your time devotion but
Please Understand i want to use digital signatures issued by 3rd party 
here : http://www.codeproject.com/KB/cpp/RsaSignatureAppendix.aspx 
it is encrypting and decrypting the file.
and here
http://www.4guysfromrolla.com/articles/022807-1.aspx
it has used SQL server